ContinuousFlowProcessfor Cr(VI)RemovalfromDrinkingWaterthrough

ReductionontoFeOOH byISRs

E.Kaprara,F.Pinakidou,E.Paloura,A.Zouboulis andM.Mitrakas

AristotleUniversityofThessaloniki,Greece

13th IWASpecializedConferenceonSmallWaterandWastewaterSystems(SWWS)

5th IWASpecializedConferenceonResources‐OrientedSanitation

Introduction

• Naturallyoccurringelementfoundinrock,soilandgroundwater.• Commonlypresentintheenvironmentintwoforms:Cr(III)andCr(VI).

Chromium

• Cr(III):essentialelementforhumanandanimalnutrition.• Cr(VI):toxic,causingvarioustypesofcancerandDNAdamage.

Specialinterest

• Natural:OxidationofCr(III)toCr(VI)ontosoilsderivedfromultramaficsedimentsandophiolitic rocks.

• Anthropogenic:industrialwastesfrommanufacturingprocesses,suchasmetal’splating.

Cr(VI)origininwater

213th IWASpecializedConferenceonSmallWaterandWastewaterSystems(SWWS)5th IWASpecializedConferenceonResources‐OrientedSanitation

Chromiumregulation

Cr(VI)prioritypollutant

Crtotal <0.1mg/L

Crtotal <0.05mg/L

(‐)LackofregulationlimitforCr(VI).

(‐)TotalCrlimitunderestimatestherisk.

(!)StrongintentionforestablishingregulationlimitforCr(VI)indrinkingwater.

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(!!!)U.S.StateofCalifornia:MCL=10μgCr(VI)/L (1/7/2014).

13th IWASpecializedConferenceonSmallWaterandWastewaterSystems(SWWS)5th IWASpecializedConferenceonResources‐OrientedSanitation

Cr(VI)indrinkingwaterofGreece

Kaprara et al (2015), J. Hazard. Mater. 281, 2–11.4

ContactwithultramaficrocksactivatesCr(VI)formationbyacatalyticmechanism.

Cr(VI)concentrationinwatersamplesaccountsfor96%oftotalchromiuminaverage.

2Cr3+ + 3MnO2(s) + 2H2O → 2HCrO4‐ + 3Mn2+ + 2H+

Cr(OH)2+ + 3MnO2(s) + 2OH‐ → HCrO4‐ + 3MnΟΟΗ(s)

Chemical reactions for geogenic Cr(VI) formation

MnO2(s) + Mn2+ → MnO2(s) • Mn2+

MnO2(s) • Mn2+ + O2 → 2MnO2(s)

2MnO2(s)  + 2MnΟΟΗ(s) → 2MnO2• MnΟΟΗ(s)

2MnO2• MnΟΟΗ(s) + 1/2O2 →  4MnO2 + H2O

TreatmenttechnologiesforCr(VI)removal

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Chemicalreductionandprecipitation. Adsorption. Ionexchange. MembraneseparationNF,RO. Electro‐dialysis. Electro‐coagulation. Phyto‐remediation. Flotation. Solventextraction.

13th IWASpecializedConferenceonSmallWaterandWastewaterSystems(SWWS)5th IWASpecializedConferenceonResources‐OrientedSanitation

Evaluationcriteriaoftechnologiesfordrinkingwatertreatment

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ResidualconcentrationofCr(VI)atlowppblevel. Lowreactiontime. Feasibilityforfullscaleoperation. Sustenanceofphysicalandchemicalcharacteristicsofwater. Lowcapitalandrunningcost.

13th IWASpecializedConferenceonSmallWaterandWastewaterSystems(SWWS)5th IWASpecializedConferenceonResources‐OrientedSanitation

QualifiedtreatmenttechnologyforCr(VI)removalfromdrinkingwater

hemicalreductionofCr(VI)andremovalofC(III)by:‐ precipitation‐ adsorption

emical reductionandprecipitation‐ adsorption

ostwidelypracticedmethodsighlyefficientandfastandeducesCr(VI)tothenon‐toxicinsolubleCr(III)formmonreductantsro‐valentiron(ZVI) surfacepassivation,enrichestreatedwaterwithdissolvedFe(II)rrousironsalts(FeSO4,FeCl2) BAT ‐ productionofsludgeorganicsulphurreductants,ISRs(NaHSO3,Na2S,CaS5,Na2S2O3,Na2S2O4)erestingresults highdosedemand

micalreductionandprecipitationnorganicSulfurReductantsperimentalbatchevaluation:emaximumdose50mgS/L(increaseSO42‐by150mg/L)ISRsprovedveryeffectiveatpH≤4(!)eptableefficiencyatpH7onlybysodiumdithionite(Na2S2O4)

uenceofreactionpHonCr(VI)removal

(Cr(VI)=100μg/L,CISR=10mgS/L,reactiontime24h,20±1oC)

InfluenceofISRsdoseonCr(VI)removal(Cr(VI)=100μg/L,pH7,reactiontime

24h,20±1oC)

imization of Cr(VI) removal from drinking water by ISRsThrough surface “catalysis” Under continuous flow configuration. 

AimoftheStudy

Materialsandmethods

ntsants examined:NaHSO3,Na2S2O3,Na2S2O4,Na2S2O5 and Na2S.catalyst:synthesizedFeOOHmainlyconsistingofFe16O16(OH)10(SO4)3 ∙10H2O.

Cations (mg/L) Anions (mg/L)

Na+ 88.8 HCO3‐ 183

Ca2+ 40.0 SO42‐ 50

Mg2+ 12.7 Cl‐ 71

NO3‐‐N 2

F‐ 1

PO43‐‐P 0.04

ArtificialwaterpreparedwithcompositionclosetothatofnaturalonesaccordingtotheNSFstandard.

Materialsandmethods

rimentalproceduredSmallScaleColumnTests(RSSCTs)smentoftreatmentefficiencyrcontinuousflowconditions.rptioncolumns:OOH granules(0.25– 0.5mm).CT:3min,pH:7.0,T:20oC./hof100μg/LCr(VI)inartificialwater.5L/hofISRsolution.ationytodecreaseCr(VI)concentrationbelow10μg/L

S: Investigation of Cr(VI) sorption mechanism

esultsanddiscussion

ugh curve of Cr(VI) adsorption at FeOOH column (initial Cr(VI):

Assessment of FeOOH effectivenessto adsorb Cr(VI) under continuousflow conditions

(‐)lowadsorptioncapacity

(+)abilitytodecreaseresidualCr(VI)tosub‐ppblevels.

(+) Promoteselectrontransfer

Cr(VI)+3e+→Cr(III)

esultsanddiscussionapidSmallScaleColumnTests

ISR inflow ISR outflow Cr(VI) outflow O2outflowmgS/L mgS/L μg/L mg/L

O320 8 47 3.5

40 26 26 2.5

O320 14 50 3.5

40 33 28 2.5

O420 13 ND 4.5

40 31 ND 2.5

O520 4 42 1.5

40 21 29 <1

S20 <1 ND <1

AdditionofISRssolutionatdosesof20and40mgS/L. Na2S2O4,Na2S:highestefficiency.

Na2S:unpleasantodourtotreatedwater.

NaHSO3,Na2S2O3,Na2S2O5:

(‐)failedtodeceaseCr(VI)tosingleppblevels,

Na2S2O4: qualifiedandfurtherexaminedatcolumnexperiments.

esultsanddiscussionapidSmallScaleColumnTests

kthroughcurvesofCr(VI)uptakebyFeOOH columndifferent Na S O concentrations (i iti l C (VI) 100

ForbetterestimationofNa2S2O4dose: TheFeOOH columnwasinitiallysaturated

at100μg/LCr(VI)and

• Thesurpluswasevaluatedbythecurve’sslope

10mg/LS‐Na2S2O4:Cr(VI)5±2μg/L

15and20mgS‐Na2S2O4:Cr(VI)<1 μg/L

(+)“buffer”adsorptioncapacityofFeOOHcolumn.

esultsanddiscussionptakemechanism

gationofCr(VI)reductionreactionandsorptionmechanismofCr.measurementsH /absenceofISRs:Cr(VI)isphysisorbed ontotheFeOOH surface.H /additionofNa2S2O4:Cr(III)formsinnerspherecomplexes,Cr(VI)involvedinspherecomplexes.

Cr(III)Fe

Fe

Fe

Mononuclear(2E)(3.00‐3.05Å)(2C)

6Å)

Bidentate

Mononuclear(1V)(3.60Å)

Chemisorptioninnerspherecomplexes

Physisorptionouterspherecomplexes

Cr

Monodentate

dsorptionmechanismofCroxyanions ontosurfaces

esultsanddiscussionptakemechanism

onclusions

SignificantcontributionofFeOOH onCr(VI)removalbyISRs.

Highestefficiency:Na2S2O4,Na2S.

Na2S:residualunpleasantodour additionaltreatmentstep(‐)

Continuousflowconfiguration:• A10mgS/LdoseofNa2S2O4 ensuresthereductionof100μg/LCr(VI)concentrationbelowtheupcominglimitof10μg/L.

• HigherNa2S2O4dose(15 mg/L)candiminishCr(VI)belowD.L.• “Buffer”uptakecapacityformorethan3d(~1.500BV).

EXAFS study:chromiumuptakeontoFeOOH proceedsviabothphysisorption andchemisorption.• Cr(VI):outerspherecomplexes• Cr(III):innerspherecomplexes.

Thankyouforyourattention!

tinuousFlowProcessofCr(VI)RemovalfromDrinkingWaterthroughReductionontoFeOOH byISRs

E.Kaprara,F.Pinakidou,E.Paloura,A.Zouboulis andM.Mitrakas

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