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JOURNALOFENVIRONMENTALSCIENCESISSN1001-0742CN11-2629/X(11)1900–1907Reductivetransformationanddetoxificationmechanismof2,4-dinitrochlorobenzeneincombinedzerovalentironandanaerobic-aerobicprocessJinyouShen1,ZongyuanZhou1,ChangjinOu1,XiuyunSun1,JianshengLi1,WeiqingHan1,LinZhou2,LianjunWang1,1.JiangsuKeyLaboratoryofChemicalPollutionControlandResourcesReuse,SchoolofEnvironmentalandBiologicalEngineering,NanjingUniversityofScienceandTechnology,Nanjing210094,China.E-mail:shenjinyou@mail.njust.edu.cn2.SchoolofMechatronicalEngineering,BeijingInstituteofTechnology,Beijing100081,ChinaReceived04February2012;revised26March2012;accepted28March2012AbstractAcombinedzerovalentiron(ZVI)andanaerobic-aerobicprocesswasadoptedforthetreatmentof2,4-dinitrochlorobenzene(DNCB)-containingwastewater.Thetransformationpathway,reductionofacutetoxicityandenhancementofbiodegradabilitywereinvestigated.AfterpretreatmentbyZVI,DNCBinwastewatercouldbecompletelyconvertedinto2,4-diaminochlorobenzene(DACB).TheratioofBOD5/CODincreasedfrom0.0050.001to0.1680.007,whileEC50,48hr(V=V)increasedfrom0.65%to5.20%,indicatingtheenhancementofbiodegradabilityandreductionofacutetoxicitywiththepretreatmentbyZVI.DACBwasfurtherdechlorinatedtom-phenylenediamineduringtheanaerobicprocessusingmethanolaselectrondonor,withEC50,48hrincreasingfrom5.20%to48.2%.Afterthesubsequentanaerobic-aerobicprocess,m-phenylenediaminewasdegradedcompletely,witheffluentCODof67.510.8mg/L.Thiseffluentofthesubsequentanaerobic-aerobicprocesswasnottoxictozebrafish.ThecombinedZVIandanaerobic-aerobicprocessoffersbrightprospectsforthetreatmentofchlorinatednitroaromaticcompound-containingwastewater.Keywords:2,4-dinitrochlorobenzene;zero-valentiron;toxicity;biodegradabilityDOI:10.1016/S1001-0742(11)61054-1IntroductionChlorinatednitroaromaticcompoundsarewidespreadintheenvironmentduetothemanufacturingandprocessingofavarietyofindustrialproducts,suchaspharmaceuticals,explosives,dyesandpesticides(Linetal.,2011;Liuetal.,2011).Theyareofinteresttoenvironmentalscien-tistsbecausetheyareknownorsuspectedtobehumancarcinogens,mutagensortoxins(Linetal.,2011;Shenetal.,2008).Inaddition,theyhavebeenlistedasaclassofpriorityenvironmentalpollutants.Therefore,thereisinterestinremovingthemfromcontaminatedsites.Manytreatmenttechnologiessuchasphotocatalysis(Yeetal.,2010;Zhangetal.,2006),adsorption(Guoetal.,2009),ozonation(Shenetal.,2008),andbio-logicaltreatment(Niuetal.,2009;Wuetal.,2009)havebeendevelopedtoremovechlorinatednitroaromaticcompoundsfromcontaminatedenvironments.Physico-chemicalmethodshaveproventobecostlyandhaveinherentdrawbacksduetothetendencyfortheformationofsecondarytoxicmaterials.Biologicaltreatment,whichisenvironmentallyfriendlyandcost-effective,hasturned*Correspondingauthor.E-mail:wanglj@mail.njust.edu.cnouttobeafavorablealternative(Zhangetal.,2009;Shenetal.,2009).However,duetothepronouncedelectron-withdrawingcharacterofthenitrogroupandchlorogroup,chlorinatednitroaromaticcompounds,suchas2,4-dinitrochlorobenzene(DNCB),harborahighlyelectrondeficient-electronsystem(Linetal.,2011).Electrophilicattack,whichisusuallythefirststepinoxidationoraerobicbiodegradation,becomesmoredifficult(Zhangetal.,2009).What’smore,withincreasingnumbersofnitroandchlorogroups,chlorinatednitroaromaticcompoundsbecomemoreresistanttomineralizethroughoxidativepathwaysandaresubjecttoinitialreductivetransformation(Shenetal.,2009;Susarlaetal.,1998).Inordertodevelopacost-effectivewastewatertreatmentsystemforchlorinatednitroaromaticcompounds,studieshaveexaminedbiologicalorchemicalprocessestoreduc-tivelytransformthenitrofunctionalgroupsordechlorinatethecompoundstoovercomethehindrancetooxidation(Barreto-Rodriguesetal.,2009).Amongthereductivetransformationprocesses,anaerobicreductionandzero-valentironreductionhaveturnedouttobepromising.Underanaerobicconditions,someanaerobicmicroor-ganismsareabletoreducechlorinatednitroaromaticcompoundsintotheircorrespondingchlorinatedaminoaro-No.11Reductivetransformationanddetoxificationmechanismof2,4-dinitrochlorobenzene1901maticcompounds.However,theprocessisusuallyveryslowandrequiresanelectrondonor(organiccosubstrate)tocreatethenecessaryreductiveconditions(Muetal.,2009).Thecompetitionforelectrondonorsbyothermicroorganismsmayupsettheenrichmentofthenitro-reducingpopulationandthenitroreductionofchlorinatednitroaromaticcompounds(Linetal.,2011;H¨aggblometal.,2000;Lietal.,2008).Therefore,inthisprocess,anadditionalorganiccosubstrateisoftenrequiredasanelectrondonor,inamountswhichmayfarexceedthestoichiometricrequirements(Muetal.,2009;Leetal.,2011).Zero-valentiron(ZVI),asaninexpensive,reliableandmoderatelystrongreducingagent,hasbeenwidelyusedtotreatmanykindsofenvironmentalcontaminants,suchashalogenatedorganiccompounds,azodyes,andnitroaro-matics(Linetal.,2011;Fanetal.,2010;ArnoldandRoberts,2000;Shuetal.,2010;MaandZhang,2008).Anassessmentoftheliteratureonzero-valentironreductionshowsapredominanceofarticleswiththefocusofinterestmainlyonthepre