### MEMORANDUM

TO: Steam Electric Rulemaking Record

FROM: Anna Dimling, ERG

DATE: September 30, 2015

SUBJECT: Evaluation of Emerging Technologies for the Treatme nt of Flue Gas

Desulfurization Wastewater

ERG is providing technical support to the U.S. Envi ronmental Protection Agency’s (EPA’s) Office of Water, Engineering and Analysis D ivision for development of effluent limitations guidelines and standards (ELGs) for the Steam Electric Power Generating Industry. EPA, with the support of ERG, identified and evalua ted technologies available for the treatment of power plant wastewater, specifically flue gas de sulfurization (FGD) wastewater, to form the basis for the technology-based effluent limitations included in the proposed revisions to the

Steam Electric ELGs. Based on the evaluation of the technologies, EPA selected the following three treatment technologies as the basis for poten tial revisions to the ELGs for FGD wastewater:

• Chemical precipitation (including hydroxide precipi tation, sulfide precipitation, and iron coprecipitation).

• Chemical precipitation (including hydroxide precipi tation, sulfide precipitation, and iron coprecipitation) followed by an anoxic/anaerob ic fixed-film biological treatment

system.

• Chemical precipitation (including hydroxide precipi tation, sulfide precipitation, and iron coprecipitation) followed by vapor-compression evaporation (evaporation).

EPA also identified other emerging treatment techno logies that can be used for the treatment of FGD wastewater. Currently, most of the se technologies have only been evaluated at bench- or pilot-scale levels, although some technol ogies have been tested at limited full-scale levels. This memorandum identifies these emerging t echnologies, describes the processes for treating FGD wastewater, and presents data currentl y available regarding the technologies’ treatment performance. Additionally, this memorandu m discusses several specific issues related to the treatment of FGD wastewater, including the t reatment of dissolved arsenic and bromide.

1.0 Z ERO V ALENT I RON C EMENTATION

The zero valent iron (ZVI) cementation process con sists of contacting a wastewater with an iron powder, which reduces a contaminant to its elemental form (i.e., cementation). ZVI

cementation has been used since the 1500s to remove many types of contaminants. The iron is oxidized and dissolves (i.e., corrodes or oxidizes) while the contaminant is reduced and precipitates from solution. As an example, the foll owing equation shows a cementation reaction between zero-valent iron and copper:

Fe 0 + Cu 2+  Fe 2+ + Cu 0Memorandum

September 30, 2015 Page 2

For FGD wastewater, ZVI cementation is being evaluated for heavy metal removals. The addition of a source of iron during wastewater treatment is showing promise for removal of metals such as arsenic, chromium, cadmium, selenium, and many others. Advantages of this technology include relatively low cost and no requiremen t for significant pretreatment. A disadvantage of this technology is that for the best r esults, the required retention time may be longer than is practical for high volume systems.

1.1 EPRI Study

In 2008, the Electric Power Research Institute (EPRI) per formed bench- and pilot-scale studies at a coal-fired power plant to evaluate ZVI ceme ntation for selenium removal. Initial bench-scale testing using the plant’s FGD wastewater sugge sted that ZVI cementation has the potential to reduce the effluent selenium concentration to less than 50 micrograms (μg)/liter (L) with minimal sludge production. EPRI tested various pH, rea ction time, and post-cementation pH adjustments to optimize the removal of selenium.

EPRI conducted a pilot-scale study based on the results of the bench-scale study to evaluate the ZVI cementation technology under continuous flow conditions at a coal-fired power plant. For this pilot study, EPRI used FGD wastewater tha t had already undergone hydroxide precipitation and clarification for initial desaturation of the wastewater. Metallic iron (as an iron powder) was added to the Iron Reactor where it is oxidized to ferrous iron during the selenium reduction process (Figure 1). Sulfuric acid was added to mainta in pH. A clarifier was used to

recover iron from the wastewater. The recovered iron was recycled back into the Iron Reactor. The overflow from the clarifier was sent to a pH adj ustment tank. In the pH adjustment tank, the pH was maintained at 8.5 S.U. by addition of caustic. The pH increase resulted in precipitation of solids that contain the target metals as well as the iron that dissolved in the Iron Reactor. The pH adjustment tank effluent was then sent to a flocculan t mixing tank, where it was mixed with a diluted flocculant solution. The flocculant aided coagula tion and settling of solids in the process

water. 1 EPRI noted that for a full-scale system, clarifiers could be used in series with aeration

and filtration.

The pilot-study showed that selenium removal improved a s the pH was lowered and reaction time was increased; however, this combination also resulted in higher costs (i.e., higher iron consumption) and increased sludge production. The pilot study also showed that the effectiveness of removing selenium from the FGD wastewa ter using ZVI cementation is dependent on the species of the selenium present. During t he pilot study, the iron cementation system was able to remove greater than 99% of the selenit e at each pH tested. In comparison, the system was able to remove 95% of selenate at a pH of 4.5 S.U., but the system was only able to remove 37.4% of the selenate at a pH of 5.5 S.U. EPRI noted that the system also achieved significant removals of mercury, ranging from 84.5 to 97.8 pe rcent. 2

1 The report does not describe any solids removal mechani sms used to remove solids from the pH adjustment tank or the flocculation tank, but ERG expects that additional soli ds removal would be required.

2 Because mercury was not a defined target pollutant for th e study, only a limited set of data were evaluated for mercury. The range of percent removals is based on three measurements.Memorandum

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Figure 1: Basic Schematic of EPRI ZVI Cementation Pilot Study

This pilot study demonstrated that the ZVI cementation t echnology can remove selenium from FGD wastewater containing elevated selenium levels; 3 however, like chemical precipitation, the removal of selenite is more easily achieved than removal of selenate. Ultimately, the study was not able to achieve the target effluent total selenium concentration of 50 μg/L; the lowest effluent selenium concentration that the system achieved was 159 μg/L, while the highest effluent selenium concentration was 2,240 μg/L. Additionally, relationships between iron retention time, dissolved iron, and sele nium reduction were identified to allow further optimization of the process during future studies [ EPRI, 2009].

1.2 Texas A&M University Study

In addition to the research conducted by EPRI, research ers at Texas A&M University demonstrated successful heavy metals removals using an Activ ated Iron Process (AIP) which uses what the researchers call hybrid zero-valent iron (hZVI). The study confirmed that the technology can simultaneously reduce many heavy metals, i ncluding selenium, mercury, arsenic, iron, chromium, copper, and cadmium from FGD wastewate r at relatively low costs. Based on results from successful bench-scale tests, a pilot st udy was implemented at an unidentified power plant located in the Southeastern United States. The p ilot system consisted of four stainless steel zero-valent iron (ZVI) reactors where the iron cemen tation occurs followed by post-treatment units including aeration, clarification, and sand filtratio n. Figure 2 presents a diagram of the set up for the pilot scale test.

The study occurred over approximately five months and con sisted of two phases. The first phase (January-April) was set up to treat 3.8 L/minute (min) (1 gallon per minute (gpm)), while the second phase (April-May) was set up to treat 7.6 L/min (2 gpm). As shown in Figure 2, the pilot study used the effluent from the plant’s FGD pon d as the influent to the system. The FGD wastewater had typical characteristics of the 22 c oal-fired plants that are operated by the host power company. As the researchers were concerne d mostly with the removal of selenium and mercury, each of those contaminants were spiked in th e feed water to raise their concentrations. In addition, researchers were interes ted in results from just the initial ZVI reactor (i.e., stage one reaction tank) and from the combinatio n of all four ZVI reactors. Table 1 shows the average influent and effluent results from the study.

3 The selenium concentrations of the primary clarifi er effluent entering the pilot study ranged from 6,840 μg/L to 8,350 μg/L for total selenium and 5,620 μg/L to 7,060 μg/L for dissolved selenium.Memorandum

September 30, 2015 Page 4

Source: [Huang, 2012a]

Figure 2. Diagram of Hybrid ZVI Treatment System Pi lot Study

Table 1. Average Influent and Effluent Concentratio ns for Hybrid ZVI Treatment System Pilot Study

Contaminant FGD Wastewater

Influent (μg/L) One Reactor Effluent (μg/L) Four Reactor s Effluent (μg/L)

Selenium (as Selenate) 22,000 (spiked) 8,000 4,000 (< 1000 towards the end of the study) Mercury (total) 1,150 (spiked) 0.05 0.025 (< 0.01 towards the end of the study)

Lead ( dissolved ) 5,000 <1 <1

Cadmium (total) 2,500 10 <1 Copper (dissolved) 5,000 1

- 3 1

Arsenic (total) 20 <1 <1

Chromium (as chromate) 5,000 10 2

Nitrate 10,000 NR 100
Source: [Huang, 2012] NR - Not reported in the study.

Over the five-month period of the pilot test, the average consumption rate was 0.3 kg ZVI per 1 m

3 FGD wastewater treated (0.0025 lbs ZVI/gal FGD was tewater treated). This consumption rate resulted in a cost of approximatel y $0.6-1.0 per 1 m 3 ($0.0023-0.0038 per gal) FGD wastewater for just the chemical consumption. C osts associated with sludge generation and disposal were not reported. The pilot study demonst rated that the ZVI process is scalable (i.e., multiple reactors can be utilized to achieve additi onal removals or expand treatment capacity) [Huang, 2012].

1.3 Evoqua Water Technologies (Evoqua) Pironox TM System

EPRI, in collaboration with South Carolina Electri c and Gas (SCANA), conducted a pilot study on FGD wastewater treatment using Evoqua’s Pi ronox TM system, a reactive media system

that utilizes ZVI and other reactants to remove sel enium, mercury, and other metals. The pilotMemorandum

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study was conducted from September 2013 through April 2014; however , there was a period of about two months in which the pilot system was out of se rvice. Therefore, the pilot study was split into two phases: Phase 1 (September 11, 2013 through Dec ember 3, 2014) and Phase 2 (January 21, 2014 through April 2, 2014). FGD wastewater influent w as pumped at a rate of 0.5 - 1 gpm from a segregated FGD impoundment into the Pironox TM system. The wastewater flowed through a series of four reactors containing the Pironox TM advance reactive media and additional reagents. The total hydraulic residence time in these re actors was 13 to 26 hours. Post-treatment of the FGD wastewater consisted of an aerating basin ( where sodium hydroxide (NaOH) is added), a clarifier, and sand filter. During Phase 2 of the pilot operation, Evoqua added a sedimentation step after the second reactor and recycl ed the sludge, consisting of ZVI, back to

the first reactor and directed the overflow to the third reactor.

The treatment effluent from the Pironox TM system was analyzed using EPA Method 200.8

and 200.7. The selenium concentration in the treatment ef fluent was significantly less in Phase 2 (compared to Phase 1) and ranged from 17 μg/L to 27 μg/L. In addi tion, the effluent in Phase 2 met the final ELG limitations for arsenic and mercury. H owever, Evoqua observed elevated levels of nitrates throughout the pilot study, but in gener al was able to maintain less than 10 mg/L of nitrate/nitrite as N in the effluent. However, Evoqua was unable to consistently meet the final ELG monthly limitations of 3.5 mg/L for nitrate/nitri te as N [EPRI, 2014b].

1.4 Libery Hydro ZVI Blue TM Media

EPA obtained information from two pilot studies conducted as a partnership between EPRI and SCANA at a coal-fired power plant that evaluate d a ZVI technology for treating FGD wastewater. The pilot studies were performed from Novem ber 2013 to March 2014 and tested two different system configurations using the Liberty Hydro’s ZVI Blue TM media. The pilot test used FGD surface impoundment effluent as the initial influe nt stream to the system; however, on February 28, 2014, a pilot-scale chemical precipitation syst em was added upstream of the pilot technologies to pretreat the FGD wastewater. The fi rst ZVI system configuration (System 1) used a 1.0 gpm FGD wastewater influent flow rate and treate d the wastewater using the following design elements:

• One sand filter.

• Three bag filters (25 micrometers (μm), 10μm, and 1μm).

• Eight vessels (125 gallons) containing stacks of porous ZVI Bl ue TM media loaded with fine ZVI shavings.

This pilot test was not able to achieve effluent concent rations that met the final rule ELG limitations for selenium, mercury, arsenic, and nitrate/nitrite as N. However, after chemical precipitation was installed upstream of the pilot test, this system configuration consistently maintained selenium concentrations less than 100 ppb in the effluent, compared to an effluent selenium concentration of 1,200 to 1,400 ppb when the FGD surfa ce impoundment effluent was used as the influent. The second ZVI system configuration ( System 2) maintained an influent flow rate of 0.00132 gpm and treated the FGD wastewater using the following design elements:

• One anaerobic membrane bioreactor (continuous stirred tan k reactor, followed by an ultrafilter membrane).Memorandum

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• An ultraviolet (UV) disinfection step.

• Four columns (2.5” diameter; 12.5” media) containing porous ZVI Blue TM media loading with fine ZVI shavings.

The bioreactor was added before the ZVI columns to remove the nitrates because nitrate and nitrite compete with the selenium species to react w ith the ZVI media which significantly

inhibits selenium removal from the FGD wastewater. Th e second ZVI system configuration, containing the pretreatment bioreactor, was able to meet t he ELG limitations for selenium, mercury, nitrate/nitrite as N, and arsenic. In addition, the ZVI media chemically reduced and removed other selenium compounds, such as selenocyanate and m ethyl seleninic acid [EPRI, 2014a; ERG, 2015a].

EPA also obtained information from a pilot study conducte d at another coal-fired power plant also using the ZVI Blue TM media. The plant conducted a pilot study from March 2014 to July 2014 using the effluent from its chemical precipitation system. This ZVI system (System 3) consisted of a sand filter, bag filters, and eight vess els containing porous ZVI-loaded media (similar to System 1 described above). However, the che mical precipitation effluent from this plant contained lower levels of nitrates than the othe r coal-fired power plant (where System 1 and 2 were studied) and did not need biological pretreatment. The pilot study demonstrated that this ZVI system met the ELG limitations for selenium, arsenic, and mercury. More specifically, the average selenium in the wastewater was less than 10 ppb for the entire 12 week time period; however, when the influent flow was increased from 1-2 gpm to 4 gpm the selenium concentration increased to above 10 ppb [ERG, 2015a; ERG, 2015b].

Liberty Hydro is in the process of drafting a design for a full-scale FGD wastewater treatment system with an engineering firm. The initial full-scale design consists of a chemical precipitation system, a “simple” biological treatment system, the ZVI Blue TM system, and a filtration system. The system will be designed for FGD wastewater flow of 350 gpm. The biological system will consist of a reactor containing carbon-rich media and microbes, which utilize carbon and nitrate in the wastewater as energy sources. The ZVI Blue TM system, in the initial design, will contain 15 reactor vessels contai ning stacks of media (see Figure 2). Adjustments to the design configuration will be evaluated o ver time [ERG, 2015a].Memorandum

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Source: [ERG, 2015a]

Figure 3. Full-Scale Design Process Flow Diagram fo r the ZVI Blue TM System

The reactor system is designed in a way that if an y particular stack of media is not operating properly, that particular stack can be re moved and repaired without causing a system shut-down. Liberty Hydro is still working on method s for cleaning and regenerating the media and investigating if the wastewater generated from cleaning the media can be recycled back into the system. Liberty Hydro indicated that the media is able to last anywhere between 6 months to 5 years, however more studies are needed to refine the longevity estimates for different operating conditions. Liberty Hydro has been collaborating wi th an engineering firm to prepare capital and operation and maintenance (O&M) cost estimates for the system [ERG, 2015a].

2.0 R EVERSE O SMOSIS

Reverse osmosis (RO) is a well-established membrane treatment process used for

desalination of seawater and removal of dissolved m aterials from industrial wastewater. RO systems use thin semi-permeable film membranes that allow water to pass through, but collect dissolved solids. In an RO system, high-pressure pu mps are used to apply pressure to the solution from one side of the semi-permeable membra ne to force the water through the membrane, leaving behind the dissolved solids and a portion of the water. The rate that water passes through the membrane depends on the operatin g pressure, concentration of dissolved materials, and temperature, as well as the permeabi lity of the membrane.Memorandum

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As described above, the RO system separates the feed wa stewater into two product streams: the permeate, which is the clean water that has passed through the membrane, and the concentrate, which has been retained (“rejected”) by the membrane. The percentage of membrane system feed that emerges from the system as pe rmeate (i.e., the volume of permeate divided by the volume of feed) is known as the water reco very. One of the advantages of a RO system is that it can be used to achieve zero liquid disch arge in certain applications. One of the disadvantages is that the system requires pretreatment to remove excess total suspended solids (TSS) and organics to prevent scaling and fouling. 4

RO systems are currently in use at some steam electri c power plants, usually to treat boiler make-up water or cooling tower blowdown. For example , the Harry Allen Gas Turbine Combined Cycle power plant, located in Nevada, utilizes RO as part of a zero liquid discharge system. This wastewater treatment system treats a co mbination of reverse osmosis concentrate, steam generator blowdown, evaporative cooler blowdown, wet surface air cooler blowdown, multimedia backwash water, oil/water separator wastes, and other service water wastes. The wastewater is treated with several filters (e.g. mult i-media filters, tubular microfiltration, and filter press for the concentrate), two passes through RO systems, an ion exchange tank, and two reactors for chemical precipitation. This system desig n operates at an overall recovery of greater than 95%. A stream of treated wastewater is discharged to evaporation ponds and solid waste are trucked off site [Alexander, 2012].

While RO systems may be compatible for the treatment of boiler make-up water or cooling tower blowdown, they are of limited use for the tr eatment of FGD wastewater because of the high chloride levels typically present in FGD wastew ater. High chloride levels lead to a high osmotic pressure, which limits the effectiveness of an RO system.

2.1 Hatfield’s Ferry Evaluation

Allegheny Energy’s Hatfield’s Ferry Power Plant, loc ated in Pennsylvania, considered RO as a potential treatment option to reduce total dissolv ed solids (TDS) from their FGD wastewater. However, based on research conducted by the plant, they did not feel RO was a practical treatment method for two reasons. First, th e high osmotic pressure of the FGD blowdown, due to high TDS, caused a 50 percent or less RO recov ery and cause the concentrate stream flow rate from the RO system to be too large an d thus too costly to manage. Secondly, using RO for the FGD blowdown causes scaling and fouling issue s, due to high concentrations of TDS and organic constituents. No laboratory or field tests were performed as part of this evaluation [Black and Veatch, 2008].

2.2 EPRI’s Evaluation of High-Efficiency Reverse Osmosis (HERO TM )

RO systems currently in use at steam electric power pl ants are usually used to treat boiler make-up water or cooling tower blowdown. EPRI identified a hig h-efficiency reverse osmosis (HEROTM) process that operates at a high pH, allowing the system to treat wastewaters with high silica concentrations without scaling or membrane fouli ng because silica is more soluble at a

4 Fouling occurs when both dissolved and suspended solids depos it onto a membrane surface and degrade its overall performance, thereby decreasing permeate quality and wat er recovery percentage.Memorandum

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higher pH. Silica is a common foulant in many RO applic ations. The wastewater undergoes a water-softening process to raise its pH before entering the HEROTM system.

Although the HEROTM system is currently in use in the ste am electric power generating industry to treat cooling tower blowdown, its potential for us e for FGD wastewater is limited because of the osmotic pressure of the FGD wastewater due to high concentrations of chlorides and TDS [EPRI, 2007]. Although many plants may not be able to use the HEROTM system to treat FGD wastewater, some plants with lower TDS an d chloride concentrations may be able to. The HEROTM system is of particular interest for treati ng boron in FGD wastewaters. Boron becomes ionized at elevated pH and, therefore, could be re moved using an RO system [EPRI, 2007].

3.0 S ORPTION M EDIA

Sorption media systems adsorb pollutants onto the media ’s surface area using physical and chemical reactions. A variety of sorption media technologies have been used for water treatment. The sorbents are typically designed for th e removal of specific pollutants; however, they may also remove other pollutants simultaneously. T he advantages of sorption media are the ease of installation, efficiency of contaminant remova l, and effectiveness under various pH and contaminant conditions. Some disadvantages with sorpti on media are that they are typically single use products that require replacement instead of re generation. Furthermore, they are subject to fouling that may require pretreatment of wastew ater to remove suspended solids and organics.

3.1 EPRI Study

EPRI research determined that the most common types of adsorbents are metal-based, single use applications, such as granular ferric oxide (or hydroxide) and titanium-based oxides. The advantages of the adsorption media are that they ca n operate over a wide pH range and have relatively little interference from other contaminants present in FGD wastewater. One of the disadvantages of the adsorption media is that pretreat ment is required to remove excess TSS and bioactive organics to prevent plugging and fouling of the media [EPRI, 2007].

3.2 MAR Systems, Inc. Study

The vendor of Sorbster® dry media, MAR Systems, exami ned the single pass-through media proprietary functionalized alumina adsorbent technol ogy for its ability to remove both

selenite and selenate in a standard filtration vessel. This proprietary adsorption media was developed from various other proprietary chemistries to fo rm functionalized sites in the media

that will form covalent bonds with selected soluble me tals. As these materials and reactions are all proprietary, details of the chemistry were not report ed. At least three of the chemical components forming the functionalized sites on the medi a are known to complex with soluble selenium in the selenate and selenite oxyanion forms. Th e removal is accomplished by the formation of various selenite and selenate complexes suc h as aluminum selenite, aluminum selenate, and others. The study observed selenium removal rates from 16% to 50% [Sherwood, 2012].Memorandum

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3.3 Evoqua GFH® Media

Evoqua installed two types of full-scale sorbent media systems at the Public Service Company of New Hampshire's Merrimack Station for removal of mercury and arsenic. Evoqua provided details of these media to ERG in a conference ca ll held on January 2, 2013 [ERG, 2013b]. These systems include the SCU Adsorbent and the GF H® Media. The SCU Adsorbent is a single use granular carbonaceous adsorbent media which selectively adsorbs dissolved metal cations, including cadmium (Cd 2+ ), trivalent chromium (Cr 3+ ), copper (Cu 2+ ), lead (Pb 2+ ), mercury (Hg 2+ ), nickel (Ni 2+ ), and zinc (Zn 2+ ). At the Merrimack Station, the SCU Adsorbent is specifically used for mercury removal. The permitted maxim um effluent mercury concentration at the Merrimack Station was set at 14 parts per trilli on (ppt), based on the plant’s projected performance (i.e., the technology vendor’s guarantee). Th e plant operates a physical/chemical precipitation system, including hydroxide and sulfide precipit ation, prior to the sorption media systems. Evoqua designed the system based on an influent mercury concentration entering the media at 100 ppt. According to Evoqua personnel, the system h as been achieving low single digit ppt mercury levels.

To address the arsenic concerns at the Merrimack Station , Evoqua utilized its GFH® Media. The GFH® Media is a granulated ferric hydroxide medi a that is used primarily for the removal of arsenic (i.e. arsenite: As+3 and arsenate: A s+5), but it can also achieve removals of other heavy metals. According to Evoqua personnel, the GFH ® Media is best suited for arsenic

removals from wastewater with low silica concentrat ions. Evoqua did not disclose arsenic removal rates during the call [Evoqua, 2014; ERG, 2013b].

Both media developed by Evoqua are single use media, with no regeneration. Therefore, when the media are spent, which is determined based on ef fluent sampling results, the media must be replaced. The media can either be replaced by sw apping out the entire vessel or vacuuming out the spent media and replacing with new media. Evoqua estimates that the capital costs for a system utilizing both media could range from $200,000 to $2,000,000, depending on the flow rate, influent concentrations, and system conf iguration. Specific costs associated with the Merrimack Station are proprietary; however, Evoqua pr ovided some general operation and maintenance (O&M) cost estimates based on Merrimack’ s operations. From April to December 2012, the system processed approximately 10 million gallons of w ater at a rate of approximately 40 gallon per minute. Based on the replacement frequency obs erved at Merrimack, the media costs for the SCU Adsorbent is approximately $2 per 1,000 gal lons and the GFH® Media is approximately $1 per 1,000 gallons. There are additional costs associated with these systems, such as O&M labor and analytical monitoring/sampling that are not included in these estimates [ERG, 2013b].

3.4 Zorbtech Environmental Solutions Testing

Zorbtech Environmental Solutions has performed bench- a nd pilot-scale testing on a nonactivated carbon adsorbent media for mercury removal. The company conducted a bench-scale study on power plant scrubber water (which ERG assumes is FGD wastewater, but this is not specifically stated in the article). The article descr ibing the study contains limited information regarding the treatment steps used in the study and the e ffluent concentrations achieved, but the article did indicate that mercury removal was achieved [ Purves, 2013].Memorandum

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4.0 I ON E XCHANGE

Ion exchange systems remove specific constituents fro m wastewater; therefore, the system can target specific metals to be removed. The i on exchange resin works by substituting one ion for another on a specific resin, which must be replaced or regenerated when the resin becomes full [AEP, 2010]. While the ion exchange process do es not generate a residual waste, it does generate a regenerant stream that contains the met als stripped from the wastewater. Ion exchange can be complicated by other contaminants presen t in the wastewater; as such, ion exchange systems require pretreatment to remove excess TSS to prevent scaling and fouling of the resin. A study by ResinTech, Inc. discusses how tr ace contaminant removal in wastewater by ion exchange is highly dependent on the other ions that sur round the contaminant [Meyers, 2012].

4.1 Conemaugh Generating Station

EPA and ERG conducted a visit at GenOn Energy Northeast M anagement Company’s Conemaugh Generating Station (Conemaugh), which operates an ion exchange system for the treatment of boron in FGD wastewater. Upstream of th e ion exchange system, the plant treats the FGD wastewater with a physical/chemical precipitation system consisting of hydroxide precipitation and clarification. The overflow from th e clarifier is fed to the ion exchange system. The ion exchange system consists of two parallel train s, each capable of handling 75 percent of the flow. The wastewater is first pumped through pressure sand filters and is then transferred to the ion exchange resin vessels. Each train contains tw o vessels. As designed, the vessels operate in series, except when one of the vessels is being regener ated. The system was originally designed for regeneration to occur every six hours; howev er, because of scaling issues, the plant has needed to operate the system such that one of the v essels in each train is always being regenerated. As the regeneration of one vessel is comp leted, the other vessel begins its regeneration process.

The plant uses sulfuric acid and caustic soda washes to r egenerate the resins. The waste from the regeneration process is transferred to a precip itation tank where the plant adds ferric chloride and lime. The plant then feeds the water to a clarifier where a polymer is added. The plant operates filter presses to create a filter cake w ith the clarifier underflow; therefore, the ion exchange process at this plant generates a residual sludge, which is landfilled. The clarifier overflow and the filtrate from the filter presses are recycled back to the front of the FGD wastewater treatment system (i.e., the influent to th e chemical precipitation process) for additional processing. The effluent from the ion exchange vessels is transferred to an anaerobic bioreactor prior to discharge. For more information about Conemaugh’s biological treatment system, see Section 6.3.

Plant personnel reported observing a roughly 85% reduction in b oron concentrations across the chemical precipitation and ion exchange syst ems. The plant measured boron concentrations between 400 and 600 ppm in the purge stream and c oncentrations of 75 ppm in the effluent from the ion exchange system. Roughly 45% of t he boron reduction occurs in the chemical precipitation system with the ion exchange sy stem removing approximately 70-75Memorandum

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percent of the boron that remains in the wastewater f ollowing the chemical precipitation step [ERG, 2013a].

4.2 AEP’s Mountaineer Plant

As part of American Electric Power’s (AEP) permittin g process for several of its power plants along the Ohio River, the company conducted a pilot s tudy at its Mountaineer Plant that evaluated four mercury removal technologies for FGD wast ewater. One of the four systems evaluated was an ion exchange resin, referred to in the study as “Technology B.” The ion exchange resin was formulated to specifically target remo val of mercury. The objective of the study was to find a technology that will reduce total mercur y concentrations to less than 12 ppt. Table 2 presents the influent and effluent concentrations for the ion exchange resin observed throughout the pilot study as well as a calculated remova l percentage rate.

As Table 2 indicates, the ion exchange resin technology was fairly effective at removing total mercury with an average removal rate of 88.4 percent ; however, researchers concluded that although the resin effectively removed dissolved mercury it was not effective at removing particulate-bound or colloidal mercury [AEP, 2010].

Table 2 . AEP Pilot Study Ion Exchange Total Mercury Removal Results

Sample Date Influent to Ion Exchange (ppt) I on Exchange Resin

Technology Effluent (ppt) Removal Rate

7/23/2008 1

, 210 451 62.7%

7/30/2008 1

, 550 652 57.9%

8/6/2008 895 231 74.2%

8/13/2008 1

, 530 408 73.3%

8/20/2008 612 48.7 92.0%

8/27/2008 851 200 76.5%

9/3/2008 1,940 125 93.6%

9/10/2008 758 45.2 94.0%

9/17/2008 1,990 15.4 99.2%

9/24/2008 1,840 14.1 99.2%

10/1/2008 643 4.8 99.3%

10/8/2008 665 NM NM

10/15/2008 651 NM NM

10/22/2008 437 13.4 96.9%

10/29/2008 205 8.9 95.7%

11/5/2008 282 3.1 98.9%

11/12/2008 505 4.7 99.1%

11/19/2008 224 10.3 95.4%

11/26/2008 342 NM NM

12/3/2008 181 NM NM

12/10/2008 261 12.6 95.2% Average 836.8 132.2 88.4%

Source: AEP, 2010.

NM: Not MeasuredMemorandum

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5.0 E LECTRO -C OAGULATION

Electro-coagulation (EC) is a technique used in wastewate r treatment in which an electrical charge is applied to the water causing a change in particle surface charge, allowing suspended solids to fall out of solution. These systems typ ically use aluminum or iron electrodes, which dissolve into the wastestream during the process. The dissolved metallic ions precipitate with the other pollutants in the wastewater and form i nsoluble metal hydroxides. According to EPRI, the pollutants removed by iron coprecipitation in a standard chemical precipitation system should also be removed by an electro-coagulation system using an iron electrode. One of the advantages of the EC system is that is has the potentia l to remove hard-to-treat pollutants such as selenium. Some of the disadvantages of the system are that it requires a constant power source and it may increase the wastewater concentrations of the metals forming the electrodes used in the system (e.g., aluminum, iron). Additionally, the EC system requires pretreatment to adjust the pH to between 7.5 and 9.0 S.U.

The Duke Energy Mayo plant at one point considered EC as a possible treatment option for treating its FGD wastewater; however, the plant h as chosen to install an evaporation system. Duke Energy chose zero liquid discharge based on multi-poll utant removal ability, the evaporation system being considered a proven technology, a nd cost [Loewenburg, 2012].

5.1 University of Florida Study

A University of Florida study for the installation of a new FGD wastewater system at a power plant in Crystal River, Florida proposed using a com bination of EC, ion exchange, and evaporation. EC was identified as a potential treatment option based on bench-scale testing using FGD wastewater from a plant in Roxboro, NC. The ben ch-scale test determined that EC could be

used to remove selenium from FGD wastewater and that the best setup for EC was two aluminum plates separated with U-shaped rubber spaces. In this bench-scale study, using a peristaltic pump, researchers pumped filtered FGD wastewat er at pH 8 S.U. through a small Tygon® tube into the bottom of the EC, through a hole in the rubber space. The researchers chose a pH of 8 S.U. for the influent water because it minimizes the contribution of solids from the electrodes. The researchers conducted two separate te sts using the same FGD wastewater for

the tests.

Analytical results from the bench-scale study are i ncluded in Table 3. For every analyte, the researchers used two detection wavelengths and the table presents the results for the two bench-scale tests for both wavelengths. The specific w avelengths used for the analyses were not provided in the study report. In this study, calcium and magn esium are controlled in order to meet the total water hardness limit for the plant, but do not have specific goal discharge limits.

As shown in Table 3, removals of selenium were achieved f or both EC samples, for at least one of the wavelengths used for the analyses. Ho wever, the EC system increased the

aluminum and iron concentrations across the treatment system. The researchers determined that

aluminum and iron could be removed downstream of the EC s ystem using water softening [University of Florida, 2010].Memorandum

September 30, 2015 Page 14

Table 3. University of Florida EC Study Results

Analyte Equipment

Detection Limits (ppm) Goal

Discharge Limits (ppm) Influent

(ppm) EC Treated

Sample 1 (ppm) EC Treated

Sample 2 (ppm)

Silver 0.0009 0.1 0.006 0.006 BDL

0.0009 0.1 0.015 BDL BDL

Al uminum 0.003 1.5 0.071 528.200 533.900

0.003 1.5 BDL 1066.000 1080.000

Ca lcium 0.0002

--- 2179.667 120.700 131.600

0.0002

--- 2181.000 109.200 117.900

Iron 0.002 0.3 0.014 6.453 6.928

0.002 0.3 0.012 6.357 6.810

M agnesium 0.00007

--- 532.667 21.190 23.330

0.00007

--- 534.333 20.430 22.560

M anganese 0.0004 0.1 1.508 25.880 26.520

0.0004 0.1 1.490 25.720 26.380

Se lenium 0.05 0.071 1.580 0.092 BDL

0.05 0.071 BDL BDL BDL

BDL – Below detection limit.

6.0 B IOLOGICAL T REATMENT

EPA’s selected BAT technology basis for FGD wastewat er is chemical precipitation followed by anoxic/anaerobic biological treatment using a fixed-film bioreactor. Several vendors have developed these biological treatment systems and oth ers designed to treat selenium and nitrate/nitrite as N, which are discussed in this sectio n.

6.1 Frontier Water Systems Modular System

Frontier Water Systems developed a fixed-film bioreactor technology that is similar to the biological treatment used in the selected BAT techno logy basis. The design of the system from Frontier Water Systems is a modular-based bioreac tor, where the system is prefabricated and can be delivered directly to the site. Frontier Wate r Systems manufactures four different sizes; therefore, plants can buy several different m odules of varying sizes to meet the flow rate and retention time needed for treatment [Frontier, 2014]. According to Frontier, the system is capable of meeting the final limitations for the steam electric ELGs for FGD wastewater. More specifically, the modular biological treatment systems are able to achieve effluent concentrations of less than 10 μg/L for selenium, 0.1 mg/L for nitrate/nitr ite as N, 100 ng/L for mercury, and 5 μg/L for arsenic. The system has not yet been installe d at a full-scale installation for the treatment of FGD wastewater [Frontier, 2014; Pickett, 2013] . At this time, the system is in the pilot-testing phase for FGD wastewater treatment.

6.2 Envirogen’s Fluidized Bed Reactor/Membrane Bioreactor (FBR/ MBR)

EPRI conducted a pilot-scale study of Envirogen’s FBR/MBR te chnology for treating FGD wastewater. This technology is currently used to re move nitrate and selenium from coalMemorandum

September 30, 2015 Page 15

mining wastewater and prior to this study had never been applied to FGD wastewater. EPRI evaluated a pilot-scale FBR/MBR technology at a SCA NA coal-fired power plant from July 2013 to March 2014. The pilot FBR/MBR system pumped FGD wastewater from a segregated FGD impoundment into a 50-gallon break tank at a ra te of 0.5-2.0 gpm. The water was then pumped through the FBR column followed by a Granula r Activated Carbon (GAC) media-settled bed. The effluent from the GAC flowed into a 50-gal lon MBR tank, where it was pumped through a cross-flow membrane, and then recirculate d back to the MBR tank.

Note: This simplified process flow diagram was based on Figure 2-3 in the EPRI report. Source: [EPRI, 2014c].

Figure 4. Envirogen’s FBR/MBR Pilot Process Flow Di agram

EPRI measured ORP in the influent, FBR column, and MBR tank throughout the pilot study with a platinum electrode referenced to a sil ver/silver chloride (Ag/AgCl) electrode. Field measurements were converted to the theoretical hydr ogen reference electrode and an ORP control system was linked to the organic carbon fee d pump. During the first five months of the pilot, the FGD wastewater influent contained high l evels of oxidants and higher levels of heavy metals (e.g., selenium, mercury) than the last thre e months of the pilot, which EPRI posits may have inhibited the growth and activity of the micro organisms. However, after the start-up period of five months, the treatment effluent consistently achieved much lower effluent concentrations.

The concentration of nitrate/nitrite as N in the ef fluent measured below 0.10 mg/L from September 2013 to February 2014. The FBR/MBR never achieved the selenium effluent limitations; however, the concentrations decreased over the time and dipped below 50 mg/L at the end of the pilot test period. Mercury concentra tions were below the final effluent limitations and decreased further over the pilot test period to concentrations around 300 ng/L in February

and March 2014. The FBR/MBR effluent contained arse nic concentrations below the final limitations and standard for the entirety of the pi lot test period [EPRI, 2014c].

6.3 Degremont Technologies (IDI) iBio TM Biological Treatment System

The iBio TM biological treatment system is a type of anoxic/an aerobic biological treatment system that consists of suspended growth flow-throu gh bioreactors instead of fixed-film bioreactors. A pilot study of the iBio TM biological treatment system at Yates Station demonstrated that the system could remove nitrate ( < 1.0 mg/L), selenium (< 0.2 mg/L), and chromium (< 0.005 mg/L) from FGD wastewater [Teng, n.d.]. In addition, Conemaugh beganMemorandum

September 30, 2015 Page 16

operating an iBio TM biological treatment system to treat FGD wastewater generated from FGD systems servicing steam electric generating units 1 and 2. Thi s system was designed to target

selenium in order to achieve National Pollutant Dischar ge Elimination System (NPDES) limits established due to a consent order and agreement with the Pe nnsylvania Department of

Environmental Protection. The iBio TM biological treatment system reactors follow an ion exchange system (see Section 4.1). The start-up period for the treatment system lasted about six months and no plant shutdown was necessary. According to GenOn Energy, the iBio TM
biological treatment system removed selenium and achiev ed approximately 150 ppb or less in the effluent [ERG, 2013a].

7.0 Z ERO L IQUID D ISCHARGE T ECHNOLOGIES

As part of the technology options considered for BAT, E PA evaluated an evaporation system consisting of chemical precipitation (using hydroxide precipitation, sulfide precipitation and iron coprecipiation) followed by a falling-film evapor ator (also known as a brine concentrator) to produce a concentrated wastewater stre am (brine) and a distillate stream. An evaporation system traditionally consists of a softeni ng step (e.g., lime addition), brine concentrator, and crystallizer and generates a reusable distillate stream and solids requiring disposal. Several vendors have developed evaporation syst ems designed for zero liquid discharge (ZLD) of FGD wastewater.

7.1 Veolia Water Solutions & Technologies CoLD TM Process

Veolia Water Solutions & Technologies developed an evapor ation system that does not require a chemical precipitation or softening step. The F GD wastewater is transferred directly into the evaporation and crystallization process that is operated at a low temperature for optimizing the FGD wastewater chemistry. At a lower t emperature, dissolved solids will crystallize (e.g., hydrates and double salts) at lower con centrations. Therefore, this system does not produce any additional sludge from chemical addition, al lows the evaporated water to be reused, and produces stable solids for disposal [Veolia Wate r Solution, 2013]. In addition, one coal-fired power plant operates a full-scale CoLD TM process system to treat steam electric power plant wastewater.

7.2 Pilot-Scale ZLD System

At least one vendor of the evaporation system for tre ating FGD wastewater has been pilot-testing a process to solidify the concentrated brine from the evaporation system. The solidification process consists of mixing the concentra ted brine with fly ash and other reagents to form a solidified material via a pozzolanic reaction. Th e vendor’s pilot testing has shown that the solidified material passes all the toxicity characteri stic leachating procedure criteria. According to the vendor, by solidifying the material, it is not nec essary to soften the wastewater prior to the evaporation system, which significantly reduces the opera tion and maintenance (O&M) costs and the amount of solids generated by the system. It also r educes the capital costs because the solidification process equipment is significantly less expensive than a forced-circulation crystallizer [ERG, 2015d].Memorandum

September 30, 2015 Page 17

7.3 Heartland Technology Partners, LLC (Heartland) Low Momentum- High Turbulence (LM-HT ® ) Wastewater Concentrator

Heartland developed an adiabatic evaporator system that utilizes an evaporation zone, entrainment separator, and solid/liquid separator to achieve ZLD without a crystallizer. First the system injects wastewater and hot feed gas into the evapo ration zone to form water vapor and concentrated wastewater. The feed gas is maintained bet ween 150 oF and 800oF and may be pulled from other processes within the coal-fired power plan t (e.g., slip stream from flue gas). Next the LM-HT® concentrator separates the air-water mixture in the entrainment chamber, sends the wastewater to the solid/liquid separator, and e xhausts the water vapor. After the solid/liquid separator, the concentrated wastewater recyc les back to the evaporation zone and the solids are transported for disposal (e.g., landfill, repur posing, sale) [Duesel, et. al, 2013].

There are several advantages to this ZLD technology, including a compact design and low O&M costs. Costs are kept low because there is n o need for a crystallizer or heat exchangers and the waste heat can be reused. The system has high c orrosion/erosion resistance, proven on heavy brines (> 250,000 ppm total solids in feed).

Heartland has implemented full-scale systems for other types of wastewater. For instance, the system achieved ZLD on impoundment water from a produce d water disposal facility in Utah, wastewater at Waste Management’s power plant i n New Hampshire, and fracking wastewater at Seneca Energy Resources’ well pad in Penns ylvania. Heartland is currently demonstrating the LM-HT® wastewater concentrator on FGD wastewater and other steam electric wastewaters at Southern Company’s Plant Bowe n. Heartland treated the FGD wastewater and discovered that fly ash in the flue gas, used as the feed gas, improved the performance of the LM-HT® concentrator [Heartland, 2012; He artland, 2014].

8.0 R EMOVAL OF D ISSOLVED A RSENIC

Many treatment systems remove arsenic from FGD wastew ater, such as chemical precipitation, ZVI cementation, and RO. Arsenic may be present in FGD wastewater as particulate or dissolved. Arsenic is generally present in the particulate phase in FGD wastewater generated from limestone forced oxidation FGD systems. D issolved arsenic may also be present, and can take the form of arsenite (As+3) or arsenate (A s+5). Arsenite is more soluble than arsenate and can be more difficult to remove using chem ical precipitation.

EPA is regulating total recoverable arsenic and the final limitations were based on total arsenic in treatment system effluent. However, EPA r eceived public comments claiming EPA’s

evaluation of BAT for arsenic removal does not accuratel y represent the range of influent dissolved arsenic levels within the industry and inhibited oxi dation wet FGD systems generate FGD wastewater where arsenic is predominately dissolved . Therefore, they maintain chemical precipitation would not be able to treat dissolved arsenic [EPRI, 2013b; AEP, 2013]. Section 3.3 presented information on a sorption media technology tha t treats dissolved arsenic. The remainder of this section presents information on additio nal sources for dissolved arsenic treatability.Memorandum

September 30, 2015 Page 18

8.1 Industrial Wastewater Pilot Study

A study conducted by the Water Environment Federation eval uated the removal of total arsenic in ash pond effluent for a steam electric plan t. 5 The study evaluated a chemical precipitation system with ferric chloride coagulation f ollowed by two types of membrane filtration (pressure filtration and microfiltration) a nd spanned about 3 months. The system configuration with the best results used a high ferric chl oride dose (~9.3 mg/L), high pH (~9.1 S.U.), and microfiltration (50 m 2 surface area with 0.1μm pore size). These operating cond itions reduced the total arsenic (primarily in the As 5+ form) from 262 μg/L, in the ash pond effluent, to less than 4 μg/L, in the treated wastewater (> 98% remo val). One of the findings from the pilot study is that arsenic speciation can be an obstacle to e ffective treatment in the chemical precipitation system. The authors suggest that a pre-oxida tion step using chlorine, ozone, or potassium permanganate additives would ensure the dominance of As 5+ species in the wastewater prior to chemical precipitation [Younan, 2008].

9.0 R EMOVAL OF B ROMIDE

FGD systems are designed to convert gaseous sulfur dioxide (S O 2 ) into soluble H 2 SO 4 ; this process has a similar effect on halogens, converti ng gaseous chlorine (Cl 2 ) and bromine (Br 2 ) to their soluble ionic forms chloride (Cl

- ) and bromide (Br - ). Therefore, bromide in the coal and

air intake is transferred into the FGD wastewater in wet FGD systems. Halogens (e.g., chloride and bromide) are sometimes added at various locations in coal-fired steam electric generating units to improve mercury removal. Bromide is known to achie ve the highest removals. Bromide can be added to the flue gas upstream of the particulate co ntrol device through brominated activated carbon injection (BACI), into the coal feed as a salt through calcium bromide (CaBr 2 ) addition, or into the flue gas upstream of the preheater t hrough hydrogen bromide (HBr) addition [EPRI, 2013a]. Bromide (as HOBr) is also used as a biocide i n power plant cooling towers because it is more reactive then chlorine, thus has str onger biocidal activity. When brominated wastewater is discharged, the bromide concentrations i n the receiving surface water increases, impacting the environment and human health [VanBriesen, 2013].

Although the use of bromide can have positive results suc h as increasing metals removal from the flue gas, decreasing mercury re-emissions, and co ntrolling biological fouling in cooling water, elevated bromide in wastewater has harmful im pacts when released into the environment and can be difficult to treat. In addition to being toxic to aquatic organisms, brominated wastewater can lead to higher bromide levels in drinking w ater intake and can form chlorinatedbrominated disinfection by-products (DBPs) when bromide rea cts with natural organic matter (NOM) in the presence of disinfectants (chlorine, typi cally as hypochlorous acid, HOCl).

HOCl + NOM + (Br

- ) ⇒ DBPs

Studies have identified DBPs as potential carcinogens. Ot her studies report that exposure to some DBPs can result in adverse reproductive outcomes (i.e., anemia, development abnormalities). Brominated DBPs are consistently more toxic than chlorinated DBPs. Bromide-

5 The source states that, “Preliminary sampling via speci ation method showed that the predominant form of arsenic in this wastewater was As V (95 %)” [Younan, 2008].Memorandum

September 30, 2015 Page 19

contaminated wastewater is typically treated using desali nation techniques (membrane or thermal), there are other methods that have not yet r eached full-scale development. The main thermal desalination technique used at coal-fired power plan ts is the evaporation system (vaporcompression evaporation system). Reverse osmosis (known as membrane desalination) can also be used to remove bromide (see section 2.0).

9.1 UNC Chapel Hill Study

The University of North Carolina (UNC) at Chapel Hill performed a bench-scale study using ion exchange to remove bromides (for more on ion e xchange, see section 4.0). Bromide removal was evaluated with a polyacrylate-based magnetic ion exchange (MIEX) resin and two polystyrene resins, Iona A-641 and Amberlite IRA910, using simu lated natural waters containing NOM, bicarbonate, chloride, and bromide. This study achiev ed bromide removal to some extent and demonstrated that the polystyrene resins were the m ost effective. However, the alkalinity (bicarbonate), dissolved organic carbon (DOC), and chloride were found to inhibit bromide

removals at some concentrations and recommended that m ore extensive studies be performed before considering ion exchange as an option for bromid e treatment [Hsu, 2010].

9.2 University of Granada

This study analyzed the absorption of bromide and iodide using a type of sorption media, metal-doped aerogels, which retains the halide on the aero gel surface through the chemisorption process (for more on sorption media, see section 3.0). The study used silver-doped aerogels in 25

cm 3 columns to remove bromide from Lake Zurich and mineral water. Once the columns were saturated with bromide and iodide, they were regenerated w ith ammonium hydroxide (NH 4 OH). The aerogel filled columns had a high efficiency of remo ving the bromide from the water before and after regeneration (see Figure 3) [Sanchez-Polo, 2007].

Source: [Sanchez-Polo, 2007] Regeneration with NH 4 OH (0.02 M)

First absorption process

Second absorption processMemorandum

September 30, 2015 Page 20

Figure 5. Breakthrough curves of bromide on A-Ag aerogel

Therefore, this study demonstrates that silver-doped aero gels are a possible use for removing bromide from drinking water intake (Lake Zurich wate r); however, more studies are needed to determine whether this type of sorption media wo uld be effective for FGD wastewater.

9.3 Zhejiang University Study

A bench-scale study conducted at Zhejiang University was performed to evaluate the removal of bromide from raw water (obtained from wate r source of a drinking water plant) and deionized water through aluminum (Al(III)) coagulation. Th e bromide removal efficiency was examined at varying pH, aluminum concentrations, bromide concentrations, and concentrations of anions (i.e., SO 4 2- ). The coagulation removed between 62.1 and 87.8 percent of br omide in raw water and between 82.8 and 99.2 percent of bromide in deio nzed water. However, when

other anions were added to the raw water the bromide remova l efficiency decreased. For example, the following represent the percent decreases i n bromide removal efficiency that were observed when the specific ion was present:

• Nitrate (NO 3 - ): 8.0 percent decrease in bromide removal;

• Bicarbonate (HCO 3 - ): 11.5 percent decrease in bromide removal;

• Chloride (Cl

- ): 14.6 percent decrease in bromide removal;

• Sulfate (SO 4 - ): 21.2 percent decrease in bromide removal; and

• Dihydrogen Phosphate (H 2 PO 4 - ): 40.8 percent decrease in bromide removal [Ge, 2008].

9.4 Electrochemical Removal

A bench-scale study performed by the University of Calif ornia, Los Angeles (UCLA), examined the removal of bromide from raw lake water (i. e., Castaic Lake) using the Wunsche and Kossuth processes. The Wunsche process uses mono-pola r carbon electrodes with a diaphragm to separate the anode and the cathode, while t he Kossuth process uses dipolar carbon electrodes without a diaphragm. Both processes remove b romide by oxidizing the halogen to bromide, then heating and air stripping to volatize the bromide [Kimbrough, 2002].

2 Br - → Br 2 + 2e – E° = -1.1 V

Similarly, a pilot-scale study of the electrolytic volatization method was recently published on naturally-occurring bromide (~42-424 μg/L) in Castaic Lake. The bromide was volatized when passed between electrodes, clarified in a n upflow sand clarifier, and filtered through a deep-bed anthracite coal filter. This study estim ated that the costs for a demonstrationscale electrolytic reactor would be $1,549 - 2,099 per million ga llons of water treated [Kimbrough, 2013]. The earlier report published on this pilot-s cale study, performed in 2006, determined that up to 35% bromide removal and 60% less DBPs could be achieved through electrolysis [Kimbrough, 2006].Memorandum

September 30, 2015 Page 21

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