## EPRI Assessment of Past EPRI FGD Water Characterizations Introduction

The US EPA recently announced its intention to conduct a two-year study to determine whether the Steam Electric Categorical Effluent Guidelines should be revised. An element ofEPA's two-year study

### will involve data collection at various sites to provide some data on waste streams from power utilities. To provide information to the EPA inits Effluent Guidelines Study, the Electric Power Research Institute (EPRI) is providing the results from its earlier research studies which attempted to characterize powerplantFGD wastewater streams at a limited number offacilities. EPRI's efforts were research oriented, and the objectives of thevarious studies differed. The samplingprotocols between the studies varied significantly and the FGD systems evaluated also differed. Because of these potentialissues, EPRIbelieves it is critical to provide ourperspectives on

### the results of these studies. The following documentis an evaluation of the FGD wastewater data obtained during the subject EPRI field studies. The evaluationincludes a critical assessment of the data quality and collection techniques based on insights gained during and after the studies. This evaluation reflects how representative the data set is of Steam Electric Utility industry's FGD wastewater as a whole, and includes key lessons learned in attempting to characterize powerplantFGD wastewater accurately. 

## Overview of EPRI FGD Studies
In 1988, EPRI initiated the PowerPlant Integrated System·Chemical Emissions Study (PISCES) project to characterize the distribution of trace substances in air and liquid streams from fossil-fuel-fired electric utility powerplants. The originalPISCES program included study of trace substance concentrations in internal and effluentwastewater streams in fossil-fuel power plants. However, the PISCES sites gave only limited insight on wastewater from FGD systems. As described in our earlier March 9, 2007 assessment, at the time of the PISCES field studies, mostpowerplants did notemploy wetFGDs and only 3 of the 7 sites employed FGDs. Two sites (Sites D and F) had FGDs with once-through systems rather 

### than recycling absorber 

### slurrywhichis more representative ofmost,butnot all, new FGDs. A third site (Site E) had FGDs built in 1982 and 1995 that were operated more conventionally, but only one sample was collected. Therefore, with the recent wave ofnew and planned FGD installations, EPRI recently conducted additional FGD studies to better characterize this wastewater stream. 

## FGD Screening Study (1010162) Report Overview As power plantsbegan to install FGDs in response to the CAIR (Clean Air Interstate Rule), CA VR (Clean Air Visibility Ru1e), and CAMR (Clean Air Mercury Ru1e), EPRI initiated a "screening" study to evaluate thepotentialissues associated with FGD wastewater. The



### 1results are summarized inthe EPRI report- Flue Gas Desulfurization (FGD) Wastewater Characterization: Screening Study ("Screening Study"). This report summarizes and evaluates the results of grab samples ofFGD wastewaterfrom
seven facilities collected inJanuary to December 2005, and incorporates the earlier PISCES data from Site E. Samples were collected ofthe FGD wastewater at a point that the facility felt was representative ofits final FGD wastewater entering the site's overall wastewater management (such as an ashpond). At sites thathad no discharge ofFGD wastewater (Sites P, RandY), they were asked to collect water from a location similar to where FGD wastewater wouldbe discharged at otherfacilities. Sampling locations are described in Table 1-1 ofthis report. In order to minimize costs for this study, EPRI requestedpowerplantpersonnel or other EPRI contractors on-site (primarily conductingflue gas measurements) to submit wastewater samples to a common laboratory for trace metals analyses. Samples were collected and sentunfiltered, unpreserved and on ice to the CH2M HILL Analytical Laboratory. Three samples were generated for each site: a "total" sample generated by shakingthe liquid, a settled sample generatedby decanting water onehour after the shaking, and a filtered sample of decanted water passed through a 0.45-micron filter. No data outliers were noted. No matrix interference was documented, as the laboratory addressed interference issues by diluting samples, up to 100 times, to keep the major chemical interferants (such as Ca, Mg, AI, Fe) in the range inwhich they couldbe quantified. 1hiswas definedby quarterly Linear Dynamic Range studies on the analytical instrument. Ifan element such as calcium was above this range, the sample was diluted until the elementwas within therange. Getting a result within this range was necessary so that the result could be used in inner-element correction factors for the trace metals.


### Report Limitations In the Screening Study, the objective was to determinepotential wastewaterissues, and this work was conductedunder a limited budget. The limitations in this Study include:

o Available personnel (either site personnel or EPRI contractors conducting air studies) were used to collect FGD wastewater samples at the seven facilities; the water discharged to theirlarger wastewatermanagement systems was targeted.

o Because samples were collectedbyplantpersonnel, the quality of sampling is not known, and consistency of approachis not certain. Sample collectors were instructed to collect atleast 2 gallons in a 5-gallon cubitainer and ship the sample to the laboratory. Samples were collected and shipped on ice to an off-site laboratory, where they were filtered several days after being collected which couldhave affected the partitioningbetweenthe solids and aqueous phases for various metals.

o There were large variations between facilities' FGD systems, especially the solids separation and wastewater treatment. These variations in system configuration and samplingpoints led to widelyvaried samples. The 8 data sets represented vastly different levels of solids removal, rangingfrom -35 to 170,000 mg/L total suspended solids (TSS).

2 

# . ' 'o The focus was on limestone-based FGDs to the exclusion ofother types of FGD. However, there 

### was no "bigpicture" design indetermining the sites so that the set represented a range ofcoal types and powerplant/FGD designs. Fewnew FGDs
were yet installed and operational during the time ofthis study, so all the FGDs tested were older designs, i.e. began operation before 1996.

o No FGDs were tested with a wastewater treabnentsystem specifically designed for trace metals removal. Due to these limitations, EPRI believes that these data shouldnotbe usedby the Agency in its Effluent Guidelines Study. EPRI's primary concern is the partitioningbetween dissolved and particulate trace metals due to possible issues withlaboratory and field filtration. The mercury data are the most uncertain,primarilybecause data exist that suggest differentlevels ofmercurypartitioningto the dissolved and particulate fractions. This is discussed in more details on the Samplingand Analytical Methods Section. While the total trace metalresults are likely notimpactedby the filtration issues, the variation in the 1SS levels between the eight samples could directly impact the total trace metal concentrations. 

## Guidance Manual (1 013313) Report Overview To assist powerplants in assessing future FGD wastewater managementissues and to develop solutions, EPRI prepared 

### EPRI Technical Manual: Guidancefor Assessing Wastewater Impacts of FGD Scrubbers whichprovides an overall look at FGD wastewater including its composition, variables affecting composition,how to evaluatepotential regulatory limits, FGD wastewater management options includinghow FGDwastewaterwill impact ash ponds, and other FGD operationalissues. FGD wastewater characterization data from the Screening Study were used, and thus no new wastewatercharacterizationdata are presented. Laboratory treatability testing ofFGD wastewatercollected from four sites was described. These samples were from four of the sites inthe Screening Study; however, the liquid was collected from a pointinthe FGD system that differed from the samples in the Screening Study, each was from a consistentpointofthe hydroclone overflow. Analyses of the water produced during treatabilty testing were done in the CH2M IDLL Analytical Laboratory. 

### Report Limitations 1his Guidance Manual incmporates the earlier data from the Screening Study, and thus there areno new FGD wastewatercharacterization data. The treatabilty testing results were limited by the small number of FGD wastewater samples available. One sample 

### was from a small Chiyoda FGD system, the other three were limestone forced oxidation systemsbuilt between 1985 and 1995.



### 3

## Fate of Mercury (1 009955) and Update on Enhanced Mercury Capture 

## by Wet FGD (1012673) Report Overview To address issues withmercuryflue gas "re-emissions" as well as potential issues with the management ofmercury in the FGD solids and gypsum, EPRI conducted a series of investigations to characterize the fate ofmercury inwetFGDs. This workis summarized in two EPRI reports: The Fate ofMercury Absorbed in Flue Gas Desulfurization (FGD) Systems and its update in Section 3 ofUpdate onEnhanced Mercury CapturebyWet FGD: Teclurical Update. These reports summarized the status of a multi-plant assessment of mercury partitioning inFGD systems. Only mercury and cations and anions were reported in these reports. Results arepresented for water at various points in the FGD system, though not specifically for the final wastewater produced. The information in the update is not the final product of the study, so some data areas are notyetcomplete. Two other studies are summarized in the Update, which focus on re-emission ofmercury from FGD liquid back to FGD outlet flue gas.
Inthe Fate ofMercury study (1009955 and 1012673), samples were collected by EPRI's contractor, URS. Samples were collected and filtered on-site using a 0.7-micron filter. The focus ofthese two reports are on mercury since the objective was to understand the mercury chemistry in the FGD water management system as to optimize flue gas mercury removal as well as to assist inmanaging the mercury in the FGD solids. Samples were collected from several locations in the FGD system from seven sites reported in the first report (1009955). Sample location varied between sites due to differences in the plants. Liquid sample locations included FGD absorber slurry, thickener overflow and underflow, primary and secondary hydroclone overflow and underflow, and "otherliquor" (belt filter filtrate, pond discharge water, and wastewater treatmentplant effluent). Samples
were collected from a total often FGD systems (at seven sites) reported in the update (1012673). Results are presented for the absorber liquor. Additional information from this evaluationwillbepresented inlater reports. Samples were collected, filtered on-site, preserved and sent to URS laboratories for mercury and otherconventionalwater parameters analyses.


### Report Limitations The key objective was to understand the FGD mercury chemistry, and thus the results are primarily limited 

### to mercury. The sites were selected to represent a range of FGD designs and operating conditions, such

### as reagent 

### type, oxidation mode, 

### fines blowdown, and coal type. The limitations 

### in the sites selected are thatmost ofthe FGDs are older design (only
onebuilt after 1996), and only one of the sites was tested with the SCR in operation. Note four sites were tested in the non-ozone season with the SCR off-line. For the one power plantwith the 

### SCR on-line, this site measuredflue gas mercury removals of about35%

- as compared to otherEPRI, DOE, EPA, et. al. studies 

### that indicate that for bituminous coals, the SCR/FGD combination were able to achieve**~85%** flue gas removals. Thus EPRI believes thatthe tested SCR site may notbe representative ofotherbituminousplants with SCR and wet FGD.



### 4The Update 1012673 sununarizes the results of an evaluation ofvaryingfield filtration and preservation techniques;however this evaluation did notinclude the limitation of laboratory-filtered samples. 

## Sampling Methods, Locations, and Overall Representativeness

For the FGD wastewater characterization studies, EPRI partneredwithvarious host utilities thatvoluntarilyparticipated. Because ofthis, the sites sampled werebased inlarge part on a willingness to participate. Few ofthe newer FGDs were yetinstalled and operational during these studies, so most ofthe FGDs tested were older designs, i.e. only one ofthe FGDs tested began operation after 1997. Therefore, the overall representativeness is focused
on older generation FGD systems, and notthenewer systems being installed this decade.

To help encourage participation inthese wastewater characterization studies, EPRI agreed to notidentify thename ofthe utility and the powerplant. A description of the FGD studies is provided in Table 1.

Table 1 SummaryDescription ofEPRI FGD Wastewater Characterization Sites FGD Liquid- Year Solid FGD Sampling Separation SCR Online srte Location Process TypeofFGD FGD Mfr. ? Coal Screening_ Studr_£10101621 E* Sludge fixation Thickener Umestone, Babcock& N Bituminous 1982 & process inhibited Wilcox 1995 overflow and oxidation with (B&W) waste sludge fixation p Downstream of Thickener Limestone, natural CE y Bituminous 1996 FGD blowdown oxidation (Combustion

holding tank, Engineering) upstream of

thickener R Between FGD Thickener Limestone, natural MHI y Bituminous 1983 blowdown holding oxidation tank and thickener 

## s· From primary Primary Limestone forced Company· y Bituminous 1985 hydroclone hydroclone oxidation designed (B&W overflow, before (water also assistance on sent to ash pond wasted from the upgrades • gypsum trays) dewatering

press)

5Table 1 Summary Description ofEPRI FGD Wastewater Characterization Sites FGD Liquid- Year Solid FGD Sampling Separa'lion SCR Online Site Location Process Type of FGD FGDMfr. ? Coal

T No distinct chloride Primary Limestone ex-situ ABB y Bituminous 1990 purge stream. hydroclone forced oxidation Collected from

tank which contains a mixture of -60% primary hydroclone overflow, belt rinse water, and hydroclone underHow water. 

### u At reclaim tank Thickener Limestone, natural ABB N Sub- 1992 (which is after the oxidation Bituminous thickener which removes nearly all solids) y Downstream end Gypsum stacking Limestone, forced Chlyoda and N Bituminous 1992 of the 3rd gypsum pond oxidation owner

stacking pond 

## z· From tank Overflow from Limestone, ABB/Aistom N Bituminous 1995 beforeWWTP primary forced oxidation (overflow from hydroclone

the clarifier) goes to a clarifier The Fate ofMercuryAbsorbed In Flue Gas Desulfurization (FGO) Systems (1009955) from Table 2-1



### 1 Thickener, Mg-lime, ex-situ Wheelabrator y High-S 1980 hydrocyclones, forced oxidation /Pullman- Bituminous belt filter Kellogg 4 Thickener Mg-lime with Marsulexl y High-S 1976, combined Chemico Bituminous 77 particulate removal, inhibited oxidation 

### 6 

### ** Hydroclones, Limestone, GEESI/ y High-S 1994 two stage, belt forced oxidation Marsulex Bituminous filter 

### 7 Hydroclones, Limestone, GEESI/ y High-S 1995 belt filter forced oxidation Marsulex Bituminous 

### 8 Thickener, Limestone, Wheelabrator N TX lignite 1985 drum filter inhibited /UOP oxidation 

### 9 

### ** Thickener, Umestone, Whee!abrator y High-S 1977 drum filter inhibited /UOP Bituminous oxidation 

### 10 Thickener, Limestone, CE/Aistom N Sub- 1992 belt filter natural oxidation Bituminous Urzdate on Enhanced Mercua. CaQture br: Wet FGD £1012673l from Table 3-1



### 6Table 1 Summary Description ofEPRI FGD Wastewater Characterization Sites FGD LiquidSolid Sampling Separation Site Location Process Thickener



# . Thickener

1---- Sampled FGD absorber liquor, Thickener
as well as overflow and 

### * underflow of Hydroclone, twoliquid-solid stage



## - separation Hydroclone, one- devices stage * Hydroclone, onestage



# .. Hydroclones, two-stage; belt filter Notes: ABB

- Asea Brown Boveri B&W = Babcock and Wilcox Company DOE 

### =U.S. Department of Energy FGD = flue gas desulfurization MG = million gallons MHI

- Mitsubishi Heavy Industries TypeofFGD Mg-lime, External forced oxidation Limestone,

inhibited oxidation Limestone, natural oxidation
Limestone, forced oxidation Limestone, forced oxidation Limestone, forced oxidation Limestone, forced oxidation SCR FGD Mfr. ? Coal

GEESI/ N High-S Marsulex Bituminous

B&W N High-S Bituminous

Pullman- N SubKellogg/ Bituminous Wheelabmtor ABB/Aistom N Medium-S Bituminous ABB!Aistom N Medium-S Bituminous American Air N High-S Filter Bituminous GEESI/ y High-S Marsulex Bituminous

PRB 

## =Powder River Basin S =sulfur WWTP = wastewater treatment plant Year FGD Online

1994

1995

1979/ 1980

1994/ 1995 2001

1982/ 1985 1994

* - Site tested in both the Screening Study and Fate of Mercury Studies **

- Site tested in both the 2005 and 2007 Fate of Mercury Studies.

Watermanagement varies widely between FGD systems, and therefore there is a wide range in the quantity and characteristics ofthe wastewater generated. Inevaluating whether the FGD sites studied representFGDs across the industry as a whole, it is useful to understand what factors may affect FGD wastewater (for full discussion, see Section 2 ofthe Guidance Manualr 1013313).

• Fuel characteristics: Variation incoal characteristics can affect FGD wastewater metals content, especially for those metals likely to significantlypartition from the coal to the flue gas vapor phase entering the FGD. Coal chloride level (specifically the ratio ofcoal chloride to sulfur) typically drives the amountofFGD wastewaterproduced as FGD operations are often controlled based on chloride levels.

• Liquid/Solid separation technology: There is a wide range ofliquid/solid separation devices inuse for removing solids from the recirculated FGD liquid. These canproduce wastewater with very different solids content.



### 7

### • Oxidation and Organic add additives: Limited data suggestthat organic acid additives (e.g. dibasic acid orDBA) may affect the speciation of selenium. Most, ifnot all, new FGDs use forced oxidation which may affect selenium speciation.

• Gypsummanagement: If

### gypsumproduced in an FGD is 

### sold for wallboard production, itwill likelybewashed, sendingmore fine particulate matter to the FGD wastewater stream.

• Reagant and/or sourcewater characteristics. Lime, limestone, and otherreagents will 

### introduce varying amounts of solids and trace metals. Most, if

### not all, new FGDs use limestone. The impact ofthe trace metal loadings in

### the reagent (e.g. limestone) on the trace metal loadings in 

### the wastewater is 

### notknown. 

### Our review ofthe available data and comparison with the overall industryidentified the following gaps and analytical needs.

• Most ofthe EPRI FGD field study systemsbegan operationbefore 1997. FGD design has evolved over thepast30 years, e.g. high-efficiency S02 removal absorber designs as well as employinghydroclones instead ofthickeners for solids separation. Newer FGDs have much tighterwaterbalances than the older technologies and therefore tend to discharge at much lower flow rates.

• For the data available, none ofthe EPRI FGD sites included a wastewater treatment system designed specifically for trace metals removal. Two ofthe later Fate ofMercury Study sites did sample atvarious locations around the wastewater treatment system and these analyses are on-going.

• Itis 

### critical to understand the impact of on-site filtration as comparedwith laboratory filtration, but there hasbeen no study yet making this 

### comparison. This 

### could be importantfor mercurybecause itmayhave differentpartitioningbetween dissolved and particulate based on the limited available data with field filtering versus those with lab filtering. No data are currently available to assess if

### othermetals had differences in partitioningbetween the two filtration methods.

• A massbalance of all streams into and out ofa FGD wastewater system shouldbe done to betterunderstandpartitioning ofmetals thatpass through an FGD system. 

## Sampling and Analytical Methods: Lessons Learned
The FGD field studies provide useful insights inconducting future sampling and analytical studies. Guidance hasbeenprovided to EPA in 

### a separate report "Sampling and Analytical PlanGuidance for Water Characterization of Coal-Fired Steam Electric Utility Facilities" dated March 2007, "Supplemental Information: Sampling Coal-Fired Electric Power Plant Wastewaters" dated May 17, 2007, and 

### "Summary ofPowerPlantWastewater Matrix Interferences and Suggested Remedies" dated March 30, 2007. Information on mercury partitioning and arsenic and selenium speciation specific to the FGD studies is 

### presented below.

8 ' 

## .

## Mercury Partitioning The partitioning ofmercury within the FGD system is important, since mercury that partitions into solids will likely be removed in the gypsum stream and inthe solids separated outofthe FGD wastewater stream. Therefore the mass ofmercury in the wastewater stream discharged from the FGD wouldbemuchlower than the total mass captured by the FGD. The various studies described herein each collected some information towards understandingpartitioning ofmercury, however, differences intheproject objective and approachbetween the studies makes itdifficult to draw definitive conclusions. The plants visited had different types ofFGD systems, differing powerplant designs such as SCR operation, differing coals, and differentwatermanagement approaches. Sample locations also differed, as is 

### shownin Tables 1 and 2. Ofpotential importance were the differences in samplingmethods. One studyincluded field filtering while 

### the other studyused lab filtering. Lab filtering simplified the sampling effort and mayhave reduced the likelihood ofcontamination. However, the several days that the samplewas allowed to sit mayhave allowed mercury to partition from dissolved intoparticulate form in shipment. The total mercuryin FGD wastewater was relatively similarbetween the studies, as is 

### shown in Table 2. However, thepartitioning between liquid and solid phase varied widely. In 

### the Screening Study, nearly all mercury in the wastewater was in 

### particulate form. However, in the Fate ofMercury Study, samples were filtered on-site- and indicated a wide range ofmercury in theparticulate fraction, varying from 20 to 99%. This 

### difference inthe mercury partitioning maybe related to the differences in the filtration approach and/or differences in the powerplants tested. Thus EPRibelieves the dissolved/particulate mercury data from the Screening Studyincludes significantuncertainty and recommends to the 

### Agency 

### that these results notbe used in

### its Effluent Guidelines Study.

Table 2. MercuryPartitioning Comparison Between Studies Parameter Fate of Mercury Study Screening Study

**~otal** Mercury''" (J.'9/L) 

## p.s to 79 (median "" 17) 1 to 48 (median = 7) Partitioning % of mercury in 20 to 99% solids in absorber liquid for the S2% to 99% particulate* solid or particulate form in limestone forced-oxidation systems FGD wastewater or absorber

**~6** to 99% in the other systems iquid
Method of filtering Field filtered with a 0.7 micron filter Lab filtered with a 0.45 micron filter Sampling location that best pyertlow from the dewatering device such !sites were asked to sample the represented wastewater from 

### as hydroclone orthickener

**~stewater** produced and sent to FGDsystem reatment. For several sites, where r.vastewater was not discharged, the

**~ample** was taken from a location

**~ere** wastewater could be blown

**~own.** SCR? pnly tested one FGD with an SCR on-line

**~** sites had SCRs, 4 did not

*- Particulate fraction of for those samples with typical suspended solids loading (two sites had <40mg/L TSS and correspondingly had low percent particulate mercury: 5% and 56%)

••- It should be noted that this set of data come from varvina sample locations and using different methods for



### 9filtration so care is needed in comparing the data points.


## Analytical Procedures including Arsenic and Selenium Speciation A finding of the Screening Studywas that forced oxidation systems mayproduce selenium primarily in the oxidized selenate form, while other FGDs produced the reduced form selenite. This 

### wouldbe significant as selenate is more difficult to treat, though less toxic, then selenite.
The arsenic and selenium speciation methods used in the FGD studies varied. In

### the Screening Study, Sites Rand U used the inductively coupledplasma mass spectromeiry (ICICP-MS) method, while Sites Sand T used the hydride method (EPA 1632). See the "EPRI Assessment of the PISCES Water CharacterizationStudies" letter dated March 9, 2007 for further discussion of speciation methods. Furtherresearch is needed to confirm these arsenic and selenium speciation trends. 

## Key Observations and Lessons Learned
There are a number ofpotentialvariables thatmay impact FGD wastewater, including coal properties, FGD type, source water, and FGD operation. There is potentiallyvery wide variability in 

### FGD wastewater characteristics as coal usage changes and due to cycles of concentration used for blowdowninFGD system operations. Because a number ofnew FGDs are nowbeing installed, it is

### important to understand how older (i.e. 1980's vintage) and currentFGD designs may impactwastewater characterization. In 

### addition to the S02- removal efficiencies, FGD systems mayvary widely in 

### the waywater is 

### managed in terms of solids removal (percent solids), method of solids removal (hydroclones, thickeners, and settlingponds), how theblowdown is managed to control chlorides and/or fines, where the blow down stream is taken, and trace metals treatment (settling pond, iron coprecipitation, constructed wetlands). All ofthese factors mayresult in a wide range ofwastewater characteristics between facilities. The EPRI studies to characterize FGD wastewaters havebeen oflimited scope and duration (typically 1 to 3 sampleseach). Therefore, conclusions based on the studies maynotbe generally applicable to the rest ofthe industry, and in 

### fact, none ofthe collected samples are fully representative ofthe newer FGD technologies currentlybeing built. The key lessons learned during the studies include:

• Sampling: It is 

### vitally important to design and documentproper sampling and analysis protocols inadvance ofanyFGD sampling. 

### Itis 

### imperative to understand the operation ofthe system in 

### order to collect representative wastewater samples. If

### planningwith site personnel is limited tothe phone,it is 

### challenging and shouldbe done withprocess flow diagrams or other tools to clarify sampling locations. Further, itis

### recommended that fuhrre samplesbe collected ofwastewater at the discharge from the FGD (as was done in the Screening Study),but also ata point that can be standardizedbetween facilities to allow cross-plantcomparisons.

10 • I

### • Analysis: Analysis ofFGD wastewater 

### is very complicated due to matrix interferences
as was discussed in the March 30, 2007 EPRI "Summary ofPower PlantWastewater Matrix Interferences and Suggested Remedies" memorandum to EPA.

• Mercury: The various studies employed different sampling and filtration techniques, and tested different sites. The number of variables makes the results difficult to interpret and compare across thevarious sites. Based on the limited available data, laboratory filtration 

### may impact the partitioning ofmercurybetween the dissolved and particulate fractions. Additional researchisneeded to betterevaluate the various filtration approaches.

11