arsenic removal technologies and the effect of source water quality on performance

8/3/2019 Arsenic Removal Technologies and the Effect of Source Water Quality on Performance

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y~n~.l*8~ . .SAND REPORT

echnologies and theEffect of Source Water Quality onD?rforp CP

A Prepared bySandia NationaAlbuquerque, NSandias laborat nion.a Lockheed pEirtin Company. oEnergy underContract DE-ACW- d

ved for publ&..phse; 8Iionunlimited.*. .> ,..,, .National lat,,dories


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Issued by Sand ia National Laboratories, operated for the United States Department of EnergyySandia Corpxation.NOTICE: Thi s report was prepared as an account of work sponsored by an agency of the Unitedtheir employees, norany of heir contrac tors, subcontractors, or theiremployees,make anyStates Government. Neither the United States Government, nor any agency thereof, nor any ofwarranty, express or implied, or assumeany egal iability or responsibility for the accuracy,completeness. or usefulnessofany information, apparatus, prcduct, or processdisclosed, orrepresent that its use would not infringe privately owned rights. Reference herein to a n y specificcomm ercial product, process, or service by trade name, trademark, manufacturer. or otherw ise,does not necessarily WnStiNte or imply its endorsement, recommendation, or favoring by theUnited States G o v e m n t , any agency thereof, or an y of their contractors or subcontractors. Theviews and opinions expressed hexein do not necessarily state or reflect those of the United StatesGovernment, any agency thereof,r any of their contractors.Printed in the United States of America. This report has been reproduced directly from the bestavailable copy.Available to DOE and DOE contractorsrom

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SAND2002-2423Unlimited ReleasePrinted July2002

Arsenic Removal Technologies and the Effect of Source Water Qualityon Performance

Nadim Reza Khandaker and Patrick Vane BradyGeochemistry Dept.

Sandia National LaboratoriesP.O. Box 5800Albuquerque, NM 87185-0750

Abstract

Arsenic removal technologies that are effective at the tens of ppb evel ncludecoagulation,ollowedy settling/microfiltration, ion exchange by mineralsurfaces,ndressure-drivenembranerocessesreversesmosis,nanofiltrationndltrafiltration).hiseportescribes the fundamentalmechanisms of operation of the arsenic removal systems and addresses hecritical issues of arsenic speciation, source water quality on the performance ofthe arsenic removal systems and costs associated with the different treatmenttechnology categories.

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TABLEOF CONTENTSPage

1 02.02.12.2

Abstract................................................................................................................... 3htroduction........................................................................................................... 5Fundamentals of Arsenic Removal Processes......................................... 6

Coagulation Using Metal Salts.......................................................... 6Adsorption Processes ......................................................................... 8

Aquatic Chemistryof Arsenic

2.2.1 Activated Ahmina.................................................................... 92.2.2 lon-exchange........................................................................... 102.2.3dsorptionoron-oxyhydroxideurfaces ........................ 112.2.4 Manganeseioxideoatedand ...................................... 112.3 Membraneeparationrocesses ................................................... 123.0 Oxidizing Agents Usedn Preoxidation of Arsenite to Arsenate........... 134.0 EffectsofWater Quality on Performance..................................................... 145.0 Cost of TreatmentandResidualHandling ................................................... 166.0 References................................................................... "................................... 17List of Figures

1 Eh-pHdiagram for ArsenicSpecies ............................................................ 52Thecoagulation settlinghicrofiltration process for arsenic emoval ... 73Sorptionprocess for arsenic emoval .......................................................... 94 Membrane systems for arsenic emoval ..................................................... 13

List of Tables1 Effect of water quality parameters on treatment........................................ 152 Estimated capital and operating costs of different arsenic...................... 16

removal technologies with the design capacityf 2.3 mg


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I O IntroductionAquatic Chemistry of Arsenic

Arsenic is a metalloid found in group V of the periodic table, along with nitrogen,phosphorus, antimony, and bismuth. Arsenic can occur in water in four oxidationstates: +V (arsenate), +I11 (arsenite), 0 (arsenic), and -111 (arsine) (Clifford andZhang,1993). In oxygenatedwaters,hepredominantorm of arsenicsarsenate, which hydoxylizes into anionic forms - H~AsO;, HA SO^", or AsO4 (5< pH


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2.0 Fundamentals of Arsenic Removal

2.1 CoagulationUsingMetal SaltsEdwards 1994)definesarsenic emoval romwaterbycoagulation as theconversion of dissolvedrsenic to insoluble products byheombinedmechanisms of precipitation, co-precipitation and adsorption. Precipitation is theinsolubilization of contaminantsyxceeding the solubilityroduct. Co-precipitations the incorporationofsolublearsenicspecies into agrowinghydroxide phase, via inclusion, occlusion, or adsorption and adsorption is theformation of surfaceomplexesetweenolublersenic and theolidoxyhydroxide surface sites (Edwards, 1994),e.g:=Fe-OH + H + HzAs04-+ =Fe-H2As04 + Hz0 (arsenate sorption)=Fe-OH + H++ H~As03+ =Fe-HzAsOs + Hz0 (arsenite sorption)Where:=Fe-OH denotesasurfacesiteexposedat heoxyhydroxide-waterinterface. The trivalent metal salts used for arsenic removal by coagulation arealum and ferric salts (see reviews of Harper et al., 1992, Cheng, et al., 1994,Edwards,1994,Scott et al.,1995,Hering and Elimelech,1996,McNeillandEdwards, 1997 and Banerjee et al., 1999). Under comparable conditions (pH,arsenic concentrations, coagulant type and coagulant dosage), As (111) removalefficiency is less than that of As (V). This is because below a pH of 9.2, arsenic(Ill) exists n the uncharged form asH3As03 and thus is not electrostaticallyfavored to form to any great extent to the positively charged metal oxyhydroxidesurface. In the treatment of groundwater containing arsenic (111) and arsenic v),species oxidation is therefore, a required pre-treatment step.Figure 2 summarizes the process of arsenic removal using alum and ferric salts.The treatment train for arsenic removal from groundwater requires a preoxidationstep to convert all the arsenite to arsenate, pH adjustment for enhancement ofcoagulation ollowedby coagulation toconvertdissolvedarsenic to insolubleproductsnd settlinglmicro-filtration to removehensolubleroducts of

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coagulation. In general, greater arsenic removal is achieved by coagulation withferric salts with than alum salts at near neutral pH. Greater process attention isrequired for aluminum han iron saltsbecauseof hedifferentialsolubility ofAI(0H)s. In eneral, perationaleatures critical to rsenicemoval fromgroundwater using coagulation settling/microfiltration are pH, coagulant type anddosage, oxidant addition, efficient mixing of coagulant with source water nd rateof settling/filtration. Naturally occurring organic matter, competing ons such assulphates, nitrates, phosphates and silicates can decrease the removal efficiencyof arsenic by coagulation. by nterfering or by competing for binding sites on thecoagulant sulface. Researchershavealsoshown hatpresence of certaindivalent metal ions in water can enhance the process of removal of arsenic fromwater by coagulation ettlinglmicrofiltration.

OXIDANTOAGULANT!i !' RAPIDMIX Arsenicf ree waterj !ii

iRaw ----- * 't $.-T-.m SETTLING "7

BASIN IIIIIIII

water j IIIIIIII MICRO-FILTRATION

pHADJUSTMENT t ___----- -__-______IFigure 2. The coagulationsettlinglmicrofiltration process for arsenic removal.


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2.2 AdsorptionrocessesAdsorption is a mass transfer process in which a substance is transferred fromthe liquid phase to the surface of a solidwhere it becomes bound by chemical orphysicalorces. In the case of oxyanions,suchasarsenate and arsenite,adsorption occurs on the oxide water interface by forming a complex with surfacesites hatmay be positivelycharged, such asaprotonatedsurfacehydroxylgroup. In othernstancesheeactionmaynvolveigandxchangemechanism in which the surface hydroxyl group is displaced by the adsorbing ion(AWWA Research Foundation, 2000). The adsorption eactionmechanismofarsenicspeciesonto solid metaloxyhydroxidesurfacesmay be genericallyrepresented by (AWWA Research Foundation, 2000 and Edwards, 1994):=S-OH + H* + HzAs04-+ =S-H2As04 + Hz0 (arsenate sorption)---OH + H' + HzAsOY -+ S-HzAs03 + Hz0 (arsenite sorption)Ion-exchange s a special case of adsorption where onic species in aqueoussolutionare emovedbyexchangeonsofasimilarchargeattached oasynthetic resin surface.Adsorption processes commonly used in water reatment are: adsorption ontoactivatedalumina, on-exchange, ronoxyhydroxides and manganesedioxidecoated sand. (Banerjee, et al., 1999, Torrens, 1999). Figure 3summarizes thetypical treatment set-up for sorption process for arsenic removal. The efficiencyof each media depends on operating conditions, such as: pH, the presence ofinterfering ions, speciation of arsenic, system dependent parameterse.g., emptybedcontact time,surfaceoading ates,bed-porosityetc.) and the use ofoxidizingagent(s) in thepre-treatment rain. ngeneral,As (V) iseasier toremove from water, since it has a residual negative charge above a pH of 2.2and isattractedopositivelychargedmetalhydroxidesurfaces.As (111) isuncharged in most natural waters below pH 9.2 and has no charge affinity tosurfaces. The charge neutrality makes it difficult to remove As (111) from naturalwaters (Edwards, 1994).


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OXIDANTIIII

ARSENIC FREEWATER

water -aw -3 II SORPTION COLUMNIpH ADJUSTMENT

Figure 3. Sorption process for arsenic removal.2.2.1 Activated AluminaActivated alumina is known to be effective in the removalof arsenate, but pH hasa strong effect. The optimal pH range for arsenate removal is5.5 o 6.0. Abovea pH of 8.2 (point of zero charge (ZPC) below which activated alumina surfacehas a positive charge and above which activated alumina surface has a negativecharge and acts as a cation exchanger) arsenate removal efficiency decreasesgreatly (Clifford, 1990). For feed water at or near neutral pH, adjustment of pHmay be necessary for effective arsenate removal. The adsorption capacity andbed breakthroughsdependentonhepHofhenfluentwaterand theconcentration of arsenic in the feed water.The ability of activated alumina to remove arsenite s considerably ess hanarsenate and breakthrough occurs faster (Frank and Clifford, 1986). Adsorptioncapacity is dependent on pH. Maximum adsorption occurs at a pH of 6, whilearound neutral pH, the adsorption capacity decreases greatly (Clifford and Lin,1991). Surface oxidation of arsenite to arsenate may occur to a small degree atthe activated alumina surface (Driehaus t al., 1995).

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Competitive ions have a less pronounced effect on activated alumina adsorptionthan heydo for ionexchangesystems.Phosphates and fluoridescompetedirectly for the exchange sites with arsenate. Sulphates, silicates, and chloridesalso reduce adsorption f arsenate to activated alumina (Rosenblumand Clifford.1984).Activated alumina is typically regenerated with a2-5% sodium hydroxide solutionand the bed is hen lushed with acid to re-establish a positive charge on thegrainsurface.Regenerationofactivatedalumina is moredifficult and lesseffective than ion-exchange regeneration (Clifford, 1986). With activated alumina,sites are saturated by arsenate ions that are irreversibly dsorbed to the sorptionsurface. Regeneration also reduces the active bed volume due to dissolution ofalumina (Ghurye et al., 1999).2.2.2 Ion-exchanaeIon-exchangemedium, ypicallysyntheticresins,aremade up of cross-linkedpolymermatricespossessingcharged unctionalgroupsattachedbycovalentbonding (Clifford, 1990). Both strong and weak base functional groups are usedto prepare ion exchangeresins.Strong base resins operateovera wide pHrange in contrast to weak base resins which are effective at acidic pH ranges(Clifford,1990).Theoretically,anionic ion exchange esins can removeonlyarsenate.Pre-oxidations equired for arsenite emoval FrankandClifford,1986).Anionexchangeesinsareegeneratedbylushingwith olutionscontaining weakly sorbing anion species uch as chloride.Ion selectivity s a key Performance ssue in ion exchange processes. For thisreason, anion exchange is not an attractive process for arsenic removal at hightotal dissolved solids (>500 mglL) and high sulphate concentrations (> 25 mglL).Atelevated otaldissolvedsolidsandsulphateconcentrations, on-exchangesystemsareproneoouling, decrease in performance ycle length andchromatographic peaking (i.e. effluent concentrations are greater han nfluentconcentrationsuringyclefperation).orxample,levated

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2.2.3 Adsomtion to Iron-oxvhvdroxide SurfacesThegenericmechanism for the removal of arsenicbysorptionontometaloxide--oxyhydroxide surfaces has been explained earlier. Both arsenate, and toa limited degree arsenite, are removed by iron oxyhydroxides.Adsorptionsofarsenateandarsenite have different ensitivitiesopH.LoweringhepHenhances the removal of arsenate, whereas arsenite removal is not affected bypH change (Edwards, 1994). The sorption capacityor arsenate can be twice thatof arsenite. Studies with packed columns containing ron oxyhydroxide showedthatarsenitebreakthroughoccursconsiderably aster hanarsenate AWWAResearch Foundation, 2000). For efficient arsenic removal from groundwater, theaddition ofoxidantand oweringofpHaround5.5-6.0should be astandardoperational procedure. Regeneration of iron oxyhydroxides can be achieved withsodium hydroxide, but complete removal ofall the arsenic attached to the surfacemay not be possible (AWWA Research Foundation, 2000). As in the case withactivated alumina, competitive ons have a less pronounced effect on arsenicadsorption to iron oxyhydroxide surfaces than they door ion exchange systems.Phosphates and fluorides directly compete or the exchange sites with arsenate.Sulphates,silicates, and chloridesalsoreduceadsorptionofarsenate to ironoxyhydroxide surfaces (Rosenblum and Clifford, 1984).2.2.4 Manganese Dioxide Coated SandManganesedioxide oated andMDCS) is preparedbyheoxidation ofmanganeseonscoatedon sand surfaces (Muny, 1974).Researchershaveshown MDCS has the ability to remove arsenic from water (Viraraghavan et al.,

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1999 and Bajpai and Chaudhuri, 1999). The mechanism s hought o involveoxidation of arsenite to arsenate followed by sorption (Oscerson et al., 1983 andTakamatsu et al.,1985, Bajpai and Chaudhuri,1999).Arsenic emovalwithMDCSs still in thedevelopment tageand uccess of thisprocess atcommercial scale s yet to be determined.2.3 MembraneSeparationProcessesPressure driven membrane separation process nvolves the forced passage ofwater through a selective membrane, which rejects undesirable species (refer to.Figure 4). The potential that controls the flux f water across the membrane (i.e.the driving force), is the difference in pressure across the membrane. In terms ofincreasingelectivity,ressurerivenembranerocessesnclude:microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis(RO).Separation in MF and UF membranesoccurs via mechanicalsieving,whereas capillary flow or solution diffusion s responsible for separation in NFand RO. It should be noted that as membrane selectivity increases, the requireddriving pressure increases (AWWA Membrane Technology Research Committee,1992).Both RO and NF membranes have high rejection rates at high flux for As (V). Inthecase of As (Ill), only RO and tight NFmembraneshavehigh rates ofrejection, but the rejection rate decreases with flux. Pre-oxidation enhances therate of removal of As (111) by NF. Substantial arsenic removal may be obtainedwith coagulation as a pre-treatment or use with membranes with largerpore size(Brandhuber and Amy, 1998).Removal ofarsenicbymembranes s ndependentof hepHof he nfluent.However, an operating pH of 5 to 6.5 is preferred to prevent deterioration of thecellulose acetate membrane. Co-occurring onic species generally do not affectmembrane processes; however, control of scale formation on membrane in hardwatersbypHadjustmentpH< 6) and controloforganicouling may be

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necessary for prolongedoperation of the membrane systems (Waypa, et al.,1997).

Semi-permeablemembranePressurizedfeed water---e-,

Arsenic freewater

Arsenic richReject water

Figure 4 Membrane Systems for Arsenic Removal.3.0 Oxidizing Agents Used in Preoxidation of Arsenite to ArsenateArsenitecan be oxidized oarsenatebyozone,chlorineandpermanganateunder given appropriate oxidant dosages and residence times, with ozone beingthe uperior xidant on an equivalentdosagebasis.Generally ompleteconversionofarsenite oarsenate can be achievedby he hreeoxidantsmentionedabove if an excess of thestoichiometricamount of oxidant isprovided. The theoretical stoichiometric equivalent oxidant for arsenite oxidationby oxidants are: 0.64, 1.41 and 0.99 mg of oxidanthng of arsenite respectively,for ozone, potassium permanganate, nd sodium hypochlorate.

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4.0 Effect of Water Quality on PerformanceGroundwaterypicallyncludeselementsotherhanarsenic,whichgreatlyinfluencesarsenic emoval in either an antagonistic (e.g., anions such asphosphate competing with arsenate in the removal echnology), or synergisticway (e.g., iron oxidation and precipitation which enhances arsenic removal). Theredox state of water and consequently he oxidation state of he anions andcations will dictate which chemical reactions are dominant. The three aspects ofwater chemistry, which nfluence reatment efficiency, are: matrix components,pH and redoxstate.Note first ofall hat heparentmineralogyof hesoilsthrough which the aquifer flows largely controls all of these through determiningthe onspresent;and hepresenceorabsenceofparticulatephaseorganiccarbon.Oxidationoforganic arbon onsumesdissolvedoxygen and canchange the edoxstate romaerobic to anoxic.Consequently,waters fromanaerobic aquifers will require more oxidative pre-treatment han waters romaerobic aquifers.

Arsenic emoval echnologyperformanceworksbetterwhenoptimized for aparticular water source. The optimization process may nclude design changesto the technology (i.e. increased hydraulic retention time) or the inclusion of pre-treatment to remove interferences from the influent water. Table1 is a summaryofwaterqualityparameters,whichmayaffect heperformance of arsenicremoval technologies. The impact of the water quality parameter dependsn thedegree ofeviationrom the optimumange. Also potential combinedinteraction(s) between two or more water quality parameters must be accountedfor.

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Table 1. Effectof Water Quality Parameters on Treatment.

rreatment:oagulation

4dsorption

on-Exchange

Pressure-drivenmembraneprocesses

Water Quality ParameterNeutral to high pH, variationin concentration andspeciation of arsenic,presenceof phosphates,sulfates, silicates, fluoride,iron and instances of hardwater.

Near neutral o highpH.variation in concentrationand speciationof arsenic,presence of phosphates,fluoride, sulfates. silicatesiron and manganese ions,and instancesof hardwater. High total dissolvedsolids (TDS) and naturalorganic matter (NOMs).Variation in concentrationand speciation of arsenic,presence of phosphates,sulfates, silicates,bicarbonate alkalinity, andfluoride, iron and hardwater. High total dissolvedsolids (TDS), NOMs.

Near neutral pH, iron andhard water. Presence ofNOM.

EffectAdjustment in pH, coagulant dosageandoxidant dosage will be required fromwell towellfor optimal removal efficiency and filter life.Presence of iron and hardness ions mayenhance arsenic removal efficiency but mayirreversibly foul filter media. Presence ofphosphate, fluoride, sulfate and silicate onsmay compete for oxyhydroxide surface sites.Arsenic sorption is highly sensitiveo pH andarsenic speciation. Variation n pH andspeciation will affect process efficiency nd bedlife. Phosphate, sulfate, fluoride and silicateions will compete with arsenic for sorption sites.Irreversible fowling due to high concentrationsof iron, manganese, and hardness isofconcern. HighTDS may cause media foulingand NOMs Presence of NOMs may enhancebio-fouling.

pre-oxidation is necessary, pH adjustment islon-exchange can only remove arsenic V), thus

such as phosphate, sulfate, fluoride, ilicate,not required between pH of 2 .2 to 11.Anionsand bicarbonate will compete or sorption Sitesand may contribute o chromatographicpeaking. Fouling due to the presence of excessiron and hardness is of concern. Precipitationof insoluble iron salts and calcium andmagnesium salts may oul media. High TDSmay cause media fouling and NOMs Presenceof NOMs may enhance bio-fouling.The concern is more towards membrane ifeoptimization and preventing membrane ouling.Adequate pretreatment and pH adjustment maybe necessary. Presence of NOMs mayenhance bio-fouling of membrane.

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5.0 Cost of TreatmentandResidualHandlingThe cost of treatment and residualhandlingsgreatlydependent on thecharacteristics of thegroundwater.Waterqualityparameters uch as pH,concentration of arsenic,speciation of arsenic and the presence of suifatesgreatly affect both capital and operating cost of the treatment system. Table 2illustrates the cost associatedwithreatinggroundwatercontaminatedwitharsenic.Thesereatment ostestimatesarebased on Albuquerque,NewMexico groundwater with design treatment capacity of 2.3 mgd (Chwirka et al.,2000).

Table 2. EstimatedCapital ndOperatingCosts of DifferentArsenicRemoval Technologies With The Design Capacity of 2.3 mgd(Chwirka et al., 2000).TechnologyapitalostncludingnnualOperatingostost (S) to Treat

~~ ~~~~ ~~~ ~~

ResidualHandling ($) IncludingResidual 1000gallonsHandling ($)I lonexchange I 5,243,000 1 447,000 1 0.53 I

Activatedlumina 4,557,00044,000adsorptionCoagulationmicrofiltration

0.54

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6.0 ReferencesAWWA (American Water Works Association). 2000. Arsenic Treatability Optionsand Evaluation of Residuals Management Issues. Denver, Colorado. :AWWA.Bajpi, S., andChaudri, M. 1999. Removal ofArsenic romGroundwaterbyManganese Dioxide-Coated Sand. Journal of Environmental Engineering. 125(8): 782-784.Banerjee,K.,Helwick,R.P., and Gupta, S. 1999. A TreatmentProcess forRemoval of Mixed norganic and Organic Arsenic Species From Groundwater.Environmental Progress.18 (4): 280-284.Brady, P. V., Spalding, B. P., Krupka, K. M., Borns, D. J., Waters, R. W., andBrady, W . D. 1999. Site-screening and technical guidelines for implementation ofmonitorednaturalattenuationatDOE ites.SandiaNationalLaboratories.SAND99-0464.Brandhuber, P., Amy, G. 1998. Alternative Methods or Membrane Filtration ofArsenic from Drinking Water. Dealination. 117: 1-10,Chwirka, J.D., Thomson,B.M.,andStomp 111, J.M.2000. RemovingArsenicfrom Groundwater. JournalAWWA. 29 (3):79-87.Clifford, D.A. 1990. Ion Exchange and Inorganic Adsorption. Water Quality andTreatment. Edited by F. W. Pontius.New York: McGraw-Hill, 561-639.Clifford, D., andLin,C.C.1991.Arsenic (111) and Arsenic (IV) Removal romDrinking Water in San Ysidro, New Mexico. USEPA, Project Summary 600/S2-91/011.Clifford, D., Subramonium, S., and Sorg, T.J. 1986.RemovingDissolvedInorganicContaminants from Water. Environmental Science and Technology,20: 1072-1 080.Clifford, D.A., and Zhang, 2. 1993.ArsenicChemistry and Speciation. Roc.AWWA WQTC: Miami, Fla., Nov. 7-11.Driehaus, W., Seith, R., and Jekal,M.1995.Oxidation of Arsenate (111) withManganese Oxide in Water Treatment. Water Research. 29 (1).Edwards, M. 1994. Chemistry of Arsenic Removal During Coagulation and Fe-Mn Oxidation. Journal ofAmerican Water Works Association. 86(9): 64-78.Frank, P., nd Clifford,D.1986. As(lll) Oxidation and Removal romDrinkingWater. USEPA, Project Summary 600/S2-86/021.

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Ghurye, G., Clifford,D.,andTripp, A. 1999.CombinedArsenic and NitrateRemoval by on exchange. Journal of American Water Works Association. 91(IO): 85-96.Harper, T., andKingham,N.W.1992. Removal of Arsenic from WastewaterUsing ChemicalPrecipitationMethods.Water Environment Research. 64 (3):200-203.Hem, J. 1961. Stability Field Diagrams as Aids in Iron Chemistry Studies.ournalofAmerican Water Works Association. 53 (2): 21 11-232.Hering, J.G., and Elimelech, M. 1996. Arsenicemoval by EnhancedCoagulationandMembraneProcesses.FinalReport (No. 90706).AWWAResearch. Foundation. Denver Colorado.Hurlbut, C. 1987. Manualof Mineralogy. John Wiley & Sons, Inc. New York, NewYork.Korte, N E 8 Q Fernando,1991.AReview of Arsenic (111) in Groundwater.Current Reviews in Environmental Control, 21(1): 1-39.Legaulet, AS., Volchek, K., Tremblay, A.Y., and Whittaker, H. 1993. Removal ofArsenic from GroundwaterUsingReagentinding/Membraneeparation.EnvironmentalProgress. 12 2) :157-159.McNeill, L.S. and Edwards, M. 1997.Predicting As RemovalDuringMetalHydroxide Removal. Journal of American Water Works Association. 89(1): 75-84.McNeill, L., and Edwards,M.1995.SolubleArsenicRemovalnFull-ScaleTreatment Plants.Journal of American Water Works Association. 87(4): 105-1 13.Mok,WM & C MWai,1994.Mobilization of Arsenic in Contaminated RiverWaters. In J 0 Nriagu (Ed.) Arsenic in theEnvironment, Part l Cycling andCharacterization. pp. 99-1 17, ohn Wiley 8 Sons, Inc.Oscerson, D.W.,Huan,P.M., Liaw, W.K., and Hammer, U.T. 1983. Kinetics ofOxidation of Arsenite by Various Manganese Dioxides. American Journal of SoilScience Society. 47: 644-648.Pontius, F.W., Brown, K.G., and Chen, C-J. 1994. Health Implications of Arsenicin Drinking Water. Journal ofAmerican Water Works Association.86 (9): 52-63.


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Rosenblum, E.R., and Clifford, D.A.1984.The equlibrium Arsenic Capacity ofActivated Alumina. National Technical Information Service. PB 84/10527. SpringField, Virginia.Scott,K.,Green, J.F., Do,H.D., and McLean, S.J. 1995. Arsenic Removal byCoagulation. Journal ofAmerican Wafer Works Association.87 (4): 114-126Takamatsu, T., Kwashima, M., and Koyama, M. 1985. The Role of Mn2- RichHydrous Manganese Oxide n the Accumulation of Arsenic in Lake sediments.Wafer Research. 19 ( 8 ) :1029-1032.Torrens, K. 1999.valuatingrsenicemovalechnologies.ollutionngineering@http://~.pollutionengineering.com/archives/1999/po1070199/pol9907works.htmlUS EPA, 1998. Research Plan for Arsenic in Drinking Water. Office of Researchandevelopmentationalenter for Environmentalssessment U.S.Environmental Protection Agency. Cincinnati, OH 45268Viraraghavan, T., Subramanian, K.S., and Aruldoss, J.G.1999.Arsenic inDrinking Water Problems and Solutions. Wafer Science and Technology. 40 (2):69-76.Waypa, J., Elimelech, M. and Hering J.G. 1997. Arsenic Removal by RO and NFMembranes. Journal ofAmerican Wafer Works Association. 89 (10): 102-1 13.

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Distribution:Internal:H. R. Westrich, MS0750Department File, MS0750N. R. Khandaker, MS0750 (4)P.V. Brady, MS0750 (2)W. R. Cieslak, 6100, MS0701 (3)Central Technical Files, 8945-1 ,MS9018Technical Library, 9616, MS0899(2)Review & Approval Desk, 961 12, MS0612For DOWOSTI

arsenic removal technologies and the effect of source water quality on performance

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