搜索
Int.J.Environ.Res.,5(2):403-412,Spring2011ISSN:1735-6865Received12Sep.2009;Revised17Aug.2010;Accepted25Aug.2010*CorrespondingauthorE-mail:alavim@yahoo.com403AComparisonBetweenAluminumandIronElectrodesonRemovalofPhosphatefromAqueousSolutionsbyElectrocoagulationProcessBehbahani,M.1,AlaviMoghaddam,M.R.1*andArami,M.21CivilandEnvironmentalEngineeringDepartment,AmirkabirUniversityofTechnology(AUT),HafezSt.,Tehran,15875-4413,Iran2TextileEngineeringDepartment,AmirkabirUniversityofTechnology(AUT),HafezSt.,Tehran,15875-4413,IranABSTRACT:Thisstudypresentsacomparisonbetweenaluminumandironplateelectrodesonphosphateremovalfromaqueoussolutionsbyelectrocoagulationprocess.TheeffectivenessofmainoperationalparameterssuchasinitialpH,initialphosphateconcentrationandcurrentdensitywereexamined.Inaddition,treatedsolutionandsludgecharacteristics,energyconsumptionandelectrodemassdepletionwerecomparedforbothelectrodes.Allexperimentsweredoneinanelectrocoagulationcellwitheffectivevolumeof2liters.Itwasfoundthatthealuminumelectrodehashigherremovalefficiencycomparedtotheironelectrodeinthesameoperationalconditions.Phosphateremovalefficienciesof100%and84.7%wereobservedforaluminumandironelectrodeinaspecialcasewithoptimuminitialpH,maximumcurrentdensityandmaximuminitialphosphateconcentrationequalto3,250A/m2,400mg/lPO43-,respectively.Furthermore,lesstreatedsolutionturbidity,highersecondarypollution(remainedAl)andlesselectrodemassdepletionwasobservedforthealuminumelectrode.Keywords:ElectrochemicalProcess,Removalefficiency,Operationalparameters,Differentelectrodes,SolutioncharacteristicsINTRODUCTIONModerntechnologieshavebeenintroducedforremovingspecificelementsfromdifferentkindsofwasteduringrecentyears(RajasimmanandKarthikeyan,2009,Nourietal.,2010,Rahmanietal.,2010,Naimetal.,2010,Tashauoeietal.,2010).Presenceofexcessiveamountsofvariousanionssuchasphosphatemaycauseproblemsinwaterresources(PelekaandDelianny,2009).Themainformsofphosphateinwaterbodiesareorthophosphate،polyphosphateandorganicphosphate(Caravellietal.,2010).Asamainnutrient,phosphateisveryessentialforgrowthoforganismsinmostecosystems,butexcessivephosphateconcentrationsreleasetoconfinedwaterbodiesleadtoeutrophicationandsubsequentdeteriorationofwaterqualitymainlythroughoxygendepletionasthealgaedecay(Zhangetal.,2009;Zhaoetal.,2009)Therefore,phosphatecontentofeffluentsorstreamsthataredischargeddirectlytotheenvironmentisregulatedbythenationalandinternationalwastewaterstandardauthoritieswithmaximumlimitsrangingfrom0.1to2mg/lasP(Kamiyangoetal.,2009).ForexampletheUS،IndiaandIrandischargelimitsofphosphateare(0.5-1),5and6mg/lasPrespectively(Vasudevanetal.,2009;Iranianenvironmentalprotectionregulations&standards,2004).Phosphateremovalhasreceivedconsiderableattentionsincethelate1960s(PelekaandDelianny,2009;Vasudevanetal.,2009).Varioustechnologieswereusedforphosphateremovalfromwastewaterthatdividedintophysical,chemicalandbiologicalmethods(Hosnietal.,2007;Huangetal.,2008;Kamiyangoetal.,2009;PelekaandDelianny2009;Vasudevanetal.,2009;Zhangetal.,2009;Zhaoetal.,2009;Caravellietal.,2010).Physicalmethodsareusuallytooexpensive,asinthecaseelectrodialysisorreverseosmosis(Zhaoetal.,2009).Inabiologicaltreatmentplant,itisnecessarytotransferphosphatefromliquidtosludgephase,removalefficiencyusuallydoesn´texceed30%,whichmeansthattheremainingphosphateshouldberemovedbyothertechnologies(Hosnietal.,2007).Nowadays,chemicalprocessesarealsolessattractiveduetodisadvantagessuchasfurthercostforbuyingandinstallationofdosingequipments,problemsof404Behbahani,M.etal.sludgehandlinganddisposal,maintenancecostsandchemicalused(Vasudevanetal.,2009;Kimetal.,2010).Anothermethodthathasattractedgreatattentioninwastewatertreatmentiselectrocoagulation(EC).EChasbeensuccessfullyusedtoremovedifferentkindsofpollutantssuchasorganiccompounds(Wangetal.,2010),dyesandtextilewastewater(Heetal.,2007;Phalakornkuleetal.,2010),heavymetals(Zaroualetal.,2009;Zongoetal.,2009;Nourietal.,2010;SanjeevKumarandGoel,.2010;Shafaeietal,.2010),dairywastewater(Tchamangoetal.,2010),biodieselwastewater(ChavalparitandOngwandee.,2009),hardness(Malakootianetal.,2010),petroleumrefinerywastewater(El-Naasetal.,2009),COD(Wangetal,.2009),importantanionssuchasnitrate(Emamjomehetal.,2009),fluoride(Ghoshetal.,2008;Zuoetal.,2008)andphosphate(Bektasetal.,2004;Irdemezetal.,2006(a,b,c);Yuetal.,2006;Vasudevanetal.,2009;Kobyaetal.,2010).Inthisprocess,passingdirectcurrentthroughsacrificialanodes(usuallyaluminumoriron)causescorrosionofelectrodesandproductionofmetalcations.Thesecationsthenformpolymericmetalhydroxidespeciesinsolutionsimilartocoagulantsaltslikealuminconventionalchemicalcoagulation.Thesecationsandotherchargedpolymericmetalhydroxidespeciescanneutralizenegativelychargedparticles.Afterneutralization,theparticlesbindtogethertoformaggregatesofflocs,resultinginpollutantremoval.Additionally,generationofgasbubblesatbothelectrodescauseelectroflotation,whichresultsinbetterremovalofcontaminants(Arroyoetal.,2009;El-Naasetal.,2009;Linares-Hernandezetal.,2009;Wangetal,.2009;Zaroualetal.,2