DegradationanddecolorizationofreactiveredX3Baqueou

SeparationandPurificationTechnology74(2010)195–201ContentslistsavailableatScienceDirectSeparationandPurificationTechnologyjournalhomepage:∗,Yan-HuaDingResearchCenterofEnvironmentalScience,WuhanUniversityofScienceandEngineering,1TextileRoad,Wuhan,Hubei430073,ChinaarticleinfoArticlehistory:Received29January2010Receivedinrevisedform1June2010Accepted2June2010Keywords:ReactiveredX-3BInternalmicro-electrolysisOzoneSynergeticeffectabstractOzoneintegratedwithinternalmicro-electrolysis(O3/IE)wasappliedtoelectrochemicallyoxidizereac-tiveredX-3Bowingtoitswell-establishedsynergeticeffectinthepresentstudy.Thefinalremovalratesofcolor,COD,TOCandAOXwerefoundtobe99%,85%,59%,and74%,respectively,whenthefollowingoptimalconditionswereused:dyestuffconcentrationof1g/LwithapHof9.0,areactiontemperatureof60◦C,400gofironscrapswiththediameterintherangeof0.9–2.0mmand10g/hozoneflowrate.ThedominantdegradationmechanismofreactiveredX-3Bwaselucidatedbytheadditionofradicalscav-enger/enhancer.TheresultsindicatedthattheformationofhydroxylradicalsinthepresenceofozonewasthemajorcontributingfactorinO3/IEsystem.©2010ElsevierB.V.Allrightsreserved.1.IntroductionSyntheticazodyestuffwitharomaticringshasbeenreleasedintotheenvironmentasdyewastewaterafterthebleaching,wash-inganddyeingprocessesoffabric,andhasbecomeanimportantsourceofenvironmentalpollutionduetoitshighcolor,hightoxic,recalcitrantandnon-biodegradablecharacteristics.Inrecentyears,methodsfordecolorizationanddegradationoftextileeffluentshavereceivedconsiderableattention.Variousconventionalphys-ical,chemical,electrochemical[1–4]andbiologicalmethodshavebeenexploredforthetreatmentofsyntheticandactualtextileeffluents.Internalmicro-electrolysis(IE),basedonreactionofgalvaniccelloxidationreduction,operatesontheprincipleverysimilartotheprincipleofelectrolysis[1,4]withtheexceptionthattheelectronsaresuppliedfromthegalvaniccorrosionofmanymicro-scalesac-rificialanodesinsteadofexternalpower[5].Forexample,whenamixtureofmetalscraps,e.g.,ironoraluminumandgranularactivatedcarbon(GAC)particlesareincontactwithwastewa-ter(electrolytesolution),numerousmicroscopicgalvaniccellsareformedbetweentheparticlesofmetalandcarbon.Thehalf-cellreactionscanberepresentedas[6,7]:Ironanode(oxidation):Fe(s)→Fe2+(aq)+2eE0(Fe2+/Fe)=−0.44V(1)∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](Q.-F.Zeng).Fe2+(aq)→Fe3+(aq)+eE0(Fe3+/Fe2+)=+0.77V(2)Carboncathode(reduction)inthepresenceofoxygen:Acid:O2(g)+4H+(aq)+4e→2H2OE0(O2/H2O)=+1.23V(3)O2(g)+2H++2e→H2O2(aq)E0(O2/H2O2)=+0.68V(4)Neutraltoalkaline:O2(g)+2H2O+4e→4OH−(aq)E0(O2/OH−)=+0.40V(5)Thesehalf-cellreactionsoccuronmicroscopicscales,butsimul-taneousoccurrencesofthesereactionsonthesurfaceofalargenumberofironscrapsandGACparticlescanresultinsignificantelectronflowsinthesystem.Accordingtotheabovelistedstandardredoxpotential,FecanbeoxidizedtoFe2+,andFe2+canbeoxidizedtoFe3+byoxygen,whereFe2+combinedwithH2O2canformFentonreagent.Especially,whenO3existsinthesystem,plentyofhydroxylradicalsandH2O2willbeproduced.Additionally,Fe3+mainlypre-cipitatesasFe(OH)3whenthepHvalueofsolutionishigherthan4,theflocculationprecipitationprocessfromferrichydroxideswillresultinfurtherdisposaloforganiccontaminants[7].Themecha-nismofIEhasbeensummarizedbymanyreports[5,6,8,9].Briefly,(1)largeparticulatesprecipitateonthesurfaceofmicro-electrodeduetotheelectromigrationandelectrophoresiseffectundermicro-electricfield;(2)thereductionoforganiccontaminantsoccursduetotheoxidationofironatlowpH;(3)theredoxreactionsofdyewastewaterareincurredinthatactivehydrogenstemsfromthe1383-5866/$–seefrontmatter©2010ElsevierB.V.Allrightsreserved.doi:10.1016/j.seppur.2010.06.005196X.-C.Ruanetal./SeparationandPurificationTechnology74(2010)195–201reductionofH+atcathodewithacidiccondition;(4)coagulationinthetreatmentsystemisincurredbytheferrousandferrichydrox-idesformedfromoxidationandprecipitationofFe2+releasedfromtheanodes.Therefore,organiccontaminantscanbeoxidizedbyradicalsandoxidantsproducedduringIE;(5)organiccontaminantscanalsoberemovedthroughadsorptionandreductionofGAC.Therefore,IE,asoneofelectrochemicaloxidationmethodsbasedontheformationofelectricfieldamongiron,carbonandwastewater,iscelebratedaslittleornoharmfuleffectsontheenvironmentfortheuseofharmlessreagents,andnoextraenergyneeded[10].ThereisanincreasingattractioninapplyingIEtothedisposalofeitherinorganic[11]ororganiccontaminants[12].Ozone,asawell-knownpowerfuloxidant,isveryeffectiveindecolorizingtextileeffluentsbecauseitattacksconjugateddoublebondswhichareoftenassociatedwithcolor[13]andcon-vertsbiorefractorydyesinwastewaterintobiodegradablespecies[14–16].Ithasbeenwidelyusedaloneorincombinationwithotheroxidationprocessesindrinkingwaterdisinfectionandwastewatertreatment[17–21].ThepurposeofthepresentstudyistostudythefeasibilityofthecombinationofO3withIE(O3/IE)forthedegradationofazodyesolution.Re