MEMORANDUM 

TO: Steam Electric Rulemaking Record 

FROM: Anna Dimling, ERG 

 

DATE: September 30, 2015 

SUBJECT: Evaluation of Emerging Technologies for the Treatment of Flue Gas 

Desulfurization Wastewater 

ERG is providing technical support to the U.S. Environmental Protection Agency’s 

(EPA’s) Office of Water, Engineering and Analysis Division for development of effluent 

limitations guidelines and standards (ELGs) for the Steam Electric Power Generating Industry. 

EPA, with the support of ERG, identified and evaluated technologies available for the treatment 

of power plant wastewater, specifically flue gas desulfurization (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 potential revisions to the ELGs for FGD wastewater: 

• Chemical precipitation (including hydroxide precipitation, sulfide precipitation, and 

iron coprecipitation). 

• Chemical precipitation (including hydroxide precipitation, sulfide precipitation, and 

iron coprecipitation) followed by an anoxic/anaerobic fixed-film biological treatment 

system. 

• Chemical precipitation (including hydroxide precipitation, sulfide precipitation, and 

iron coprecipitation) followed by vapor-compression evaporation (evaporation). 

EPA also identified other emerging treatment technologies that can be used for the 

treatment of FGD wastewater. Currently, most of these technologies have only been evaluated at 

bench- or pilot-scale levels, although some technologies have been tested at limited full-scale 

levels. This memorandum identifies these emerging technologies, describes the processes for 

treating FGD wastewater, and presents data currently available regarding the technologies’ 

treatment performance. Additionally, this memorandum discusses several specific issues related 

to the treatment of FGD wastewater, including the treatment of dissolved arsenic and bromide. 

1.0 ZERO VALENT IRON CEMENTATION

 The zero valent iron (ZVI) cementation process consists 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 following equation shows a cementation reaction 

between zero-valent iron and copper: 

Fe0 + Cu2+  Fe2+ + Cu0 
Memorandum 

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 requirement for significant pretreatment. A 

disadvantage of this technology is that for the best results, 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) performed bench- and pilot-scale 

studies at a coal-fired power plant to evaluate ZVI cementation for selenium removal. Initial 

bench-scale testing using the plant’s FGD wastewater suggested 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, reaction 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 that 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 maintain 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 adjustment 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 flocculant mixing tank, where it was mixed with a 

diluted flocculant solution. The flocculant aided coagulation 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 as 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 wastewater using ZVI cementation is 

dependent on the species of the selenium present. During the pilot study, the iron cementation 

system was able to remove greater than 99% of the selenite 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 percent.2 

 

1

 The report does not describe any solids removal mechanisms used to remove solids from the pH adjustment tank or 

the flocculation tank, but ERG expects that additional solids removal would be required. 

2

 Because mercury was not a defined target pollutant for the study, only a limited set of data were evaluated for 

mercury. The range of percent removals is based on three measurements. 
Memorandum 

September 30, 2015 

Page 3 

Figure 1: Basic Schematic of EPRI ZVI Cementation Pilot Study 

 This pilot study demonstrated that the ZVI cementation technology 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 selenium 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, researchers at Texas A&M University 

demonstrated successful heavy metals removals using an Activated 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, including selenium, mercury, arsenic, 

iron, chromium, copper, and cadmium from FGD wastewater at relatively low costs. Based on 

results from successful bench-scale tests, a pilot study was implemented at an unidentified power 

plant located in the Southeastern United States. The pilot system consisted of four stainless steel 

zero-valent iron (ZVI) reactors where the iron cementation occurs followed by post-treatment 

units including aeration, clarification, and sand filtration. Figure 2 presents a diagram of the set 

up for the pilot scale test. 

 The study occurred over approximately five months and consisted 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 pond as the influent to the system. The 

FGD wastewater had typical characteristics of the 22 coal-fired plants that are operated by the 

host power company. As the researchers were concerned mostly with the removal of selenium 

and mercury, each of those contaminants were spiked in the feed water to raise their 

concentrations. In addition, researchers were interested in results from just the initial ZVI reactor 

(i.e., stage one reaction tank) and from the combination of all four ZVI reactors. Table 1 shows 

the average influent and effluent results from the study. 

 

3

 The selenium concentrations of the primary clarifier 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 Pilot Study 

 

Table 1. Average Influent and Effluent Concentrations for 

Hybrid ZVI Treatment System Pilot Study 

Contaminant FGD Wastewater 

Influent (μg/L) 

One Reactor 

Effluent (μg/L) 

Four Reactors

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 m3 FGD wastewater treated (0.0025 lbs ZVI/gal FGD wastewater treated). This 

consumption rate resulted in a cost of approximately $0.6-1.0 per 1 m3

 ($0.0023-0.0038 per gal) 

FGD wastewater for just the chemical consumption. Costs associated with sludge generation and 

disposal were not reported. The pilot study demonstrated that the ZVI process is scalable (i.e., 

multiple reactors can be utilized to achieve additional removals or expand treatment capacity) 

[Huang, 2012]. 

1.3 Evoqua Water Technologies (Evoqua) PironoxTM System 

 EPRI, in collaboration with South Carolina Electric and Gas (SCANA), conducted a pilot 

study on FGD wastewater treatment using Evoqua’s PironoxTM system, a reactive media system 

that utilizes ZVI and other reactants to remove selenium, mercury, and other metals. The pilot 
Memorandum 

September 30, 2015 

Page 5 

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 service. Therefore, the pilot study was 

split into two phases: Phase 1 (September 11, 2013 through December 3, 2014) and Phase 2 

(January 21, 2014 through April 2, 2014). FGD wastewater influent was pumped at a rate of 0.5 - 

1 gpm from a segregated FGD impoundment into the PironoxTM system. The wastewater flowed 

through a series of four reactors containing the PironoxTM advance reactive media and additional 

reagents. The total hydraulic residence time in these reactors 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 recycled the sludge, consisting of ZVI, back to 

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

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

and 200.7. The selenium concentration in the treatment effluent was significantly less in Phase 2 

(compared to Phase 1) and ranged from 17 μg/L to 27 μg/L. In addition, the effluent in Phase 2 

met the final ELG limitations for arsenic and mercury. However, Evoqua observed elevated 

levels of nitrates throughout the pilot study, but in general 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/nitrite as N [EPRI, 2014b]. 

1.4 Libery Hydro ZVI BlueTM Media 

EPA obtained information from two pilot studies conducted as a partnership between 

EPRI and SCANA at a coal-fired power plant that evaluated a ZVI technology for treating FGD 

wastewater. The pilot studies were performed from November 2013 to March 2014 and tested 

two different system configurations using the Liberty Hydro’s ZVI BlueTM media. The pilot test 

used FGD surface impoundment effluent as the initial influent stream to the system; however, on 

February 28, 2014, a pilot-scale chemical precipitation system was added upstream of the pilot 

technologies to pretreat the FGD wastewater. The first ZVI system configuration (System 1) 

used a 1.0 gpm FGD wastewater influent flow rate and treated 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 BlueTM media loaded 

with fine ZVI shavings. 

This pilot test was not able to achieve effluent concentrations 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 surface 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 tank reactor, followed by an 

ultrafilter membrane). 
Memorandum 

September 30, 2015 

Page 6 

• An ultraviolet (UV) disinfection step. 

• Four columns (2.5” diameter; 12.5” media) containing porous ZVI BlueTM 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 with the ZVI media which significantly 

inhibits selenium removal from the FGD wastewater. The second ZVI system configuration, 

containing the pretreatment bioreactor, was able to meet the 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 methyl seleninic acid [EPRI, 

2014a; ERG, 2015a]. 

EPA also obtained information from a pilot study conducted at another coal-fired power 

plant also using the ZVI BlueTM 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 vessels containing porous ZVI-loaded media 

(similar to System 1 described above). However, the chemical precipitation effluent from this 

plant contained lower levels of nitrates than the other 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 BlueTM 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 BlueTM system, in the 

initial design, will contain 15 reactor vessels containing stacks of media (see Figure 2). 

Adjustments to the design configuration will be evaluated over time [ERG, 2015a]. 
Memorandum 

September 30, 2015 

Page 7 

Source: [ERG, 2015a] 

Figure 3. Full-Scale Design Process Flow Diagram for the ZVI BlueTM System 

 The reactor system is designed in a way that if any particular stack of media is not 

operating properly, that particular stack can be removed and repaired without causing a system 

shut-down. Liberty Hydro is still working on methods 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 with an engineering firm to prepare capital and 

operation and maintenance (O&M) cost estimates for the system [ERG, 2015a]. 

2.0 REVERSE OSMOSIS

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

desalination of seawater and removal of dissolved materials 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 pumps are used to apply pressure to the 

solution from one side of the semi-permeable membrane 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 operating pressure, concentration of dissolved 

materials, and temperature, as well as the permeability of the membrane. 
Memorandum 

September 30, 2015 

Page 8 

 As described above, the RO system separates the feed wastewater 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 permeate (i.e., the volume of permeate 

divided by the volume of feed) is known as the water recovery. One of the advantages of a RO 

system is that it can be used to achieve zero liquid discharge 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 electric 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 combination 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. multi-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 design 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 treatment of FGD wastewater because of 

the high chloride levels typically present in FGD wastewater. 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, located in Pennsylvania, considered 

RO as a potential treatment option to reduce total dissolved 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, the high osmotic pressure of the FGD 

blowdown, due to high TDS, caused a 50 percent or less RO recovery and cause the concentrate 

stream flow rate from the RO system to be too large and thus too costly to manage. Secondly, 

using RO for the FGD blowdown causes scaling and fouling issues, 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 (HEROTM) 

RO systems currently in use at steam electric power plants are usually used to treat boiler 

make-up water or cooling tower blowdown. EPRI identified a high-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 fouling because silica is more soluble at a 

 

4

 Fouling occurs when both dissolved and suspended solids deposit onto a membrane surface and degrade its overall 

performance, thereby decreasing permeate quality and water recovery percentage. 
Memorandum 

September 30, 2015 

Page 9 

higher pH. Silica is a common foulant in many RO applications. 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 steam electric power generating 

industry to treat cooling tower blowdown, its potential for use 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 and chloride concentrations may be able to. 

The HEROTM system is of particular interest for treating boron in FGD wastewaters. Boron 

becomes ionized at elevated pH and, therefore, could be removed using an RO system [EPRI, 

2007]. 

3.0 SORPTION MEDIA

 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 the removal of specific pollutants; however, 

they may also remove other pollutants simultaneously. The advantages of sorption media are the 

ease of installation, efficiency of contaminant removal, and effectiveness under various pH and 

contaminant conditions. Some disadvantages with sorption media are that they are typically 

single use products that require replacement instead of regeneration. Furthermore, they are 

subject to fouling that may require pretreatment of wastewater 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 can 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 pretreatment 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, examined the single pass-through 

media proprietary functionalized alumina adsorbent technology 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 form functionalized sites in the media 

that will form covalent bonds with selected soluble metals. As these materials and reactions are 

all proprietary, details of the chemistry were not reported. At least three of the chemical 

components forming the functionalized sites on the media are known to complex with soluble 

selenium in the selenate and selenite oxyanion forms. The removal is accomplished by the 

formation of various selenite and selenate complexes such as aluminum selenite, aluminum 

selenate, and others. The study observed selenium removal rates from 16% to 50% [Sherwood, 

2012]. 
Memorandum 

September 30, 2015 

Page 10 

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 call held on January 2, 2013 [ERG, 

2013b]. These systems include the SCU Adsorbent and the GFH® Media. The SCU Adsorbent is 

a single use granular carbonaceous adsorbent media which selectively adsorbs dissolved metal 

cations, including cadmium (Cd2+), trivalent chromium (Cr3+), copper (Cu2+), lead (Pb2+), 

mercury (Hg2+), nickel (Ni2+), and zinc (Zn2+). At the Merrimack Station, the SCU Adsorbent is 

specifically used for mercury removal. The permitted maximum effluent mercury concentration 

at the Merrimack Station was set at 14 parts per trillion (ppt), based on the plant’s projected 

performance (i.e., the technology vendor’s guarantee). The plant operates a physical/chemical 

precipitation system, including hydroxide and sulfide precipitation, 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 has 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 media that is used primarily for the 

removal of arsenic (i.e. arsenite: As+3 and arsenate: As+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 concentrations. 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 effluent sampling results, the media 

must be replaced. The media can either be replaced by swapping 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 configuration. Specific costs associated with 

the Merrimack Station are proprietary; however, Evoqua provided 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 water at a rate of approximately 

40 gallon per minute. Based on the replacement frequency observed at Merrimack, the media 

costs for the SCU Adsorbent is approximately $2 per 1,000 gallons 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- and 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 describing the study contains limited information 

regarding the treatment steps used in the study and the effluent concentrations achieved, but the 

article did indicate that mercury removal was achieved [Purves, 2013]. 
Memorandum 

September 30, 2015 

Page 11 

4.0 ION EXCHANGE

 Ion exchange systems remove specific constituents from wastewater; therefore, the 

system can target specific metals to be removed. The ion 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 does not generate a residual waste, it 

does generate a regenerant stream that contains the metals stripped from the wastewater. Ion 

exchange can be complicated by other contaminants present 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 trace contaminant removal in wastewater by 

ion exchange is highly dependent on the other ions that surround the contaminant [Meyers, 

2012]. 

4.1 Conemaugh Generating Station 

EPA and ERG conducted a visit at GenOn Energy Northeast Management Company’s 

Conemaugh Generating Station (Conemaugh), which operates an ion exchange system for the 

treatment of boron in FGD wastewater. Upstream of the ion exchange system, the plant treats the 

FGD wastewater with a physical/chemical precipitation system consisting of hydroxide 

precipitation and clarification. The overflow from the clarifier is fed to the ion exchange system. 

The ion exchange system consists of two parallel trains, 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 two vessels. As designed, the vessels operate 

in series, except when one of the vessels is being regenerated. The system was originally 

designed for regeneration to occur every six hours; however, because of scaling issues, the plant 

has needed to operate the system such that one of the vessels in each train is always being 

regenerated. As the regeneration of one vessel is completed, the other vessel begins its 

regeneration process. 

The plant uses sulfuric acid and caustic soda washes to regenerate the resins. The waste 

from the regeneration process is transferred to a precipitation 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 with 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 the 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 boron concentrations 

across the chemical precipitation and ion exchange systems. The plant measured boron 

concentrations between 400 and 600 ppm in the purge stream and concentrations of 75 ppm in 

the effluent from the ion exchange system. Roughly 45% of the boron reduction occurs in the 

chemical precipitation system with the ion exchange system removing approximately 70-75 
Memorandum 

September 30, 2015 

Page 12 

percent of the boron that remains in the wastewater following the chemical precipitation step 

[ERG, 2013a]. 

4.2 AEP’s Mountaineer Plant 

 As part of American Electric Power’s (AEP) permitting process for several of its power 

plants along the Ohio River, the company conducted a pilot study at its Mountaineer Plant that 

evaluated four mercury removal technologies for FGD wastewater. 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 removal of mercury. The objective of the 

study was to find a technology that will reduce total mercury 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 removal 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) 

Ion 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 Measured 
Memorandum 

September 30, 2015 

Page 13 

5.0 ELECTRO-COAGULATION

 Electro-coagulation (EC) is a technique used in wastewater 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 typically 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 insoluble 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 potential 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 has chosen to install an evaporation system. 

Duke Energy chose zero liquid discharge based on multi-pollutant removal ability, the 

evaporation system being considered a proven technology, and 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 combination 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 bench-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 wastewater 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 tests using the same FGD wastewater for 

the tests. 

 Analytical results from the bench-scale study are included 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 wavelengths used for the analyses were not 

provided in the study report. In this study, calcium and magnesium 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 for both EC samples, for at 

least one of the wavelengths used for the analyses. However, 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 system 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

Aluminum 0.003 1.5 0.071 528.200 533.900

0.003 1.5 BDL 1066.000 1080.000

Calcium 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

Magnesium 0.00007 --- 532.667 21.190 23.330

0.00007 --- 534.333 20.430 22.560

Manganese 0.0004 0.1 1.508 25.880 26.520

0.0004 0.1 1.490 25.720 26.380

Selenium 0.05 0.071 1.580 0.092 BDL

0.05 0.071 BDL BDL BDL

BDL – Below detection limit. 

6.0 BIOLOGICAL TREATMENT 

EPA’s selected BAT technology basis for FGD wastewater is chemical precipitation 

followed by anoxic/anaerobic biological treatment using a fixed-film bioreactor. Several vendors 

have developed these biological treatment systems and others designed to treat selenium and 

nitrate/nitrite as N, which are discussed in this section. 

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 technology basis. The design of the system 

from Frontier Water Systems is a modular-based bioreactor, where the system is prefabricated 

and can be delivered directly to the site. Frontier Water Systems manufactures four different 

sizes; therefore, plants can buy several different modules 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/nitrite as N, 100 ng/L for mercury, and 5 

μg/L for arsenic. The system has not yet been installed 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 technology for treating 

FGD wastewater. This technology is currently used to remove nitrate and selenium from coal 
Memorandum 

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 SCANA 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 rate of 0.5-2.0 gpm. The water was then 

pumped through the FBR column followed by a Granular Activated Carbon (GAC) media-settled 

bed. The effluent from the GAC flowed into a 50-gallon MBR tank, where it was pumped 

through a cross-flow membrane, and then recirculated 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 Diagram

EPRI measured ORP in the influent, FBR column, and MBR tank throughout the pilot 

study with a platinum electrode referenced to a silver/silver chloride (Ag/AgCl) electrode. Field 

measurements were converted to the theoretical hydrogen reference electrode and an ORP 

control system was linked to the organic carbon feed pump. During the first five months of the 

pilot, the FGD wastewater influent contained high levels of oxidants and higher levels of heavy 

metals (e.g., selenium, mercury) than the last three months of the pilot, which EPRI posits may 

have inhibited the growth and activity of the microorganisms. 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 effluent 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 concentrations 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 arsenic concentrations below the final 

limitations and standard for the entirety of the pilot test period [EPRI, 2014c]. 

6.3 Degremont Technologies (IDI) iBioTM Biological Treatment System 

The iBioTM biological treatment system is a type of anoxic/anaerobic biological treatment 

system that consists of suspended growth flow-through bioreactors instead of fixed-film 

bioreactors. A pilot study of the iBioTM 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 began 
Memorandum 

September 30, 2015 

Page 16 

operating an iBioTM biological treatment system to treat FGD wastewater generated from FGD 

systems servicing steam electric generating units 1 and 2. This system was designed to target 

selenium in order to achieve National Pollutant Discharge Elimination System (NPDES) limits 

established due to a consent order and agreement with the Pennsylvania Department of 

Environmental Protection. The iBioTM 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 iBioTM

biological treatment system removed selenium and achieved approximately 150 ppb or less in 

the effluent [ERG, 2013a]. 

7.0 ZERO LIQUID DISCHARGE TECHNOLOGIES

As part of the technology options considered for BAT, EPA evaluated an evaporation 

system consisting of chemical precipitation (using hydroxide precipitation, sulfide precipitation 

and iron coprecipiation) followed by a falling-film evaporator (also known as a brine 

concentrator) to produce a concentrated wastewater stream (brine) and a distillate stream. An 

evaporation system traditionally consists of a softening step (e.g., lime addition), brine 

concentrator, and crystallizer and generates a reusable distillate stream and solids requiring 

disposal. Several vendors have developed evaporation systems designed for zero liquid discharge 

(ZLD) of FGD wastewater. 

7.1 Veolia Water Solutions & Technologies CoLDTM Process 

Veolia Water Solutions & Technologies developed an evaporation system that does not 

require a chemical precipitation or softening step. The FGD 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 temperature, dissolved solids will 

crystallize (e.g., hydrates and double salts) at lower concentrations. Therefore, this system does 

not produce any additional sludge from chemical addition, allows the evaporated water to be 

reused, and produces stable solids for disposal [Veolia Water Solution, 2013]. In addition, one 

coal-fired power plant operates a full-scale CoLDTM process system to treat steam electric power 

plant wastewater. 

7.2 Pilot-Scale ZLD System 

At least one vendor of the evaporation system for treating FGD wastewater has been 

pilot-testing a process to solidify the concentrated brine from the evaporation system. The 

solidification process consists of mixing the concentrated brine with fly ash and other reagents to 

form a solidified material via a pozzolanic reaction. The vendor’s pilot testing has shown that the 

solidified material passes all the toxicity characteristic leachating procedure criteria. According 

to the vendor, by solidifying the material, it is not necessary to soften the wastewater prior to the 

evaporation system, which significantly reduces the operation and maintenance (O&M) costs and 

the amount of solids generated by the system. It also reduces 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 evaporation zone to form water vapor and 

concentrated wastewater. The feed gas is maintained between 150 oF and 800oF and may be 

pulled from other processes within the coal-fired power plant (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 exhausts the water vapor. After the 

solid/liquid separator, the concentrated wastewater recycles back to the evaporation zone and the 

solids are transported for disposal (e.g., landfill, repurposing, 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 no need for a crystallizer or heat exchangers 

and the waste heat can be reused. The system has high corrosion/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 produced water disposal facility in 

Utah, wastewater at Waste Management’s power plant in New Hampshire, and fracking 

wastewater at Seneca Energy Resources’ well pad in Pennsylvania. Heartland is currently 

demonstrating the LM-HT® wastewater concentrator on FGD wastewater and other steam 

electric wastewaters at Southern Company’s Plant Bowen. 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; Heartland, 2014]. 

8.0 REMOVAL OF DISSOLVED ARSENIC 

Many treatment systems remove arsenic from FGD wastewater, 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. Dissolved arsenic may also be present, 

and can take the form of arsenite (As+3) or arsenate (As+5). Arsenite is more soluble than 

arsenate and can be more difficult to remove using chemical precipitation. 

EPA is regulating total recoverable arsenic and the final limitations were based on total 

arsenic in treatment system effluent. However, EPA received public comments claiming EPA’s 

evaluation of BAT for arsenic removal does not accurately represent the range of influent 

dissolved arsenic levels within the industry and inhibited oxidation 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 that treats dissolved arsenic. The 

remainder of this section presents information on additional 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 evaluated the removal of total 

arsenic in ash pond effluent for a steam electric plant. 5 The study evaluated a chemical 

precipitation system with ferric chloride coagulation followed by two types of membrane 

filtration (pressure filtration and microfiltration) and spanned about 3 months. The system 

configuration with the best results used a high ferric chloride dose (~9.3 mg/L), high pH (~9.1 

S.U.), and microfiltration (50 m2 surface area with 0.1μm pore size). These operating conditions 

reduced the total arsenic (primarily in the As5+ form) from 262 μg/L, in the ash pond effluent, to 

less than 4 μg/L, in the treated wastewater (> 98% removal). One of the findings from the pilot 

study is that arsenic speciation can be an obstacle to effective treatment in the chemical 

precipitation system. The authors suggest that a pre-oxidation step using chlorine, ozone, or 

potassium permanganate additives would ensure the dominance of As5+ species in the 

wastewater prior to chemical precipitation [Younan, 2008]. 

9.0 REMOVAL OF BROMIDE 

 FGD systems are designed to convert gaseous sulfur dioxide (SO2) into soluble H2SO4; 

this process has a similar effect on halogens, converting gaseous chlorine (Cl2) and bromine (Br2) 

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 achieve the highest removals. Bromide 

can be added to the flue gas upstream of the particulate control device through brominated 

activated carbon injection (BACI), into the coal feed as a salt through calcium bromide (CaBr2) 

addition, or into the flue gas upstream of the preheater through hydrogen bromide (HBr) addition 

[EPRI, 2013a]. Bromide (as HOBr) is also used as a biocide in power plant cooling towers 

because it is more reactive then chlorine, thus has stronger biocidal activity. When brominated 

wastewater is discharged, the bromide concentrations in the receiving surface water increases, 

impacting the environment and human health [VanBriesen, 2013]. 

 Although the use of bromide can have positive results such as increasing metals removal 

from the flue gas, decreasing mercury re-emissions, and controlling biological fouling in cooling 

water, elevated bromide in wastewater has harmful impacts 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 water intake and can form chlorinatedbrominated disinfection by-products (DBPs) when bromide reacts with natural organic matter 

(NOM) in the presence of disinfectants (chlorine, typically as hypochlorous acid, HOCl). 

HOCl + NOM + (Br- ) ⇒ DBPs 

Studies have identified DBPs as potential carcinogens. Other 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 speciation 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 desalination techniques (membrane or 

thermal), there are other methods that have not yet reached full-scale development. The main 

thermal desalination technique used at coal-fired power plants 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 exchange, 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 simulated natural waters containing 

NOM, bicarbonate, chloride, and bromide. This study achieved bromide removal to some extent 

and demonstrated that the polystyrene resins were the most effective. However, the alkalinity 

(bicarbonate), dissolved organic carbon (DOC), and chloride were found to inhibit bromide 

removals at some concentrations and recommended that more extensive studies be performed 

before considering ion exchange as an option for bromide 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 aerogel surface through the chemisorption 

process (for more on sorption media, see section 3.0). The study used silver-doped aerogels in 25 

cm3 columns to remove bromide from Lake Zurich and mineral water. Once the columns were 

saturated with bromide and iodide, they were regenerated with ammonium hydroxide (NH4OH). 

The aerogel filled columns had a high efficiency of removing the bromide from the water before 

and after regeneration (see Figure 3) [Sanchez-Polo, 2007]. 

Source: [Sanchez-Polo, 2007] 

Regeneration with NH4OH (0.02 M) 

First absorption process 

Second absorption process 
Memorandum 

September 30, 2015 

Page 20 

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

 Therefore, this study demonstrates that silver-doped aerogels are a possible use for 

removing bromide from drinking water intake (Lake Zurich water); however, more studies are 

needed to determine whether this type of sorption media would 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 water source of a drinking water plant) and 

deionized water through aluminum (Al(III)) coagulation. The bromide removal efficiency was 

examined at varying pH, aluminum concentrations, bromide concentrations, and concentrations 

of anions (i.e., SO4

2-). The coagulation removed between 62.1 and 87.8 percent of bromide in 

raw water and between 82.8 and 99.2 percent of bromide in deionzed water. However, when 

other anions were added to the raw water the bromide removal efficiency decreased. For 

example, the following represent the percent decreases in bromide removal efficiency that were 

observed when the specific ion was present: 

• Nitrate (NO3

-

): 8.0 percent decrease in bromide removal; 

• Bicarbonate (HCO3

-

): 11.5 percent decrease in bromide removal; 

• Chloride (Cl-): 14.6 percent decrease in bromide removal; 

• Sulfate (SO4

-

): 21.2 percent decrease in bromide removal; and 

• Dihydrogen Phosphate (H2PO4

-

): 40.8 percent decrease in bromide removal [Ge, 2008]. 

9.4 Electrochemical Removal 

 A bench-scale study performed by the University of California, 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-polar carbon electrodes with a 

diaphragm to separate the anode and the cathode, while the Kossuth process uses dipolar carbon 

electrodes without a diaphragm. Both processes remove bromide by oxidizing the halogen to 

bromide, then heating and air stripping to volatize the bromide [Kimbrough, 2002]. 

2 Br - → Br2 + 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 an upflow sand clarifier, and filtered 

through a deep-bed anthracite coal filter. This study estimated that the costs for a demonstrationscale electrolytic reactor would be $1,549 - 2,099 per million gallons of water treated 

[Kimbrough, 2013]. The earlier report published on this pilot-scale 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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