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Water2011,3,495-525;doi:10.3390/w3020495waterISSN2073-4441*,Yung-TseHung1,RuthYu-LiYeh2andMohammedSuleimanAlAhmad11DepartmentofCivilandEnvironmentalEngineering,ClevelandStateUniversity,Cleveland,OH44115,USA;E-Mails:yungtsehung@yahoo.com(Y.-T.H.);arabee2000@yahoo.com(M.S.A.A.)2DepartmentofChemicalEngineering,MinghsinUniversityofScienceandTechnology,Hsin-Chu,304Taiwan;E-Mail:yehyl@must.edu.tw*Authortowhomcorrespondenceshouldbeaddressed;E-Mail:rick.ben.butler@gmail.com;Tel.:+1-216-687-2596;Fax:+1-216-687-5395.Received:15February2011;inrevisedform:18March2011/Accepted:28March2011/Published:6April2011Abstract:Areviewoftheliteraturepublishedinfrom2008to2010ontopicsrelatedtoelectrochemicaltreatmentwithinwastewaterwaspresented.Thereviewincludedseveralsectionssuchasoptimization,modeling,variouswastewatertreatmenttechniques,analyticalandinstrumentation,andcomparisonwithothertreatmentmethods.Keywords:wastewatertreatment;electrochemicaltreatment;electrocoagulation;coagulation;sacrificialanodes1.DefinitionofElectrocoagulation-Flotation(ECF)Electrocoagulation-electroflotation(ECF)technologyisatreatmentprocessofapplyingelectricalcurrenttotreatandflocculatecontaminantswithouthavingtoaddcoagulations.Shammasetal.statedthatcoagulationoccurswiththecurrentbeingapplied,capableofremovingsmallparticlessincedirectcurrentapplied,settingthemintomotion.Alsoelectrocoagulationcouldreduceresidueforwasteproduction[1].Electrocoagulationconsistsofpairsofmetalsheetscalledelectrodes,thatarearrangedinpairsoftwo—anodesandcathodes.Usingtheprinciplesofelectrochemistry,thecathodeisoxidized(loseselectrons),whilethewaterisreduced(gainselectrons),therebymakingthewastewaterbettertreated.Whenthecathodeelectrodemakescontactwiththewastewater,themetalisemittedintotheapparatus.OPENACCESSWater2011,3496Whenthishappens,theparticulatesareneutralizedbytheformationofhydroxidecomplexesforthepurposeofformingagglomerates.Theseagglomeratesbegintoformatthebottomofthetankandcanbesiphenoutthroughfiltration.However,whenoneconsidersanelectrocoagulation-flotationapparatus,theparticulateswouldinsteadfloattothetopofthetankbymeansofformedhydrogenbubblesthatarecreatedfromtheanode.Thefloatedparticulatescanbeskimmedfromthetopofthetank.ToconsiderhoweffectivetheECFreactorcanbe,onemustconsiderthefollowinginputsorvariables—wastewatertype,pH,currentdensity,typeofmetalelectrodes(aluminum,steel,iron),numberofelectrodes,sizeofelectrodes,andconfigurationofmetals.Thesevariableswouldaffecttheoveralltreatmenttime,kinetics,andalsotheremovalefficiencymeasured.Electrocoagulation-flotationisanalternativemethodtoclassicchemicalcoagulationformanyreasons.ECFiscapableofreducingtheneedforchemicalsduetothefactthattheelectrodesprovidethecoagulant.However,manyindividualsstillusechemicalcoagulantstoattempttoenhancetreatment.Traditionally,chemicalcoagulationinvolvestheuseofalum(aluminumsulfate),ferricchloride(FeCl3),orferroussulfate(Fe2SO4)whichcanbeveryexpensivedependingonthevolumeofwatertreated.Whenapplyingthecoagulant,thecoagulantperformsasimilarfunctionastheelectrodes,neutralizingthechargeoftheparticulates,therebyallowthemtoagglomerateandsettleatthebottomofthetank.Inaddition,electrocoagulation-flotationiscapableofreducingwasteproductionfromwastewatertreatmentandalsoreducesthetimenecessaryfortreatment.2.OptimizationByconsideringtheBox-Behnkendesignofsurfaceresponseanalysisforcolorremovalwithindistilleryspentwash,KrisnaPrasadetal.foundthat95%colorremovalwasobtainedwith31mA/cm2,dilutionof17.5%,and4hourelectrolysisdesign.Atoptimumconditions,thetreatmentefficiencywasat93.5%[2].ChavalparitandOngwandeeconcludedthatremovalof55.43%COD,98.4%oilandgrease,and96.59%suspendedsolidswasobtainedusingapHof6.06,appliedvoltageof18.2V,andreactiontimeof23.5minuteswhenusingtheBox-Behnkendesignforbiodieselwastewater[3].Kaparaletal.wasabletodeterminethedyeremovalbytheTaguchimethod,byusinganinitialdyeconcentrationof100mg/L,pHof3,currentdensityof0.5mA/cm2,CaCl2concentrationof2.5mMforthetreatmentofBompalexRedCR-Ldye.Experimentaldesigninvolvedanorthogonalarrayusing5simultaneousparameters[4].Tchamangoetal.usedelectrocoagulationforartificialwastewaterwithmilkpowdertosimulatedairyeffluents,CODwasreducedby61%,phosphoursby89%,nitrogen81%,and100%turbidity.InadditionwithlowconductivityandneutralpH,treatedwaterwouldbepossiblereused,asreagentrequiredwasloweredforthealuminumanodefortreatment[5].KörbahtiandTanyolaçconcludedthat100%pollutionload,61.6%COD,99.6%colorremoval,and66.4%turbiditywereaccomplishedbyanelectrochemicalreactor,whereoptimumconditionsforconductingtheexperimentwereattemperatureof30degreesCelsius,25g/Lelectrolyteconcentration,8Velectricalpotential,witha35.5mA/cm2currentdensity.ThiswasaccomplishedtotreatsimulatedtextiledyewastewaterwithNaClelectrolytebasedonresponsesurfacemethodology[6].Hammamietal.concludedthatelectrochemicaloxidationofchromium(III)fromchromium(VI)wasaccomplishedwithtitanium-platinumanodesforthepurposeoftreatingtanningbathe