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Executive Summary

The following is an overview of the environmental process and operations seen in Environmental Process and Operations I (ENV 4531) and Chemical Process Control (EES 4202C), which are prerequisites for this course, Environmental Engineering Water Treatment Design (ENV4562C). Most or none of the material covered in Environmental Process and Operations II (ENV 4561) will not be included in this document since the author has not covered the material yet. A matrix of the effectiveness of a process as a function of the removal of a particular contaminant(s) has been constructed to compare and contrast which method(s) is or are more adequate for the removal of the contaminant(s) in a particular water sample for treatment to obtain, as an end product, potable water or water of a better quality that meets US EPA standards for human consumption or release into a reservoir or a water stream. The processes are arranged in columns while the contaminants are arranged in rows in the matrix. The processes in the matrix are scored from 0 to 5 being 0 poor contaminant removal and 5 excellent contaminant removal. At the bottom of each process’s column, scores will be averaged to obtain and overall comparison between processes. Keep in mind that the overall score is not a reflection of how “better” a process is compared to another one, but will only gives a vague idea of how good a process is at removing several contaminants. Each process has been describes and next to its name in parenthesis you will find its column letter, below its description you will find the matrix footnotes which are a justification of the score given to that process for the removal of the particular contaminant of the corresponding row, not all cells in the matrix have a footnote. Some footnotes have been included in the process’s description as a superscript. In water treatment processes such as chemical coagulation, disinfection, water softening and corrosion control, pH plays a very important role since it determines how effective the process will be in removing a particular contaminant.

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Process Description Aeration (a)

Is a unit process in which air and water are brought into intimate contact and

turbulence is increased to increment the aeration of flowing streams. In industrial processes the water flow is usually directed countercurrent to the atmospheric or forced-draft airflow. The contact time and the ratio of air to water must be sufficient for effective removal of the unwanted gas (HIWT Ch. 4, 2007). Water treatment aeration reduce dissolved carbon dioxide (decarbonation) (Fries, 2013 p. 86, 169); oxidizes, if present in the free ion form, iron a11 (Fe) and frequently manganese (Mn) to insoluble compounds removable by coagulation (if required), sedimentation and filtration (Reynolds & Richards, 1996, p.130). It also oxidizes volatile organic chemicals (VOCs)7 (MWWOA Ch.11 p.1, 2001) and strips, concentration reduction, ammonia (NH3) and hydrogen sulfide (H2S) (HIWT Ch. 4, 2007).

Limitations: Air stripping processes is affected significantly by temperature; hence it might not be effective in colder climates. Theoretically, at 68°F the carbon dioxide content of the water can be reduced to 0.5 ppm by aeration to equilibrium conditions but this is not economically feasible, but a reduction to 10 ppm of CO2 is considered satisfactory in most cases. Aeration also removes free CO2 making the water basic and lowers its corrosiveness but it also saturates the water with dissolved oxygen (DO) which presents an issue for water with high CO2 concentration but lacks oxygen, like in well water, since aeration simply exchanges corrosive gas for another. The efficiency of aeration increases as the initial concentration of the gas to be removed increases above its equilibrium value. Therefore, with waters containing only a small amount of CO2, neutralization by alkali addition is usually more cost-effective. The complete removal of H2S must be combined with pH reduction or chemical oxidation. Nonvolatile organic compounds cannot be removed by air stripping like phenols and creosols are unaffected by the aeration process alone (HIWT Ch. 4, 2007). Aeration footnotes 1 “Aeration is also an effective method of bacteria control.” (HIWT Ch. 4, 2007),

nothing found on bacteria removal. 3 and 26

“Aeration is a practical solution for taste and odor control when volatile compounds, such as hydrogen sulfide, cause the problem. It is generally not the best method for controlling taste and odors that are caused by algae (MWWOA Ch.20 p.4, 2001)”. Cascade aeration, for example, has “little use in removing odors due to algae” (Reynolds & Richards, 1996, p.130). Nothing found on algae removal, it only serves as a controlling method for algae.

14 and 26

The sulfate (SO42-) contained in the water reacts with hydrogen to form hydrogen

sulfide, if appropriate conditions are met, which gives the water a rotten egg odor. H2S forms when sufficient contact with the water is given, and appropriate temperature and pressure are met which is common in wastewater, sewage water. Microbes in anaerobic conditions consume oxygen from sulfate and release sulfur: 𝑆𝑂!!! → 𝑆!! +2𝑂!. The remaining sulfur (S2-) bonds with hydrogen to form hydrogen sulfide:

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𝑆!! + 2𝐻! → 𝐻!𝑆 (Fries, 2013 p. 148).. 15 Proven effective in removing cyanide to below 0.2 mg/L or 200 ppb by granular

activated carbon in combination with packed tower aeration (Basic Information about Cyanide in Drinking Water, 2010).

7 and 17

Depending upon which aeration device is used, removal of TOC and SOC can be most suitable (Organic Removal, 2009).

8 Helps remove dissolved metals through oxidation, which produces particles that will either precipitate (sink) in or float on the water, then they can be removed by filtration or flotation (e.g. skimmer or weir) (MWWOA Ch.11 p.1, 2001). MWWOA does not mention anything about heavy metal removal specifically; hence a score of 2 is given since “metals” in that context might include some heavy metals as well.

9 Oxidizes chlorine (Cl) into chloride (Cl-) that in turn combines into free chlorine (Cl2) to become stable. Recall from EES 4202C that free chlorine is used as a disinfecting agent for potable water and the US EPA requires a certain chlorine residual concentration in the produce water to help protect it from bacteria and other contaminants from forming in the pipes while it reaches its final destination (Sawyer et al, 2003). E.g: 𝐻!𝑆 + 𝐶𝑙! →  2𝐻𝐶𝑙 + 𝑆 (Equation 20.9 from Sawyer et al, 2003 p. 577)

Settling (b)

Also known as sedimentation (Reynolds & Richards, 1996, p.219) or clarification (MWWOA Ch.13 p.1, 2001). Is the separation of suspended solids from a solid-liquid phase by reducing the velocity of the fluid to a point were gravity overcomes the dragging force created by the motion of the fluid, letting the particles settle. Suspended solids are particles such as grit, clay, sand, silts or flocs that are created from materials in the fluid or from previous treatment processes such as coagulation or lime softening.

Settling velocity (Vs) is the velocity at which particles will start to separate from the fluid and start to conglomerate at the bottom of the quiescent tank or basin; it is a function of the particle’s size, type, density, shape, its relationship with the fluid and the temperature of the fluid. Detention time (θ) is the time required to settle 100% of the particles of a particular size or larger. Round particles will settle faster than ragged or irregularly edged ones, hence requiring a shorter detention time; likewise, the denser a particle is and the warmer the fluid is, the detention time will be shorter (MWWOA Ch.13 p.1, 2001). Settling velocities usually are less than one feet per second and generally, hydrophobic particles will require a greater settling velocity than colloidal or hydrophilic particles since hydrophilic particles tend to bond with water molecules requiring coagulation before sedimentation, and in some cases the fluid requires to be filtered after settling to meet quality standards.

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CFS: Coagulation-Flocculation-Sedimentation (c) Coagulation, flocculation and Sedimentation are three separate processes that are used in sequence to settle particles that will not settle by a unit operation alone. Sedimentation has already been described on the previous section. Coagulation is the addition of a floc-forming chemical reagent (coagulant) and rapid mixing of the coagulant, to destabilize colloidal and fine suspended solids, until initial aggregation of the destabilized particles (insoluble hydroxide precipitates). Principal coagulants are aluminum and iron salts, and in some cases polyelectrolytes are used for both potable and wastewater, lime is also used for wastewater. Flocculation is the gentle agitation or slow stirring of the fluid to aggregate the destabilized particles contained in it, to form a rapid settling floc. The use of the coagulation-flocculation process allows the enmeshment or combination of nonsettleable colloidal for subsequent sedimentation and if required, filtration (Reynolds & Richards, 1996, p.166). The effectiveness of the coagulation is dependent on the pH and alkalinity of the water as it affects the equilibria between most chemical species and corrosivity suitable for water to support living organisms (Sawyer et al, 2003 p. 121). Generally, coagulation is best carried out at the pH of the lowest solubility. Destabilization of hydrophobic colloids is most commonly achieved by adding electrolytes that act as a double layer compressor, monovalent ions like NaCl are used as electrolytes but divalent ions with opposite charge of that of the colloid will exert better coagulation. Likewise, trivalent ions are even more effective than the two previous ones since multivalent ions are considered to penetrate the diffuse layer of the colloid, neutralizing its charge. CFS footnotes 7 and 17

Enhanced Coagulation: Is the optimization of the process by the addition of coagulation aids. This can optimize the process to remove natural organic materials (excludes SOC) that serve as a precursor to trihalomethanes (THMs) during chlorine disinfection (Sawyer et al, 2003 p. 371).

8 Sulfates salts used instead of chloride salts to compress the diffuse layer of the metal hydroxide (Sawyer et al, 2003 p. 371); metal hydroxides like Aluminum hydroxide and Beryllium hydroxide are considered heavy metals (Toxic Metals, 2009).

14 “Electrocoagulation is an effective technology for nitrate removal because nitrate anions preferentially adsorb onto the surfaces of growing metal-hydroxide precipitates” (Lacasa et al, 2011 p. 1012–1017)

19 and 20

Coagulation is the best available technology for DBP control; it has been shown to be very effective for removing DBP precursors in certain types of waters. Waters dominated by hydrophobic organic carbon, with high SUVA values, are more amenable to the removal of organic precursors (Disinfectant Byproducts (THM) in Drinking Water: Past Present, and Future).

21 US EPA has tested and proven effective removal of radionuclides with this process, along with the aid of post-filtration (Basic Information about Radionuclides in Drinking Water, 2010).

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22 Turbidity is best reduced when the fluid has undergone physical and chemical processes before filtration. Flocculation allows the mass of the particles to increase and the number of suspended particles decreases by conglomeration (Turbidity, WWDL)

23 and 24

The removal of colloids decreases the color and turbidity of the fluid (Sawyer et al, 2003 p. 369-370).

Lime Softening (d) Is a chemical treatment system in which calcium and magnesium ions, which represent the water hardness, are precipitated when they react with lime (CaO or Ca(OH)2) and soda ash (Na2CO3) since they form nearly insoluble precipitates. Lime removes the carbonate hardness while soda ash removes chemicals that cause non-carbonate hardness. Calcium hardness is precipitated as calcium carbonate (CaCO3) and magnesium hardness as magnesium hydroxide (Mg(OH)2) that are removable by conventional CFS and filtration. Softening also reduces alkalinity, silica and among other constituents serving as a pretreatment for ion exchange. It is effective in the removal of high alkalinity and hardness concentrations (150-500 ppm as CaCO3) (HIWT Ch. 7, 2007). Precipitates are slightly soluble; therefore, some hardness remains in the effluent water (50-85 mg/l as CaCO3) that prevents corrosion from the water being too soft or having insignificant to none hardness (MWWOA Ch.16 p.1, 2001). Excessive hardness in the effluent water is not desired since it produces scaling inside the pipelines that reduces the hydraulic radius increasing the velocity and head produces by the pumps hence incrementing operation and maintenance cost (Fries, 2013 p. 89). Scaling is produced because calcium and magnesium ions will react with soap to form insoluble organics salts that are present as scum on the water, which adhere to the interior surface of the pipes (Reynolds & Richards, 1996, p. 206). The follow equations represent the precipitation by lime of the chemicals:

Note that carbon dioxide does not contribute to hardness but lime still reacts with it, consuming some lime that must be accounted for.

For conventional water softening treatment it is required a minimum of 30 minutes of contact time with the lime and soda ash and a setting time of 1.5-3 hours. Some design considerations include 10-25% sludge recirculation of the influent water. A jar test is recommended to achieve optimum chemical dosage. In the case of warm lime softening (120-140ºF) the solubility of calcium, magnesium and silica are reduced due to the temperature

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making the dosage of lime and soda ash required to be lower but increases operation cost. To offset the operation cost from warming the influent water, the effluent water goes through a heat exchanger in order to recuperate some of the heat transferred into the water before the process (HIWT Ch. 7, 2007).

Lime softening use is only limited by the operational difficulties that may be encountered if the following parameters are not controlled:

- Temperature: Warm and cold units may suffer carryover if temperature varies more than 4ºF per hour. “Hot process units are less sensitive to slight temperature variations (HIWT Ch. 7, 2007)” and inadequate spray patterns or clogging can cause insufficient heat transfer into the water resulting in a carryover.

- Hydraulics: Inadequate optimization of the steady-state system can cause rapid variation in water flow that severely upsets the system; hence an equalizer basin is recommended to solve this issue.

- Chemical Control: Chemical feed rate swings produce poor water quality, which is a function of flow alone. Since surface water quality can vary hourly, proper control of chemical adjustment must be done followed by quality testing to ensure standards are met. Recarbonation is the addition of carbon dioxide into the water; it is generally required

after lime softening since the pH of the effluent water is 10 or higher. Lowering the pH to less than 8.7 in most cases to stabilize the water and prevents carbonate scale deposition on the sand filters and piping system by removing excess lime. Recarbonation proceeding lime softening is a two-stage process in which first, excess lime is precipitated and second, final water pH is achieved.

Indices have been developed to determine the required dosage of carbon dioxide as a function of the effluent water pH and the desired pH to be obtained. Lime Softening footnotes 10 It can remove fluoride through coprecipitation with magnesium hydroxide, or by alum

coagulation at a high dosage (Sawyer et al, 2003 p. 666) 11 This process reduces oxidized iron and manganese, with the aid of filters, to about

0.05 and 0.01ppm, respectively (HIWT Ch. 7, 2007). 12 Calcium reacts with lime and is then precipitated, filtration and/or sedimentation are

required after softening. 13, 14 and 24

Softening is insufficient in the removal of dissolved solids like sodium, silica and mineral anions such as sulfate and nitrate (HIWT Ch. 8, 2007).

21 US EPA has tested and proven the removal of Radium 226 and 228 combined and Uranium (Basic Information about Radionuclides in Drinking Water, 2010).

22 Reduces turbidity, present in most surface waters, to about 1 NTU with filtration followed by a chemical treatment (HIWT Ch. 7, 2007). US EPA set the standard for drinking water at no more than 1 NTU at any time and must not exceed 0.3 NTU in

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95% of the daily samples in any given month (US EPA, January 2012). 23 Since turbidity is a function of TSS, a low turbidity implies a low concentration of

TSS. 25 Reduces color by removing colloids from raw water organics (HIWT Ch. 7, 2007). Ion Exchange (e) Is a treatment methodology involving the reversible exchange of ions between a liquid and a solid (sols) by chemical reactions. The ion removal is achieved by replacing an undesirable ion for a more desirable one; the undesirable ion is hold temporarily and then released into a regenerant solution. This process can be used to soften water by removing calcium and magnesium ions; also in demineralization (removal of inorganic salts), desalting, ammonia removal, treatment of heavy metals, some radioactive waste among other cations and anions (Reynolds & Richards, 1996, p.336-377). Sodium zeolite softener efficiently reduces the amount of dissolved hardnesse24 but the total solids content, silica and alkalinity remain the same. This makes sodium zeolite softener a bad replacement for hot lime soda softener. Since this media does not function as a filter for other constituents, it does not reduce turbiditye22 effectively. Reported turbidity of effluent product usually exceeds 1.0 JTU. This process can be used in source water with consistent water characteristics such as ground water (HIWT Ch. 8, 2007).

If strong oxidizing agents such as chlorine, that are present in most municipal supplies raw water, can attack and degrade the resin (sodium zeolite) used for softening; therefore, activated carbon filtration or sodium sulfite should be used prior to this process in this case. Ion Exchange footnotes 9 Ion exchanged used as a softening process is ineffective in removing chlorine but if it

is used as a demineralizer it can chloride, sulfate and nitrate (HIWT Ch. 8, 2007). 11 “The resin can be fouled by heavy metal contaminants, such as iron and aluminum,

which are not removed during the course of a normal regeneration” (HIWT Ch. 8, 2007).

13 and 14

Demineralization by ion exchange does remove sulfate and nitrate (see 9e).

16 Sodium chloride from water can be removed by reverse osmosis, electrodialysis, distillation techniques or ion exchange (Sodium (Na) and water by Lenntech).

21 US EPA has tested and proven effective removal of radionuclides with this process (Basic Information about Radionuclides in Drinking Water, 2010).

24 This process can also be used to deionize water (DI) which removes TDS by controlling the electric charge of the ions (Deionization (DI)/Ion Exchange, 2012).

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Sand or Media Filtration (f) Filtration is a solid-liquid separation in which the fluid passes through a porous medium or material where the fine suspended solids are deposited. It involves mechanism of adsorption, both physical and chemical; straining, sedimentation, interception, diffusion, and inertial compaction for effective removal of a contaminat. This process usually relies on gravity to force the water and its contaminants through the medium. Backwash is required to remove the contaminants from medium, usually 1-5% of the water filtered is used for backwash (Reynolds & Richards, 1996, p.284). This unit operation precedes regular CFS for both water and wastewater Sand or Media Filtration footnotes 5 Since it is resistant to disinfection, filtration is required (Reynolds & Richards, 1996,

p.315) 22, 23 and 25

A media filter will perform effectively with TSS equal to 100 mg/l (ppm) or less, hence higher TSS concentrations require pretreatment: CFS. The removal of TSS changes the color and reduces turbidity (TSS, 2013). Clarifier effluents of 2-10 NTU may be improved to 0.1-1.0 NTU by conventional sand filtration, ensuring acceptable suspended solids concentrations in the finished water even when upsets occur in the clarification processes (HIWT Ch. 6, 2007).

24 Does not removing TDS; unless used after softening, then it can remove some dissolves solids (HIWT Ch. 6, 2007).

Membrane Processes

A membrane is a thin layer of semi-permeable material that can separate substances when a force is applied to substance to go through the think layer. Some common membrane processes include ultrafiltration (UF), reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), electrodialysis reversal (EDR). These processes (with the exception of UF) reduce most ions; RO and UF systems also provide efficient reduction of nonionized organics and particulates. Because UF membrane porosity is too large for ion rejection, the UF process is used to reduce contaminants, such as oil and grease, and suspended solids. They also remove bacteria, microorganisms, particulates, and natural organic material, which can impart color, tastes, and odors to water and react with disinfectants to form disinfection byproducts. The following chart illustrates the difference between the filters by their pore space:

Osmosis is a process by which molecules of a solvent pass through a semipermeable

membrane from solute (solution of lower concentration) to a solvent (higher concentration solution) in order to reach equilibrium on each side of the membrane. Reverse Osmosis (g)

Is the process by which a solvent goes to a solute by overcoming the osmotic pressure to breaking equilibria. This process removes nearly all inorganic contaminants and radium, natural organic substances, pesticides, cysts, bacteria and viruses. It is limited by its capital and operation costs since it produces most wastewater (25-50% of the feed). They remove

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95% of dissolved salts but due to its molecular porosity it does not remove free chlorine, carbon dioxide nor oxygen (HIWT Ch. 9, 2007). Nanofiltration (g) This filters have pore sixe of about 0.001 microns and have a molecular weight cut off of 1,000 to 100,000 daltons, making it possible to remove all cysts, bacteria, viruses, and humic materials and also hardness and alkalinity but it needs to be pretreated. They can control DBP formation if a disinfecting residual has been added after the membrane filtration phase. Since a higher pressure is needed to push the fluid through the membrane it requires more energy than micro and ultrafiltatrion. RO-NF (g) footnotes 4 See 4i 16 See 16e 21 See 21e 25 Removes a wide range of colors from water, TOC, minerals like iron that causes red or

yellow color. Ultrafiltration (h) This filters have a pore size of about 0.002-2 micron and a molecular weight cut off (MWCO) of about 10 thousand to 100 thousand daltons. 30 to 100 psi is required for operation and remove microbes and humic materials but it is not the final barrier for viruses Ultrafiltration (h) footnotes 2 Removal of pathogens and complete removal of viruses is effectively

achieved. 4 See 4i Microfiltration (i) Is the separation through a media with pore size of 0.03 -10 microns (1 micron =10-4 mm), it removes sand, silt, clays, Giardia lamblia and Cryptosporidium cysts, algae, and some bacterial species but not an adequate viruses removal. It is advantageous to use MF since no chemicals are need for contaminant removal. Micro filtration (i) 1 They remove all bacteria 2 Partially removes viruses (A Guide to Drinking Water Treatment and Sanitation for

Backcountry & Travel Use, 2008) 4 This method is highly effective in removing protozoa and also removes cysts when a 1

micron or less filter is used (NSF Standard 53 or 58 rated "cyst reduction / removal" filter).

5 “[It] is effective for treating the full range of biological contaminants,

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including hard-shelled cysts like Cryptosporidium” (Carbon Filters, 2012).

Electro Dialysis or Electrodialysis reversal (j)

Is an electrochemical membrane process during which ions are transported through semi permeable membrane, under the influence of an electric potential. The membrane serves as a cation or anion that will attract a desired ion when then electric current passes through it. It separates inorganic electrolytes from a solution; it can be used for demineralization of seawater and brackish water. It is recommended to pretreat influent water to remove scaling and organic fouling from occurring

ED-EDR (j) footnotes 16 See 16e Activated Carbon (k) Adsorption is the use of an adsorbent such as activated carbon to remove certain substances from a solution. It adsorbs a wide range of organic compounds and is economically feasible to use. It removes compounds causing taste, odor, color25k, 26k and 27k and toxic organic compounds (Reynolds & Richards, 1996, p.350). Activated Carbon (k) footnotes 15 See 15a 7 and 17

If appropriate technology is applied, removal of this contaminant can be effective (Organic Removal, 2003).

9 This process does effectively remove chlorine (HIWT Ch. 8, 2007) Ultraviolet (l) The irradiation of UV light can be used to disinfect water but since no residual is left to protect the water, bacteria and virus population can grow rapidly. Therefore, UV must be used with other unit process such as chlorination to protect the water after disinfection. UV removes viruses better than chloramines (Reynolds & Richards, 1996, p.752-753). Chemical Disinfection (n) 4 and 5

They are resistant to desinfection (Reynolds & Richards, 1996, p.315).

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Work Cited (JAWRA Format)

A Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel Use.

September 16, 2010. Centers for Disease Control and Prevention. http://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html Accessed on Januray 21, 2014.

Basic Information about Cyanide in Drinking Water. April 5, 2010. Water: Basic Information about Regulated Drinking Water Contaminants. United States Environmental Protection Agency. http://water.epa.gov/drink/contaminants/basicinformation/cyanide.cfm#eight. Accessed on Januray 21, 2014. Basic Information about Radionuclides in Drinking Water. April 5, 2010. Water: Basic

Information about Regulated Drinking Water Contaminants. United States Environmental Protection Agency. http://water.epa.gov/drink/contaminants/basicinformation/radionuclides.cfm#How%20will%20radionuclides%20be%20removed%20from%20my%20drinking%20water Accessed on Januray 21, 2014.

Carbon Filters. 2012. HM Digital. http://www.tdsmeter.com/what-is?id=0012 Accessed on Januray 21, 2014.

Deionization (DI)/Ion Exchange. 2012. HM Digital. http://www.tdsmeter.com/what-is?id=0015 Accessed on Januray 21, 2014.

Disinfectant Byproducts (THM) in Drinking Water: Past Present, and Future. Np.Water/Wastewater Distance Learning (WWDL) Website. Mountain Empire Community College. Richmond, Virginia, United States http://water.me.vccs.edu/exam_prep/THM.html Accessed on Januray 21, 2014

Fries, Benjamin M., 2013. ENV 4531 – Environmental Engineering Operations & Processes I Workbook and Handout Manual. Np. Orlando, Florida, United States. Print.

Handbook of Industrial Water Treatment (HIWT). April 4, 2007. GE Power & Water.  http://www.gewater.com/handbook/index.jsp. Accessed on January 18, 2014.

Lacasa, Engracia; Cañizares, Pablo; Sáez, Cristina; Fernández, Francisco J., & Rodrigo, Manuel A. 2011. Removal of Nitrates from Groundwater by Electrocoagulation. Chemical Engineering Journal, Volume171, Issue 3, July 15, 2011, Pages 1012–1017. Print. http://www.sciencedirect.com/science/article/pii/S1385894711005249. Accessed on January 21, 2014.

Minnesota Water Works Operations Manual (MWWOA), 3rd Ed. Summer 2001.Minnesota Rural Water Association. Elbow Lake, United States. http://www.mrwa.com/mnwaterworksmnl.html

Organic Removal. September 3,2009. Tech Brief: A National Drnking Water Clearinghouse Fact Sheet. National Drinking Water Clearinghouse. Print. http://www.nesc.wvu.edu/pdf/dw/publications/ontap/2009_tb/organic_removal_DWFSOM47.pdf . Accessed on Januray 21, 2014.

Reynolds, Tom D., & Richards, Paul A., 1996. Unit Operations and Processes in Environmental Engineering. PWS Pub., Boston, United Sates. Print.

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Sawyer, Clair N., Perry L. McCarty, & Gene F. Parkin. 2003. Chemistry for Environmental Engineering and Science. McGraw-Hill, Boston, United States. Print.

Sodium (Na) and water. N.p. Lenntech: Water Treatment Solution. http://www.lenntech.com/periodic/water/sodium/sodium-and-water.htm#ixzz2qy7yZ1Gs. Accessed on Januray 21, 2014.

Total Suspended Solids (TSS). March 14, 2013. Everfit.. Web. http://everfilt.com/tag/total-suspended-solids. Accessed on Januray 21, 2014.

Toxic Metals. June 2, 2009. Occupational Safety & Health Administration (OSHA). https://www.osha.gov/SLTC/metalsheavy/index.html. Accessed on Januray 21, 2014

Turbidity. Np.Water/Wastewater Distance Learning Website (WWDL). Mountain Empire Community College. Richmond, Virginia, United States http://water.me.vccs.edu/exam_prep/THM.html Accessed on Januray 21, 2014http://water.me.vccs.edu/exam_prep/turbidity.html