电絮凝Newhybridelectrocoagulationmembrane

Desalination201(2006)290–296NewhybridelectrocoagulationmembraneprocessforremovingseleniumfromindustrialwastewaterV.Mavrova,c,S.Stamenovb,E.Todorovab,H.Chmielc,T.ErweaaDepartmentofProcessTechnology,SaarlandUniversity,ImStadtwald47,D-66123Saarbrücken,GermanyTel.+49(681)934-5317;Fax:[phone];email:[e-mail]Geology,DepartmentofMineralProcessing,1700Sofia,BulgariacInstituteforEnvironmentallyCompatibleProcessTechnology(upt),ImStadtwald47,D-66123Saarbrücken,GermanyReceived7February2006;Accepted22June2006AbstractHighconcentrationsofheavymetalcationssuchasCd,Cu,Zn,PbandFeaswellasheavymetalanionssuchasAsandSearecontainedinthewastewatergeneratedbyindustrialCuproduction.Theconventionaltechnologyfortreatingthiskindofwastewater,whichconsistsoflimeneutralisation/FeCl3coagulationandflocculation,doesnotsatisfytherequirementsfordirectwastewaterdischargewhichspecifythatSeconcentrationshouldbelessthan30µg/l.Theresidualseleniumconcentration,thelargesludgequantitiesgeneratedaswellastheexpenseofreagentsarejustsomeoftheshortcomingsofthistechnology.Tocombattheseproblems,anewhybridprocesscombiningelectrocoagulationandmicrofiltrationwasdrawnupandverifiedinexperiments.Verygoodadsorption/co-precipitationpropertiesforseleniumremovalwereobservedforironhydroxide,generatedbyelectrocoagulationalthoughprecipitationwasdifficult,duetothefinesofsludge.Ironhydroxidecouldbecompletelyremovedfromthewaterbyapplyinganintegratedfiltrationprocessinvolvingsubmergedmicrofiltrationflatsheetceramicmembranes(meanporesizeof0.3µm).Furthermore,thecake,formedonthemicrofiltrationmembranes,couldbeusedasabarrieradsorbentforreducingtheresidualSe.Anewbench-scaleelectrocoagulation/membranefiltrationcellwasdevelopedandoptimisedinexperimentstotestthenewhybridprocess.Firstly,veryextensiveoptimisationexperimentsusingmodelwastewaterwereperformedfollowedbybench-scaleexperimentswithrealindustrialwastewaterfromCuproduction.Resultsshowedthat,atacontinuousregimewithatreatmenttimeof20minandacurrentdensityoftheanodeof4.8mA/cm2,Sereductionwas98.7%,As99.9%,CuandPbmorethan98.0%,ZnandCdmorethan99.9%.Keywords:Industrialwastewater;Heavymetals;Selenium;Electrocoagulation;Microfiltration;Hybridprocess*Correspondingauthor.doi:10.1016/j.desal.2006.06.0050011-9164/06/$–Seefrontmatter©2006ElsevierB.V.Allrightsreserved.V.Mavrovetal./Desalination201(2006)290–2962911.IntroductionIndustrialwastewaterfromCuproductionhashighconcentrationsnotonlyofheavymetalcations(Cd,Cu,Zn,Pb,Fe),butalsoofheavymetalanionssuchasAs(upto500mg/l)andSeasoxyanionsat2–3mg/l(upto6mg/linsomepartialstreams).Mostoftheheavymetals,cationsandanions,canberemovedwithoutproblems,withtheexceptionofSe,toachievethedischargeconcentrationrequired.Thetechnolo-giesforSeremoval,experimentedwithandpartiallyapplied,areasfollows[1]:Cprecipitationasselenate,selenite,selenideorelementalselenium;Cadsorptiononferrihydrite,activatedalumina,ferricoxyhydroxide(theseprocessesareeffectivefortheremovalofSe(IV)butnotforSe(VI));Cion-exchange(thisprocessiseffectivefortheremovalofSe(VI)ratherthanforSe(IV));Creverseosmosisandnanofiltration(pre-treat-mentforreverseosmosisandnanofiltrationisverycomplicatedandtheselectivityofthemembrane,especiallyreverseosmosis,isverypoor);Cemulsionliquidmembranes(inthisprocess,Se(VI)isextractedrapidlyeveninthepresenceofsulphateatallpHvalues2butSe(IV)extractionisinfluencedbythepresenceofsulphate);Creductionprocesses(ferroushydroxide,ironreductantetc.);Cbiologicalprocesses:bacterialreductionwithPseudomonasstutzeriofseleniumspeciesSe(IV)andSe(VI)toelementalseleniumhasbeenshowntobeapotentialcandidatefortreatingwatercontainingSe.However,oneproblemisthehighoperatingtimeandthesizeoftheapparatus;Cconventionaltreatment:limeneutralisation-softening/ferriccoagulation/flocculation/fil-tration.Thisisthebestavailabletechnology(BAT)forthetreatmentofdrinkingandgroundwateraswellaswastewatercontami-natedwithmetalbutitisdoubtfulifseleniumremovalcancomplywiththeregulationsondirectdischarge(Seconcentrationlessthan30µg/l).ThedrawbackswiththistechnologyaretheresidualSeconcentrationofmorethan30µg/l,generationoflargevolumesofsludgeandthehighcostofreagents;Chybridprocessessuchascoagulation/crossflowmicrofiltration[2],adsorption(ionexchange)/crossflowmicrofiltration,adsorp-tion(ionexchange)/flotation/submergedmicrofiltration[3–8]havebeenmostlyexperi-mentedwithinthelastdecadefortheremovalofdifferentimpuritiesincludingheavymetals.Oneofthepromisingmethodsforremovingseleniumandarsenicfromwateristheelectro-chemicalmethodusingdissolvablemetalelec-trodes.InsolubleprecipitatesareobtainedfromthecompoundsofSe,Asaswellasotherheavymetalionswiththeionsofthedissolvedmetalelectrode.Themostwide-spreadelectrochemicalmethodforprocessingindustrialwastewaterappearstobethemethodofelectrocoagulation,appliedindivid-uallyorincombinationwithothermethods,e.g.,electrocoagulation/flotationorcrossflowmicro-filtration[2].Inelectrocoagulation,chemicalcompounds,whichadsorbthewastewaterimpuri-ties,areobtainedelectrochemically.Thewateri