https://processdesign.mccormick.northwestern.edu/api.php?action=feedcontributions&user=Pdtravan&feedformat=atomprocessdesign - User contributions [en]2024-03-29T15:03:19ZUser contributionsMediaWiki 1.39.2https://processdesign.mccormick.northwestern.edu/index.php?title=Desalination_-_Team_A&diff=5276Desalination - Team A2016-03-12T03:34:27Z<p>Pdtravan: /* Brine Heater */</p>
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<div>Author: Pear Dhiantravan<sup>[2016]</sup>, Reed Kolbe<sup>[2016]</sup>, Sheridan Lichtor<sup>[2016]</sup>, John Marsiglio<sup>[2016]</sup>, Ellen Zhuang<sup>[2016]</sup><br />
<br />
Instructors: Fengqi You, David Wegerer<br />
<br />
Winter 2016<br />
<br />
=Executive Summary=<br />
Seawater desalination is an attractive approach to address the world’s freshwater shortage in light of the increasing global water scarcity. Our team decided to tackle California's growing drought crisis by designing a multistage flash desalination plant in Richmond, CA. Based on market analysis of existing desalination plants and water demands, this is a strategic location for the desalination of 50 million gallons per day of water from the San Francisco Bay.<br />
<br />
The MSF process contains 18 flash stages in series. Seawater is taken in from the San Francisco Bay at a rate of 398 million gallons per day and mixed with brine recycled from the system. Within the MSF process, seawater is heated through a series of 18 heat exchangers and a brine heater before enters a series of 18 evaporation chambers. In the evaporation chambers, the seawater flashes and the freshwater vapor is condensed, collected, and sent to a water treatment facility. The brine stream proceeds to the next chamber, and the process continues. Upon exiting the last flashing chamber, the brine stream is split into a recycle brine stream that is mixed with the seawater inlet feed and a waste stream that is diluted with fresh seawater and returned to the sea. Overall, the process yield is 13%. This process was constructed in Aspen HYSYS and optimized around utility costs using the HYSYS Economic Analyzer. Based on duties, temperatures and pressures reported by HYSYS, as well as fundamental mass and energy balances, the equipment were sized appropriately and the economics of the process was analyzed.<br />
<br />
The design has a total capital cost of $485.2 MM, an annual operating cost of $144.7 MM ($103.7 MM of which is utilities), and an annual plant revenue of $134.3 MM. Economic analysis reveals that the project has a negative NPV of -$495.7 MM and operates at a loss of $10.4 MM per year. Thus, the proposed design is not profitable. Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing while California is experiencing harsher droughts each year. Given the dire situations, the government may support the proposed clean water project with subsidies. Building the facility may be a strategic investment, especially since greater water scarcity is predicted in the future.<br />
<br />
Our design meets various environmental, ethical, social and health related constraints. The brine discharged back to the bay is diluted to at most 0.2% above the natural background salinity as required by law so that the plant does not impose harm on any local marine life. The demographic that the plant serves is largely invested in the protection of the environment, which we addressed by reducing energy consumption through direct energy integration with the nearby Chevron plant. Lastly, the product meets the specifications of the California Safe Water Drinking Act by producing water with no impurities.<br />
<br />
<br />
__TOC__<br />
<br />
=Introduction=<br />
An increasing global water scarcity is fueling initiatives everywhere for clean water treatment, making efficient seawater desalination an attractive aim for chemical plant design. A 2015 market analysis found that the global desalination market earned revenues of $11.66 billion, and this number is expected to reach over $19 billion by 2019. Furthermore, the 17,000 desalination plants currently in operation are expected to double in number by 2020.<sup>1</sup> <br />
<br />
As fresh water sources become increasingly scarce, strict water conservation measures are being observed. California is entering the fourth year of one of its most severe droughts on record. Cities are required to reduce their water usage by 35% to avoid facing fines.<sup>2</sup> In lieu of these pressing conditions, California is looking for ways to provide more accessible fresh water to its citizens. This high demand for clean water motivated our choosing Richmond, CA as our plant location. At Richmond, the desalination plant can convert readily available seawater from the San Francisco Bay into fresh water. We propose to desalinate 50 million gallons of water per day to be sent to water treatment plants for potability. This aim is based on the capacity of the desalination plant in Carlsbad, California, which services a similar population.<br />
<br />
The salinity of the water in the San Francisco Bay is seasonal. During the dry seasons of summer and fall, salinity is high around 10 PSU (10,000 ppm) because water from the Pacific Ocean flows into the San Francisco Bay. During the wet winter season, fresh water from the rivers flows into the Bay, and salinity drops to around 2 PSU (2,000).3 Designed to meet the “worst case” scenario, our plant will process 398 million gallons of water per day with 10,000 ppm of salt to produce 50 million gallons of distilled water. This gives a yield of 13%.<br />
<br />
The desalination plant proposed consists of 18 flash stages in series. This report outlines our investigation of this potential water desalination plant, including design and optimization of the desalination process, an analysis of its energy consumption and environmental impacts, and a study of its economic implications.<br />
<br />
=Technical Approach=<br />
For the desalination step of our process, we selected a multistage flash (MSF) distillation process. Not only is MSF distillation a very viable method, but it is also the most common method, currently producing about 60% of the world’s desalinated water. MSF and reverse osmosis (RO) are the two major methods being used in large-scale desalination plants. Both processes require considerable amounts of energy. RO typically has a lower energy demand; however, the high impurity content of the Bay water would frequently necessitate membrane cleaning and/or exchange. Feed going through a RO system requires extensive pretreatment to remove biological organisms and other solids to control the pH and the chemical composition of the water. With the San Francisco Bay as our source of water, MSF is an attractive option because sediment and other large impurities can be separated from the feed before distillation occurs. Additionally, MSF distillation plants can be located near power plants and paired to their waste heat streams to conserve energy. This can reduce energy needs by half or two thirds, making MSF increasingly more practical. Due to the maintenance required in the RO system, the MSF distillation is the better option in terms of operation cost.<sup>4</sup><br />
<br />
A HYSYS model was built to simulate the MSF distillation section of the process, which spans after seawater pretreatment and before local potable water treatment. The model is used to simulate the distillation steps and to calculate necessary heating, cooling, and input flow rates to produce the required 50 million gallons of distillated water per day. For the simulation, the 398 million gallons per day of seawater feed stream is defined to be composed of 3.31 mol% sodium chloride (NaCl) and 96.69 mol% water. The percentage of NaCl is set to account for other ions and chemicals present after the pretreatment phase. NaCl alone is added to the HYSYS system due to the capabilities of the fluid package used to simulate this process, ElectroNRTL. The feed is set at 22°C, which is the approximate the temperature of the San Francisco Bay year round.<br />
<br />
=Process Design=<br />
==Design Overview==<br />
The proposed desalination plant uses MSF distillation to convert the San Francisco Bay water to fresh water. The final process design contains 18 flash stages in series. Overall, 398 million gallons per day of of brackish water is converted to 50 million gallons per day of deionized water, a 13% yield. The production meets the required production rate of 50 million gallons of freshwater per day. <br />
<br />
Seawater is taken in from the San Francisco Bay and mixed with the brine recycle stream produced downstream. The feed is then heated through a series of condensers and a heater. Distilled water vapor in each flash stage contacts the tubes carrying the seawater feed and condenses into a liquid stream by exchanging heat with the cooler seawater feed stream. The seawater is sent through a heater to increase its thermal energy before entering the first stage of the MSF. In each flashing stage, some of the water evaporates, leaving the salt behind. The freshwater vapors condense, as described above, and is collected and sent to a water treatment plant. The brine stream is split into the recycle stream and a waste stream, and the waste stream is diluted with fresh seawater before being discharged back into the bay.<br />
<br />
A process flow diagram of the process is depicted in Appendix A. <br />
<br />
==Pretreatment==<br />
Sediment is removed to prevent solids from plugging the process downstream. Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime, and is controlled for by lowering pH. Acidifying the water will also remove CO2, which is a corrosive gas. To control for oxygen, oxygen scavengers will be included in the system to sequester it. Sodium bisulfate will be used as the scavenger.<sup>5</sup><br />
<br />
==Condensers (Heat Exchanger Networks)==<br />
In order to conserve and recycle energy, the condensation of the distillate and heating of the seawater feed will be coupled in countercurrent heat exchanger networks. These heat exchanger networks are condensers of the design. The cold feed, which is a mixture of fresh seawater and brine recycle, is fed through multiple heat exchangers in series. Each heat exchanger corresponds to a different evaporation chamber. This process consists of 18 heat exchangers: E-101, E-102, … E-117, and E-118, which correspond to evaporation chambers V-102, V-103, … V-118, and V-119, respectively. <br />
<br />
The heat exchangers can be viewed similarly to a shell and tube setup, however there is no actual physical shell. The tubes simply run through the top of the evaporation chambers, where vaporized distilled water in the chamber acts as the shell side fluid. The tube bundles are arranged in long tube configuration and are aligned parallel to the direction of the flashing brine flow in the evaporation chamber. The evaporating brine in an evaporation chamber rise up to the the corresponding heat exchanger and condense on the outside of the tubes, creating collectable pure water. This condensing water is what heats up the seawater in the tubes. <br />
<br />
E-101 was used as the basis for the condenser sizing since it has the highest heat requirement, and thus will be the largest heat exchanger. From the HYSYS model, the overall system requires 2.24 x 10<sup>6</sup> kW of duty. Assuming this energy requirement, 5000 tubes, and 18 m length tubes (the diameter of the evaporation chambers, explained further on the next page), the diameter of each tube was calculated to be 0.4 m. Based on the temperature of the streams and flow, the thickness of the tube is 7 x 10<sup>-4</sup> m.<br />
<br />
==Brine Heater==<br />
After the seawater exits the final heat exchanger, it enters a brine heater (E-119) where it is brought up to the temperature necessary for the flashing process to begin. This means that the seawater must be overheated compared to stage one, so that the seawater will flash in the evaporation chamber, i.e. release heat and vapor to reach equilibrium with stage conditions. After flowing through the condensers, the seawater enters the brine heater at 91.6ºC and is heated to 120ºC. The overall system requires 2.31 x 106 kW of duty. This is supplied by a total of 4.15 x 106 kg per hour of steam.<br />
<br />
==Evaporation Chambers==<br />
When the seawater has been brought to a temperature appropriate for flashing, it enters the first evaporation chamber (V-102). Upon entering the chamber, the water is flashed. Some of the water evaporates, leaving the salt behind. The vapor rises up to the heat exchanger tubes in each evaporation chamber and condenses on the outside into the distilled water product. This condensing water is what heats up the seawater in the tubes discussed above. The seawater that does not evaporate moves to the next stage, which operates at a higher temperature and lower pressure, and the process is repeated. This continues in series through a total of 18 flashing chambers (V-102, V-103, … V-118, and V-119). All of the distillate is collected into one stream and all of the brine is mixed with seawater before being disposed of back in the bay in order to dilute it enough so it does not have an adverse effect on marine life.<br />
<br />
Each respective heat exchanger fully condenses the vapor product stream from each stage. However, when all of the individual product streams are consolidated into the final combined product stream, some water exists in the vapor phase due to temperature and pressure changes associated with mixing all of the streams together. Although the vapor product stream from each stage condenses completely across its respective heat exchanger, the total product stream contains some water in the vapor phase due to the temperature change when the mixer sums all the streams. In order to fully condense this stream, which will be sent to local water treatment plans, a heat exchanger (E-120) is put in place to cool down the product using the process feed stream. <br />
<br />
The correlations of El-Dessouky and Ettouney were employed in order to size the flash chambers. They specified that conventional MSF plants that operate at a capacity between 27,000 and 36,000 m3/day use flashing stages of the dimensions 18 m diameter and 4 m height.<sup>6</sup><br />
<br />
==Valves==<br />
The model requires valves in between the evaporation chambers. The seawater streams flow through valves with large pressure drops to flash a portion the liquid into vapor that can then be separated in the vessels. Large pressure drops provide the thermodynamic driving force to vaporize more of the liquid, and are required to achieve high product yield. <br />
<br />
==Material of Construction==<br />
Before 1980, the shells and internals of the MSF units were commonly constructed from carbon steel. Seawater, however, corrodes carbon steel. To compensate for this, the thickness of the carbon steel has an additional corrosion allowance, which increases the size and weight of the equipment. After 1980, the stainless steel and duplex stainless steel became increasingly common. Stainless steel metal requires less thickness for equivalent strength and corrosion resistance, which allows for a reduction in the size, weight, and therefore cost of units. Major units in our process will be constructed from stainless steel.<sup>6</sup><br />
<br />
==Process Alternatives==<br />
In order to ensure that our design is fully optimized, we wanted to consider several alternatives for our process. We looked at alternatives associated with water pretreatment, the distillation process itself and product treatment.<br />
<br />
===Water Pretreatment===<br />
Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime. Scaling can be controlled by adjusting pH, temperature, and bicarbonate concentration. We selected acidification to control for process scaling. This is because lowering a process temperature would decrease overall efficiency, and decreasing bicarbonate concentration would be comparatively expensive. Lowering pH would have the added benefit of controlling CO2 concentrations since CO2 is a corrosive gas. To control for corrosion we looked at how to remove oxygen. To target the oxygen we chose an oxygen scavenger. This was chosen over other options such as a deaerator, or a protective coating because a deaerator would have a large capital cost, and the equipment itself would experience corrosion, and a tank coating such as zinc orthophosphate has a mixed effectiveness.<sup>7</sup><br />
<br />
===MSF: Brine Recycle vs. Once-Through System===<br />
We explored two options for the overall layout of the MSF distillation plant. In the first, the brine passes through the process once; in the second, a portion of the brine is recycled from the last stage to the incoming seawater feed. The largest draw towards implementing a brine recycle is that it would significantly reduce the overall amount of seawater needed to produce the daily target of 50 million gallons per day. This in turn would lower the amount of energy required to run the pump feeding seawater to the process. Another positive is that, with a brine recycle, the amount of water conditioning chemicals that must be added to the seawater feed is reduced. The negative aspects mainly revolve around the fact that the solution throughout the process will be higher in salt concentration. This increase in salinity both raises the likelihood of scaling and corrosion in the plant and raises the amount of seawater that must be added to the final brine to make it safe for discharge back into the environment. Additionally, boiling point of each stage is raised when adding the brine recycle. After weighing both alternatives against one another, we have decided to include a brine recycle in our plant design. Most of the negative aspects of the brine recycle can be combated (e.g. include anti-scaling agents in the feed pretreatment), and the economic benefits of including the brine recycle are very significant.<sup>8</sup><br />
<br />
===MSF: Continuous vs. Batch===<br />
The distillation step can be done in continuous or batch processes. Batch distillation is more versatile and often used when the product is in small amounts and very high purity. A continuous distillation is more efficient thermodynamically and economically for large amounts of material of constant composition, whereas batch distillation is more effective for small amounts of material of varying compositions. Since the plant is processing large amounts of seawater of relatively constant composition, the distillation system will utilize continuous distillation.<sup>9</sup><br />
<br />
===MSF: Long Tube vs. Crossed Tube ===<br />
Inside the evaporator stage, the condenser tube bundles may be arranged in either long tube or cross tube design. In the long tube arrangement, the tubes are aligned parallel to the direction of the flashing brine flow. The tubes go from stage to stage without water boxes. In the cross tube arrangement, the tubes are lined perpendicular to the flow of the flashing brine. Water boxes transfer brine between the stages.<sup>10 11</sup> While the water boxes in crossed tube bundles allow for more customization, the long tube configuration allows for construction of large unit sizes, as there are manufacturing restrictions with cross tubes. Long tube design can easily accommodate a large number of stages, which lead us to choose long tube for our design.<sup>11 12</sup><br />
<br />
===MSF: Venting System===<br />
Noncondensable gases exist in the process because of air leakages into stages under vacuum conditions and the release of dissolved gases from the heated brine. These gases are removed by venting the system. An air cooler section concentrates the gas before they are vented, and baffles direct the vapor and condensates out. There are two venting arrangements to consider: series and parallel. The system in series moves gas from one stage directly to the next, and the only loss in the system is vapor in the last stage (since some vapor is extracted with gases). This system is economical, however this configuration increases the amount of noncondensable gases passing from one stage to the next, and disrupting the venting system in one stage will affect the entire system. In parallel venting, gas is released through parallel takeoff pipes at each stage. Although this arrangement allows for venting at any stage to be controlled, the design and maintenance is more complex, and more vapor is lost than in the venting system in series. A third alternative is to use a combination of venting in parallel and in series, which is the common method in industry. For this process, our team chose to do venting in parallel and in series.<sup>12</sup><br />
<br />
===Additional Energy Source Alternatives===<br />
Energy for the process can also be coupled with renewable energy sources to reduce the desalination plant’s carbon footprint. Energy integration can be direct or indirect. In direct integration, thermal waste heat from industrial sources provide thermal energy or pressure as energy sources. Direct integration is advantageous at the modular level, as it avoids energy losses with electricity conversion. Within indirect integration, there are modular integration and grid/utility-scale integration. Modular integration integrates the plant with wind turbines and other small-scale renewable power generators with mobile deployment. A “hybridization” of renewable power sources with natural gas power generation is also an option, and the coupling of the two provides a stable power source. Indirect renewable energy integration is growing as the cost of renewable energy continues to decreases and provides an economy of scale that direct integration does not, but there are several obstacles towards indirect integration, such as the plant’s finance and engineering the integration of the two systems.<sup>13</sup> This distillation plant will be directly integrated with neighboring plants such as Chevron that produce thermal waste heat.<br />
<br />
===Product Treatment===<br />
Since the product is distilled water, it needs additional ions to a concentration of around 0.01% before going to the end user. The three alternatives considered were building a water treatment facility on site, simply adding the correct salts to the product stream and then sending the stream for bacterial treatment at a water plant, or simply sending the product distilled water for complete treatment to another facility. Due to the number of nearby water treatment plants and their demand for water, we elected to simply send the product to a nearby water treatment facility.<br />
<br />
==Design Constraints and Tradeoffs==<br />
While designing our process, we wanted to make sure that we met several outside constraints, including environmental, political, ethical, social, sustainability, health and safety constraints. First and most importantly, we wanted to ensure that the brine discharged back to the bay would not harm local marine life. Our process was designed around the constraint of diluting the exiting brine to within 0.2% salinity of background seawater. This is not only compliant with California law, but was also verified to be safe for surrounding marine life through our own outside research. We also addressed many of these considerations by deciding to pursue direct energy integration with the nearby Chevron plant in order to reduce environmental impact of our process. Additionally, we ensured that our plant would be located in an area that is densely populated and in great need of fresh drinking water. Finally, we addressed health and safety considerations by making sure we would be able to send our product distilled water to local treatment plants for proper potabilization.<br />
<br />
===Design Tradeoffs: Thermodynamics=== <br />
Adjusting elements within this process is iterative, and optimization thereof required changing multiple parameters at once. An example of this is in tuning the temperature increase by heater E-100; if the temperature of the stream entering the vessels is too high, the heat exchange between the vapor product and the feed stream will not be realizable because it causes the feed to be too hot to cool and condense the product. Higher temperatures, however, provide greater thermodynamic driving forces for flashing. Setting the entering stream temperature at 120°C provides enough heat for substantial flash at 130 kPa. This is the only heater required until the very last flash stage, which is added to provide more heat for vaporization. This heater (E-105) increases the stream temperature by 15°C, and the vapor product from the last vessel increases the feed stream temperature by almost 30°C. The added energy increases vaporization by 3%, which is a substantial 2.2 million kg/h. The temperature of the streams entering and leaving each stage decreases with each additional flash stage such that the last vessel has the lowest temperature, according to realistic operating guidelines. <br />
<br />
===Design Tradeoffs: Energy Consumption, Environmental Impacts, and Product Optimization===<br />
Increases in the pressure drop across any of the valves in this final design causes a temperature cross in the heat exchangers unless a proper increase in pump energy is provided. There is thus a design tradeoff between lowering energy usage and increasing product yield. For example, lowering the operating pressure of the process dictates that the pressure difference used to flash seawater must be smaller, possibly decreasing the amount that is vaporized. The final design aims for a yield of 50 million gallons per day. The 18 stage model was chosen for its low annual utility cost. This is a reflection of environmental mindfulness because energy consumption is an ongoing aspect of the process and should be lowered as much as possible.<br />
<br />
==Mass and Energy Balances==<br />
The model of the desalination system assumes that: (1) the properties are uniform in each phase within a stage, (2) heat losses are negligible due to the small surface area to volume ratio for each stage and properly insulated units (heat losses to the surrounding vary from 2 to 5% of the total system energy), (3) the distillate is salt free since the boiling point of water is much lower than that of salt, (4) the subcooling or superheating effects on the system energy balances are negligible, (5) the only contaminant is sodium chloride (there are no non-condensable gases to consider, so no vapors are vented), and (6) the process has 3 evaporation chambers.<br />
<br />
The major balances are that the feed is a mixture of the fresh seawater stream and the recycle stream, and that the brine stream exiting the last evaporation chamber is divided into the recycle stream and the waste stream. Within each stage, the change in mass of a phase over time is the balance between the net flow of that phase from the chamber and the rates of evaporation and condensation of water into and out of that phase. The equations governing the mass and energy balances on the system is displayed in Appendix C. <br />
<br />
=Optimization=<br />
As initiatives for reduced energy usage and increased environmental sustainability become more prevalent, efforts to minimize the utility cost in plants has increased to accommodate these incentives. Utilities are a continual source of expenditure and consumption, and a well-designed chemical process should seek to minimize this element. The annualized utility cost is a useful parameter to optimize given that its value depends on variations in energy costs; thus, annualized utility costs do not correlate with conventional indices of inflation, such as capital and labor costs. Additionally, utility costs, like other variable costs, can be minimized by improving the design or operational efficiency of the plant.<br />
<br />
In optimizing our MSF process, the design variable of focus was the number of stages to use in our process. The performance measure was the annualized utility cost, which was the parameter that was minimized for optimization. The process is constrained by the product specifications, which are kept constant and serve as the standard for comparison between each model. These specifications are to produce 50 million gallons of desalinated liquid water per day. <br />
<br />
One feasibility constraint in the process is the size of the heat exchangers, which must provide a large enough area for total condensation of the vapor stream coming out of the flash stages. In order to restrict the heat exchange area needed within each exchanger, the number of stages must be at least 11. Increasing the number of stages decreases the vapor flow rate at each, and decreases the heat exchange area required as well. An 11-stage process allows for appropriate heat exchange between the feed stream and the vapor product, according to the HYSYS economic analyzer. The optimization analysis thus was conducted incorporating only models with 11 or more stages. <br />
<br />
The HYSYS economic analyzer was used to systematically optimize the process by finding the model with the lowest annualized utility cost. The performance parameters kept constant across each model were: the inlet composition, pressure, and temperature, the brine outlet temperature, the total product flow rate and composition, and the flash stage schematic. Table 1 displays the annualized utility cost for each model, and illustrates that a clear dip in the utility cost occurs in an 18 stage model. Thus, 18 is the optimal number of stages to use for our MSF distillation given utility costs as the optimized parameter.<br />
[[File:Table_1.PNG|center|500x300px]]<br />
<br />
=Economic Evaluation=<br />
In order to evaluate our process from a fiscal standpoint, we used Aspen Process Economic Analyzer and Aspen cost estimator to determine capital and operating costs for our plant. These costs were calculated based on calculated equipment sizes, as well as energy requirements reported by our HYSYS model. The capital cost was found to be $485.2MM and annual total operating cost was found to be $144.7MM ($103.7MM of which was utilities). Annual plant revenue was estimated based on prices that water districts in the county currently pay for outside water sources, and was found to be $134.3MM.<sup>14</sup> <br />
<br />
The NPV analysis we conducted assumed that the plant would take two years to build, would operate at half capacity during the first year of operation (year 3), and have a 20 year lifetime. We also assumed that our plant would be in operation 350 days per year. A constant discount rate of 12% was assumed to hold throughout the plant’s lifetime. The final NPV of this project is -$495.7MM. This is due to both the large capital cost of the plant and the annual loss of $10.4MM while in full operation. A graph of cumulative cash flow versus time can be found in Appendix E. Tax rates and depreciation do not directly impact the NPV of this project due to operating at a loss, however for future calculations it should be noted that we used a straight line depreciation schedule over a seven year period with a 40% tax rate. <br />
<br />
Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing, while California is experiencing harsher droughts each year. A consequence of this is the possibility of receiving government subsidies for our clean water product. The similarly scaled desalination plant in Carlsbad, CA operates at a loss as well, but receives significant government subsidies. Building this facility may be a strategic investment, especially since greater water scarcity is predicted in the future. <br />
<br />
=Sensitivity Analysis=<br />
We wanted to determine how sensitive NPV of our project is to the cost of capital, price of utilities and price we would be able to sell our clean water product at. We conducted this analysis by varying each of these variables independently between 0.5 times and 1.5 times the original value we calculated. As to be expected, NPV grows more negative with increasing capital costs and utility prices and decreasing water prices. Conversely, NPV becomes less negative as price of water rises and capital and utility costs decrease. A plot summarizing the effects of varying these costs can be found in Appendix E. NPV is most sensitive to the price at which we will be selling our clean water product. It is worth noting that NPV is more sensitive to utilities cost than it is to capital cost, which is why we focused on optimizing the cost of utilities. In future steps, trying to reduce utilities cost even more would be worth looking into to decrease the amount of money being lost on this project.<br />
<br />
=Conclusions and Final Recommendation=<br />
The final design achieves the project goal of producing 50 million gallons per day of distilled water at a yield of 13%, comparable to other similarly sized plants. An optimization of the number of MSF stages is realistic, and can be improved upon by taking into account other process parameters. <br />
<br />
The proposed design was optimized around utility costs, comparing plants with 11 to 25 stages. The process is constrained by product specifications and by the thermodynamics of the heat exchange between the feed and the product streams. Energy conservation was achieved in using the seawater feed to condense the final product, as well as in all of the heat exchangers increasing the thermal energy of the seawater feed stream before it enters the flash stages. <br />
<br />
In order to further optimize this process, other design parameters should be considered such as the brine recycle ratio, the cooler duty of the recycle stream, the pressure drop across each valve at the flash stages, and other economic factors. An optimization around maximizing NPV, for example, might be more comprehensive than that conducted regarding only utility costs. Tuning brine recycle rates could greatly improve process efficiency, and standardizing flash stage pressure drops would make operations more feasible and controlled. <br />
<br />
Given our in depth economic analysis, this project would lose an average of $10.4MM per year, and has an NPV of -$495.7MM for a 20 year plant lifetime. From an economic perspective alone it would not be a good project to build. However, other factors need to be considered when building a project with enormous public value. In recent years California droughts have become more severe. Implementing a drought-proof supply of water now could avert a disaster later on. Even without a large disaster, having the desalination plant could also be expected to pay off in the future with the increasing price of water. Considerations such as these were the deciding factors in building the Carlsbad desalination plant. Since there are currently no desalination plants in the Bay area we recommend that preparations should be made to move forward with a desalination plant.<br />
<br />
=References=<br />
[1] Lyons J. Environmental Leader. Environmental Leader 2015. Available at: http://www.environmentalleader.com/2015/10/27/desalination-plants-to-double-by-2020. Accessed 2016.<br />
<br />
[2] Fitzsimmons E. In California, Cities Braced to Cut Water by 10 to 35%. The New York Times 2015. Available at: <br />
http://www.nytimes.com/2015/04/09/us/in-california-cities-braced-to-cut-water-by-10-to-35.html. Accessed 2016. <br />
<br />
[3] Salinity Times Series - USGS Water Quality of SF Bay. Salinity Times Series - USGS Water Quality of SF Bay. Available at:<br />
http://sfbay.wr.usgs.gov/access/wqdata/overview/examp/charts/salin.html. Accessed 2016.<br />
<br />
[4] Reverse Osmosis vs. Multi Stage Flash Distillation: A Comparison Between Different Desalination Methods. Brighthub Engineering. Available at:<br />
http://www.brighthubengineering.com/power-plants/29621-comparison-between-the-reverse-osmosis-and-multi-stage-flash-distillation-methods/. Accessed 2016.<br />
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[5] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
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[6] H. El-Dessouky. Fundamentals of salt water desalination, 1st Ed., Elsevier Science, 2002.<br />
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[7] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[8] Guasp RE, Bello CP, Jara JG, Vega JP, Damien T, Winkel C, Smith HH. Desalination by distillation. Organization of American States website. oas.org. Accessed January 28, 2015.<br />
<br />
[9] Batch Distillation. AE 335 Separation Processes website. http://prodpran.che.engr.tu.ac.th/AE335/AE335.html. Accessed January 26, 2016.<br />
<br />
[10] Morris R. The development of the multi-stage flash distillation process: A designer's viewpoint. Desalination. 1993;93:57-68. <br />
<br />
[11] Darwish MA. Developments in the multi-stage flash desalting system. Desalination. 1995;100:35-64.<br />
<br />
[12] Wade N. Distillation plant development and cost update. Desalination. 2001;136:3-12.<br />
<br />
[13] Desalination Technologies and the Use of Alternative Energies for Desalination. World Intellectual Property Organization website. http://www.wipo.int/export/sites/www/patentscope/<br />
en/programs/patent_landscapes/documents/patent_landscapes/948-2E-WEB.pdf. Updated November 2011. Accessed January 23, 2016.<br />
<br />
[14] California Turns to the Pacific Ocean for Water | MIT Technology Review.MIT Technology Review 2014. Available at:<br />
http://www.technologyreview.com/featuredstory/533446/desalination-out-of-desperation/. Accessed 2016.<br />
<br />
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<br />
=Appendix A. Process Flow Diagram=<br />
[[File:Appendix 1.PNG]]<br />
<br />
'''Figure A1''' Process Flow Diagram of the MSF System<br />
<br />
=Appendix B. HYSYS Simulation=<br />
The HYSYS model of the process is shown below.<br />
<br />
[[File:AppendB.PNG]]<br />
<br />
'''Figure B1.''' The HYSYS model of the MSF distillation process.<br />
<br />
=Appendix C. Mass and Energy Balances=<br />
Below are equations that describe the mass and energy balances of the system.<br />
<br />
In MSF system with brine recycle, the mass flow of the intake seawater I is mixed with the mass flow of the recycle brine R to create the feed seawater stream F. Since this model assumes no non-condensable gases, the feed stream is overall balanced by the brine waste stream W, the recycle brine stream, and the distillate stream D. The brine stream exiting the last evaporation chamber B is divided into the recycle and waste streams. The amount of salt that enters the series of evaporation chambers is the amount of salt that leaves (X is the salt mass fraction).<br />
<br />
[[File:Overallmasss.PNG]]<br />
<br />
Within each stage, the change in mass of a phase is the mass flows of that phase into and out of the chamber and the rates of evaporation or condensation of the water into and out of that phase.<br />
[[File:Masss2.PNG]]<br />
<br />
The energy balances are summarized below.<br />
<br />
[[File:Mass3.PNG]]<br />
<br />
[[File:Mass4.PNG]]<br />
<br />
=Appendix D. Summary of Process Units=<br />
<br />
[[File:AppendD1.PNG]]<br />
[[File:AppenD2.PNG]]<br />
<br />
=Appendix E. MSF Stage Parameters=<br />
[[File:AppendE.PNG]]<br />
<br />
[[File:Appendix E3.PNG]]<br />
<br />
[[File:Appendix E4.PNG]]<br />
<br />
=Appendix F. Process Units Calculations=<br />
[[File:AppendF.PNG]]<br />
<br />
[[File:AppendF2.PNG]]<br />
<br />
[[File:AppendF3.PNG]]<br />
<br />
=Appendix G. Economic Analysis=<br />
[[File:Econanalysis.PNG]]</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Desalination_-_Team_A&diff=5274Desalination - Team A2016-03-12T03:33:33Z<p>Pdtravan: /* Evaporation Chambers */</p>
<hr />
<div>Author: Pear Dhiantravan<sup>[2016]</sup>, Reed Kolbe<sup>[2016]</sup>, Sheridan Lichtor<sup>[2016]</sup>, John Marsiglio<sup>[2016]</sup>, Ellen Zhuang<sup>[2016]</sup><br />
<br />
Instructors: Fengqi You, David Wegerer<br />
<br />
Winter 2016<br />
<br />
=Executive Summary=<br />
Seawater desalination is an attractive approach to address the world’s freshwater shortage in light of the increasing global water scarcity. Our team decided to tackle California's growing drought crisis by designing a multistage flash desalination plant in Richmond, CA. Based on market analysis of existing desalination plants and water demands, this is a strategic location for the desalination of 50 million gallons per day of water from the San Francisco Bay.<br />
<br />
The MSF process contains 18 flash stages in series. Seawater is taken in from the San Francisco Bay at a rate of 398 million gallons per day and mixed with brine recycled from the system. Within the MSF process, seawater is heated through a series of 18 heat exchangers and a brine heater before enters a series of 18 evaporation chambers. In the evaporation chambers, the seawater flashes and the freshwater vapor is condensed, collected, and sent to a water treatment facility. The brine stream proceeds to the next chamber, and the process continues. Upon exiting the last flashing chamber, the brine stream is split into a recycle brine stream that is mixed with the seawater inlet feed and a waste stream that is diluted with fresh seawater and returned to the sea. Overall, the process yield is 13%. This process was constructed in Aspen HYSYS and optimized around utility costs using the HYSYS Economic Analyzer. Based on duties, temperatures and pressures reported by HYSYS, as well as fundamental mass and energy balances, the equipment were sized appropriately and the economics of the process was analyzed.<br />
<br />
The design has a total capital cost of $485.2 MM, an annual operating cost of $144.7 MM ($103.7 MM of which is utilities), and an annual plant revenue of $134.3 MM. Economic analysis reveals that the project has a negative NPV of -$495.7 MM and operates at a loss of $10.4 MM per year. Thus, the proposed design is not profitable. Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing while California is experiencing harsher droughts each year. Given the dire situations, the government may support the proposed clean water project with subsidies. Building the facility may be a strategic investment, especially since greater water scarcity is predicted in the future.<br />
<br />
Our design meets various environmental, ethical, social and health related constraints. The brine discharged back to the bay is diluted to at most 0.2% above the natural background salinity as required by law so that the plant does not impose harm on any local marine life. The demographic that the plant serves is largely invested in the protection of the environment, which we addressed by reducing energy consumption through direct energy integration with the nearby Chevron plant. Lastly, the product meets the specifications of the California Safe Water Drinking Act by producing water with no impurities.<br />
<br />
<br />
__TOC__<br />
<br />
=Introduction=<br />
An increasing global water scarcity is fueling initiatives everywhere for clean water treatment, making efficient seawater desalination an attractive aim for chemical plant design. A 2015 market analysis found that the global desalination market earned revenues of $11.66 billion, and this number is expected to reach over $19 billion by 2019. Furthermore, the 17,000 desalination plants currently in operation are expected to double in number by 2020.<sup>1</sup> <br />
<br />
As fresh water sources become increasingly scarce, strict water conservation measures are being observed. California is entering the fourth year of one of its most severe droughts on record. Cities are required to reduce their water usage by 35% to avoid facing fines.<sup>2</sup> In lieu of these pressing conditions, California is looking for ways to provide more accessible fresh water to its citizens. This high demand for clean water motivated our choosing Richmond, CA as our plant location. At Richmond, the desalination plant can convert readily available seawater from the San Francisco Bay into fresh water. We propose to desalinate 50 million gallons of water per day to be sent to water treatment plants for potability. This aim is based on the capacity of the desalination plant in Carlsbad, California, which services a similar population.<br />
<br />
The salinity of the water in the San Francisco Bay is seasonal. During the dry seasons of summer and fall, salinity is high around 10 PSU (10,000 ppm) because water from the Pacific Ocean flows into the San Francisco Bay. During the wet winter season, fresh water from the rivers flows into the Bay, and salinity drops to around 2 PSU (2,000).3 Designed to meet the “worst case” scenario, our plant will process 398 million gallons of water per day with 10,000 ppm of salt to produce 50 million gallons of distilled water. This gives a yield of 13%.<br />
<br />
The desalination plant proposed consists of 18 flash stages in series. This report outlines our investigation of this potential water desalination plant, including design and optimization of the desalination process, an analysis of its energy consumption and environmental impacts, and a study of its economic implications.<br />
<br />
=Technical Approach=<br />
For the desalination step of our process, we selected a multistage flash (MSF) distillation process. Not only is MSF distillation a very viable method, but it is also the most common method, currently producing about 60% of the world’s desalinated water. MSF and reverse osmosis (RO) are the two major methods being used in large-scale desalination plants. Both processes require considerable amounts of energy. RO typically has a lower energy demand; however, the high impurity content of the Bay water would frequently necessitate membrane cleaning and/or exchange. Feed going through a RO system requires extensive pretreatment to remove biological organisms and other solids to control the pH and the chemical composition of the water. With the San Francisco Bay as our source of water, MSF is an attractive option because sediment and other large impurities can be separated from the feed before distillation occurs. Additionally, MSF distillation plants can be located near power plants and paired to their waste heat streams to conserve energy. This can reduce energy needs by half or two thirds, making MSF increasingly more practical. Due to the maintenance required in the RO system, the MSF distillation is the better option in terms of operation cost.<sup>4</sup><br />
<br />
A HYSYS model was built to simulate the MSF distillation section of the process, which spans after seawater pretreatment and before local potable water treatment. The model is used to simulate the distillation steps and to calculate necessary heating, cooling, and input flow rates to produce the required 50 million gallons of distillated water per day. For the simulation, the 398 million gallons per day of seawater feed stream is defined to be composed of 3.31 mol% sodium chloride (NaCl) and 96.69 mol% water. The percentage of NaCl is set to account for other ions and chemicals present after the pretreatment phase. NaCl alone is added to the HYSYS system due to the capabilities of the fluid package used to simulate this process, ElectroNRTL. The feed is set at 22°C, which is the approximate the temperature of the San Francisco Bay year round.<br />
<br />
=Process Design=<br />
==Design Overview==<br />
The proposed desalination plant uses MSF distillation to convert the San Francisco Bay water to fresh water. The final process design contains 18 flash stages in series. Overall, 398 million gallons per day of of brackish water is converted to 50 million gallons per day of deionized water, a 13% yield. The production meets the required production rate of 50 million gallons of freshwater per day. <br />
<br />
Seawater is taken in from the San Francisco Bay and mixed with the brine recycle stream produced downstream. The feed is then heated through a series of condensers and a heater. Distilled water vapor in each flash stage contacts the tubes carrying the seawater feed and condenses into a liquid stream by exchanging heat with the cooler seawater feed stream. The seawater is sent through a heater to increase its thermal energy before entering the first stage of the MSF. In each flashing stage, some of the water evaporates, leaving the salt behind. The freshwater vapors condense, as described above, and is collected and sent to a water treatment plant. The brine stream is split into the recycle stream and a waste stream, and the waste stream is diluted with fresh seawater before being discharged back into the bay.<br />
<br />
A process flow diagram of the process is depicted in Appendix A. <br />
<br />
==Pretreatment==<br />
Sediment is removed to prevent solids from plugging the process downstream. Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime, and is controlled for by lowering pH. Acidifying the water will also remove CO2, which is a corrosive gas. To control for oxygen, oxygen scavengers will be included in the system to sequester it. Sodium bisulfate will be used as the scavenger.<sup>5</sup><br />
<br />
==Condensers (Heat Exchanger Networks)==<br />
In order to conserve and recycle energy, the condensation of the distillate and heating of the seawater feed will be coupled in countercurrent heat exchanger networks. These heat exchanger networks are condensers of the design. The cold feed, which is a mixture of fresh seawater and brine recycle, is fed through multiple heat exchangers in series. Each heat exchanger corresponds to a different evaporation chamber. This process consists of 18 heat exchangers: E-101, E-102, … E-117, and E-118, which correspond to evaporation chambers V-102, V-103, … V-118, and V-119, respectively. <br />
<br />
The heat exchangers can be viewed similarly to a shell and tube setup, however there is no actual physical shell. The tubes simply run through the top of the evaporation chambers, where vaporized distilled water in the chamber acts as the shell side fluid. The tube bundles are arranged in long tube configuration and are aligned parallel to the direction of the flashing brine flow in the evaporation chamber. The evaporating brine in an evaporation chamber rise up to the the corresponding heat exchanger and condense on the outside of the tubes, creating collectable pure water. This condensing water is what heats up the seawater in the tubes. <br />
<br />
E-101 was used as the basis for the condenser sizing since it has the highest heat requirement, and thus will be the largest heat exchanger. From the HYSYS model, the overall system requires 2.24 x 10<sup>6</sup> kW of duty. Assuming this energy requirement, 5000 tubes, and 18 m length tubes (the diameter of the evaporation chambers, explained further on the next page), the diameter of each tube was calculated to be 0.4 m. Based on the temperature of the streams and flow, the thickness of the tube is 7 x 10<sup>-4</sup> m.<br />
<br />
==Brine Heater==<br />
After the seawater exits the final heat exchanger, it enters a brine heater (E-119) where it is brought up to the temperature necessary for the flashing process to begin. This means that the seawater must be overheated compared to stage one, so that the seawater will flash in the evaporation chamber, i.e. release heat and vapor to reach equilibrium with stage conditions. After flowing through the condensers, the seawater enters the brine heater at 91.6 oC and is heated to 120 oC. The overall system requires 2.31 x 106 kW of duty. This is supplied by a total of 4.15 x 106 kg per hour of steam.<br />
<br />
==Evaporation Chambers==<br />
When the seawater has been brought to a temperature appropriate for flashing, it enters the first evaporation chamber (V-102). Upon entering the chamber, the water is flashed. Some of the water evaporates, leaving the salt behind. The vapor rises up to the heat exchanger tubes in each evaporation chamber and condenses on the outside into the distilled water product. This condensing water is what heats up the seawater in the tubes discussed above. The seawater that does not evaporate moves to the next stage, which operates at a higher temperature and lower pressure, and the process is repeated. This continues in series through a total of 18 flashing chambers (V-102, V-103, … V-118, and V-119). All of the distillate is collected into one stream and all of the brine is mixed with seawater before being disposed of back in the bay in order to dilute it enough so it does not have an adverse effect on marine life.<br />
<br />
Each respective heat exchanger fully condenses the vapor product stream from each stage. However, when all of the individual product streams are consolidated into the final combined product stream, some water exists in the vapor phase due to temperature and pressure changes associated with mixing all of the streams together. Although the vapor product stream from each stage condenses completely across its respective heat exchanger, the total product stream contains some water in the vapor phase due to the temperature change when the mixer sums all the streams. In order to fully condense this stream, which will be sent to local water treatment plans, a heat exchanger (E-120) is put in place to cool down the product using the process feed stream. <br />
<br />
The correlations of El-Dessouky and Ettouney were employed in order to size the flash chambers. They specified that conventional MSF plants that operate at a capacity between 27,000 and 36,000 m3/day use flashing stages of the dimensions 18 m diameter and 4 m height.<sup>6</sup><br />
<br />
==Valves==<br />
The model requires valves in between the evaporation chambers. The seawater streams flow through valves with large pressure drops to flash a portion the liquid into vapor that can then be separated in the vessels. Large pressure drops provide the thermodynamic driving force to vaporize more of the liquid, and are required to achieve high product yield. <br />
<br />
==Material of Construction==<br />
Before 1980, the shells and internals of the MSF units were commonly constructed from carbon steel. Seawater, however, corrodes carbon steel. To compensate for this, the thickness of the carbon steel has an additional corrosion allowance, which increases the size and weight of the equipment. After 1980, the stainless steel and duplex stainless steel became increasingly common. Stainless steel metal requires less thickness for equivalent strength and corrosion resistance, which allows for a reduction in the size, weight, and therefore cost of units. Major units in our process will be constructed from stainless steel.<sup>6</sup><br />
<br />
==Process Alternatives==<br />
In order to ensure that our design is fully optimized, we wanted to consider several alternatives for our process. We looked at alternatives associated with water pretreatment, the distillation process itself and product treatment.<br />
<br />
===Water Pretreatment===<br />
Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime. Scaling can be controlled by adjusting pH, temperature, and bicarbonate concentration. We selected acidification to control for process scaling. This is because lowering a process temperature would decrease overall efficiency, and decreasing bicarbonate concentration would be comparatively expensive. Lowering pH would have the added benefit of controlling CO2 concentrations since CO2 is a corrosive gas. To control for corrosion we looked at how to remove oxygen. To target the oxygen we chose an oxygen scavenger. This was chosen over other options such as a deaerator, or a protective coating because a deaerator would have a large capital cost, and the equipment itself would experience corrosion, and a tank coating such as zinc orthophosphate has a mixed effectiveness.<sup>7</sup><br />
<br />
===MSF: Brine Recycle vs. Once-Through System===<br />
We explored two options for the overall layout of the MSF distillation plant. In the first, the brine passes through the process once; in the second, a portion of the brine is recycled from the last stage to the incoming seawater feed. The largest draw towards implementing a brine recycle is that it would significantly reduce the overall amount of seawater needed to produce the daily target of 50 million gallons per day. This in turn would lower the amount of energy required to run the pump feeding seawater to the process. Another positive is that, with a brine recycle, the amount of water conditioning chemicals that must be added to the seawater feed is reduced. The negative aspects mainly revolve around the fact that the solution throughout the process will be higher in salt concentration. This increase in salinity both raises the likelihood of scaling and corrosion in the plant and raises the amount of seawater that must be added to the final brine to make it safe for discharge back into the environment. Additionally, boiling point of each stage is raised when adding the brine recycle. After weighing both alternatives against one another, we have decided to include a brine recycle in our plant design. Most of the negative aspects of the brine recycle can be combated (e.g. include anti-scaling agents in the feed pretreatment), and the economic benefits of including the brine recycle are very significant.<sup>8</sup><br />
<br />
===MSF: Continuous vs. Batch===<br />
The distillation step can be done in continuous or batch processes. Batch distillation is more versatile and often used when the product is in small amounts and very high purity. A continuous distillation is more efficient thermodynamically and economically for large amounts of material of constant composition, whereas batch distillation is more effective for small amounts of material of varying compositions. Since the plant is processing large amounts of seawater of relatively constant composition, the distillation system will utilize continuous distillation.<sup>9</sup><br />
<br />
===MSF: Long Tube vs. Crossed Tube ===<br />
Inside the evaporator stage, the condenser tube bundles may be arranged in either long tube or cross tube design. In the long tube arrangement, the tubes are aligned parallel to the direction of the flashing brine flow. The tubes go from stage to stage without water boxes. In the cross tube arrangement, the tubes are lined perpendicular to the flow of the flashing brine. Water boxes transfer brine between the stages.<sup>10 11</sup> While the water boxes in crossed tube bundles allow for more customization, the long tube configuration allows for construction of large unit sizes, as there are manufacturing restrictions with cross tubes. Long tube design can easily accommodate a large number of stages, which lead us to choose long tube for our design.<sup>11 12</sup><br />
<br />
===MSF: Venting System===<br />
Noncondensable gases exist in the process because of air leakages into stages under vacuum conditions and the release of dissolved gases from the heated brine. These gases are removed by venting the system. An air cooler section concentrates the gas before they are vented, and baffles direct the vapor and condensates out. There are two venting arrangements to consider: series and parallel. The system in series moves gas from one stage directly to the next, and the only loss in the system is vapor in the last stage (since some vapor is extracted with gases). This system is economical, however this configuration increases the amount of noncondensable gases passing from one stage to the next, and disrupting the venting system in one stage will affect the entire system. In parallel venting, gas is released through parallel takeoff pipes at each stage. Although this arrangement allows for venting at any stage to be controlled, the design and maintenance is more complex, and more vapor is lost than in the venting system in series. A third alternative is to use a combination of venting in parallel and in series, which is the common method in industry. For this process, our team chose to do venting in parallel and in series.<sup>12</sup><br />
<br />
===Additional Energy Source Alternatives===<br />
Energy for the process can also be coupled with renewable energy sources to reduce the desalination plant’s carbon footprint. Energy integration can be direct or indirect. In direct integration, thermal waste heat from industrial sources provide thermal energy or pressure as energy sources. Direct integration is advantageous at the modular level, as it avoids energy losses with electricity conversion. Within indirect integration, there are modular integration and grid/utility-scale integration. Modular integration integrates the plant with wind turbines and other small-scale renewable power generators with mobile deployment. A “hybridization” of renewable power sources with natural gas power generation is also an option, and the coupling of the two provides a stable power source. Indirect renewable energy integration is growing as the cost of renewable energy continues to decreases and provides an economy of scale that direct integration does not, but there are several obstacles towards indirect integration, such as the plant’s finance and engineering the integration of the two systems.<sup>13</sup> This distillation plant will be directly integrated with neighboring plants such as Chevron that produce thermal waste heat.<br />
<br />
===Product Treatment===<br />
Since the product is distilled water, it needs additional ions to a concentration of around 0.01% before going to the end user. The three alternatives considered were building a water treatment facility on site, simply adding the correct salts to the product stream and then sending the stream for bacterial treatment at a water plant, or simply sending the product distilled water for complete treatment to another facility. Due to the number of nearby water treatment plants and their demand for water, we elected to simply send the product to a nearby water treatment facility.<br />
<br />
==Design Constraints and Tradeoffs==<br />
While designing our process, we wanted to make sure that we met several outside constraints, including environmental, political, ethical, social, sustainability, health and safety constraints. First and most importantly, we wanted to ensure that the brine discharged back to the bay would not harm local marine life. Our process was designed around the constraint of diluting the exiting brine to within 0.2% salinity of background seawater. This is not only compliant with California law, but was also verified to be safe for surrounding marine life through our own outside research. We also addressed many of these considerations by deciding to pursue direct energy integration with the nearby Chevron plant in order to reduce environmental impact of our process. Additionally, we ensured that our plant would be located in an area that is densely populated and in great need of fresh drinking water. Finally, we addressed health and safety considerations by making sure we would be able to send our product distilled water to local treatment plants for proper potabilization.<br />
<br />
===Design Tradeoffs: Thermodynamics=== <br />
Adjusting elements within this process is iterative, and optimization thereof required changing multiple parameters at once. An example of this is in tuning the temperature increase by heater E-100; if the temperature of the stream entering the vessels is too high, the heat exchange between the vapor product and the feed stream will not be realizable because it causes the feed to be too hot to cool and condense the product. Higher temperatures, however, provide greater thermodynamic driving forces for flashing. Setting the entering stream temperature at 120°C provides enough heat for substantial flash at 130 kPa. This is the only heater required until the very last flash stage, which is added to provide more heat for vaporization. This heater (E-105) increases the stream temperature by 15°C, and the vapor product from the last vessel increases the feed stream temperature by almost 30°C. The added energy increases vaporization by 3%, which is a substantial 2.2 million kg/h. The temperature of the streams entering and leaving each stage decreases with each additional flash stage such that the last vessel has the lowest temperature, according to realistic operating guidelines. <br />
<br />
===Design Tradeoffs: Energy Consumption, Environmental Impacts, and Product Optimization===<br />
Increases in the pressure drop across any of the valves in this final design causes a temperature cross in the heat exchangers unless a proper increase in pump energy is provided. There is thus a design tradeoff between lowering energy usage and increasing product yield. For example, lowering the operating pressure of the process dictates that the pressure difference used to flash seawater must be smaller, possibly decreasing the amount that is vaporized. The final design aims for a yield of 50 million gallons per day. The 18 stage model was chosen for its low annual utility cost. This is a reflection of environmental mindfulness because energy consumption is an ongoing aspect of the process and should be lowered as much as possible.<br />
<br />
==Mass and Energy Balances==<br />
The model of the desalination system assumes that: (1) the properties are uniform in each phase within a stage, (2) heat losses are negligible due to the small surface area to volume ratio for each stage and properly insulated units (heat losses to the surrounding vary from 2 to 5% of the total system energy), (3) the distillate is salt free since the boiling point of water is much lower than that of salt, (4) the subcooling or superheating effects on the system energy balances are negligible, (5) the only contaminant is sodium chloride (there are no non-condensable gases to consider, so no vapors are vented), and (6) the process has 3 evaporation chambers.<br />
<br />
The major balances are that the feed is a mixture of the fresh seawater stream and the recycle stream, and that the brine stream exiting the last evaporation chamber is divided into the recycle stream and the waste stream. Within each stage, the change in mass of a phase over time is the balance between the net flow of that phase from the chamber and the rates of evaporation and condensation of water into and out of that phase. The equations governing the mass and energy balances on the system is displayed in Appendix C. <br />
<br />
=Optimization=<br />
As initiatives for reduced energy usage and increased environmental sustainability become more prevalent, efforts to minimize the utility cost in plants has increased to accommodate these incentives. Utilities are a continual source of expenditure and consumption, and a well-designed chemical process should seek to minimize this element. The annualized utility cost is a useful parameter to optimize given that its value depends on variations in energy costs; thus, annualized utility costs do not correlate with conventional indices of inflation, such as capital and labor costs. Additionally, utility costs, like other variable costs, can be minimized by improving the design or operational efficiency of the plant.<br />
<br />
In optimizing our MSF process, the design variable of focus was the number of stages to use in our process. The performance measure was the annualized utility cost, which was the parameter that was minimized for optimization. The process is constrained by the product specifications, which are kept constant and serve as the standard for comparison between each model. These specifications are to produce 50 million gallons of desalinated liquid water per day. <br />
<br />
One feasibility constraint in the process is the size of the heat exchangers, which must provide a large enough area for total condensation of the vapor stream coming out of the flash stages. In order to restrict the heat exchange area needed within each exchanger, the number of stages must be at least 11. Increasing the number of stages decreases the vapor flow rate at each, and decreases the heat exchange area required as well. An 11-stage process allows for appropriate heat exchange between the feed stream and the vapor product, according to the HYSYS economic analyzer. The optimization analysis thus was conducted incorporating only models with 11 or more stages. <br />
<br />
The HYSYS economic analyzer was used to systematically optimize the process by finding the model with the lowest annualized utility cost. The performance parameters kept constant across each model were: the inlet composition, pressure, and temperature, the brine outlet temperature, the total product flow rate and composition, and the flash stage schematic. Table 1 displays the annualized utility cost for each model, and illustrates that a clear dip in the utility cost occurs in an 18 stage model. Thus, 18 is the optimal number of stages to use for our MSF distillation given utility costs as the optimized parameter.<br />
[[File:Table_1.PNG|center|500x300px]]<br />
<br />
=Economic Evaluation=<br />
In order to evaluate our process from a fiscal standpoint, we used Aspen Process Economic Analyzer and Aspen cost estimator to determine capital and operating costs for our plant. These costs were calculated based on calculated equipment sizes, as well as energy requirements reported by our HYSYS model. The capital cost was found to be $485.2MM and annual total operating cost was found to be $144.7MM ($103.7MM of which was utilities). Annual plant revenue was estimated based on prices that water districts in the county currently pay for outside water sources, and was found to be $134.3MM.<sup>14</sup> <br />
<br />
The NPV analysis we conducted assumed that the plant would take two years to build, would operate at half capacity during the first year of operation (year 3), and have a 20 year lifetime. We also assumed that our plant would be in operation 350 days per year. A constant discount rate of 12% was assumed to hold throughout the plant’s lifetime. The final NPV of this project is -$495.7MM. This is due to both the large capital cost of the plant and the annual loss of $10.4MM while in full operation. A graph of cumulative cash flow versus time can be found in Appendix E. Tax rates and depreciation do not directly impact the NPV of this project due to operating at a loss, however for future calculations it should be noted that we used a straight line depreciation schedule over a seven year period with a 40% tax rate. <br />
<br />
Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing, while California is experiencing harsher droughts each year. A consequence of this is the possibility of receiving government subsidies for our clean water product. The similarly scaled desalination plant in Carlsbad, CA operates at a loss as well, but receives significant government subsidies. Building this facility may be a strategic investment, especially since greater water scarcity is predicted in the future. <br />
<br />
=Sensitivity Analysis=<br />
We wanted to determine how sensitive NPV of our project is to the cost of capital, price of utilities and price we would be able to sell our clean water product at. We conducted this analysis by varying each of these variables independently between 0.5 times and 1.5 times the original value we calculated. As to be expected, NPV grows more negative with increasing capital costs and utility prices and decreasing water prices. Conversely, NPV becomes less negative as price of water rises and capital and utility costs decrease. A plot summarizing the effects of varying these costs can be found in Appendix E. NPV is most sensitive to the price at which we will be selling our clean water product. It is worth noting that NPV is more sensitive to utilities cost than it is to capital cost, which is why we focused on optimizing the cost of utilities. In future steps, trying to reduce utilities cost even more would be worth looking into to decrease the amount of money being lost on this project.<br />
<br />
=Conclusions and Final Recommendation=<br />
The final design achieves the project goal of producing 50 million gallons per day of distilled water at a yield of 13%, comparable to other similarly sized plants. An optimization of the number of MSF stages is realistic, and can be improved upon by taking into account other process parameters. <br />
<br />
The proposed design was optimized around utility costs, comparing plants with 11 to 25 stages. The process is constrained by product specifications and by the thermodynamics of the heat exchange between the feed and the product streams. Energy conservation was achieved in using the seawater feed to condense the final product, as well as in all of the heat exchangers increasing the thermal energy of the seawater feed stream before it enters the flash stages. <br />
<br />
In order to further optimize this process, other design parameters should be considered such as the brine recycle ratio, the cooler duty of the recycle stream, the pressure drop across each valve at the flash stages, and other economic factors. An optimization around maximizing NPV, for example, might be more comprehensive than that conducted regarding only utility costs. Tuning brine recycle rates could greatly improve process efficiency, and standardizing flash stage pressure drops would make operations more feasible and controlled. <br />
<br />
Given our in depth economic analysis, this project would lose an average of $10.4MM per year, and has an NPV of -$495.7MM for a 20 year plant lifetime. From an economic perspective alone it would not be a good project to build. However, other factors need to be considered when building a project with enormous public value. In recent years California droughts have become more severe. Implementing a drought-proof supply of water now could avert a disaster later on. Even without a large disaster, having the desalination plant could also be expected to pay off in the future with the increasing price of water. Considerations such as these were the deciding factors in building the Carlsbad desalination plant. Since there are currently no desalination plants in the Bay area we recommend that preparations should be made to move forward with a desalination plant.<br />
<br />
=References=<br />
[1] Lyons J. Environmental Leader. Environmental Leader 2015. Available at: http://www.environmentalleader.com/2015/10/27/desalination-plants-to-double-by-2020. Accessed 2016.<br />
<br />
[2] Fitzsimmons E. In California, Cities Braced to Cut Water by 10 to 35%. The New York Times 2015. Available at: <br />
http://www.nytimes.com/2015/04/09/us/in-california-cities-braced-to-cut-water-by-10-to-35.html. Accessed 2016. <br />
<br />
[3] Salinity Times Series - USGS Water Quality of SF Bay. Salinity Times Series - USGS Water Quality of SF Bay. Available at:<br />
http://sfbay.wr.usgs.gov/access/wqdata/overview/examp/charts/salin.html. Accessed 2016.<br />
<br />
[4] Reverse Osmosis vs. Multi Stage Flash Distillation: A Comparison Between Different Desalination Methods. Brighthub Engineering. Available at:<br />
http://www.brighthubengineering.com/power-plants/29621-comparison-between-the-reverse-osmosis-and-multi-stage-flash-distillation-methods/. Accessed 2016.<br />
<br />
[5] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[6] H. El-Dessouky. Fundamentals of salt water desalination, 1st Ed., Elsevier Science, 2002.<br />
<br />
[7] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[8] Guasp RE, Bello CP, Jara JG, Vega JP, Damien T, Winkel C, Smith HH. Desalination by distillation. Organization of American States website. oas.org. Accessed January 28, 2015.<br />
<br />
[9] Batch Distillation. AE 335 Separation Processes website. http://prodpran.che.engr.tu.ac.th/AE335/AE335.html. Accessed January 26, 2016.<br />
<br />
[10] Morris R. The development of the multi-stage flash distillation process: A designer's viewpoint. Desalination. 1993;93:57-68. <br />
<br />
[11] Darwish MA. Developments in the multi-stage flash desalting system. Desalination. 1995;100:35-64.<br />
<br />
[12] Wade N. Distillation plant development and cost update. Desalination. 2001;136:3-12.<br />
<br />
[13] Desalination Technologies and the Use of Alternative Energies for Desalination. World Intellectual Property Organization website. http://www.wipo.int/export/sites/www/patentscope/<br />
en/programs/patent_landscapes/documents/patent_landscapes/948-2E-WEB.pdf. Updated November 2011. Accessed January 23, 2016.<br />
<br />
[14] California Turns to the Pacific Ocean for Water | MIT Technology Review.MIT Technology Review 2014. Available at:<br />
http://www.technologyreview.com/featuredstory/533446/desalination-out-of-desperation/. Accessed 2016.<br />
<br />
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<br />
=Appendix A. Process Flow Diagram=<br />
[[File:Appendix 1.PNG]]<br />
<br />
'''Figure A1''' Process Flow Diagram of the MSF System<br />
<br />
=Appendix B. HYSYS Simulation=<br />
The HYSYS model of the process is shown below.<br />
<br />
[[File:AppendB.PNG]]<br />
<br />
'''Figure B1.''' The HYSYS model of the MSF distillation process.<br />
<br />
=Appendix C. Mass and Energy Balances=<br />
Below are equations that describe the mass and energy balances of the system.<br />
<br />
In MSF system with brine recycle, the mass flow of the intake seawater I is mixed with the mass flow of the recycle brine R to create the feed seawater stream F. Since this model assumes no non-condensable gases, the feed stream is overall balanced by the brine waste stream W, the recycle brine stream, and the distillate stream D. The brine stream exiting the last evaporation chamber B is divided into the recycle and waste streams. The amount of salt that enters the series of evaporation chambers is the amount of salt that leaves (X is the salt mass fraction).<br />
<br />
[[File:Overallmasss.PNG]]<br />
<br />
Within each stage, the change in mass of a phase is the mass flows of that phase into and out of the chamber and the rates of evaporation or condensation of the water into and out of that phase.<br />
[[File:Masss2.PNG]]<br />
<br />
The energy balances are summarized below.<br />
<br />
[[File:Mass3.PNG]]<br />
<br />
[[File:Mass4.PNG]]<br />
<br />
=Appendix D. Summary of Process Units=<br />
<br />
[[File:AppendD1.PNG]]<br />
[[File:AppenD2.PNG]]<br />
<br />
=Appendix E. MSF Stage Parameters=<br />
[[File:AppendE.PNG]]<br />
<br />
[[File:Appendix E3.PNG]]<br />
<br />
[[File:Appendix E4.PNG]]<br />
<br />
=Appendix F. Process Units Calculations=<br />
[[File:AppendF.PNG]]<br />
<br />
[[File:AppendF2.PNG]]<br />
<br />
[[File:AppendF3.PNG]]<br />
<br />
=Appendix G. Economic Analysis=<br />
[[File:Econanalysis.PNG]]</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Desalination_-_Team_A&diff=5271Desalination - Team A2016-03-12T03:32:45Z<p>Pdtravan: /* Brine Heater */</p>
<hr />
<div>Author: Pear Dhiantravan<sup>[2016]</sup>, Reed Kolbe<sup>[2016]</sup>, Sheridan Lichtor<sup>[2016]</sup>, John Marsiglio<sup>[2016]</sup>, Ellen Zhuang<sup>[2016]</sup><br />
<br />
Instructors: Fengqi You, David Wegerer<br />
<br />
Winter 2016<br />
<br />
=Executive Summary=<br />
Seawater desalination is an attractive approach to address the world’s freshwater shortage in light of the increasing global water scarcity. Our team decided to tackle California's growing drought crisis by designing a multistage flash desalination plant in Richmond, CA. Based on market analysis of existing desalination plants and water demands, this is a strategic location for the desalination of 50 million gallons per day of water from the San Francisco Bay.<br />
<br />
The MSF process contains 18 flash stages in series. Seawater is taken in from the San Francisco Bay at a rate of 398 million gallons per day and mixed with brine recycled from the system. Within the MSF process, seawater is heated through a series of 18 heat exchangers and a brine heater before enters a series of 18 evaporation chambers. In the evaporation chambers, the seawater flashes and the freshwater vapor is condensed, collected, and sent to a water treatment facility. The brine stream proceeds to the next chamber, and the process continues. Upon exiting the last flashing chamber, the brine stream is split into a recycle brine stream that is mixed with the seawater inlet feed and a waste stream that is diluted with fresh seawater and returned to the sea. Overall, the process yield is 13%. This process was constructed in Aspen HYSYS and optimized around utility costs using the HYSYS Economic Analyzer. Based on duties, temperatures and pressures reported by HYSYS, as well as fundamental mass and energy balances, the equipment were sized appropriately and the economics of the process was analyzed.<br />
<br />
The design has a total capital cost of $485.2 MM, an annual operating cost of $144.7 MM ($103.7 MM of which is utilities), and an annual plant revenue of $134.3 MM. Economic analysis reveals that the project has a negative NPV of -$495.7 MM and operates at a loss of $10.4 MM per year. Thus, the proposed design is not profitable. Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing while California is experiencing harsher droughts each year. Given the dire situations, the government may support the proposed clean water project with subsidies. Building the facility may be a strategic investment, especially since greater water scarcity is predicted in the future.<br />
<br />
Our design meets various environmental, ethical, social and health related constraints. The brine discharged back to the bay is diluted to at most 0.2% above the natural background salinity as required by law so that the plant does not impose harm on any local marine life. The demographic that the plant serves is largely invested in the protection of the environment, which we addressed by reducing energy consumption through direct energy integration with the nearby Chevron plant. Lastly, the product meets the specifications of the California Safe Water Drinking Act by producing water with no impurities.<br />
<br />
<br />
__TOC__<br />
<br />
=Introduction=<br />
An increasing global water scarcity is fueling initiatives everywhere for clean water treatment, making efficient seawater desalination an attractive aim for chemical plant design. A 2015 market analysis found that the global desalination market earned revenues of $11.66 billion, and this number is expected to reach over $19 billion by 2019. Furthermore, the 17,000 desalination plants currently in operation are expected to double in number by 2020.<sup>1</sup> <br />
<br />
As fresh water sources become increasingly scarce, strict water conservation measures are being observed. California is entering the fourth year of one of its most severe droughts on record. Cities are required to reduce their water usage by 35% to avoid facing fines.<sup>2</sup> In lieu of these pressing conditions, California is looking for ways to provide more accessible fresh water to its citizens. This high demand for clean water motivated our choosing Richmond, CA as our plant location. At Richmond, the desalination plant can convert readily available seawater from the San Francisco Bay into fresh water. We propose to desalinate 50 million gallons of water per day to be sent to water treatment plants for potability. This aim is based on the capacity of the desalination plant in Carlsbad, California, which services a similar population.<br />
<br />
The salinity of the water in the San Francisco Bay is seasonal. During the dry seasons of summer and fall, salinity is high around 10 PSU (10,000 ppm) because water from the Pacific Ocean flows into the San Francisco Bay. During the wet winter season, fresh water from the rivers flows into the Bay, and salinity drops to around 2 PSU (2,000).3 Designed to meet the “worst case” scenario, our plant will process 398 million gallons of water per day with 10,000 ppm of salt to produce 50 million gallons of distilled water. This gives a yield of 13%.<br />
<br />
The desalination plant proposed consists of 18 flash stages in series. This report outlines our investigation of this potential water desalination plant, including design and optimization of the desalination process, an analysis of its energy consumption and environmental impacts, and a study of its economic implications.<br />
<br />
=Technical Approach=<br />
For the desalination step of our process, we selected a multistage flash (MSF) distillation process. Not only is MSF distillation a very viable method, but it is also the most common method, currently producing about 60% of the world’s desalinated water. MSF and reverse osmosis (RO) are the two major methods being used in large-scale desalination plants. Both processes require considerable amounts of energy. RO typically has a lower energy demand; however, the high impurity content of the Bay water would frequently necessitate membrane cleaning and/or exchange. Feed going through a RO system requires extensive pretreatment to remove biological organisms and other solids to control the pH and the chemical composition of the water. With the San Francisco Bay as our source of water, MSF is an attractive option because sediment and other large impurities can be separated from the feed before distillation occurs. Additionally, MSF distillation plants can be located near power plants and paired to their waste heat streams to conserve energy. This can reduce energy needs by half or two thirds, making MSF increasingly more practical. Due to the maintenance required in the RO system, the MSF distillation is the better option in terms of operation cost.<sup>4</sup><br />
<br />
A HYSYS model was built to simulate the MSF distillation section of the process, which spans after seawater pretreatment and before local potable water treatment. The model is used to simulate the distillation steps and to calculate necessary heating, cooling, and input flow rates to produce the required 50 million gallons of distillated water per day. For the simulation, the 398 million gallons per day of seawater feed stream is defined to be composed of 3.31 mol% sodium chloride (NaCl) and 96.69 mol% water. The percentage of NaCl is set to account for other ions and chemicals present after the pretreatment phase. NaCl alone is added to the HYSYS system due to the capabilities of the fluid package used to simulate this process, ElectroNRTL. The feed is set at 22°C, which is the approximate the temperature of the San Francisco Bay year round.<br />
<br />
=Process Design=<br />
==Design Overview==<br />
The proposed desalination plant uses MSF distillation to convert the San Francisco Bay water to fresh water. The final process design contains 18 flash stages in series. Overall, 398 million gallons per day of of brackish water is converted to 50 million gallons per day of deionized water, a 13% yield. The production meets the required production rate of 50 million gallons of freshwater per day. <br />
<br />
Seawater is taken in from the San Francisco Bay and mixed with the brine recycle stream produced downstream. The feed is then heated through a series of condensers and a heater. Distilled water vapor in each flash stage contacts the tubes carrying the seawater feed and condenses into a liquid stream by exchanging heat with the cooler seawater feed stream. The seawater is sent through a heater to increase its thermal energy before entering the first stage of the MSF. In each flashing stage, some of the water evaporates, leaving the salt behind. The freshwater vapors condense, as described above, and is collected and sent to a water treatment plant. The brine stream is split into the recycle stream and a waste stream, and the waste stream is diluted with fresh seawater before being discharged back into the bay.<br />
<br />
A process flow diagram of the process is depicted in Appendix A. <br />
<br />
==Pretreatment==<br />
Sediment is removed to prevent solids from plugging the process downstream. Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime, and is controlled for by lowering pH. Acidifying the water will also remove CO2, which is a corrosive gas. To control for oxygen, oxygen scavengers will be included in the system to sequester it. Sodium bisulfate will be used as the scavenger.<sup>5</sup><br />
<br />
==Condensers (Heat Exchanger Networks)==<br />
In order to conserve and recycle energy, the condensation of the distillate and heating of the seawater feed will be coupled in countercurrent heat exchanger networks. These heat exchanger networks are condensers of the design. The cold feed, which is a mixture of fresh seawater and brine recycle, is fed through multiple heat exchangers in series. Each heat exchanger corresponds to a different evaporation chamber. This process consists of 18 heat exchangers: E-101, E-102, … E-117, and E-118, which correspond to evaporation chambers V-102, V-103, … V-118, and V-119, respectively. <br />
<br />
The heat exchangers can be viewed similarly to a shell and tube setup, however there is no actual physical shell. The tubes simply run through the top of the evaporation chambers, where vaporized distilled water in the chamber acts as the shell side fluid. The tube bundles are arranged in long tube configuration and are aligned parallel to the direction of the flashing brine flow in the evaporation chamber. The evaporating brine in an evaporation chamber rise up to the the corresponding heat exchanger and condense on the outside of the tubes, creating collectable pure water. This condensing water is what heats up the seawater in the tubes. <br />
<br />
E-101 was used as the basis for the condenser sizing since it has the highest heat requirement, and thus will be the largest heat exchanger. From the HYSYS model, the overall system requires 2.24 x 10<sup>6</sup> kW of duty. Assuming this energy requirement, 5000 tubes, and 18 m length tubes (the diameter of the evaporation chambers, explained further on the next page), the diameter of each tube was calculated to be 0.4 m. Based on the temperature of the streams and flow, the thickness of the tube is 7 x 10<sup>-4</sup> m.<br />
<br />
==Brine Heater==<br />
After the seawater exits the final heat exchanger, it enters a brine heater (E-119) where it is brought up to the temperature necessary for the flashing process to begin. This means that the seawater must be overheated compared to stage one, so that the seawater will flash in the evaporation chamber, i.e. release heat and vapor to reach equilibrium with stage conditions. After flowing through the condensers, the seawater enters the brine heater at 91.6 oC and is heated to 120 oC. The overall system requires 2.31 x 106 kW of duty. This is supplied by a total of 4.15 x 106 kg per hour of steam.<br />
<br />
==Evaporation Chambers==<br />
When the seawater has been brought to a temperature appropriate for flashing, it enters the first evaporation chamber (V-102). Upon entering the chamber, the water is flashed. Some of the water evaporates, leaving the salt behind. The vapor rises up to the heat exchanger tubes in each evaporation chamber and condenses on the outside into the distilled water product. This condensing water is what heats up the seawater in the tubes discussed above. The seawater that does not evaporate moves to the next stage, which operates at a higher temperature and lower pressure, and the process is repeated. This continues in series through a total of 18 flashing chambers (V-102, V-103, … V-118, and V-119). All of the distillate is collected into one stream and all of the brine is mixed with seawater before being disposed of back in the bay in order to dilute it enough so it does not have an adverse effect on marine life.<br />
<br />
Each respective heat exchanger fully condenses the vapor product stream from each stage. However, when all of the individual product streams are consolidated into the final combined product stream, some water exists in the vapor phase due to temperature and pressure changes associated with mixing all of the streams together. Although the vapor product stream from each stage condenses completely across its respective heat exchanger, the total product stream contains some water in the vapor phase due to the temperature change when the mixer sums all the streams. In order to fully condense this stream, which will be sent to local water treatment plans, a heat exchanger (E-120) is put in place to cool down the product using the process feed stream. <br />
<br />
The correlations of El-Dessouky and Ettouney were employed in order to size the flash chambers. They specified that conventional MSF plants that operate at a capacity between 27,000 and 36,000 m<sup>3</sup>/day use flashing stages of the dimensions 18 m diameter and 4 m height.<sup>6</sup><br />
<br />
==Valves==<br />
The model requires valves in between the evaporation chambers. The seawater streams flow through valves with large pressure drops to flash a portion the liquid into vapor that can then be separated in the vessels. Large pressure drops provide the thermodynamic driving force to vaporize more of the liquid, and are required to achieve high product yield. <br />
<br />
==Material of Construction==<br />
Before 1980, the shells and internals of the MSF units were commonly constructed from carbon steel. Seawater, however, corrodes carbon steel. To compensate for this, the thickness of the carbon steel has an additional corrosion allowance, which increases the size and weight of the equipment. After 1980, the stainless steel and duplex stainless steel became increasingly common. Stainless steel metal requires less thickness for equivalent strength and corrosion resistance, which allows for a reduction in the size, weight, and therefore cost of units. Major units in our process will be constructed from stainless steel.<sup>6</sup><br />
<br />
==Process Alternatives==<br />
In order to ensure that our design is fully optimized, we wanted to consider several alternatives for our process. We looked at alternatives associated with water pretreatment, the distillation process itself and product treatment.<br />
<br />
===Water Pretreatment===<br />
Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime. Scaling can be controlled by adjusting pH, temperature, and bicarbonate concentration. We selected acidification to control for process scaling. This is because lowering a process temperature would decrease overall efficiency, and decreasing bicarbonate concentration would be comparatively expensive. Lowering pH would have the added benefit of controlling CO2 concentrations since CO2 is a corrosive gas. To control for corrosion we looked at how to remove oxygen. To target the oxygen we chose an oxygen scavenger. This was chosen over other options such as a deaerator, or a protective coating because a deaerator would have a large capital cost, and the equipment itself would experience corrosion, and a tank coating such as zinc orthophosphate has a mixed effectiveness.<sup>7</sup><br />
<br />
===MSF: Brine Recycle vs. Once-Through System===<br />
We explored two options for the overall layout of the MSF distillation plant. In the first, the brine passes through the process once; in the second, a portion of the brine is recycled from the last stage to the incoming seawater feed. The largest draw towards implementing a brine recycle is that it would significantly reduce the overall amount of seawater needed to produce the daily target of 50 million gallons per day. This in turn would lower the amount of energy required to run the pump feeding seawater to the process. Another positive is that, with a brine recycle, the amount of water conditioning chemicals that must be added to the seawater feed is reduced. The negative aspects mainly revolve around the fact that the solution throughout the process will be higher in salt concentration. This increase in salinity both raises the likelihood of scaling and corrosion in the plant and raises the amount of seawater that must be added to the final brine to make it safe for discharge back into the environment. Additionally, boiling point of each stage is raised when adding the brine recycle. After weighing both alternatives against one another, we have decided to include a brine recycle in our plant design. Most of the negative aspects of the brine recycle can be combated (e.g. include anti-scaling agents in the feed pretreatment), and the economic benefits of including the brine recycle are very significant.<sup>8</sup><br />
<br />
===MSF: Continuous vs. Batch===<br />
The distillation step can be done in continuous or batch processes. Batch distillation is more versatile and often used when the product is in small amounts and very high purity. A continuous distillation is more efficient thermodynamically and economically for large amounts of material of constant composition, whereas batch distillation is more effective for small amounts of material of varying compositions. Since the plant is processing large amounts of seawater of relatively constant composition, the distillation system will utilize continuous distillation.<sup>9</sup><br />
<br />
===MSF: Long Tube vs. Crossed Tube ===<br />
Inside the evaporator stage, the condenser tube bundles may be arranged in either long tube or cross tube design. In the long tube arrangement, the tubes are aligned parallel to the direction of the flashing brine flow. The tubes go from stage to stage without water boxes. In the cross tube arrangement, the tubes are lined perpendicular to the flow of the flashing brine. Water boxes transfer brine between the stages.<sup>10 11</sup> While the water boxes in crossed tube bundles allow for more customization, the long tube configuration allows for construction of large unit sizes, as there are manufacturing restrictions with cross tubes. Long tube design can easily accommodate a large number of stages, which lead us to choose long tube for our design.<sup>11 12</sup><br />
<br />
===MSF: Venting System===<br />
Noncondensable gases exist in the process because of air leakages into stages under vacuum conditions and the release of dissolved gases from the heated brine. These gases are removed by venting the system. An air cooler section concentrates the gas before they are vented, and baffles direct the vapor and condensates out. There are two venting arrangements to consider: series and parallel. The system in series moves gas from one stage directly to the next, and the only loss in the system is vapor in the last stage (since some vapor is extracted with gases). This system is economical, however this configuration increases the amount of noncondensable gases passing from one stage to the next, and disrupting the venting system in one stage will affect the entire system. In parallel venting, gas is released through parallel takeoff pipes at each stage. Although this arrangement allows for venting at any stage to be controlled, the design and maintenance is more complex, and more vapor is lost than in the venting system in series. A third alternative is to use a combination of venting in parallel and in series, which is the common method in industry. For this process, our team chose to do venting in parallel and in series.<sup>12</sup><br />
<br />
===Additional Energy Source Alternatives===<br />
Energy for the process can also be coupled with renewable energy sources to reduce the desalination plant’s carbon footprint. Energy integration can be direct or indirect. In direct integration, thermal waste heat from industrial sources provide thermal energy or pressure as energy sources. Direct integration is advantageous at the modular level, as it avoids energy losses with electricity conversion. Within indirect integration, there are modular integration and grid/utility-scale integration. Modular integration integrates the plant with wind turbines and other small-scale renewable power generators with mobile deployment. A “hybridization” of renewable power sources with natural gas power generation is also an option, and the coupling of the two provides a stable power source. Indirect renewable energy integration is growing as the cost of renewable energy continues to decreases and provides an economy of scale that direct integration does not, but there are several obstacles towards indirect integration, such as the plant’s finance and engineering the integration of the two systems.<sup>13</sup> This distillation plant will be directly integrated with neighboring plants such as Chevron that produce thermal waste heat.<br />
<br />
===Product Treatment===<br />
Since the product is distilled water, it needs additional ions to a concentration of around 0.01% before going to the end user. The three alternatives considered were building a water treatment facility on site, simply adding the correct salts to the product stream and then sending the stream for bacterial treatment at a water plant, or simply sending the product distilled water for complete treatment to another facility. Due to the number of nearby water treatment plants and their demand for water, we elected to simply send the product to a nearby water treatment facility.<br />
<br />
==Design Constraints and Tradeoffs==<br />
While designing our process, we wanted to make sure that we met several outside constraints, including environmental, political, ethical, social, sustainability, health and safety constraints. First and most importantly, we wanted to ensure that the brine discharged back to the bay would not harm local marine life. Our process was designed around the constraint of diluting the exiting brine to within 0.2% salinity of background seawater. This is not only compliant with California law, but was also verified to be safe for surrounding marine life through our own outside research. We also addressed many of these considerations by deciding to pursue direct energy integration with the nearby Chevron plant in order to reduce environmental impact of our process. Additionally, we ensured that our plant would be located in an area that is densely populated and in great need of fresh drinking water. Finally, we addressed health and safety considerations by making sure we would be able to send our product distilled water to local treatment plants for proper potabilization.<br />
<br />
===Design Tradeoffs: Thermodynamics=== <br />
Adjusting elements within this process is iterative, and optimization thereof required changing multiple parameters at once. An example of this is in tuning the temperature increase by heater E-100; if the temperature of the stream entering the vessels is too high, the heat exchange between the vapor product and the feed stream will not be realizable because it causes the feed to be too hot to cool and condense the product. Higher temperatures, however, provide greater thermodynamic driving forces for flashing. Setting the entering stream temperature at 120°C provides enough heat for substantial flash at 130 kPa. This is the only heater required until the very last flash stage, which is added to provide more heat for vaporization. This heater (E-105) increases the stream temperature by 15°C, and the vapor product from the last vessel increases the feed stream temperature by almost 30°C. The added energy increases vaporization by 3%, which is a substantial 2.2 million kg/h. The temperature of the streams entering and leaving each stage decreases with each additional flash stage such that the last vessel has the lowest temperature, according to realistic operating guidelines. <br />
<br />
===Design Tradeoffs: Energy Consumption, Environmental Impacts, and Product Optimization===<br />
Increases in the pressure drop across any of the valves in this final design causes a temperature cross in the heat exchangers unless a proper increase in pump energy is provided. There is thus a design tradeoff between lowering energy usage and increasing product yield. For example, lowering the operating pressure of the process dictates that the pressure difference used to flash seawater must be smaller, possibly decreasing the amount that is vaporized. The final design aims for a yield of 50 million gallons per day. The 18 stage model was chosen for its low annual utility cost. This is a reflection of environmental mindfulness because energy consumption is an ongoing aspect of the process and should be lowered as much as possible.<br />
<br />
==Mass and Energy Balances==<br />
The model of the desalination system assumes that: (1) the properties are uniform in each phase within a stage, (2) heat losses are negligible due to the small surface area to volume ratio for each stage and properly insulated units (heat losses to the surrounding vary from 2 to 5% of the total system energy), (3) the distillate is salt free since the boiling point of water is much lower than that of salt, (4) the subcooling or superheating effects on the system energy balances are negligible, (5) the only contaminant is sodium chloride (there are no non-condensable gases to consider, so no vapors are vented), and (6) the process has 3 evaporation chambers.<br />
<br />
The major balances are that the feed is a mixture of the fresh seawater stream and the recycle stream, and that the brine stream exiting the last evaporation chamber is divided into the recycle stream and the waste stream. Within each stage, the change in mass of a phase over time is the balance between the net flow of that phase from the chamber and the rates of evaporation and condensation of water into and out of that phase. The equations governing the mass and energy balances on the system is displayed in Appendix C. <br />
<br />
=Optimization=<br />
As initiatives for reduced energy usage and increased environmental sustainability become more prevalent, efforts to minimize the utility cost in plants has increased to accommodate these incentives. Utilities are a continual source of expenditure and consumption, and a well-designed chemical process should seek to minimize this element. The annualized utility cost is a useful parameter to optimize given that its value depends on variations in energy costs; thus, annualized utility costs do not correlate with conventional indices of inflation, such as capital and labor costs. Additionally, utility costs, like other variable costs, can be minimized by improving the design or operational efficiency of the plant.<br />
<br />
In optimizing our MSF process, the design variable of focus was the number of stages to use in our process. The performance measure was the annualized utility cost, which was the parameter that was minimized for optimization. The process is constrained by the product specifications, which are kept constant and serve as the standard for comparison between each model. These specifications are to produce 50 million gallons of desalinated liquid water per day. <br />
<br />
One feasibility constraint in the process is the size of the heat exchangers, which must provide a large enough area for total condensation of the vapor stream coming out of the flash stages. In order to restrict the heat exchange area needed within each exchanger, the number of stages must be at least 11. Increasing the number of stages decreases the vapor flow rate at each, and decreases the heat exchange area required as well. An 11-stage process allows for appropriate heat exchange between the feed stream and the vapor product, according to the HYSYS economic analyzer. The optimization analysis thus was conducted incorporating only models with 11 or more stages. <br />
<br />
The HYSYS economic analyzer was used to systematically optimize the process by finding the model with the lowest annualized utility cost. The performance parameters kept constant across each model were: the inlet composition, pressure, and temperature, the brine outlet temperature, the total product flow rate and composition, and the flash stage schematic. Table 1 displays the annualized utility cost for each model, and illustrates that a clear dip in the utility cost occurs in an 18 stage model. Thus, 18 is the optimal number of stages to use for our MSF distillation given utility costs as the optimized parameter.<br />
[[File:Table_1.PNG|center|500x300px]]<br />
<br />
=Economic Evaluation=<br />
In order to evaluate our process from a fiscal standpoint, we used Aspen Process Economic Analyzer and Aspen cost estimator to determine capital and operating costs for our plant. These costs were calculated based on calculated equipment sizes, as well as energy requirements reported by our HYSYS model. The capital cost was found to be $485.2MM and annual total operating cost was found to be $144.7MM ($103.7MM of which was utilities). Annual plant revenue was estimated based on prices that water districts in the county currently pay for outside water sources, and was found to be $134.3MM.<sup>14</sup> <br />
<br />
The NPV analysis we conducted assumed that the plant would take two years to build, would operate at half capacity during the first year of operation (year 3), and have a 20 year lifetime. We also assumed that our plant would be in operation 350 days per year. A constant discount rate of 12% was assumed to hold throughout the plant’s lifetime. The final NPV of this project is -$495.7MM. This is due to both the large capital cost of the plant and the annual loss of $10.4MM while in full operation. A graph of cumulative cash flow versus time can be found in Appendix E. Tax rates and depreciation do not directly impact the NPV of this project due to operating at a loss, however for future calculations it should be noted that we used a straight line depreciation schedule over a seven year period with a 40% tax rate. <br />
<br />
Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing, while California is experiencing harsher droughts each year. A consequence of this is the possibility of receiving government subsidies for our clean water product. The similarly scaled desalination plant in Carlsbad, CA operates at a loss as well, but receives significant government subsidies. Building this facility may be a strategic investment, especially since greater water scarcity is predicted in the future. <br />
<br />
=Sensitivity Analysis=<br />
We wanted to determine how sensitive NPV of our project is to the cost of capital, price of utilities and price we would be able to sell our clean water product at. We conducted this analysis by varying each of these variables independently between 0.5 times and 1.5 times the original value we calculated. As to be expected, NPV grows more negative with increasing capital costs and utility prices and decreasing water prices. Conversely, NPV becomes less negative as price of water rises and capital and utility costs decrease. A plot summarizing the effects of varying these costs can be found in Appendix E. NPV is most sensitive to the price at which we will be selling our clean water product. It is worth noting that NPV is more sensitive to utilities cost than it is to capital cost, which is why we focused on optimizing the cost of utilities. In future steps, trying to reduce utilities cost even more would be worth looking into to decrease the amount of money being lost on this project.<br />
<br />
=Conclusions and Final Recommendation=<br />
The final design achieves the project goal of producing 50 million gallons per day of distilled water at a yield of 13%, comparable to other similarly sized plants. An optimization of the number of MSF stages is realistic, and can be improved upon by taking into account other process parameters. <br />
<br />
The proposed design was optimized around utility costs, comparing plants with 11 to 25 stages. The process is constrained by product specifications and by the thermodynamics of the heat exchange between the feed and the product streams. Energy conservation was achieved in using the seawater feed to condense the final product, as well as in all of the heat exchangers increasing the thermal energy of the seawater feed stream before it enters the flash stages. <br />
<br />
In order to further optimize this process, other design parameters should be considered such as the brine recycle ratio, the cooler duty of the recycle stream, the pressure drop across each valve at the flash stages, and other economic factors. An optimization around maximizing NPV, for example, might be more comprehensive than that conducted regarding only utility costs. Tuning brine recycle rates could greatly improve process efficiency, and standardizing flash stage pressure drops would make operations more feasible and controlled. <br />
<br />
Given our in depth economic analysis, this project would lose an average of $10.4MM per year, and has an NPV of -$495.7MM for a 20 year plant lifetime. From an economic perspective alone it would not be a good project to build. However, other factors need to be considered when building a project with enormous public value. In recent years California droughts have become more severe. Implementing a drought-proof supply of water now could avert a disaster later on. Even without a large disaster, having the desalination plant could also be expected to pay off in the future with the increasing price of water. Considerations such as these were the deciding factors in building the Carlsbad desalination plant. Since there are currently no desalination plants in the Bay area we recommend that preparations should be made to move forward with a desalination plant.<br />
<br />
=References=<br />
[1] Lyons J. Environmental Leader. Environmental Leader 2015. Available at: http://www.environmentalleader.com/2015/10/27/desalination-plants-to-double-by-2020. Accessed 2016.<br />
<br />
[2] Fitzsimmons E. In California, Cities Braced to Cut Water by 10 to 35%. The New York Times 2015. Available at: <br />
http://www.nytimes.com/2015/04/09/us/in-california-cities-braced-to-cut-water-by-10-to-35.html. Accessed 2016. <br />
<br />
[3] Salinity Times Series - USGS Water Quality of SF Bay. Salinity Times Series - USGS Water Quality of SF Bay. Available at:<br />
http://sfbay.wr.usgs.gov/access/wqdata/overview/examp/charts/salin.html. Accessed 2016.<br />
<br />
[4] Reverse Osmosis vs. Multi Stage Flash Distillation: A Comparison Between Different Desalination Methods. Brighthub Engineering. Available at:<br />
http://www.brighthubengineering.com/power-plants/29621-comparison-between-the-reverse-osmosis-and-multi-stage-flash-distillation-methods/. Accessed 2016.<br />
<br />
[5] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[6] H. El-Dessouky. Fundamentals of salt water desalination, 1st Ed., Elsevier Science, 2002.<br />
<br />
[7] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[8] Guasp RE, Bello CP, Jara JG, Vega JP, Damien T, Winkel C, Smith HH. Desalination by distillation. Organization of American States website. oas.org. Accessed January 28, 2015.<br />
<br />
[9] Batch Distillation. AE 335 Separation Processes website. http://prodpran.che.engr.tu.ac.th/AE335/AE335.html. Accessed January 26, 2016.<br />
<br />
[10] Morris R. The development of the multi-stage flash distillation process: A designer's viewpoint. Desalination. 1993;93:57-68. <br />
<br />
[11] Darwish MA. Developments in the multi-stage flash desalting system. Desalination. 1995;100:35-64.<br />
<br />
[12] Wade N. Distillation plant development and cost update. Desalination. 2001;136:3-12.<br />
<br />
[13] Desalination Technologies and the Use of Alternative Energies for Desalination. World Intellectual Property Organization website. http://www.wipo.int/export/sites/www/patentscope/<br />
en/programs/patent_landscapes/documents/patent_landscapes/948-2E-WEB.pdf. Updated November 2011. Accessed January 23, 2016.<br />
<br />
[14] California Turns to the Pacific Ocean for Water | MIT Technology Review.MIT Technology Review 2014. Available at:<br />
http://www.technologyreview.com/featuredstory/533446/desalination-out-of-desperation/. Accessed 2016.<br />
<br />
----<br />
----<br />
----<br />
<br />
=Appendix A. Process Flow Diagram=<br />
[[File:Appendix 1.PNG]]<br />
<br />
'''Figure A1''' Process Flow Diagram of the MSF System<br />
<br />
=Appendix B. HYSYS Simulation=<br />
The HYSYS model of the process is shown below.<br />
<br />
[[File:AppendB.PNG]]<br />
<br />
'''Figure B1.''' The HYSYS model of the MSF distillation process.<br />
<br />
=Appendix C. Mass and Energy Balances=<br />
Below are equations that describe the mass and energy balances of the system.<br />
<br />
In MSF system with brine recycle, the mass flow of the intake seawater I is mixed with the mass flow of the recycle brine R to create the feed seawater stream F. Since this model assumes no non-condensable gases, the feed stream is overall balanced by the brine waste stream W, the recycle brine stream, and the distillate stream D. The brine stream exiting the last evaporation chamber B is divided into the recycle and waste streams. The amount of salt that enters the series of evaporation chambers is the amount of salt that leaves (X is the salt mass fraction).<br />
<br />
[[File:Overallmasss.PNG]]<br />
<br />
Within each stage, the change in mass of a phase is the mass flows of that phase into and out of the chamber and the rates of evaporation or condensation of the water into and out of that phase.<br />
[[File:Masss2.PNG]]<br />
<br />
The energy balances are summarized below.<br />
<br />
[[File:Mass3.PNG]]<br />
<br />
[[File:Mass4.PNG]]<br />
<br />
=Appendix D. Summary of Process Units=<br />
<br />
[[File:AppendD1.PNG]]<br />
[[File:AppenD2.PNG]]<br />
<br />
=Appendix E. MSF Stage Parameters=<br />
[[File:AppendE.PNG]]<br />
<br />
[[File:Appendix E3.PNG]]<br />
<br />
[[File:Appendix E4.PNG]]<br />
<br />
=Appendix F. Process Units Calculations=<br />
[[File:AppendF.PNG]]<br />
<br />
[[File:AppendF2.PNG]]<br />
<br />
[[File:AppendF3.PNG]]<br />
<br />
=Appendix G. Economic Analysis=<br />
[[File:Econanalysis.PNG]]</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Desalination_-_Team_A&diff=5264Desalination - Team A2016-03-12T03:27:55Z<p>Pdtravan: /* Appendix B. HYSYS Simulation */</p>
<hr />
<div>Author: Pear Dhiantravan<sup>[2016]</sup>, Reed Kolbe<sup>[2016]</sup>, Sheridan Lichtor<sup>[2016]</sup>, John Marsiglio<sup>[2016]</sup>, Ellen Zhuang<sup>[2016]</sup><br />
<br />
Instructors: Fengqi You, David Wegerer<br />
<br />
Winter 2016<br />
<br />
=Executive Summary=<br />
Seawater desalination is an attractive approach to address the world’s freshwater shortage in light of the increasing global water scarcity. Our team decided to tackle California's growing drought crisis by designing a multistage flash desalination plant in Richmond, CA. Based on market analysis of existing desalination plants and water demands, this is a strategic location for the desalination of 50 million gallons per day of water from the San Francisco Bay.<br />
<br />
The MSF process contains 18 flash stages in series. Seawater is taken in from the San Francisco Bay at a rate of 398 million gallons per day and mixed with brine recycled from the system. Within the MSF process, seawater is heated through a series of 18 heat exchangers and a brine heater before enters a series of 18 evaporation chambers. In the evaporation chambers, the seawater flashes and the freshwater vapor is condensed, collected, and sent to a water treatment facility. The brine stream proceeds to the next chamber, and the process continues. Upon exiting the last flashing chamber, the brine stream is split into a recycle brine stream that is mixed with the seawater inlet feed and a waste stream that is diluted with fresh seawater and returned to the sea. Overall, the process yield is 13%. This process was constructed in Aspen HYSYS and optimized around utility costs using the HYSYS Economic Analyzer. Based on duties, temperatures and pressures reported by HYSYS, as well as fundamental mass and energy balances, the equipment were sized appropriately and the economics of the process was analyzed.<br />
<br />
The design has a total capital cost of $485.2 MM, an annual operating cost of $144.7 MM ($103.7 MM of which is utilities), and an annual plant revenue of $134.3 MM. Economic analysis reveals that the project has a negative NPV of -$495.7 MM and operates at a loss of $10.4 MM per year. Thus, the proposed design is not profitable. Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing while California is experiencing harsher droughts each year. Given the dire situations, the government may support the proposed clean water project with subsidies. Building the facility may be a strategic investment, especially since greater water scarcity is predicted in the future.<br />
<br />
Our design meets various environmental, ethical, social and health related constraints. The brine discharged back to the bay is diluted to at most 0.2% above the natural background salinity as required by law so that the plant does not impose harm on any local marine life. The demographic that the plant serves is largely invested in the protection of the environment, which we addressed by reducing energy consumption through direct energy integration with the nearby Chevron plant. Lastly, the product meets the specifications of the California Safe Water Drinking Act by producing water with no impurities.<br />
<br />
<br />
__TOC__<br />
<br />
=Introduction=<br />
An increasing global water scarcity is fueling initiatives everywhere for clean water treatment, making efficient seawater desalination an attractive aim for chemical plant design. A 2015 market analysis found that the global desalination market earned revenues of $11.66 billion, and this number is expected to reach over $19 billion by 2019. Furthermore, the 17,000 desalination plants currently in operation are expected to double in number by 2020.<sup>1</sup> <br />
<br />
As fresh water sources become increasingly scarce, strict water conservation measures are being observed. California is entering the fourth year of one of its most severe droughts on record. Cities are required to reduce their water usage by 35% to avoid facing fines.<sup>2</sup> In lieu of these pressing conditions, California is looking for ways to provide more accessible fresh water to its citizens. This high demand for clean water motivated our choosing Richmond, CA as our plant location. At Richmond, the desalination plant can convert readily available seawater from the San Francisco Bay into fresh water. We propose to desalinate 50 million gallons of water per day to be sent to water treatment plants for potability. This aim is based on the capacity of the desalination plant in Carlsbad, California, which services a similar population.<br />
<br />
The salinity of the water in the San Francisco Bay is seasonal. During the dry seasons of summer and fall, salinity is high around 10 PSU (10,000 ppm) because water from the Pacific Ocean flows into the San Francisco Bay. During the wet winter season, fresh water from the rivers flows into the Bay, and salinity drops to around 2 PSU (2,000).3 Designed to meet the “worst case” scenario, our plant will process 398 million gallons of water per day with 10,000 ppm of salt to produce 50 million gallons of distilled water. This gives a yield of 13%.<br />
<br />
The desalination plant proposed consists of 18 flash stages in series. This report outlines our investigation of this potential water desalination plant, including design and optimization of the desalination process, an analysis of its energy consumption and environmental impacts, and a study of its economic implications.<br />
<br />
=Technical Approach=<br />
For the desalination step of our process, we selected a multistage flash (MSF) distillation process. Not only is MSF distillation a very viable method, but it is also the most common method, currently producing about 60% of the world’s desalinated water. MSF and reverse osmosis (RO) are the two major methods being used in large-scale desalination plants. Both processes require considerable amounts of energy. RO typically has a lower energy demand; however, the high impurity content of the Bay water would frequently necessitate membrane cleaning and/or exchange. Feed going through a RO system requires extensive pretreatment to remove biological organisms and other solids to control the pH and the chemical composition of the water. With the San Francisco Bay as our source of water, MSF is an attractive option because sediment and other large impurities can be separated from the feed before distillation occurs. Additionally, MSF distillation plants can be located near power plants and paired to their waste heat streams to conserve energy. This can reduce energy needs by half or two thirds, making MSF increasingly more practical. Due to the maintenance required in the RO system, the MSF distillation is the better option in terms of operation cost.<sup>4</sup><br />
<br />
A HYSYS model was built to simulate the MSF distillation section of the process, which spans after seawater pretreatment and before local potable water treatment. The model is used to simulate the distillation steps and to calculate necessary heating, cooling, and input flow rates to produce the required 50 million gallons of distillated water per day. For the simulation, the 398 million gallons per day of seawater feed stream is defined to be composed of 3.31 mol% sodium chloride (NaCl) and 96.69 mol% water. The percentage of NaCl is set to account for other ions and chemicals present after the pretreatment phase. NaCl alone is added to the HYSYS system due to the capabilities of the fluid package used to simulate this process, ElectroNRTL. The feed is set at 22°C, which is the approximate the temperature of the San Francisco Bay year round.<br />
<br />
=Process Design=<br />
==Design Overview==<br />
The proposed desalination plant uses MSF distillation to convert the San Francisco Bay water to fresh water. The final process design contains 18 flash stages in series. Overall, 398 million gallons per day of of brackish water is converted to 50 million gallons per day of deionized water, a 13% yield. The production meets the required production rate of 50 million gallons of freshwater per day. <br />
<br />
Seawater is taken in from the San Francisco Bay and mixed with the brine recycle stream produced downstream. The feed is then heated through a series of condensers and a heater. Distilled water vapor in each flash stage contacts the tubes carrying the seawater feed and condenses into a liquid stream by exchanging heat with the cooler seawater feed stream. The seawater is sent through a heater to increase its thermal energy before entering the first stage of the MSF. In each flashing stage, some of the water evaporates, leaving the salt behind. The freshwater vapors condense, as described above, and is collected and sent to a water treatment plant. The brine stream is split into the recycle stream and a waste stream, and the waste stream is diluted with fresh seawater before being discharged back into the bay.<br />
<br />
A process flow diagram of the process is depicted in Appendix A. <br />
<br />
==Pretreatment==<br />
Sediment is removed to prevent solids from plugging the process downstream. Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime, and is controlled for by lowering pH. Acidifying the water will also remove CO2, which is a corrosive gas. To control for oxygen, oxygen scavengers will be included in the system to sequester it. Sodium bisulfate will be used as the scavenger.<sup>5</sup><br />
<br />
==Condensers (Heat Exchanger Networks)==<br />
In order to conserve and recycle energy, the condensation of the distillate and heating of the seawater feed will be coupled in countercurrent heat exchanger networks. These heat exchanger networks are condensers of the design. The cold feed, which is a mixture of fresh seawater and brine recycle, is fed through multiple heat exchangers in series. Each heat exchanger corresponds to a different evaporation chamber. This process consists of 18 heat exchangers: E-101, E-102, … E-117, and E-118, which correspond to evaporation chambers V-102, V-103, … V-118, and V-119, respectively. <br />
<br />
The heat exchangers can be viewed similarly to a shell and tube setup, however there is no actual physical shell. The tubes simply run through the top of the evaporation chambers, where vaporized distilled water in the chamber acts as the shell side fluid. The tube bundles are arranged in long tube configuration and are aligned parallel to the direction of the flashing brine flow in the evaporation chamber. The evaporating brine in an evaporation chamber rise up to the the corresponding heat exchanger and condense on the outside of the tubes, creating collectable pure water. This condensing water is what heats up the seawater in the tubes. <br />
<br />
E-101 was used as the basis for the condenser sizing since it has the highest heat requirement, and thus will be the largest heat exchanger. From the HYSYS model, the overall system requires 2.24 x 10<sup>6</sup> kW of duty. Assuming this energy requirement, 5000 tubes, and 18 m length tubes (the diameter of the evaporation chambers, explained further on the next page), the diameter of each tube was calculated to be 0.4 m. Based on the temperature of the streams and flow, the thickness of the tube is 7 x 10<sup>-4</sup> m.<br />
<br />
==Brine Heater==<br />
After the seawater exits the final heat exchanger, it enters a brine heater (E-119) where it is brought up to the temperature necessary for the flashing process to begin. This means that the seawater must be overheated compared to stage one, so that the seawater will flash in the evaporation chamber, i.e. release heat and vapor to reach equilibrium with stage conditions. After flowing through the condensers, the seawater enters the brine heater at 96.1 <sup>o</sup>C and is heated to 120 <sup>o</sup>C. The overall system requires 2.31 x 10<sup>6</sup> kW of duty. This is supplied by a total of 4.15 x 10<sup>6</sup> kg per hour of steam.<br />
<br />
==Evaporation Chambers==<br />
When the seawater has been brought to a temperature appropriate for flashing, it enters the first evaporation chamber (V-102). Upon entering the chamber, the water is flashed. Some of the water evaporates, leaving the salt behind. The vapor rises up to the heat exchanger tubes in each evaporation chamber and condenses on the outside into the distilled water product. This condensing water is what heats up the seawater in the tubes discussed above. The seawater that does not evaporate moves to the next stage, which operates at a higher temperature and lower pressure, and the process is repeated. This continues in series through a total of 18 flashing chambers (V-102, V-103, … V-118, and V-119). All of the distillate is collected into one stream and all of the brine is mixed with seawater before being disposed of back in the bay in order to dilute it enough so it does not have an adverse effect on marine life.<br />
<br />
Each respective heat exchanger fully condenses the vapor product stream from each stage. However, when all of the individual product streams are consolidated into the final combined product stream, some water exists in the vapor phase due to temperature and pressure changes associated with mixing all of the streams together. Although the vapor product stream from each stage condenses completely across its respective heat exchanger, the total product stream contains some water in the vapor phase due to the temperature change when the mixer sums all the streams. In order to fully condense this stream, which will be sent to local water treatment plans, a heat exchanger (E-120) is put in place to cool down the product using the process feed stream. <br />
<br />
The correlations of El-Dessouky and Ettouney were employed in order to size the flash chambers. They specified that conventional MSF plants that operate at a capacity between 27,000 and 36,000 m<sup>3</sup>/day use flashing stages of the dimensions 18 m diameter and 4 m height.<sup>6</sup><br />
<br />
==Valves==<br />
The model requires valves in between the evaporation chambers. The seawater streams flow through valves with large pressure drops to flash a portion the liquid into vapor that can then be separated in the vessels. Large pressure drops provide the thermodynamic driving force to vaporize more of the liquid, and are required to achieve high product yield. <br />
<br />
==Material of Construction==<br />
Before 1980, the shells and internals of the MSF units were commonly constructed from carbon steel. Seawater, however, corrodes carbon steel. To compensate for this, the thickness of the carbon steel has an additional corrosion allowance, which increases the size and weight of the equipment. After 1980, the stainless steel and duplex stainless steel became increasingly common. Stainless steel metal requires less thickness for equivalent strength and corrosion resistance, which allows for a reduction in the size, weight, and therefore cost of units. Major units in our process will be constructed from stainless steel.<sup>6</sup><br />
<br />
==Process Alternatives==<br />
In order to ensure that our design is fully optimized, we wanted to consider several alternatives for our process. We looked at alternatives associated with water pretreatment, the distillation process itself and product treatment.<br />
<br />
===Water Pretreatment===<br />
Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime. Scaling can be controlled by adjusting pH, temperature, and bicarbonate concentration. We selected acidification to control for process scaling. This is because lowering a process temperature would decrease overall efficiency, and decreasing bicarbonate concentration would be comparatively expensive. Lowering pH would have the added benefit of controlling CO2 concentrations since CO2 is a corrosive gas. To control for corrosion we looked at how to remove oxygen. To target the oxygen we chose an oxygen scavenger. This was chosen over other options such as a deaerator, or a protective coating because a deaerator would have a large capital cost, and the equipment itself would experience corrosion, and a tank coating such as zinc orthophosphate has a mixed effectiveness.<sup>7</sup><br />
<br />
===MSF: Brine Recycle vs. Once-Through System===<br />
We explored two options for the overall layout of the MSF distillation plant. In the first, the brine passes through the process once; in the second, a portion of the brine is recycled from the last stage to the incoming seawater feed. The largest draw towards implementing a brine recycle is that it would significantly reduce the overall amount of seawater needed to produce the daily target of 50 million gallons per day. This in turn would lower the amount of energy required to run the pump feeding seawater to the process. Another positive is that, with a brine recycle, the amount of water conditioning chemicals that must be added to the seawater feed is reduced. The negative aspects mainly revolve around the fact that the solution throughout the process will be higher in salt concentration. This increase in salinity both raises the likelihood of scaling and corrosion in the plant and raises the amount of seawater that must be added to the final brine to make it safe for discharge back into the environment. Additionally, boiling point of each stage is raised when adding the brine recycle. After weighing both alternatives against one another, we have decided to include a brine recycle in our plant design. Most of the negative aspects of the brine recycle can be combated (e.g. include anti-scaling agents in the feed pretreatment), and the economic benefits of including the brine recycle are very significant.<sup>8</sup><br />
<br />
===MSF: Continuous vs. Batch===<br />
The distillation step can be done in continuous or batch processes. Batch distillation is more versatile and often used when the product is in small amounts and very high purity. A continuous distillation is more efficient thermodynamically and economically for large amounts of material of constant composition, whereas batch distillation is more effective for small amounts of material of varying compositions. Since the plant is processing large amounts of seawater of relatively constant composition, the distillation system will utilize continuous distillation.<sup>9</sup><br />
<br />
===MSF: Long Tube vs. Crossed Tube ===<br />
Inside the evaporator stage, the condenser tube bundles may be arranged in either long tube or cross tube design. In the long tube arrangement, the tubes are aligned parallel to the direction of the flashing brine flow. The tubes go from stage to stage without water boxes. In the cross tube arrangement, the tubes are lined perpendicular to the flow of the flashing brine. Water boxes transfer brine between the stages.<sup>10 11</sup> While the water boxes in crossed tube bundles allow for more customization, the long tube configuration allows for construction of large unit sizes, as there are manufacturing restrictions with cross tubes. Long tube design can easily accommodate a large number of stages, which lead us to choose long tube for our design.<sup>11 12</sup><br />
<br />
===MSF: Venting System===<br />
Noncondensable gases exist in the process because of air leakages into stages under vacuum conditions and the release of dissolved gases from the heated brine. These gases are removed by venting the system. An air cooler section concentrates the gas before they are vented, and baffles direct the vapor and condensates out. There are two venting arrangements to consider: series and parallel. The system in series moves gas from one stage directly to the next, and the only loss in the system is vapor in the last stage (since some vapor is extracted with gases). This system is economical, however this configuration increases the amount of noncondensable gases passing from one stage to the next, and disrupting the venting system in one stage will affect the entire system. In parallel venting, gas is released through parallel takeoff pipes at each stage. Although this arrangement allows for venting at any stage to be controlled, the design and maintenance is more complex, and more vapor is lost than in the venting system in series. A third alternative is to use a combination of venting in parallel and in series, which is the common method in industry. For this process, our team chose to do venting in parallel and in series.<sup>12</sup><br />
<br />
===Additional Energy Source Alternatives===<br />
Energy for the process can also be coupled with renewable energy sources to reduce the desalination plant’s carbon footprint. Energy integration can be direct or indirect. In direct integration, thermal waste heat from industrial sources provide thermal energy or pressure as energy sources. Direct integration is advantageous at the modular level, as it avoids energy losses with electricity conversion. Within indirect integration, there are modular integration and grid/utility-scale integration. Modular integration integrates the plant with wind turbines and other small-scale renewable power generators with mobile deployment. A “hybridization” of renewable power sources with natural gas power generation is also an option, and the coupling of the two provides a stable power source. Indirect renewable energy integration is growing as the cost of renewable energy continues to decreases and provides an economy of scale that direct integration does not, but there are several obstacles towards indirect integration, such as the plant’s finance and engineering the integration of the two systems.<sup>13</sup> This distillation plant will be directly integrated with neighboring plants such as Chevron that produce thermal waste heat.<br />
<br />
===Product Treatment===<br />
Since the product is distilled water, it needs additional ions to a concentration of around 0.01% before going to the end user. The three alternatives considered were building a water treatment facility on site, simply adding the correct salts to the product stream and then sending the stream for bacterial treatment at a water plant, or simply sending the product distilled water for complete treatment to another facility. Due to the number of nearby water treatment plants and their demand for water, we elected to simply send the product to a nearby water treatment facility.<br />
<br />
==Design Constraints and Tradeoffs==<br />
While designing our process, we wanted to make sure that we met several outside constraints, including environmental, political, ethical, social, sustainability, health and safety constraints. First and most importantly, we wanted to ensure that the brine discharged back to the bay would not harm local marine life. Our process was designed around the constraint of diluting the exiting brine to within 0.2% salinity of background seawater. This is not only compliant with California law, but was also verified to be safe for surrounding marine life through our own outside research. We also addressed many of these considerations by deciding to pursue direct energy integration with the nearby Chevron plant in order to reduce environmental impact of our process. Additionally, we ensured that our plant would be located in an area that is densely populated and in great need of fresh drinking water. Finally, we addressed health and safety considerations by making sure we would be able to send our product distilled water to local treatment plants for proper potabilization.<br />
<br />
===Design Tradeoffs: Thermodynamics=== <br />
Adjusting elements within this process is iterative, and optimization thereof required changing multiple parameters at once. An example of this is in tuning the temperature increase by heater E-100; if the temperature of the stream entering the vessels is too high, the heat exchange between the vapor product and the feed stream will not be realizable because it causes the feed to be too hot to cool and condense the product. Higher temperatures, however, provide greater thermodynamic driving forces for flashing. Setting the entering stream temperature at 120°C provides enough heat for substantial flash at 130 kPa. This is the only heater required until the very last flash stage, which is added to provide more heat for vaporization. This heater (E-105) increases the stream temperature by 15°C, and the vapor product from the last vessel increases the feed stream temperature by almost 30°C. The added energy increases vaporization by 3%, which is a substantial 2.2 million kg/h. The temperature of the streams entering and leaving each stage decreases with each additional flash stage such that the last vessel has the lowest temperature, according to realistic operating guidelines. <br />
<br />
===Design Tradeoffs: Energy Consumption, Environmental Impacts, and Product Optimization===<br />
Increases in the pressure drop across any of the valves in this final design causes a temperature cross in the heat exchangers unless a proper increase in pump energy is provided. There is thus a design tradeoff between lowering energy usage and increasing product yield. For example, lowering the operating pressure of the process dictates that the pressure difference used to flash seawater must be smaller, possibly decreasing the amount that is vaporized. The final design aims for a yield of 50 million gallons per day. The 18 stage model was chosen for its low annual utility cost. This is a reflection of environmental mindfulness because energy consumption is an ongoing aspect of the process and should be lowered as much as possible.<br />
<br />
==Mass and Energy Balances==<br />
The model of the desalination system assumes that: (1) the properties are uniform in each phase within a stage, (2) heat losses are negligible due to the small surface area to volume ratio for each stage and properly insulated units (heat losses to the surrounding vary from 2 to 5% of the total system energy), (3) the distillate is salt free since the boiling point of water is much lower than that of salt, (4) the subcooling or superheating effects on the system energy balances are negligible, (5) the only contaminant is sodium chloride (there are no non-condensable gases to consider, so no vapors are vented), and (6) the process has 3 evaporation chambers.<br />
<br />
The major balances are that the feed is a mixture of the fresh seawater stream and the recycle stream, and that the brine stream exiting the last evaporation chamber is divided into the recycle stream and the waste stream. Within each stage, the change in mass of a phase over time is the balance between the net flow of that phase from the chamber and the rates of evaporation and condensation of water into and out of that phase. The equations governing the mass and energy balances on the system is displayed in Appendix C. <br />
<br />
=Optimization=<br />
As initiatives for reduced energy usage and increased environmental sustainability become more prevalent, efforts to minimize the utility cost in plants has increased to accommodate these incentives. Utilities are a continual source of expenditure and consumption, and a well-designed chemical process should seek to minimize this element. The annualized utility cost is a useful parameter to optimize given that its value depends on variations in energy costs; thus, annualized utility costs do not correlate with conventional indices of inflation, such as capital and labor costs. Additionally, utility costs, like other variable costs, can be minimized by improving the design or operational efficiency of the plant.<br />
<br />
In optimizing our MSF process, the design variable of focus was the number of stages to use in our process. The performance measure was the annualized utility cost, which was the parameter that was minimized for optimization. The process is constrained by the product specifications, which are kept constant and serve as the standard for comparison between each model. These specifications are to produce 50 million gallons of desalinated liquid water per day. <br />
<br />
One feasibility constraint in the process is the size of the heat exchangers, which must provide a large enough area for total condensation of the vapor stream coming out of the flash stages. In order to restrict the heat exchange area needed within each exchanger, the number of stages must be at least 11. Increasing the number of stages decreases the vapor flow rate at each, and decreases the heat exchange area required as well. An 11-stage process allows for appropriate heat exchange between the feed stream and the vapor product, according to the HYSYS economic analyzer. The optimization analysis thus was conducted incorporating only models with 11 or more stages. <br />
<br />
The HYSYS economic analyzer was used to systematically optimize the process by finding the model with the lowest annualized utility cost. The performance parameters kept constant across each model were: the inlet composition, pressure, and temperature, the brine outlet temperature, the total product flow rate and composition, and the flash stage schematic. Table 1 displays the annualized utility cost for each model, and illustrates that a clear dip in the utility cost occurs in an 18 stage model. Thus, 18 is the optimal number of stages to use for our MSF distillation given utility costs as the optimized parameter.<br />
[[File:Table_1.PNG|thumb|center|500x300px]]<br />
<br />
=Economic Evaluation=<br />
In order to evaluate our process from a fiscal standpoint, we used Aspen Process Economic Analyzer and Aspen cost estimator to determine capital and operating costs for our plant. These costs were calculated based on calculated equipment sizes, as well as energy requirements reported by our HYSYS model. The capital cost was found to be $485.2MM and annual total operating cost was found to be $144.7MM ($103.7MM of which was utilities). Annual plant revenue was estimated based on prices that water districts in the county currently pay for outside water sources, and was found to be $134.3MM.<sup>14</sup> <br />
<br />
The NPV analysis we conducted assumed that the plant would take two years to build, would operate at half capacity during the first year of operation (year 3), and have a 20 year lifetime. We also assumed that our plant would be in operation 350 days per year. A constant discount rate of 12% was assumed to hold throughout the plant’s lifetime. The final NPV of this project is -$495.7MM. This is due to both the large capital cost of the plant and the annual loss of $10.4MM while in full operation. A graph of cumulative cash flow versus time can be found in Appendix E. Tax rates and depreciation do not directly impact the NPV of this project due to operating at a loss, however for future calculations it should be noted that we used a straight line depreciation schedule over a seven year period with a 40% tax rate. <br />
<br />
Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing, while California is experiencing harsher droughts each year. A consequence of this is the possibility of receiving government subsidies for our clean water product. The similarly scaled desalination plant in Carlsbad, CA operates at a loss as well, but receives significant government subsidies. Building this facility may be a strategic investment, especially since greater water scarcity is predicted in the future. <br />
<br />
=Sensitivity Analysis=<br />
We wanted to determine how sensitive NPV of our project is to the cost of capital, price of utilities and price we would be able to sell our clean water product at. We conducted this analysis by varying each of these variables independently between 0.5 times and 1.5 times the original value we calculated. As to be expected, NPV grows more negative with increasing capital costs and utility prices and decreasing water prices. Conversely, NPV becomes less negative as price of water rises and capital and utility costs decrease. A plot summarizing the effects of varying these costs can be found in Appendix E. NPV is most sensitive to the price at which we will be selling our clean water product. It is worth noting that NPV is more sensitive to utilities cost than it is to capital cost, which is why we focused on optimizing the cost of utilities. In future steps, trying to reduce utilities cost even more would be worth looking into to decrease the amount of money being lost on this project.<br />
<br />
=Conclusions and Final Recommendation=<br />
The final design achieves the project goal of producing 50 million gallons per day of distilled water at a yield of 13%, comparable to other similarly sized plants. An optimization of the number of MSF stages is realistic, and can be improved upon by taking into account other process parameters. <br />
<br />
The proposed design was optimized around utility costs, comparing plants with 11 to 25 stages. The process is constrained by product specifications and by the thermodynamics of the heat exchange between the feed and the product streams. Energy conservation was achieved in using the seawater feed to condense the final product, as well as in all of the heat exchangers increasing the thermal energy of the seawater feed stream before it enters the flash stages. <br />
<br />
In order to further optimize this process, other design parameters should be considered such as the brine recycle ratio, the cooler duty of the recycle stream, the pressure drop across each valve at the flash stages, and other economic factors. An optimization around maximizing NPV, for example, might be more comprehensive than that conducted regarding only utility costs. Tuning brine recycle rates could greatly improve process efficiency, and standardizing flash stage pressure drops would make operations more feasible and controlled. <br />
<br />
Given our in depth economic analysis, this project would lose an average of $10.4MM per year, and has an NPV of -$495.7MM for a 20 year plant lifetime. From an economic perspective alone it would not be a good project to build. However, other factors need to be considered when building a project with enormous public value. In recent years California droughts have become more severe. Implementing a drought-proof supply of water now could avert a disaster later on. Even without a large disaster, having the desalination plant could also be expected to pay off in the future with the increasing price of water. Considerations such as these were the deciding factors in building the Carlsbad desalination plant. Since there are currently no desalination plants in the Bay area we recommend that preparations should be made to move forward with a desalination plant.<br />
<br />
=References=<br />
[1] Lyons J. Environmental Leader. Environmental Leader 2015. Available at: http://www.environmentalleader.com/2015/10/27/desalination-plants-to-double-by-2020. Accessed 2016.<br />
<br />
[2] Fitzsimmons E. In California, Cities Braced to Cut Water by 10 to 35%. The New York Times 2015. Available at: <br />
http://www.nytimes.com/2015/04/09/us/in-california-cities-braced-to-cut-water-by-10-to-35.html. Accessed 2016. <br />
<br />
[3] Salinity Times Series - USGS Water Quality of SF Bay. Salinity Times Series - USGS Water Quality of SF Bay. Available at:<br />
http://sfbay.wr.usgs.gov/access/wqdata/overview/examp/charts/salin.html. Accessed 2016.<br />
<br />
[4] Reverse Osmosis vs. Multi Stage Flash Distillation: A Comparison Between Different Desalination Methods. Brighthub Engineering. Available at:<br />
http://www.brighthubengineering.com/power-plants/29621-comparison-between-the-reverse-osmosis-and-multi-stage-flash-distillation-methods/. Accessed 2016.<br />
<br />
[5] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[6] H. El-Dessouky. Fundamentals of salt water desalination, 1st Ed., Elsevier Science, 2002.<br />
<br />
[7] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[8] Guasp RE, Bello CP, Jara JG, Vega JP, Damien T, Winkel C, Smith HH. Desalination by distillation. Organization of American States website. oas.org. Accessed January 28, 2015.<br />
<br />
[9] Batch Distillation. AE 335 Separation Processes website. http://prodpran.che.engr.tu.ac.th/AE335/AE335.html. Accessed January 26, 2016.<br />
<br />
[10] Morris R. The development of the multi-stage flash distillation process: A designer's viewpoint. Desalination. 1993;93:57-68. <br />
<br />
[11] Darwish MA. Developments in the multi-stage flash desalting system. Desalination. 1995;100:35-64.<br />
<br />
[12] Wade N. Distillation plant development and cost update. Desalination. 2001;136:3-12.<br />
<br />
[13] Desalination Technologies and the Use of Alternative Energies for Desalination. World Intellectual Property Organization website. http://www.wipo.int/export/sites/www/patentscope/<br />
en/programs/patent_landscapes/documents/patent_landscapes/948-2E-WEB.pdf. Updated November 2011. Accessed January 23, 2016.<br />
<br />
[14] California Turns to the Pacific Ocean for Water | MIT Technology Review.MIT Technology Review 2014. Available at:<br />
http://www.technologyreview.com/featuredstory/533446/desalination-out-of-desperation/. Accessed 2016.<br />
<br />
----<br />
----<br />
----<br />
<br />
=Appendix A. Process Flow Diagram=<br />
[[File:Appendix 1.PNG]]<br />
<br />
'''Figure A1''' Process Flow Diagram of the MSF System<br />
<br />
=Appendix B. HYSYS Simulation=<br />
The HYSYS model of the process is shown below.<br />
<br />
[[File:AppendB.PNG]]<br />
<br />
'''Figure B1.''' The HYSYS model of the MSF distillation process.<br />
<br />
=Appendix C. Mass and Energy Balances=<br />
Below are equations that describe the mass and energy balances of the system.<br />
<br />
In MSF system with brine recycle, the mass flow of the intake seawater I is mixed with the mass flow of the recycle brine R to create the feed seawater stream F. Since this model assumes no non-condensable gases, the feed stream is overall balanced by the brine waste stream W, the recycle brine stream, and the distillate stream D. The brine stream exiting the last evaporation chamber B is divided into the recycle and waste streams. The amount of salt that enters the series of evaporation chambers is the amount of salt that leaves (X is the salt mass fraction).<br />
<br />
[[File:Overallmasss.PNG]]<br />
<br />
Within each stage, the change in mass of a phase is the mass flows of that phase into and out of the chamber and the rates of evaporation or condensation of the water into and out of that phase.<br />
[[File:Masss2.PNG]]<br />
<br />
The energy balances are summarized below.<br />
<br />
[[File:Mass3.PNG]]<br />
<br />
[[File:Mass4.PNG]]<br />
<br />
=Appendix D. Summary of Process Units=<br />
<br />
[[File:AppendD1.PNG]]<br />
[[File:AppenD2.PNG]]<br />
<br />
=Appendix E. MSF Stage Parameters=<br />
[[File:AppendE.PNG]]<br />
<br />
[[File:Appendix E3.PNG]]<br />
<br />
[[File:Appendix E4.PNG]]<br />
<br />
=Appendix F. Process Units Calculations=<br />
[[File:AppendF.PNG]]<br />
<br />
[[File:AppendF2.PNG]]<br />
<br />
[[File:AppendF3.PNG]]<br />
<br />
=Appendix G. Economic Analysis=<br />
[[File:Econanalysis.PNG]]</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Desalination_-_Team_A&diff=5244Desalination - Team A2016-03-12T03:21:23Z<p>Pdtravan: /* Introduction */</p>
<hr />
<div>Author: Pear Dhiantravan<sup>[2016]</sup>, Reed Kolbe<sup>[2016]</sup>, Sheridan Lichtor<sup>[2016]</sup>, John Marsiglio<sup>[2016]</sup>, Ellen Zhuang<sup>[2016]</sup><br />
<br />
Instructors: Fengqi You, David Wegerer<br />
<br />
Winter 2016<br />
<br />
=Executive Summary=<br />
Seawater desalination is an attractive approach to address the world’s freshwater shortage in light of the increasing global water scarcity. Our team decided to tackle California's growing drought crisis by designing a multistage flash desalination plant in Richmond, CA. Based on market analysis of existing desalination plants and water demands, this is a strategic location for the desalination of 50 million gallons per day of water from the San Francisco Bay.<br />
<br />
The MSF process contains 18 flash stages in series. Seawater is taken in from the San Francisco Bay at a rate of 398 million gallons per day and mixed with brine recycled from the system. Within the MSF process, seawater is heated through a series of 18 heat exchangers and a brine heater before enters a series of 18 evaporation chambers. In the evaporation chambers, the seawater flashes and the freshwater vapor is condensed, collected, and sent to a water treatment facility. The brine stream proceeds to the next chamber, and the process continues. Upon exiting the last flashing chamber, the brine stream is split into a recycle brine stream that is mixed with the seawater inlet feed and a waste stream that is diluted with fresh seawater and returned to the sea. Overall, the process yield is 13%. This process was constructed in Aspen HYSYS and optimized around utility costs using the HYSYS Economic Analyzer. Based on duties, temperatures and pressures reported by HYSYS, as well as fundamental mass and energy balances, the equipment were sized appropriately and the economics of the process was analyzed.<br />
<br />
The design has a total capital cost of $485.2 MM, an annual operating cost of $144.7 MM ($103.7 MM of which is utilities), and an annual plant revenue of $134.3 MM. Economic analysis reveals that the project has a negative NPV of -$495.7 MM and operates at a loss of $10.4 MM per year. Thus, the proposed design is not profitable. Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing while California is experiencing harsher droughts each year. Given the dire situations, the government may support the proposed clean water project with subsidies. Building the facility may be a strategic investment, especially since greater water scarcity is predicted in the future.<br />
<br />
Our design meets various environmental, ethical, social and health related constraints. The brine discharged back to the bay is diluted to at most 0.2% above the natural background salinity as required by law so that the plant does not impose harm on any local marine life. The demographic that the plant serves is largely invested in the protection of the environment, which we addressed by reducing energy consumption through direct energy integration with the nearby Chevron plant. Lastly, the product meets the specifications of the California Safe Water Drinking Act by producing water with no impurities.<br />
<br />
<br />
__TOC__<br />
<br />
=Introduction=<br />
An increasing global water scarcity is fueling initiatives everywhere for clean water treatment, making efficient seawater desalination an attractive aim for chemical plant design. A 2015 market analysis found that the global desalination market earned revenues of $11.66 billion, and this number is expected to reach over $19 billion by 2019. Furthermore, the 17,000 desalination plants currently in operation are expected to double in number by 2020.1 <br />
<br />
As fresh water sources become increasingly scarce, strict water conservation measures are being observed. California is entering the fourth year of one of its most severe droughts on record. Cities are required to reduce their water usage by 35% to avoid facing fines.2 In lieu of these pressing conditions, California is looking for ways to provide more accessible fresh water to its citizens. This high demand for clean water motivated our choosing Richmond, CA as our plant location. At Richmond, the desalination plant can convert readily available seawater from the San Francisco Bay into fresh water. We propose to desalinate 50 million gallons of water per day to be sent to water treatment plants for potability. This aim is based on the capacity of the desalination plant in Carlsbad, California, which services a similar population.<br />
<br />
The salinity of the water in the San Francisco Bay is seasonal. During the dry seasons of summer and fall, salinity is high around 10 PSU (10,000 ppm) because water from the Pacific Ocean flows into the San Francisco Bay. During the wet winter season, fresh water from the rivers flows into the Bay, and salinity drops to around 2 PSU (2,000).3 Designed to meet the “worst case” scenario, our plant will process 398 million gallons of water per day with 10,000 ppm of salt to produce 50 million gallons of distilled water. This gives a yield of 13%.<br />
<br />
The desalination plant proposed consists of 18 flash stages in series. This report outlines our investigation of this potential water desalination plant, including design and optimization of the desalination process, an analysis of its energy consumption and environmental impacts, and a study of its economic implications.<br />
<br />
=Technical Approach=<br />
For the desalination step of our process, we selected a multistage flash (MSF) distillation process. Not only is MSF distillation a very viable method, but it is also the most common method, currently producing about 60% of the world’s desalinated water. MSF and reverse osmosis (RO) are the two major methods being used in large-scale desalination plants. Both processes require considerable amounts of energy. RO typically has a lower energy demand; however, the high impurity content of the Bay water would frequently necessitate membrane cleaning and/or exchange. Feed going through a RO system requires extensive pretreatment to remove biological organisms and other solids to control the pH and the chemical composition of the water. With the San Francisco Bay as our source of water, MSF is an attractive option because sediment and other large impurities can be separated from the feed before distillation occurs. Additionally, MSF distillation plants can be located near power plants and paired to their waste heat streams to conserve energy. This can reduce energy needs by half or two thirds, making MSF increasingly more practical. Due to the maintenance required in the RO system, the MSF distillation is the better option in terms of operation cost.<sup>4</sup><br />
<br />
A HYSYS model was built to simulate the MSF distillation section of the process, which spans after seawater pretreatment and before local potable water treatment. The model is used to simulate the distillation steps and to calculate necessary heating, cooling, and input flow rates to produce the required 50 million gallons of distillated water per day. For the simulation, the 398 million gallons per day of seawater feed stream is defined to be composed of 3.31 mol% sodium chloride (NaCl) and 96.69 mol% water. The percentage of NaCl is set to account for other ions and chemicals present after the pretreatment phase. NaCl alone is added to the HYSYS system due to the capabilities of the fluid package used to simulate this process, ElectroNRTL. The feed is set at 22°C, which is the approximate the temperature of the San Francisco Bay year round.<br />
<br />
=Process Design=<br />
==Design Overview==<br />
The proposed desalination plant uses MSF distillation to convert the San Francisco Bay water to fresh water. The final process design contains 18 flash stages in series. Overall, 398 million gallons per day of of brackish water is converted to 50 million gallons per day of deionized water, a 13% yield. The production meets the required production rate of 50 million gallons of freshwater per day. <br />
<br />
Seawater is taken in from the San Francisco Bay and mixed with the brine recycle stream produced downstream. The feed is then heated through a series of condensers and a heater. Distilled water vapor in each flash stage contacts the tubes carrying the seawater feed and condenses into a liquid stream by exchanging heat with the cooler seawater feed stream. The seawater is sent through a heater to increase its thermal energy before entering the first stage of the MSF. In each flashing stage, some of the water evaporates, leaving the salt behind. The freshwater vapors condense, as described above, and is collected and sent to a water treatment plant. The brine stream is split into the recycle stream and a waste stream, and the waste stream is diluted with fresh seawater before being discharged back into the bay.<br />
<br />
A process flow diagram of the process is depicted in Appendix A. <br />
<br />
==Pretreatment==<br />
Sediment is removed to prevent solids from plugging the process downstream. Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime, and is controlled for by lowering pH. Acidifying the water will also remove CO2, which is a corrosive gas. To control for oxygen, oxygen scavengers will be included in the system to sequester it. Sodium bisulfate will be used as the scavenger.<sup>5</sup><br />
<br />
==Condensers (Heat Exchanger Networks)==<br />
In order to conserve and recycle energy, the condensation of the distillate and heating of the seawater feed will be coupled in countercurrent heat exchanger networks. These heat exchanger networks are condensers of the design. The cold feed, which is a mixture of fresh seawater and brine recycle, is fed through multiple heat exchangers in series. Each heat exchanger corresponds to a different evaporation chamber. This process consists of 18 heat exchangers: E-101, E-102, … E-117, and E-118, which correspond to evaporation chambers V-102, V-103, … V-118, and V-119, respectively. <br />
<br />
The heat exchangers can be viewed similarly to a shell and tube setup, however there is no actual physical shell. The tubes simply run through the top of the evaporation chambers, where vaporized distilled water in the chamber acts as the shell side fluid. The tube bundles are arranged in long tube configuration and are aligned parallel to the direction of the flashing brine flow in the evaporation chamber. The evaporating brine in an evaporation chamber rise up to the the corresponding heat exchanger and condense on the outside of the tubes, creating collectable pure water. This condensing water is what heats up the seawater in the tubes. <br />
<br />
E-101 was used as the basis for the condenser sizing since it has the highest heat requirement, and thus will be the largest heat exchanger. From the HYSYS model, the overall system requires 2.24 x 10<sup>6</sup> kW of duty. Assuming this energy requirement, 5000 tubes, and 18 m length tubes (the diameter of the evaporation chambers, explained further on the next page), the diameter of each tube was calculated to be 0.4 m. Based on the temperature of the streams and flow, the thickness of the tube is 7 x 10<sup>-4</sup> m.<br />
<br />
==Brine Heater==<br />
After the seawater exits the final heat exchanger, it enters a brine heater (E-119) where it is brought up to the temperature necessary for the flashing process to begin. This means that the seawater must be overheated compared to stage one, so that the seawater will flash in the evaporation chamber, i.e. release heat and vapor to reach equilibrium with stage conditions. After flowing through the condensers, the seawater enters the brine heater at 96.1 <sup>o</sup>C and is heated to 120 <sup>o</sup>C. The overall system requires 2.31 x 10<sup>6</sup> kW of duty. This is supplied by a total of 4.15 x 10<sup>6</sup> kg per hour of steam.<br />
<br />
==Evaporation Chambers==<br />
When the seawater has been brought to a temperature appropriate for flashing, it enters the first evaporation chamber (V-102). Upon entering the chamber, the water is flashed. Some of the water evaporates, leaving the salt behind. The vapor rises up to the heat exchanger tubes in each evaporation chamber and condenses on the outside into the distilled water product. This condensing water is what heats up the seawater in the tubes discussed above. The seawater that does not evaporate moves to the next stage, which operates at a higher temperature and lower pressure, and the process is repeated. This continues in series through a total of 18 flashing chambers (V-102, V-103, … V-118, and V-119). All of the distillate is collected into one stream and all of the brine is mixed with seawater before being disposed of back in the bay in order to dilute it enough so it does not have an adverse effect on marine life.<br />
<br />
Each respective heat exchanger fully condenses the vapor product stream from each stage. However, when all of the individual product streams are consolidated into the final combined product stream, some water exists in the vapor phase due to temperature and pressure changes associated with mixing all of the streams together. Although the vapor product stream from each stage condenses completely across its respective heat exchanger, the total product stream contains some water in the vapor phase due to the temperature change when the mixer sums all the streams. In order to fully condense this stream, which will be sent to local water treatment plans, a heat exchanger (E-120) is put in place to cool down the product using the process feed stream. <br />
<br />
The correlations of El-Dessouky and Ettouney were employed in order to size the flash chambers. They specified that conventional MSF plants that operate at a capacity between 27,000 and 36,000 m<sup>3</sup>/day use flashing stages of the dimensions 18 m diameter and 4 m height.<sup>6</sup><br />
<br />
==Valves==<br />
The model requires valves in between the evaporation chambers. The seawater streams flow through valves with large pressure drops to flash a portion the liquid into vapor that can then be separated in the vessels. Large pressure drops provide the thermodynamic driving force to vaporize more of the liquid, and are required to achieve high product yield. <br />
<br />
==Material of Construction==<br />
Before 1980, the shells and internals of the MSF units were commonly constructed from carbon steel. Seawater, however, corrodes carbon steel. To compensate for this, the thickness of the carbon steel has an additional corrosion allowance, which increases the size and weight of the equipment. After 1980, the stainless steel and duplex stainless steel became increasingly common. Stainless steel metal requires less thickness for equivalent strength and corrosion resistance, which allows for a reduction in the size, weight, and therefore cost of units. Major units in our process will be constructed from stainless steel.<sup>6</sup><br />
<br />
==Process Alternatives==<br />
In order to ensure that our design is fully optimized, we wanted to consider several alternatives for our process. We looked at alternatives associated with water pretreatment, the distillation process itself and product treatment.<br />
<br />
===Water Pretreatment===<br />
Scaling of the process units leads to decreased efficiency and more frequent unplanned downtime. Scaling can be controlled by adjusting pH, temperature, and bicarbonate concentration. We selected acidification to control for process scaling. This is because lowering a process temperature would decrease overall efficiency, and decreasing bicarbonate concentration would be comparatively expensive. Lowering pH would have the added benefit of controlling CO2 concentrations since CO2 is a corrosive gas. To control for corrosion we looked at how to remove oxygen. To target the oxygen we chose an oxygen scavenger. This was chosen over other options such as a deaerator, or a protective coating because a deaerator would have a large capital cost, and the equipment itself would experience corrosion, and a tank coating such as zinc orthophosphate has a mixed effectiveness.<sup>7</sup><br />
<br />
===MSF: Brine Recycle vs. Once-Through System===<br />
We explored two options for the overall layout of the MSF distillation plant. In the first, the brine passes through the process once; in the second, a portion of the brine is recycled from the last stage to the incoming seawater feed. The largest draw towards implementing a brine recycle is that it would significantly reduce the overall amount of seawater needed to produce the daily target of 50 million gallons per day. This in turn would lower the amount of energy required to run the pump feeding seawater to the process. Another positive is that, with a brine recycle, the amount of water conditioning chemicals that must be added to the seawater feed is reduced. The negative aspects mainly revolve around the fact that the solution throughout the process will be higher in salt concentration. This increase in salinity both raises the likelihood of scaling and corrosion in the plant and raises the amount of seawater that must be added to the final brine to make it safe for discharge back into the environment. Additionally, boiling point of each stage is raised when adding the brine recycle. After weighing both alternatives against one another, we have decided to include a brine recycle in our plant design. Most of the negative aspects of the brine recycle can be combated (e.g. include anti-scaling agents in the feed pretreatment), and the economic benefits of including the brine recycle are very significant.<sup>8</sup><br />
<br />
===MSF: Continuous vs. Batch===<br />
The distillation step can be done in continuous or batch processes. Batch distillation is more versatile and often used when the product is in small amounts and very high purity. A continuous distillation is more efficient thermodynamically and economically for large amounts of material of constant composition, whereas batch distillation is more effective for small amounts of material of varying compositions. Since the plant is processing large amounts of seawater of relatively constant composition, the distillation system will utilize continuous distillation.<sup>9</sup><br />
<br />
===MSF: Long Tube vs. Crossed Tube ===<br />
Inside the evaporator stage, the condenser tube bundles may be arranged in either long tube or cross tube design. In the long tube arrangement, the tubes are aligned parallel to the direction of the flashing brine flow. The tubes go from stage to stage without water boxes. In the cross tube arrangement, the tubes are lined perpendicular to the flow of the flashing brine. Water boxes transfer brine between the stages.<sup>10 11</sup> While the water boxes in crossed tube bundles allow for more customization, the long tube configuration allows for construction of large unit sizes, as there are manufacturing restrictions with cross tubes. Long tube design can easily accommodate a large number of stages, which lead us to choose long tube for our design.<sup>11 12</sup><br />
<br />
===MSF: Venting System===<br />
Noncondensable gases exist in the process because of air leakages into stages under vacuum conditions and the release of dissolved gases from the heated brine. These gases are removed by venting the system. An air cooler section concentrates the gas before they are vented, and baffles direct the vapor and condensates out. There are two venting arrangements to consider: series and parallel. The system in series moves gas from one stage directly to the next, and the only loss in the system is vapor in the last stage (since some vapor is extracted with gases). This system is economical, however this configuration increases the amount of noncondensable gases passing from one stage to the next, and disrupting the venting system in one stage will affect the entire system. In parallel venting, gas is released through parallel takeoff pipes at each stage. Although this arrangement allows for venting at any stage to be controlled, the design and maintenance is more complex, and more vapor is lost than in the venting system in series. A third alternative is to use a combination of venting in parallel and in series, which is the common method in industry. For this process, our team chose to do venting in parallel and in series.<sup>12</sup><br />
<br />
===Additional Energy Source Alternatives===<br />
Energy for the process can also be coupled with renewable energy sources to reduce the desalination plant’s carbon footprint. Energy integration can be direct or indirect. In direct integration, thermal waste heat from industrial sources provide thermal energy or pressure as energy sources. Direct integration is advantageous at the modular level, as it avoids energy losses with electricity conversion. Within indirect integration, there are modular integration and grid/utility-scale integration. Modular integration integrates the plant with wind turbines and other small-scale renewable power generators with mobile deployment. A “hybridization” of renewable power sources with natural gas power generation is also an option, and the coupling of the two provides a stable power source. Indirect renewable energy integration is growing as the cost of renewable energy continues to decreases and provides an economy of scale that direct integration does not, but there are several obstacles towards indirect integration, such as the plant’s finance and engineering the integration of the two systems.<sup>13</sup> This distillation plant will be directly integrated with neighboring plants such as Chevron that produce thermal waste heat.<br />
<br />
===Product Treatment===<br />
Since the product is distilled water, it needs additional ions to a concentration of around 0.01% before going to the end user. The three alternatives considered were building a water treatment facility on site, simply adding the correct salts to the product stream and then sending the stream for bacterial treatment at a water plant, or simply sending the product distilled water for complete treatment to another facility. Due to the number of nearby water treatment plants and their demand for water, we elected to simply send the product to a nearby water treatment facility.<br />
<br />
==Design Constraints and Tradeoffs==<br />
While designing our process, we wanted to make sure that we met several outside constraints, including environmental, political, ethical, social, sustainability, health and safety constraints. First and most importantly, we wanted to ensure that the brine discharged back to the bay would not harm local marine life. Our process was designed around the constraint of diluting the exiting brine to within 0.2% salinity of background seawater. This is not only compliant with California law, but was also verified to be safe for surrounding marine life through our own outside research. We also addressed many of these considerations by deciding to pursue direct energy integration with the nearby Chevron plant in order to reduce environmental impact of our process. Additionally, we ensured that our plant would be located in an area that is densely populated and in great need of fresh drinking water. Finally, we addressed health and safety considerations by making sure we would be able to send our product distilled water to local treatment plants for proper potabilization.<br />
<br />
===Design Tradeoffs: Thermodynamics=== <br />
Adjusting elements within this process is iterative, and optimization thereof required changing multiple parameters at once. An example of this is in tuning the temperature increase by heater E-100; if the temperature of the stream entering the vessels is too high, the heat exchange between the vapor product and the feed stream will not be realizable because it causes the feed to be too hot to cool and condense the product. Higher temperatures, however, provide greater thermodynamic driving forces for flashing. Setting the entering stream temperature at 120°C provides enough heat for substantial flash at 130 kPa. This is the only heater required until the very last flash stage, which is added to provide more heat for vaporization. This heater (E-105) increases the stream temperature by 15°C, and the vapor product from the last vessel increases the feed stream temperature by almost 30°C. The added energy increases vaporization by 3%, which is a substantial 2.2 million kg/h. The temperature of the streams entering and leaving each stage decreases with each additional flash stage such that the last vessel has the lowest temperature, according to realistic operating guidelines. <br />
<br />
===Design Tradeoffs: Energy Consumption, Environmental Impacts, and Product Optimization===<br />
Increases in the pressure drop across any of the valves in this final design causes a temperature cross in the heat exchangers unless a proper increase in pump energy is provided. There is thus a design tradeoff between lowering energy usage and increasing product yield. For example, lowering the operating pressure of the process dictates that the pressure difference used to flash seawater must be smaller, possibly decreasing the amount that is vaporized. The final design aims for a yield of 50 million gallons per day. The 18 stage model was chosen for its low annual utility cost. This is a reflection of environmental mindfulness because energy consumption is an ongoing aspect of the process and should be lowered as much as possible.<br />
<br />
==Mass and Energy Balances==<br />
The model of the desalination system assumes that: (1) the properties are uniform in each phase within a stage, (2) heat losses are negligible due to the small surface area to volume ratio for each stage and properly insulated units (heat losses to the surrounding vary from 2 to 5% of the total system energy), (3) the distillate is salt free since the boiling point of water is much lower than that of salt, (4) the subcooling or superheating effects on the system energy balances are negligible, (5) the only contaminant is sodium chloride (there are no non-condensable gases to consider, so no vapors are vented), and (6) the process has 3 evaporation chambers.<br />
<br />
The major balances are that the feed is a mixture of the fresh seawater stream and the recycle stream, and that the brine stream exiting the last evaporation chamber is divided into the recycle stream and the waste stream. Within each stage, the change in mass of a phase over time is the balance between the net flow of that phase from the chamber and the rates of evaporation and condensation of water into and out of that phase. The equations governing the mass and energy balances on the system is displayed in Appendix C. <br />
<br />
=Optimization=<br />
As initiatives for reduced energy usage and increased environmental sustainability become more prevalent, efforts to minimize the utility cost in plants has increased to accommodate these incentives. Utilities are a continual source of expenditure and consumption, and a well-designed chemical process should seek to minimize this element. The annualized utility cost is a useful parameter to optimize given that its value depends on variations in energy costs; thus, annualized utility costs do not correlate with conventional indices of inflation, such as capital and labor costs. Additionally, utility costs, like other variable costs, can be minimized by improving the design or operational efficiency of the plant.<br />
<br />
In optimizing our MSF process, the design variable of focus was the number of stages to use in our process. The performance measure was the annualized utility cost, which was the parameter that was minimized for optimization. The process is constrained by the product specifications, which are kept constant and serve as the standard for comparison between each model. These specifications are to produce 50 million gallons of desalinated liquid water per day. <br />
<br />
One feasibility constraint in the process is the size of the heat exchangers, which must provide a large enough area for total condensation of the vapor stream coming out of the flash stages. In order to restrict the heat exchange area needed within each exchanger, the number of stages must be at least 11. Increasing the number of stages decreases the vapor flow rate at each, and decreases the heat exchange area required as well. An 11-stage process allows for appropriate heat exchange between the feed stream and the vapor product, according to the HYSYS economic analyzer. The optimization analysis thus was conducted incorporating only models with 11 or more stages. <br />
<br />
The HYSYS economic analyzer was used to systematically optimize the process by finding the model with the lowest annualized utility cost. The performance parameters kept constant across each model were: the inlet composition, pressure, and temperature, the brine outlet temperature, the total product flow rate and composition, and the flash stage schematic. Table 1 displays the annualized utility cost for each model, and illustrates that a clear dip in the utility cost occurs in an 18 stage model. Thus, 18 is the optimal number of stages to use for our MSF distillation given utility costs as the optimized parameter.<br />
[[File:Table_1.PNG|thumb|center|500x300px]]<br />
<br />
=Economic Evaluation=<br />
In order to evaluate our process from a fiscal standpoint, we used Aspen Process Economic Analyzer and Aspen cost estimator to determine capital and operating costs for our plant. These costs were calculated based on calculated equipment sizes, as well as energy requirements reported by our HYSYS model. The capital cost was found to be $485.2MM and annual total operating cost was found to be $144.7MM ($103.7MM of which was utilities). Annual plant revenue was estimated based on prices that water districts in the county currently pay for outside water sources, and was found to be $134.3MM.<sup>14</sup> <br />
<br />
The NPV analysis we conducted assumed that the plant would take two years to build, would operate at half capacity during the first year of operation (year 3), and have a 20 year lifetime. We also assumed that our plant would be in operation 350 days per year. A constant discount rate of 12% was assumed to hold throughout the plant’s lifetime. The final NPV of this project is -$495.7MM. This is due to both the large capital cost of the plant and the annual loss of $10.4MM while in full operation. A graph of cumulative cash flow versus time can be found in Appendix E. Tax rates and depreciation do not directly impact the NPV of this project due to operating at a loss, however for future calculations it should be noted that we used a straight line depreciation schedule over a seven year period with a 40% tax rate. <br />
<br />
Despite the current projections, it is important to consider the greater implications of running a desalination plant in the Bay Area. The population in the Bay Area is quickly growing, while California is experiencing harsher droughts each year. A consequence of this is the possibility of receiving government subsidies for our clean water product. The similarly scaled desalination plant in Carlsbad, CA operates at a loss as well, but receives significant government subsidies. Building this facility may be a strategic investment, especially since greater water scarcity is predicted in the future. <br />
<br />
=Sensitivity Analysis=<br />
We wanted to determine how sensitive NPV of our project is to the cost of capital, price of utilities and price we would be able to sell our clean water product at. We conducted this analysis by varying each of these variables independently between 0.5 times and 1.5 times the original value we calculated. As to be expected, NPV grows more negative with increasing capital costs and utility prices and decreasing water prices. Conversely, NPV becomes less negative as price of water rises and capital and utility costs decrease. A plot summarizing the effects of varying these costs can be found in Appendix E. NPV is most sensitive to the price at which we will be selling our clean water product. It is worth noting that NPV is more sensitive to utilities cost than it is to capital cost, which is why we focused on optimizing the cost of utilities. In future steps, trying to reduce utilities cost even more would be worth looking into to decrease the amount of money being lost on this project.<br />
<br />
=Conclusions and Final Recommendation=<br />
The final design achieves the project goal of producing 50 million gallons per day of distilled water at a yield of 13%, comparable to other similarly sized plants. An optimization of the number of MSF stages is realistic, and can be improved upon by taking into account other process parameters. <br />
<br />
The proposed design was optimized around utility costs, comparing plants with 11 to 25 stages. The process is constrained by product specifications and by the thermodynamics of the heat exchange between the feed and the product streams. Energy conservation was achieved in using the seawater feed to condense the final product, as well as in all of the heat exchangers increasing the thermal energy of the seawater feed stream before it enters the flash stages. <br />
<br />
In order to further optimize this process, other design parameters should be considered such as the brine recycle ratio, the cooler duty of the recycle stream, the pressure drop across each valve at the flash stages, and other economic factors. An optimization around maximizing NPV, for example, might be more comprehensive than that conducted regarding only utility costs. Tuning brine recycle rates could greatly improve process efficiency, and standardizing flash stage pressure drops would make operations more feasible and controlled. <br />
<br />
Given our in depth economic analysis, this project would lose an average of $10.4MM per year, and has an NPV of -$495.7MM for a 20 year plant lifetime. From an economic perspective alone it would not be a good project to build. However, other factors need to be considered when building a project with enormous public value. In recent years California droughts have become more severe. Implementing a drought-proof supply of water now could avert a disaster later on. Even without a large disaster, having the desalination plant could also be expected to pay off in the future with the increasing price of water. Considerations such as these were the deciding factors in building the Carlsbad desalination plant. Since there are currently no desalination plants in the Bay area we recommend that preparations should be made to move forward with a desalination plant.<br />
<br />
=References=<br />
[1] Lyons J. Environmental Leader. Environmental Leader 2015. Available at: http://www.environmentalleader.com/2015/10/27/desalination-plants-to-double-by-2020. Accessed 2016.<br />
<br />
[2] Fitzsimmons E. In California, Cities Braced to Cut Water by 10 to 35%. The New York Times 2015. Available at: <br />
http://www.nytimes.com/2015/04/09/us/in-california-cities-braced-to-cut-water-by-10-to-35.html. Accessed 2016. <br />
<br />
[3] Salinity Times Series - USGS Water Quality of SF Bay. Salinity Times Series - USGS Water Quality of SF Bay. Available at:<br />
http://sfbay.wr.usgs.gov/access/wqdata/overview/examp/charts/salin.html. Accessed 2016.<br />
<br />
[4] Reverse Osmosis vs. Multi Stage Flash Distillation: A Comparison Between Different Desalination Methods. Brighthub Engineering. Available at:<br />
http://www.brighthubengineering.com/power-plants/29621-comparison-between-the-reverse-osmosis-and-multi-stage-flash-distillation-methods/. Accessed 2016.<br />
<br />
[5] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[6] H. El-Dessouky. Fundamentals of salt water desalination, 1st Ed., Elsevier Science, 2002.<br />
<br />
[7] Committee on Advancing Desalination Technology, Water Science and Technology Board, Division on Earth and Life Studies, National Research Council. Desalination: A National Perspective. Washington, D.C.:The National Academies Press, 2008.<br />
<br />
[8] Guasp RE, Bello CP, Jara JG, Vega JP, Damien T, Winkel C, Smith HH. Desalination by distillation. Organization of American States website. oas.org. Accessed January 28, 2015.<br />
<br />
[9] Batch Distillation. AE 335 Separation Processes website. http://prodpran.che.engr.tu.ac.th/AE335/AE335.html. Accessed January 26, 2016.<br />
<br />
[10] Morris R. The development of the multi-stage flash distillation process: A designer's viewpoint. Desalination. 1993;93:57-68. <br />
<br />
[11] Darwish MA. Developments in the multi-stage flash desalting system. Desalination. 1995;100:35-64.<br />
<br />
[12] Wade N. Distillation plant development and cost update. Desalination. 2001;136:3-12.<br />
<br />
[13] Desalination Technologies and the Use of Alternative Energies for Desalination. World Intellectual Property Organization website. http://www.wipo.int/export/sites/www/patentscope/<br />
en/programs/patent_landscapes/documents/patent_landscapes/948-2E-WEB.pdf. Updated November 2011. Accessed January 23, 2016.<br />
<br />
[14] California Turns to the Pacific Ocean for Water | MIT Technology Review.MIT Technology Review 2014. Available at:<br />
http://www.technologyreview.com/featuredstory/533446/desalination-out-of-desperation/. Accessed 2016.<br />
<br />
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<br />
=Appendix A. Process Flow Diagram=<br />
[[File:Appendix 1.PNG]]<br />
<br />
'''Figure A1''' Process Flow Diagram of the MSF System<br />
<br />
=Appendix B. HYSYS Simulation=<br />
The outputs of the HYSYS model of the process is shown below.<br />
<br />
[[File:AppendB.PNG]]<br />
<br />
'''Figure B1.''' The HYSYS model of the MSF distillation process.<br />
<br />
=Appendix C. Mass and Energy Balances=<br />
Below are equations that describe the mass and energy balances of the system.<br />
<br />
In MSF system with brine recycle, the mass flow of the intake seawater I is mixed with the mass flow of the recycle brine R to create the feed seawater stream F. Since this model assumes no non-condensable gases, the feed stream is overall balanced by the brine waste stream W, the recycle brine stream, and the distillate stream D. The brine stream exiting the last evaporation chamber B is divided into the recycle and waste streams. The amount of salt that enters the series of evaporation chambers is the amount of salt that leaves (X is the salt mass fraction).<br />
<br />
[[File:Overallmasss.PNG]]<br />
<br />
Within each stage, the change in mass of a phase is the mass flows of that phase into and out of the chamber and the rates of evaporation or condensation of the water into and out of that phase.<br />
[[File:Masss2.PNG]]<br />
<br />
The energy balances are summarized below.<br />
<br />
[[File:Mass3.PNG]]<br />
<br />
[[File:Mass4.PNG]]<br />
<br />
=Appendix D. Summary of Process Units=<br />
<br />
[[File:AppendD1.PNG]]<br />
[[File:AppenD2.PNG]]<br />
<br />
=Appendix E. MSF Stage Parameters=<br />
[[File:AppendE.PNG]]<br />
<br />
=Appendix F. Process Units Calculations=<br />
=Appendix G. Economic Analysis=</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4607Environmental concerns2016-02-21T22:38:40Z<p>Pdtravan: /* Social */</p>
<hr />
<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
<br />
<br><br />
<br />
<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
|}<br />
</center><br />
<br />
The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location. Below is a list of some chemical pollutants that might be of concern to process designers and their LD50. <br />
<br />
[[File:toxinstable.png|frame|center|300x300px| '''Table 1:''' Chemical Pollutants and Their LD50]]<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
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[[File:decentralized_flowsheet.png|frame|center|400x400px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
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In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
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By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
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[[File:bieker.png|frame|center|500x500px| '''Figure 4:''' Semicentralized Wastewater Management Scheme. Figure from Bieker, et al. 2010]]<br />
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The EPA has provided estimates for the annual cost and operational costs of potential wastewater management systems for a rural community of approximately 450 people. Smaller communities are hypothesized to benefit most from decentralized systems, and their study confirmed that this is so. To fund a centralized system, the annual cost would be approximately $216,850- $342,500 with an additional average operational cost of $35,000. The total capital cost of a centralized system can span from $2.3M to $3.8M. Decentralized small cluster or on-site systems, on the other hand, yield a capital cost estimate of $510,000 with very low operational and annual costs. This analysis is specific to the hypothetical rural area that they assumed, but illustrates the possibility of dramatically decreasing costs when the treatment system is tuned to the local community (Bieker et al, 2010).<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 5:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
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===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
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===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
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Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
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===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 6:''' Particulate Size and Corresponding Machinery]]<br />
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For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 7:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 8:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
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===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 9:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
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Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
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Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
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===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
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Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 10:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
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[[File:RO.png|frame|right|150x200px| '''Figure 11:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 12:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
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[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
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Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
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[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 13:''' Pyrolysis of solid waste (Arc21)]]<br />
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Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
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[[File:Landfill.png|frame|center|'''Figure 14:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
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[[File:Waste_min.png| thumb| upright=2.5|'''Figure 15:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
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When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
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[[File:Waste_flowchart.png| frame| center|'''Figure 16:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
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=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
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Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
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EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
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WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
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Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
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Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
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Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
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Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
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M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
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Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
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Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
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Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
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Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
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VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
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IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
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Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
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D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
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M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
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Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
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ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
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Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
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Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
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Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
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U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
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EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
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Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
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M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
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E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
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Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
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A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
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S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
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L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4606Environmental concerns2016-02-21T22:38:20Z<p>Pdtravan: /* Human Health */</p>
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Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
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Steward: David Chen, Jian Gong, and Fengqi You<br />
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Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
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=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
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Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
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|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
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Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
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Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
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Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location. Below is a list of some chemical pollutants that might be of concern to process designers and their LD50. <br />
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[[File:toxinstable.png|frame|center|300x300px| '''Table 1:''' Chemical Pollutants and Their LD50]]<br />
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==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
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These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
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The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
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These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
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Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
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[[File:decentralized_flowsheet.png|frame|center|500x500px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
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==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
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In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
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By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
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[[File:bieker.png|frame|center|500x500px| '''Figure 4:''' Semicentralized Wastewater Management Scheme. Figure from Bieker, et al. 2010]]<br />
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The EPA has provided estimates for the annual cost and operational costs of potential wastewater management systems for a rural community of approximately 450 people. Smaller communities are hypothesized to benefit most from decentralized systems, and their study confirmed that this is so. To fund a centralized system, the annual cost would be approximately $216,850- $342,500 with an additional average operational cost of $35,000. The total capital cost of a centralized system can span from $2.3M to $3.8M. Decentralized small cluster or on-site systems, on the other hand, yield a capital cost estimate of $510,000 with very low operational and annual costs. This analysis is specific to the hypothetical rural area that they assumed, but illustrates the possibility of dramatically decreasing costs when the treatment system is tuned to the local community (Bieker et al, 2010).<br />
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=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
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<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
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RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
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==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 5:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
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===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
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==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
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===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
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Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
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===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 6:''' Particulate Size and Corresponding Machinery]]<br />
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For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
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<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 7:''' Gas Scrubbing (VITO)]]<br />
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|[[File:ESP.png|frame|center|300x300px| '''Figure 8:''' ESP (IHS GlobalSpec)]]<br />
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==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
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===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 9:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
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Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
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Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
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===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
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Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 10:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 11:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 12:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 13:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 14:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 15:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 16:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
<br />
M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
<br />
E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
<br />
Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
<br />
A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=File:Toxinstable.png&diff=4604File:Toxinstable.png2016-02-21T22:36:15Z<p>Pdtravan: Pdtravan uploaded a new version of &quot;File:Toxinstable.png&quot;</p>
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<div></div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4524Environmental concerns2016-02-21T18:47:24Z<p>Pdtravan: /* Human Health */</p>
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<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
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<br><br />
<br />
<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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</center><br />
<br />
The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location. Below is a list of some chemical pollutants that might be of concern to process designers and their LD50. <br />
<br />
Lead 450 mg/kg (human)<br />
<br />
Cadmium 890 mg/kg<br />
<br />
Mercury 100 mg/kg<br />
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Arsenic 15 mg/kg<br />
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Sulfur 3000 mg/kg<br />
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Cadmium Sulfide 7080 mg/kg<br />
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Sodium Chloride 3000 mg/kg<br />
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Mercury (II) Chloride 210 mg/kg<br />
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Sodium Fluoride 52 mg/kg<br />
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Titanium Sulfate 16 mg/kg<br />
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Sodium Cyanide 6.4 mg/kg<br />
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Ammonium 7338 mg/kg<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
<br />
An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet.png|frame|center|500x500px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
<br />
By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
<br />
[[File:bieker.png|frame|center|500x500px| '''Figure 4:''' Semicentralized Wastewater Management Scheme. Figure from Bieker, et al. 2010]]<br />
<br />
The EPA has provided estimates for the annual cost and operational costs of potential wastewater management systems for a rural community of approximately 450 people. Smaller communities are hypothesized to benefit most from decentralized systems, and their study confirmed that this is so. To fund a centralized system, the annual cost would be approximately $216,850- $342,500 with an additional average operational cost of $35,000. The total capital cost of a centralized system can span from $2.3M to $3.8M. Decentralized small cluster or on-site systems, on the other hand, yield a capital cost estimate of $510,000 with very low operational and annual costs. This analysis is specific to the hypothetical rural area that they assumed, but illustrates the possibility of dramatically decreasing costs when the treatment system is tuned to the local community (Bieker et al, 2010).<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
<br />
Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 5:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 6:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 7:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 8:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 9:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 10:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 11:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 12:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 13:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 14:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 15:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 16:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
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Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
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Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
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B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
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M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
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Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
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Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
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Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
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Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
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VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
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IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
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Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
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D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
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M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
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Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
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Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
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Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
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U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
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EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
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M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
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E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
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Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
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A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
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S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4515Environmental concerns2016-02-21T18:39:14Z<p>Pdtravan: </p>
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Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
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Steward: David Chen, Jian Gong, and Fengqi You<br />
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Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
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=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
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Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
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|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
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Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
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Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
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Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
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==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
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These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
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The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
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These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
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Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
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[[File:decentralized_flowsheet.png|frame|center|500x500px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
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==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
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In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
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By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
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[[File:bieker.png|frame|center|500x500px| '''Figure 4:''' Semicentralized Wastewater Management Scheme. Figure from Bieker, et al. 2010]]<br />
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The EPA has provided estimates for the annual cost and operational costs of potential wastewater management systems for a rural community of approximately 450 people. Smaller communities are hypothesized to benefit most from decentralized systems, and their study confirmed that this is so. To fund a centralized system, the annual cost would be approximately $216,850- $342,500 with an additional average operational cost of $35,000. The total capital cost of a centralized system can span from $2.3M to $3.8M. Decentralized small cluster or on-site systems, on the other hand, yield a capital cost estimate of $510,000 with very low operational and annual costs. This analysis is specific to the hypothetical rural area that they assumed, but illustrates the possibility of dramatically decreasing costs when the treatment system is tuned to the local community (Bieker et al, 2010).<br />
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=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
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<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
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RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
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==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 5:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
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===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
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==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
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===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
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Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
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===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 6:''' Particulate Size and Corresponding Machinery]]<br />
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For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
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<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 7:''' Gas Scrubbing (VITO)]]<br />
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|[[File:ESP.png|frame|center|300x300px| '''Figure 8:''' ESP (IHS GlobalSpec)]]<br />
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==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
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===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 9:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
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Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
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Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
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===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
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Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 10:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
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[[File:RO.png|frame|right|150x200px| '''Figure 11:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
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Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
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[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 12:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
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==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
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===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
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===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
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[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
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Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
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[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 13:''' Pyrolysis of solid waste (Arc21)]]<br />
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Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
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[[File:Landfill.png|frame|center|'''Figure 14:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 15:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 16:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
<br />
M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
<br />
E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
<br />
Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
<br />
A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4514Environmental concerns2016-02-21T18:36:38Z<p>Pdtravan: /* Economic */</p>
<hr />
<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
<br />
<br><br />
<br />
<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
|<br />
|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
|}<br />
</center><br />
<br />
The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
<br />
An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet.png|frame|center|500x500px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
<br />
By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
<br />
[[File:bieker.png|frame|center|500x500px| '''Figure 4:''' Semicentralized Wastewater Management Scheme. Figure from Bieker, et al. 2010]]<br />
<br />
The EPA has provided estimates for the annual cost and operational costs of potential wastewater management systems for a rural community of approximately 450 people. Smaller communities are hypothesized to benefit most from decentralized systems, and their study confirmed that this is so. To fund a centralized system, the annual cost would be approximately $216,850- $342,500 with an additional average operational cost of $35,000. The total capital cost of a centralized system can span from $2.3M to $3.8M. Decentralized small cluster or on-site systems, on the other hand, yield a capital cost estimate of $510,000 with very low operational and annual costs. This analysis is specific to the hypothetical rural area that they assumed, but illustrates the possibility of dramatically decreasing costs when the treatment system is tuned to the local community (Bieker et al, 2010).<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
<br />
Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
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<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
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WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
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Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
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Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
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Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
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VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
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IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
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Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
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Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
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U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
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M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
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E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
<br />
Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
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A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4362Environmental concerns2016-02-21T00:19:56Z<p>Pdtravan: /* Social */</p>
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<div><br><br />
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Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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</center><br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
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[[File:decentralized_flowsheet.png|frame|center|500x500px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
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In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
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By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
<br />
[[File:bieker.png|center|Figure from Bieker, et al. 2010]]<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
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For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
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===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
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[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
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[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
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Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
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[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
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Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
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[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
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When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
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[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
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M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
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Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
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Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
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Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
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EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
<br />
M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
<br />
E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
<br />
Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
<br />
A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4361Environmental concerns2016-02-21T00:19:35Z<p>Pdtravan: /* Social */</p>
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Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
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Steward: David Chen, Jian Gong, and Fengqi You<br />
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Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
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Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
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{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
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Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet.png|frame|center|600x600px| '''Figure 3:''' Decentralized Systems Can Accommodate Wastewater Management Needs in Developing Areas. Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
<br />
By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
<br />
[[File:bieker.png|center|Figure from Bieker, et al. 2010]]<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
<br />
[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
<br />
M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
<br />
E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
<br />
Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
<br />
A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4286Environmental concerns2016-02-20T16:31:07Z<p>Pdtravan: </p>
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<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> Michelle Spiezio<sup> [2015] </sup>, Pear Dhiantravan<sup> [2016] <sup> <br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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</center><br />
<br />
The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet.png|center|Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
<br />
By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
<br />
[[File:bieker.png|center|Figure from Bieker, et al. 2010]]<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
<br />
Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
<br />
[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
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B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
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M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
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Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
<br />
M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
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E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
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Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
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A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4285Environmental concerns2016-02-20T16:30:22Z<p>Pdtravan: /* References */</p>
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<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
<br />
<br><br />
<br />
<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
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Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
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|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
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Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
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Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
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Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
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==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
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These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
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The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
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These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
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Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
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[[File:decentralized_flowsheet.png|center|Figure from Massoud, et al. 2009]]<br />
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==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
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In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
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By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
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[[File:bieker.png|center|Figure from Bieker, et al. 2010]]<br />
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=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
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<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
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RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
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==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
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===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
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==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
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===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
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Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
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===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
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For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
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{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
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|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
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==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
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===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
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Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
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Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
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===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
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Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
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[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
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Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
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[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
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==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
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===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
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===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
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[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
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Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
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[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
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Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
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[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
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=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
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[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
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When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
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A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
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[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
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=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
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IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
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Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
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Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
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U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994. <br />
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M. Kampa and E. Castanas, Human Health Effects of Air Pollution http://www.sciencedirect.com/science/article/pii/S0269749107002849<br />
<br />
E. F. Madden and B. A. Fowler, Mechanisms of Nephrotoxicity from Metal Combinations: A Review http://www.tandfonline.com/doi/abs/10.1081/DCT-100100098?journalCode=idct20 <br />
<br />
Lin and Pan, et. al, China’s international trade and air pollution in the United States http://www.pnas.org/content/111/5/1736.short <br />
<br />
A. M. Jardim, et. al, Economics of Wastewater Treatment: cost-effectiveness, social gains and economic status http://businessperspectives.org/journals_free/ee/2012/ee_2012_03_Junior.pdf <br />
<br />
S. Bieker, P. Cornel, M. Wagner, Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas Water Sci. Technol., 61 (2010), pp. 2905–2913<br />
http://wst.iwaponline.com/content/ppiwawst/61/11/2905.full.pdf <br />
<br />
L. Giovanni, Annamaria Volpi Ghirardini, Francesco Avezzù, To centralise or to decentralise: An overview of the most recent trends in wastewater treatment management, Journal of Environmental Management, Volume 94, Issue 1, February 2012, Pages 61-68, ISSN 0301-4797. http://www.sciencedirect.com/science/article/pii/S0301479711002751</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4284Environmental concerns2016-02-20T16:29:10Z<p>Pdtravan: /* Economic */</p>
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<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
|}<br />
</center><br />
<br />
The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
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These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
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Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet.png|center|Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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Fiscal disparities between national governments as well as public socioeconomic status contribute greatly to the gap between their air and water quality standards. There is a clear lack of cohesion in the organization of wastewater collection and treatment in several developing countries (Jardim et. al, 2012). Population growth combined with insufficient infrastructure for waste treatment devolves into an overall inability to maintain, regulate, or motivate air and water quality care. This is an economic issue in its core, with towns and countries unable to obtain the resources necessary to install sufficient regulatory methods. As wastewater treatment is an effort that can most effectively be maintained by the efforts of everybody in a population, fiscal inequalities pose a burden to the efficacy of current infrastructures. <br />
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By designing integrated systems that are appropriately sized for the population that they serve, the efficiency and efficacy of wastewater treatment can be greatly improved (Bieker et al, 2010). The figure below outlines a possible schematic for a semicentralized system whereby preliminary sorting occurs on a house-by-house basis, and larger local service plants perform the final large-scale treatments. The authors of this proposed scheme suggest that semicentralized systems such as this one not only provide increased breadth in treatment capabilities across populations, but also decreases energy and clean water usage by servicing local populations based on their needs and consumption. <br />
<br />
[[File:bieker.png|center|Figure from Bieker, et al. 2010]]<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
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===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
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===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
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===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
<br />
[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
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Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
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WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
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Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
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Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
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Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
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IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
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U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994.</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=File:Bieker.png&diff=4283File:Bieker.png2016-02-20T16:27:40Z<p>Pdtravan: </p>
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<div></div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4282Environmental concerns2016-02-20T16:26:39Z<p>Pdtravan: /* Social */</p>
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<div><br><br />
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Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
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Steward: David Chen, Jian Gong, and Fengqi You<br />
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Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
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Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
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|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
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Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
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Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
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These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
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The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
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These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
<br />
An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet.png|center|Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
<br />
Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
<br />
[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994.</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4281Environmental concerns2016-02-20T16:26:10Z<p>Pdtravan: /* Social */</p>
<hr />
<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
<br />
<br><br />
<br />
<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
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Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
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|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
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Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
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Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
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Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
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The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
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Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
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==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
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These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
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The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
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These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
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An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
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Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
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[[File:decentralized_flowsheet.png|200px|thumb|left|Figure from Massoud, et al. 2009]]<br />
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==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
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The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
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In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
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=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
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==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
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===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
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<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
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RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
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===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
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==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
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===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
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===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
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==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
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===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
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Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
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===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
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Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
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For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
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{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
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|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
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==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
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===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
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Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
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Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
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===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
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Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
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[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
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Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
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[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
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==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
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===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
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===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
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[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
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Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
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[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
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Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
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[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
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=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
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[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
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When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
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A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
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[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
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=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
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==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
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=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994.</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4280Environmental concerns2016-02-20T16:25:18Z<p>Pdtravan: /* Social */</p>
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<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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</center><br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
The Clean Air Act was established in 1970 to bring a conscientious effort to air pollution. It has undergone an amendment and several reviews, and is monitored for relevance and efficacy. It gives the Environmental Protection Agency the authority to establish national standards regulating air pollution and ensuring the safety of the people (EPA). Unfortunately, national boundaries for air quality cannot be as solidified as they are for water quality due to the rapid tendency of wind to affect other nations with one’s air pollutants. A study conducted in 2013 showed that pollution stemming from product exports in China contributes to a substantial percentage of sulfate pollution in the United States (Lin and Pan, et. al 2013). Differences between nations’ standards for waste treatment can cause disparities in global air care and national concern when retroactive treatment must be installed to purify leaked contaminants. <br />
<br />
These disparities often stem from the differing societal standards between developed and developing countries. Without strong governmental motivation, the public lacks guidance in upholding quality standards. Formal education is another contributing factor, as spreading the use of treatment facilities requires that the users understand the health and environmental benefits of waste stream treatment (Jardim et al, 2012). Many underdeveloped countries may have some infrastructure for water recycling and treatment, however their efficacy depends on the contributions and participation of the public. In situations where low income is combined with a lack of general education, much of the public would choose not to pay for wastewater treatment because they cannot see its utilitarian effects on the future (Jardim et al, 2012). <br />
<br />
An additional effect of insufficient education is that children and adults in these areas are unaware of the contaminants in their water source. This leads to improper pretreatment, which can cause diseases and other harmful physiological effects (Jardim et. al, 2012). <br />
<br />
Process designers can address these challenges by catering wastewater treatment infrastructure to the needs of the society, taking into account the level of urbanization and population growth trends (Giovanni et al, 2012). These two factors continually strain the environment and clean water supply, putting many at risk of only having access to poorly sanitized drinking water. While well developed countries may benefit from fully centralized wastewater treatment systems, developing countries might require a more decentralized approach to cater to the spread of the population and to increase accessibility to treatment plants. <br />
<br />
[[File:decentralized_flowsheet|200px|thumb|left|Figure from Massoud, et al. 2009]]<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
<br />
Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
<br />
[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
<br />
WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
<br />
Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994.</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=File:Decentralized_flowsheet.png&diff=4279File:Decentralized flowsheet.png2016-02-20T16:23:31Z<p>Pdtravan: </p>
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<div></div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4278Environmental concerns2016-02-20T16:21:47Z<p>Pdtravan: /* Human Health */</p>
<hr />
<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
<br />
<br><br />
<br />
<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
<br />
<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
{|<br />
|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
|<br />
|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
|}<br />
</center><br />
<br />
The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
<br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
<br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
<br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
<br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
<br />
Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
<br />
Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
<br />
[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
<br />
[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
<br />
[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
<br />
[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
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WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
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Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
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Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
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Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
<br />
R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
<br />
Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
<br />
VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994.</div>Pdtravanhttps://processdesign.mccormick.northwestern.edu/index.php?title=Environmental_concerns&diff=4277Environmental concerns2016-02-20T16:21:27Z<p>Pdtravan: /* Human Health */</p>
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<div><br><br />
<br />
Authors: Sean Cabaniss,<sup> [2014] </sup> David Park,<sup> [2014] </sup> Maxim Slivinsky,<sup> [2014] </sup> Julianne Wagoner,<sup> [2014] </sup> and Michelle Spiezio<sup> [2015] </sup><br />
<br />
Steward: David Chen, Jian Gong, and Fengqi You<br />
<br />
Date Presented: Feb. 23, 2014<br />
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<!-- Table of Contents --><br />
__TOC__<br />
<br />
=Overview=<br />
All industrial processes produce waste in some form that must be carefully handled and disposed of according to regulations set down by governments at varying levels. The key areas for consideration are emissions to the air, water, and land, smells, noise, and visual impact, and waste management. It is important to remember that pollution considerations are both a moral and legal obligation for any engineer or industry(Towler et. al (2012). Emissions from chemical plants are regulated by both local and federal governments. Plants are required to monitor and document waste streams discharged to the environment, maintain permits from local governmental agencies, and either pay fines or directly address any violations(Towler Powerpoint, 2010). Waste management can come in many forms to minimize the impact on the environment. Some key strategies include dilution and dispersion of the harmful chemicals, discharge into foul sewer water with permission from the appropriate authorities, physical treatment methods, chemical treatments, biological treatments, incineration, landfill at controlled sites, and dumping into the sea. <br />
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<br />
=Human Health, Social and Economic costs=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Human Health==<br />
The human costs associated with chemical plant pollution come in the form of endangerment to the health of people in local communities. Because chemical plants are not going to be fully contained, it is necessary to determine how those streams and pollutants that are emitted affect the surrounding population. Figure 1 shows the various effects of pollution on the human body. A few examples of this are: contamination of the local potable water supply if, for instance, chemicals in a retention pond leech out and into groundwater; release of particulate matter reducing the air quality of a community to the point where instances of asthma increase; and, the release of hazardous chemicals causing carcinogenic effects(EPA Website- Health Effects of Air Pollution).<br />
<br />
Figure 2 below shows the world wide impact of air and water pollution as it relates to the impact of infectious disease malaria. The number of premature deaths from pollution is obviously quite high, however WHO currently estimates that the numbers are ever higher. WHO now estimates 7 million deaths annually linked to air pollution. This large number comes from new data which suggests that there is a strong link between air pollution exposure and cardiovascular diseases and cancer. Air pollution is also the cause of numerous respiratory diseases(WHO).Water pollution concerns that we hear about mostly have to do with biological pollutants, such as bacteria and parasites that cause illness. Water polluted with microorganisms causes 80% of all infectious diseases. (Environmental Pollution Centers-'Water Pollution Diseases). This, however, mostly comes from mistreatment of human waste, not from industrial pollution. Industrial chemical pollution is controlled by the EPA, thus the levels of chemicals industry can release into water is low enough to not cause any health issues in humans. However, there are still unknown health effects for a large number of chemicals.<br />
<center><br />
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|[[File:Health_effects_of_pollution.png|frame|center|300x300px| '''Figure 1:''' Health Effects of Pollution(Wikipedia-Pollution)]]<br />
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|[[File:Pollution_deaths.png|frame|center|300x300px| '''Figure 2:''' Deaths Associated with Pollution (Breath Project)]]<br />
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The effects of polluted air and water supplies on human health are as numerous as the possible industrial sources of contamination. Each organic and inorganic compound has a unique systemic effect. Despite the existence of a number of these compounds in the human body, many systems are extremely sensitive to environmental changes increasing or decreasing the amount of mineral or chemical extant. <br />
Humans may be exposed to water pollutants as immediately as in the form of drinking water and as indirectly as through the food chain. The former can directly be assessed for contaminants, while the latter is more difficult to monitor due to the involvement of many variables between the source water and the human consumer. Plants that grow near contaminated water sources can absorb harmful chemicals, which are then ingested by small animals and passed along the food chain to humans. The movement of these animals and their source of food is difficult to track, as is the balance of toxins entering and leaving their body. The effects of bad waste containment and water purification before expulsion into the environment can thus reach as far as people who live in entirely different areas. <br />
Air pollutants that result from chemical processes can easily be inhaled by close inhabitants or even by populations downwind. As airborne waste enters the atmosphere, it immediately can diffuse and can reach as far as the other side of the world.3 Pollutants can additionally travel through air and settle onto food or water sources to be ingested. Less frequently do air pollutants affect a person through physical contact, but that is also a possibility especially in cases where someone has cuts or lesions on their skin (Kampa and Castanas, 2008). <br />
Long-term effects arise if the unwanted pollutants are absorbed into the blood stream, from which they can access and accumulate on vital organs. The cardiovascular and respiratory systems were shown to be the most affected after exposure to particulate matter, which is produced by factory and power plant waste streams and incinerators, among other sources (Kampa and Castanas, 2008). Depending on the size of the particulate, it may or may not be able to enter lung alveoli by traveling through the respiratory tract. These particles can carry with them organic compounds, metals, carbon wastes, and toxic gases, which accumulate in tissues. This can cause mild to severe irritation as well as inflammation, constriction of airways, and increased susceptibility to infections. Accumulation of ions and small noxious gases can alter local or systemic pH, which is harmful as many enzymes and biological machinery are very sensitive to changes in acidity. <br />
The body may excrete ingested toxins, however the path to excretion may suffer damages as well. A study of the physiological effects of the metals lead, arsenic, and cadmium showed adverse effects on the kidney where blood is filtered into urine. Metal deposition severely disrupts kidney function, as certain proteins and other molecules will bind to them and suffer a loss of function (Madden and Fowler, 2000). <br />
<br />
Process designers can gain access to information about waste and effluent streams that are made in their plants, and can assess the dangers of the components in these streams according to EPA regulations as well as regulations within the local/ state community. The composition of these streams and the levels of particulate matter can be controlled by adding proper air filtration or wastewater treatment methods as described in the Treatment sections below. Although different locations may have different standards for pollutants, it is important to keep in mind that the plants and animals in these areas generally react to toxins in the same manner. Process designers are responsible for the ethical concerns that arise if standards are lowered and populations surrounding a plant are exposed to toxic levels of pollution, and should be mindful of these overarching safety concerns regardless of plant location.<br />
<br />
==Social==<br />
The social costs linked to environmental concerns relate to public perception of a company and its actions with regard to environmental stewardship, as well as the social impact on society. Any company that produces waste streams is going to be scrutinized by the public for the way these streams are handled. Companies caught or known for high pollution levels often receive bad press, which can also give investors a bad impression and hurt stock prices. It is to the advantage of the company, therefore, to prove to the public that every effort is being made to responsibly handle waste streams.<br />
<br />
These costs can be the burden of both society and industry. In 2011, it is estimated by the NRDC that air pollution caused the loss of 3.4 million work days in the United States(NRDC). These lost work days combined with medical bills sum to a cost as high as $78 billion dollars. Social costs to industry can come in the form of money spent to improve company image. The amount varies based on situation, but can be very high, especially in the wake of an environmental disaster. A recent example of high social costs is the outcry in the wake of the BP oil spill. In 2012, BP and the Department of Justice reached a settlement where BP would pay $4.5 billion in fines. However, BP projects that the spill will cost around $40 billion due to all of the payments to not only settle claims, but to support efforts to rehabilitate the Gulf Coast ecosystems and businesses that (not mandated by the court). Additionally, BP has to work to continue to turn around the 35% reduction in stock prices since the spill(Huffington Post).<br />
<br />
==Economic==<br />
The main economic costs come from the installation and operation of environmental control equipment(Turton et al, 2003). These costs are of separation equipment, such as settling tanks, electrostatic precipitators, and distillation columns, as well as disposal equipment, such as incinerators and reactors that neutralize or oxidize a waste stream. Another cost that companies must incur is that of the removal of these wastes. Companies will often pay third party waste management companies to take waste streams and dispose of them, through means such as burial and placing in a landfill, for example. There are also the costs of cooling towers and noise abatement measures to take into consideration. The cost of water treatment systems typically accounts for around 1.3% of fixed-capital investment, while waste disposal facilities cost up to 2% of fixed-capital investment(Peters et al, 2003).<br />
<br />
The cost of not taking the environment into consideration when designing a process can far outreach that of the equipment, however. If a company does not follow regulations, they incur legal expenses as a penalty. Additionally, failure to comply can a high cost associated with poor public perception of the company. Bad press and public protests can lead to a large loss in profit(Towler et al, 2013). For example, just to avoid strict air standards that would impose costs of better pollution control equipment, power companies spent $67 million between 2010 and 2012 lobbying congress against clean air regulations(NRDC).<br />
<br />
In the long run, it can often be in a company's best interest to take environmental factors into consideration. Optimizing a process, to reduce waste, results in less money that needs to be spent on waste disposal. Additionally, using recycle streams effectively may reduce the cost of the inputs to the process. Finally, if a process is designed in such a way (Seider 2004).<br />
<br />
<br />
=Types of Pollution and Treatment=<br />
Environmental concerns associated with process plants encompass more than just air, land, and water pollution. There are also a variety of other indirect costs that should be considered, as they too can have a large impact on both the environment and company profit if not properly addressed. These costs are directly linked to all the types of pollution that a plant releases. Whether it is air pollution, water pollution, or even excess noise, it is important to minimize the impact of these discharges on the health of both the local community and the population as a whole, due to the far reaching effects of most types of pollution. Addressing pollution responsibly will also minimize social costs, those that are linked with how the public perceives the company. Being perceived positively by the public will minimize costs associated with having to boost company image and gain the trust of communities. Environmental stewardship also ties into economic costs. Having to pay for environmental compliance equipment may be expensive, but neglecting to do so will result in even larger legal fees and costs associated with cleaning up disastrous spills. <br />
<br />
==Noise Pollution==<br />
Noise pollution is any unwanted or disturbing sound that diminished quality of life(Ulrich 1984).<br />
<br />
===Causes & Effects===<br />
Equipment that are likely to be noisy are compressors, fans, burners, and steam relief valves(Towler et. al (2012). Whereas this unwanted noise may often be considered just an annoyance, there are studies that link elevated noise to health issues. For example, being exposed to unwanted noise can lead to an increase in stress and disruption of sleep, thus leading to increased blood pressure. Exposure to high levels of sound can lead to Noise-Induced Hearing Loss (NIHL)(Towler et. al (2012). Sound is measured in decibels (dB) and is determined by the following expression:<br />
<br />
<math> Sound\ level=20*\log_{10}(\frac{RMS\ sound\ pressure}{2E-5}) </math><br />
<br />
RMS sound pressure is equal to the localized change in atmospheric pressure caused by sound waves, measured in Pa. <br />
Sound meters determine noise level as a human ear would, providing measurements in dB(A) units. The “A” term corresponds to the weighting used by the meter to mimic the human ear. Permanent damage can be caused at sound levels above 85 dB(A), and ear protection is customarily worn in areas where levels are around 80 dB(A) and above(Wikipedia page-Sound Pressure).<br />
<br />
<br />
===Treatment===<br />
To mitigate the adverse human effects of noise pollution, the EPA has included provisions in the Clean Air Act, the noise Control Act of 1972 and the Quiet Communities Act of 1978. However, the responsibility of noise control is mainly handled at the State and local level(ulrich 1984).<br />
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Some design decisions can be made to reduce the effects of noise on humans. Noisy equipment should not be placed near rooms that are often occupied. Additionally, rooms can be insulated to mitigate the length which the noise travels. If workers are to be near noise, they should wear earplugs to reduce the impact. Finally, choosing a plant location that is far from communities will reduce the amount of people exposed to any loud noises.<br />
<br />
==Thermal Pollution==<br />
[[File: Thermal.png|thumb| upright=2| alt=Alt text|'''Figure 3:''' Effects of Thermal Pollution (Tutor Vista)]]<br />
Thermal pollution relates to the heat released by a plant into the environment. This often comes from water that was used to cool down a process and then released into the environment. <br />
<br />
===Causes & Effects===<br />
The largest concern with regards to thermal pollution is water quality. The temperature of water directly relates factors such as density, surface tension, and to the solubility of gases in the water. The most important consideration is the solubility of oxygen in water. Dissolved oxygen in water is essential in maintaining aquatic life. Thus changing the temperature of water due to thermal pollution can alter water ecosystems. An additional concern is that increased water temperatures lead to a reduction in capacity for organic wastes assimilation. Figure 3 shows a summary of the effects of thermal pollution on water systems.<br />
<br />
===Treatment===<br />
Because of the negative effects of thermal pollution, and federal water temperature standards, design engineers must employ the use of various process technologies to mitigate thermal pollution. Options for reducing temperatures of water streams are: cooling towers, cooling ponds, and spray ponds. All of these technologies use the principles of heat transfer across a water-air interface, thus the heat from the water is transferred to air, which can be released into the environment. Another consideration is to recycle the heat. Hot water or fluid waste/effluent streams can be used in a heat exchange network to transfer heat to an inlet stream that requires heating before entering a process.<br />
<br />
==Air Pollution==<br />
Air pollutants can be either gases or particulate matter suspended in an effluent air stream. Some examples are: CO2, sulfates, nitrates, particulates (PM10, PM2.5), Volatile Organic Compounds (VOC) and, less commonly, chlorine compounds(Towler et. al (2012).<br />
<br />
===Causes & Effects===<br />
These pollutants often come from fired heaters, boilers or flares. These wastes are often under careful scrutiny from governments as well as the public since gases being released from towers are often the easiest forms of pollution for a casual observer to see.<br />
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Emissions to the air can be particularly dangerous because, if left unchecked, they can have far reaching consequences. Historically, the focal points for air emissions have been the effects on acid rain, ozone and greenhouse gases. Lately, greenhouse gases have been the most scrutinized due to growing concerns of global warming. <br />
<br />
===Treatment===<br />
Air emissions must be treated before being released into the atmosphere, especially given the recent emphasis on green processes and the growing alarm with regards to global warming. Due to the properties of gases, air pollution control can be the most expensive and energy intensive. Typically, there are two main classifications of air pollution control equipment: those associated with removing gaseous pollutants from streams to be released into the air and those that can physically remove particles from these streams. <br />
<br />
Equipment chosen to remove a gaseous pollutant depends on whether the gas is easily reacted into something that is less harmful to the environment. Noxious elements are often removed by absorption, using a gas scrubber which utilizes a liquid solvent, or by adsorption, using a gas adsorber utilizing either a liquid or solid as the adsorber for the pollutant being removed(Peters et al, 2003). An important note is that these pieces of equipment often do not render the pollutant harmless, but simply change the form from gas to liquid or from gas to solid, both of which needs further treatment. For those pollutants which can be reacted into something less harmful, equipment such as reactors and incinerators are used. For example, combustible vapors are often burned in either a direct incinerator or in a catalytic incinerator, to increase the efficiency of the burning reaction. However, these incinerators often require very high operating costs.<br />
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[[File:air_particles.png|frame|center|'''Figure 4:''' Particulate Size and Corresponding Machinery]]<br />
<br />
For the removal of particles from gas streams, there is a wide variety of possible equipment, chosen based on particle size and characteristics, as shown in Figure 4 above(Peters et al, 2003). Mechanical collectors are generally used when particle sizes are large. Some mechanical collection equipment are: settling chambers, which are driven by gravity; cyclones, which make use of centrifugal forces; and bag filters, which collect particles from the gas by interception on the fabric surface of the bag(ulrich, 1984). Mechanical collectors are all dry methods of particle removal. There are also a variety of wet methods that can be employed to rid gases of particles. Wet methods such as a spray tower and Venturi scrubber rely on the collision of the particles with water to remove the particles from the gas, as seen in Figure 5. A final method of particulate removal is an electrostatic precipitator (ESP), Figure 6. An ESP will charge the particles in the gas by applying a high voltage, then allow these charged particles to be attracted to oppositely charged collection plates(Peters et al, 2003). ESPs are useful for removing ultra-fine particles from corrosive gas streams, but are often sensitive to the properties of the particle. Additionally, the method of using rapping to remove the particles from the collection plates is rudimentary and often causes maintenance issues(ulrich, 1984).<br />
<br />
<center><br />
{|<br />
|[[File:Scrubbing.png|frame|center|300x300px| '''Figure 5:''' Gas Scrubbing (VITO)]]<br />
|<br />
|[[File:ESP.png|frame|center|300x300px| '''Figure 6:''' ESP (IHS GlobalSpec)]]<br />
|}<br />
</center><br />
<br />
==Water Pollution==<br />
Types of water pollutants are: chemicals, such as oil; suspended solids, such as metals and biological materials; and dissolved (aqueous) materials, such as ions. <br />
<br />
===Causes & Effects===<br />
[[File:Water_pollution.png|thumb|upright=2|alt=Alt text|'''Figure 7:''' Sources of water pollution (Environmental Working Group)]]<br />
Water pollution mainly comes from agriculture, urban runoff, and industry, as shown in Figure 7. Many of these chemical pollutants are regulated by the EPA, but there are still many that aren't. This is due to the fact that there simply is not comprehensive information on the effects of these chemicals to the environment and humans. For chemical engineering, industrial water pollution is the most applicable. This typically comes from three streams: process waste, utility waste and run-off streams. Process waste streams are the unwanted side products of reactions and include salt water, hydrocarbon contaminated water, biologically contaminated water, and water with too high or low pH. Utility waste is mainly produced from cooling tower water blowdown. The purpose of blowdown is to prevent a buildup of salts in the towers, but produces a stream of contaminated water. Finally, run-off streams come from rain water, hydrant flushing and equipment washing.<br />
<br />
Liquid wastes are typically not as far reaching as gaseous waste, but can be much more devastating. Ecosystems can be destroyed from poor wastewater policies. Local populations can suffer from a lack of clean drinking water or dying wildlife in the area. The BP oil spill was a highly visible incident that showed how much damage can be done by water borne pollutants.<br />
<br />
Aqueous wastes can be the most immediately harmful to the environment and people living nearby and must be sent immediately to an effluent treatment. Some of the most common, harmful water contaminants are ammonia, salts from deionizers, hydrocarbons, spent acids, caustics, and various forms of biological contamination. Utilities on-site can also create large wastewater flows that must be purged in order to prevent solid buildups. The most efficient way to deal with contaminated runoff is to collect and purify it on-site before disposing of it(Peters et. al, 2003). <br />
<br />
===Treatment===<br />
The main factors that usually have some sort of legislative constraints are pH levels, suspended solids, toxicity, and biological oxygen demand. Oxygen demand is often under looked as a form of pollution because there is rarely visible evidence that something is wrong in the stream. However, many local governments mandate that the water leaving a plant must have enough oxygen to sustain aquatic life before being released.<br />
<br />
Liquid wastes are usually flammable and can be burned in an incinerator as long as care is taken to insure the temperatures are high enough to destroy the harmful compounds. This only shifts the problem, however, as it creates gaseous wastes. <br />
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[[File:Sand_filter.png|frame|left|250x300px| alt=Alt text| '''Figure 8:''' Rapid Sand Filter Schematic (Virginia Tech Department of Civil Engineering, 1998)]]<br />
Wastewater that contains large particles, either floating or suspended, will usually be first treated by simply skimming off or pulling out the large masses of particles. Following this, wastewater will be sent to a sedimentation basin to allow the particles to settle due to the force of gravity. The sludge that forms on the bottom of the basin is removed with sludge scrapers. For smaller particles that are not settled out of the water, a rapid sand filter or multimedia (usually sand and anthracite) filter, shown in Figure 8, can be used.(Davis, 2010). For very small particles, membrane processes can be employed. These include ultra-filtration, which uses exclusion of particles based on size, reverse osmosis, shown in Figure 9, which excludes based on both size and particle properties, and electrodialysis, which is used to remove ionic species from the water.(Peters et. al, 2003). <br />
<br />
[[File:RO.png|frame|right|150x200px| '''Figure 9:''' Reverse Osmosis Water Treatment (Hydrocomponents & Technologies Inc.)]]<br />
To treat water contaminated with organic matter, microorganisms can be used. The microorganisms break down the organic matter, either aerobically or anaerobically depending on the organism. Aerobic biological processes either used activated sludge, shown in Figure 10, where biological growths are mixed in the wastewater and the resulting suspension is separated by gravity, or the fixed-film method, in which wastewater trickles over a biological film(Peters et. al, 2003). <br />
<br />
Chemical treatment of water is generally used to remove color, odor, acids and alkalies, heavy metals, colloids, and oil. To remove colloids, coagulation is often used. In coagulation, chemicals are added to the water to break down the electrostatic double layer or the colloidal particles, essentially to neutralize the charge of the particles, allowing them to combine during flocculation(davis 2010).To treat acid and alkaline waste, lime and sulfuric acid are often used(Peters et. al, 2003). Converse to this, distillation or salt precipitation methods can be used to recover the acid or alkali. To disinfect the water, chlorine or ozone are often used. Ozone, in addition to disinfection, is also useful for color, taste, and odor removal from the water.<br />
<br />
<br />
[[File:Activated_sludge.png|frame|center|300x300px| '''Figure 10:''' Wastewater Treatment with Activated Sludge(ChemSearch)]]<br />
<br />
==Land Pollution==<br />
Land pollution is any solid wastes that requires disposal. Solid wastes are generally identified as flammable, toxic, corrosive or reactive. Waste containing any of these characteristics must be specially handled to ensure as little damage to the local environment as possible. <br />
<br />
===Causes & Effects===<br />
Left unchecked, large amounts of flammable waste could ignite and become very difficult to control. Toxic, corrosive or reactive materials have averse affects to any local populations, often causing major health problems in humans and animals alike. Solid waste in a landfill can create chemical leachates which, if improperly handled, can seep into the ground and into groundwater. <br />
<br />
===Treatment===<br />
Solid, hazardous wastes are generally the easiest to control, but can also be the most difficult to safely discard; once created they can last much longer and do more damage than liquid or gaseous pollution. Table 1 below shows various types of solid wastes and how they can be treated.<br />
<br />
[[File:solid_wastes.png|frame|center|'''Table 1:''' Solid waste treament]]<br />
<br />
Table 1 shown above introduces several forms of solid waste disposal. The main types of disposal are recycling, chemical conversion, incineration, pyrolysis, and landfill(Peters et. al, 2003). Chemicals can be recovered from solids through extraction or stripping, while valuable solids can be recovered through a variety of methods such as flotation, electrical conductivity, or hand picking. Recycling these products or even selling them can often save company money in the long run. Chemical conversion of solid waste can often be used to convert the waste into something less harmful or sellable. Incineration is used to create a residue that is much smaller and more acceptable for landfill application. Incineration can be expensive, but if done properly can potentially recover some fuel value through the generation of steam. Pyrolysis, or the heating of the waste in an air-free chamber, is an alternative to incineration that avoids a lot of the air pollution issues associated with incineration,(Peters et. al, 2003). as the pollutants produced are contained and can be treated. Figure 11 shows pyrolysis of solid waste. <br />
<br />
[[File:Pyrolysis.png|frame|center|upright=2|'''Figure 11:''' Pyrolysis of solid waste (Arc21)]]<br />
<br />
Landfills are useful for disposing large quantities of waste, but if the contents are legally classified as "hazardous", the waste must go through a pretreatment process in order to reduce the contaminants to an acceptable level. Additionally, proper lining of the landfill must be installed to prevent leachates that seep from the landfill and into groundwater. With the proper set-up, landfills can be used as a source of methane gas. A landfill diagram depicting both the lining requirements and a methane collection system is shown below in Figure 12. <br />
<br />
[[File:Landfill.png|frame|center|'''Figure 12:''' Landfill (Ohio Wesleyan University - Environmental Geography)]]<br />
<br />
=Waste Minimization=<br />
Chemical engineers need to keep several environmental considerations in mind when designing processes. During the design of the process, the toxicities of all the products, byproducts, and wastes produced by the system must be considered. Then, the reaction pathway that minimizes toxic components should be chosen whenever possible.(Biegler et al, 1997). Emphasis must also be put on designing processes that operate at a nominal steady stare. Avoiding transient conditions, such as start-up or accidents, also avoids the production of excess waste(Biegler et al, 1997).<br />
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[[File:Waste_min.png| thumb| upright=2.5|'''Figure 13:''' Waste Minimization Hierarchy (Burnie City Council)]]<br />
The general 5-step process for waste minimization can be summarized as: 1) Identify waste components for regulatory impact. 2) Identify waste streams for size and economic impact. 3) List the root causes of the waste streams. 4) List and analyze modifications to address the root causes. 5) Prioritize and implement the best solutions(Towler et al, 2013). The hierarchy of waste management approaches is: 1) source reduction by maximizing conservation, 2) reusing materials, 3) recycling, 4) energy recovery from waste, and 5) disposal. This hierarchy is shown in Figure 13. It is evident that avoiding pollution is the best route, but, this is not usually an option.<br />
<br />
When designing a process, emphasis should be placed on reducing the source of pollution in the first place. There are a variety of strategies for reducing that source of waste. Some of these are to reduce the concentration of impurities in feed streams, protect catalysts and adsorbents from poisoning and deactivation, and to eliminate the use of extraneous materials, such as solvents. Other strategies are to improve the efficiency of the process, by increasing recovery of separations because higher purity streams means smaller waste formation. Finally, altering background processes of the plant to be more efficient can save waste. For example, using a cleaner fuel as an energy source or a more environmentally friendly supplier reduces environmental footprint(Towler et al, 2013).<br />
<br />
A good design will seek to minimize, recycle, and make use of segregated waste streams in order to satisfy the demands of the waste market(Seider 2004). Optimization is a powerful tool for waste minimization because it cuts down on toxic materials as well as improving the overall system. Optimization can be used to account for environmental impact, such as the effects of carbon monoxide or other greenhouse gases. Recycling not only reduces the amount of waste, but also provides cost savings for a company. For example, recovering heat from wastewater can eliminate both thermal pollution and water pollution, while producing energy inputs if the suspended solids can be fermented to produce fuels. Processes should also be designed, if possible, to use materials that can are considered waste to other processes. If waste produced is considered a valuable product to another process, the waste can be sold or utilized, thus avoiding some of the costs associated with treatment and disposal. Figure 14 depicts a brief methodology for waste minimization. <br />
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[[File:Waste_flowchart.png| frame| center|'''Figure 14:''' Waste Minimization Flowchart (Partha Das Sharma)]]<br />
<br />
=Legislative Action=<br />
==1972 Federal Water Pollution Control Act==<br />
The US Water Pollution Control Act set forth three major new regulations in an effort to keep toxic contaminants from getting into water supplies. Its goal was to achieve clean water for swimming, boating, and protecting fish and wildlife by 1983. This legislation said the EPA would set water quality standards for pollutants in surface water, set effluent guidelines for each industrial sector, and that it is unlawful to discharge any pollutant into navigable waters without a permit( U.S. Fish and Wildlife Service).<br />
<br />
==Resource Conservation and Recovery Act (RCRA)==<br />
The ultimate goal of this act is to protect the groundwater from contamination. The act addressed waste management from "cradle to grave". It identified wastes on regulatory lists or if it has a certain characteristic level of flammability, toxicity, corrosivity, or reactivity. The act also specified how hazardous wastes must be labeled and tracked in transport as well as the treatments required for low levels of contaminants(EPA Website "Resource Conservation and Recovery Act).<br />
<br />
<br />
=Example Environmental Design Problem=<br />
==Volatile Organic Compound Abatement(Becker, 1994)==<br />
The 1990 Clean Air Act mandates a reduction in emissions of volatile organic compounds (VOC). Any VOC emission sources exceeding 10tons/year must retrofit abatement processes with the best available control technology (BACT).<br />
<br />
A paint spraying plant emits VOCs from vents in the paint spray booths. The stream contains primarily toluene, methyl ethyl ketone (MEK), and xylene, with small impurities of silicone and phosphorus. The concentration of VOCs in the dryer effluent varies between a minimum of 0.3 wt% VOC and a maximum of 1.2 wt% VOC with an approximate composition of 50% toluene, 25% MEK, and 25% xylene. <br />
<br />
The painting company has commissioned you to evaluate three different technologies for a reduction in VOCs: thermal incineration, catalytic incineration, and carbon absorption and destruction of the VOCs. The low quality steam can be used by a nearby bottle washing plant.<br />
<br />
Design an emission control plant for 50,000 scfm of vent gas at 100F and 25% relative humidity for 99% removal. The plant is located in Dearborn, Michigan, and the paint spray booths operate on a single 12-hour shift per day. Include the necessary start-up controls. The available fuel is natural gas or oil. Calculate the capital and operating cost and the $/lb or ton of VOC removed. Compare the three processes and recommend which is most suitable for this application. <br />
<br />
<br />
=Conclusion=<br />
Nearly all industrial chemical processes have pollution in one form or another. There are several sources and compounds of waste in all phases to be aware of and to know how to dispose of properly. A proper understanding of these hazardous compounds and materials as well as the effects these pollutants can have is essential, especially as an engineer. A chemical engineer's duty is to ensure that the waste, whether a gas, liquid, or sold is disposed of or recycled in a responsible manner and according to the local and federal guidelines. Proper waste management not only reflects well on a company and its engineers, but also can have lasting benefits to profits and the well being of locals in the area. On the other hand, reckless waste handling policies are not only dangerous for a plant and those around it, but are in danger of serious repercussions from the government and in the EPA. Finally, engineers have a moral obligation to uphold certain standards even when working in countries with less strict waste management standards.<br />
<br />
<br />
=References=<br />
Towler, G.P. and Sinnot, R. (2012). Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. Elsevier.<br />
<br />
Towler, G.P. (2012). Chemical Engineering Design, PowerPoint presentation.<br />
<br />
EPA Website Health Effects of Air Pollution http://www.epa.gov/region07/air/quality/health.htm<br />
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WHO, 7 million premature deaths annually linked to air pollution, March 2014 http://www.who.int/mediacentre/news/releases/2014/air-pollution/en/<br />
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Environmental Pollution Centers, Water Pollution Diseases http://www.environmentalpollutioncenters.org/water/diseases/<br />
<br />
Wikipedia web page,Pollution http://en.wikipedia.org/wiki/Pollution<br />
<br />
Breath Project,Air Pollution World’s Top Killer by 2050 http://breatheproject.org/news/2012/03/<br />
<br />
Altman The Price Of Pollution Politics: Eight Companies Attacking Clean Air Standards and the Toll on America’s Health NRDC: June 2012. http://www.nrdc.org/air/files/Price-of-Pollution-Politics.pdf<br />
<br />
B. Skoloff, J. Wardell. BP Oil Spill Cost Hits $40 Billion, Company Returns To Profit Huff Post Green. http://www.huffingtonpost.com/2010/11/02/bp-oil-spill-costs-hit-40_n_777521.html<br />
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R.T. Turton, R.C. Bailie, W.B. Whiting, J.A. Shaeiwitz, Analysis, Synthesis, and Design of Chemical Processes, Prentice Hall: Upper Saddle River, 2003.<br />
<br />
M.S. Peters, K.D. Timmerhaus, Plant Design and Economics for Chemical Engineers, 5th Ed., McGraw-Hill: New York, 2003.<br />
<br />
Seider, W.D. (2004). Process Design Principles: Synthesis, Analysis, and Evaluation, Wiley: New York.<br />
<br />
Ulrich, A Guide to Chemical Engineering Process Design and Economics, Wiley: New York, 1984.<br />
<br />
Wikipedia page, Sound Pressure http://en.wikipedia.org/wiki/Sound_pressure<br />
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Tutor Vista Effects of Thermal Pollution http://www.tutorvista.com/biology/effects-of-thermal-pollution<br />
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VITO,Gas scrubbing - general http://emis.vito.be/techniekfiche/gas-scrubbing-general?language=en<br />
<br />
IHS GlobalSpec,Electrostatic Precipitators Information http://www.globalspec.com/learnmore/manufacturing_process_equipment/air_quality/electrostatic_precipitators<br />
<br />
Environmental Working Group - National Drinking Water Database Drinking water pollution has many sources December 2009. http://www.ewg.org/tap-water/sourcesofwaterpollution.php<br />
<br />
D. Schmitt, C. Shinault. Rapid Sand Filtration Virginia Tech Department of Civil Engineering, 1998. http://www.webapps.cee.vt.edu/ewr/environmental/teach/wtprimer/rapid/rapid.html<br />
<br />
M.L. Davis, Water and Wastewater Engineering, Professional Edition, McGraw Hill: New York, 2010.<br />
<br />
Hydrocomponents & Technologies Inc.,About Reverse Osmosis http://www.hcti.com/sm/aboutro/aboutro.html<br />
<br />
ChemSearch,Biological Wastewater Treatment Systems https://www.chemsearch.my/bioamp/Pages/BiologicalWastewaterTreatment.aspx<br />
<br />
Arc21 Energy from Waste (EfW) http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Ohio Wesleyan University - Environmental Geography Landfill Facts http://www.arc21.org.uk/opencontent/?itemid=27&section=Residual+Waste+Project<br />
<br />
Biegler, I.E. Grossmann, A.W. Westerberg, Systematic Methods of Chemical Process Design, Prentice-Hall: Upper Saddle River, 1997.<br />
<br />
Burnie City Council Waste Minimization Hierarchy http://www.burnie.net/Environment/Resource-Recovery-Initiatives/Waste-Minimisation-Hierarchy<br />
<br />
Partha Das Sharma Blog-Keeping World Environment Safer and Greener Waste Reduction and Raw material conservation are the most important functions in Waste Management https://saferenvironment.wordpress.com/2009/01/01/waste-reduction-and-raw-material-conservation-are-the-most-important-functions-in-waste-management-saves-environment-and-money/<br />
<br />
U.S. Government page "Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service" Digest of Federal Resource Laws of Interest to the U.S. Fish and Wildlife Service.<br />
<br />
EPA Website "Resource Conservation and Recovery Act (RCRA)" http://www.epa.gov/agriculture/lrca.html<br />
<br />
Robert Becker, Volatile Organic Compound Abatement, Environex, January 1994.</div>Pdtravan