电絮凝RemovalofWaterTurbiditybytheElectrocoagu

JResHealthSci,Vol.8,No.1,pp.18-24,2008RemovalofWaterTurbiditybytheElectrocoagulationMethodRahmaniAR.PhDDept.ofEnvironmentalHealthEngineering,CenterofHealthResearch,HamadanUniversityofMedicalSciences,Iran(Received5Nov2007;accepted22Mar2008)AbstractBackground:Electrocoagulationisatechniqueinvolvingtheelectrolyticadditionofcoagulatingmetalionsdirectlyfromsacrificialelectrodes.Theseionscoagulatewithturbidityagentsinthewater,inasimilarmannertotheadditionofcoagulatingchemicalssuchasalumandferricchloride,andal-lowtheeasierremovalofthepollutants.Purposeofthisstudywastoconductexperimentalinvestiga-tionofwaterturbidityremovalusingtheelectrocoagulationmethod.Methods:Removalofturbidityfromrawwaterinbatchsystemwasinvestigatedbydifferentvoltage(10,15,20,25,30V),electrodes(Al,FeandSt)andelectrolyzestime(0to40min.),electrodesdis-tance2cmandpH=7.5.Results:Theexperimentalresultsshowedthattheremovalefficiencydependsontheelectrolyzetime,typesofelectrodesandtheappliedcurrent.Fromtheexperimentscarriedoutat20V,itwasfoundthatin20minutestheremovalefficiencyforAl,FeandStelectrodeswas93,91and51percentrespec-tively.Basedonturbidityremovalefficiency,AlispriortoFeandStassacrificialelectrodematerial.Conclusion:Inanerawhenenvironmentalphenomenaattractagreatattention,electrocoagulationmethodscanbesaidtobeapromisingcleaningandpurifyingmethodforwatertreatment.Keywords:Water,Treatment,Turbidity,ElectrocoagulationIntroductionThepresenceofparticulatematerialssuchasalgae,clays,silts,organicparticlesandsolu-blesubstancesinwateroftencausesittogetturbidorcolored.Thesettleabilityoftheparticulatedependsonthedensityofthematerialandthesizeofparticles.Theparti-cleswithdensitymorethanwatershouldeventuallysettleduetogravitationalforce.Smallparticles,especiallythosewithdensityclosetowatersuchasbacteriaandcolloidalparticlesmayneversettleandremainsus-pendedinthewater.Therefore,agglomera-tionofparticlesintoalargerflocisaneces-sarystepfortheirremovalbysedimentation(1).Theconventionaltreatmentmethodconsistsofaddingmetalsalts(aluminum,ironetc.),destabilizationofcolloidalparticles(whichiscalledcoagulation),followedbyfloccula-tionandsedimentation.Inthiswaytheapplicationofchemicalreagentslikealum,lime,sodaashetc,whicharewidelyusedingoodquantity,becomesimperativeforclarification.Thismethodoftreatmenthascertaindrawbackslikehandlinglargequanti-tiesofchemicals,properassessmentofre-quirements,feedingofchemicalsandproductionoflargevolumeofsludgecaus-ingdisposalproblemandlossofwater(2).Duringrecentdecadesresearchonelectricityapplieddirectlyinwatertreatmenthaspro-gressedwell,makingitanattractivemethodforcoagulationorclarificationofwater,usu-allyknownastheelectro-coagulation/elec-trochemicalmethod(3).Inthismethoddi-18OriginalArticleJResHealthSci,Vol.8,No.1,pp.18-24,2008Correspondence:P.O.Box:4171,Hamadan,Iran.E-mail:[e-mail]:RemovalofWaterTurbidity...rectcurrentispassedthroughaluminum/ironplatessuspendedinwater(2-5).Thissystemcausessacrificialelectrodeionstomoveintoanelectrolyte.Undesirablecon-taminantsareremovedeitherbychemicalreactionandprecipitationorbycausingcolloidalmaterialstocoalesce.Theyarethenremovedbyelectrolyticflotation,orsedimentationandfiltration.Disinfectionisalsoaccomplishedbyanodicoxidation(6).Doniniatel.pointedoutthatthemecha-nismsofcoagulationweresimilarforelec-tro-coagulationandaluminumsaltstreat-ment(7).Thedifferenceismainlyinthewayaluminumionsaredelivered.Comparedtowatertreatmentwithaluminumsulphateorferrichloride,electrochemicalalumi-num/irongenerationhasseveraldistinctad-vantages.Aluminumorironisintroducedwithoutcorrespondingsulphateions.Alsothereisnoneedforanalkalinitysupplytogiveareaction.ByeliminatingcompetinganionsusingahighlypureAlorFesource,lowermetalresidualsareobtainedandlesssludgeisproduced(50-70percent).Thead-justmentofAlorFeiondoseinthewatercanbedoneeasilybymanipulatingthedialforcontrolofcurrent(2).ThefollowingelectrodereactionsforAloc-curinthisprocess(2):Anode:Al0⇔A13++3e-[1]Cathode:2H20+2e-⇔20H+H2[2]AI0+3H2⇔Al(OH)3+1.5H2[3]Pzhegorlinskietal.determinedthecontribu-tionoftheindividualreactionsofequations1to3.Eachofthesereactionswasevaluatedbytheweightlossofthecorrespondingelec-trodeandthevolumeandcompositionofthecollectedhydrogen(8).Thenascentoxygenproducedisaverypowerfuloxidizerandoxidizesmetalspre-sentinwater.ThenascentAlreactswiththewatertoforminsolublehydroxidesandthecolloiddestabilizationprocessisthereforeanalogoustothatobtainedwithtraditionalmetalsalts.Forcompletingthetreatment,electrocoagulationisfollowedbytheusualseparationprocesses,i.e.,sedimentation,flotation,filtration,etc(2).Themainobjectiveofthisresearchwastoconductexperimentalinvestigationofwaterturbidityremovalbyusingtheelectrochemi-calmethod.Sinceiron,aluminumandStainlesssteelelectrodeshavenotbeencom-paredindetailforthetreatmentofturbidwa-ter,itisthepurposeofthisstudytocomparetheturbidityremovalbyelectrocoagulationusingStainlesssteel,aluminumandironelectrodematerials.Inaddition,theeffectsofcurrentdensityandtreatmenttimeontheprocessperformanceareexplored.