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Controlfilamentousbulkingcausedbychlorine-resistantType021NbacteriathroughaddingabiocideCTABJianhuaGuoa,b,YongzhenPenga,b,*,ZhongweiWanga,ZhiguoYuana,c,XiongYanga,ShuyingWangaaKeyLaboratoryofBeijingforWaterQualityScienceandWaterEnvironmentalRecoveryEngineering,BeijingUniversityofTechnology,Beijing100124,ChinabSchoolofMunicipalandEnvironmentalEngineering,HarbinInstituteofTechnology,Harbin150090,ChinacAdvancedWaterManagementCentre(AWMC),TheUniversityofQueensland,St.Lucia,QLD4072,AustraliaarticleinfoArticlehistory:Received6February2012Receivedinrevisedform7September2012Accepted18September2012Availableonline27September2012Keywords:FilamentousbulkingsludgeFilamentousbacteriaType021NChlorinationCetyltrimethylammoniumbromide(CTAB)ActivatedsludgeabstractFilamentousbulkingsludgeduetoexcessivegrowthoffilamentousbacteriaisaseriousoperationalprobleminactivatedsludgeplants.Theadditionofchemicalsisoneofwide-spreadwaystocontrolfilamentousbulking.Inthisstudy,filamentousbulkinginacontinuousactivatedsludgesystemwasfoundtobemainlycausedbyEikelboomType021Nfilamentousbacterialikelyduetolowsubstrateconcentrationgradients.TheseType021Nbacteriawerefoundtoberesistanttochlorination,maintainingcellintegrityatadosageofupto80mgCl/gSS.Analternativebiocidalagent,cetyltrimethylammoniumbromide(CTAB),exhibitedamuchstrongerbiocidaleffectonthesefilaments,whichsignificantlyimprovedsludgesettleability.Type021Nwithfilamentousindexof5wasselectivelykilled,butfloc-formersrecoverytheiractivityafterCTABtermination.ThestudyimpliedthatCTABmighthavemorepenetrationcapacitytocellwallofchlorine-resistantType021Nbacteria.Wethereforesuggestthepenetrationpropertyoffilamentcellwallshouldbeconsideredortestedbeforetheselectionofbiocidetypeinpractice.CrownCopyrightª2012PublishedbyElsevierLtd.Allrightsreserved.1.IntroductionTheactivatedsludgeprocessiscommonlyusedbiologicaltreatmentofbothmunicipalandindustrialwastewaters.Themostimportantoperationaldifficultyassociatedwithactivatedsludgeistheseparationofsludgefromthetreatedwastewater(Jenkinsetal.,2004;Wanneretal.,2010;Martinsetal.,2011).Filamentousbulkingduetotheproliferationoffilamentousorganismsfloatingfreelyorextendingfromflocsoftencausesthedeteriorationofsludgesettleability,andinseverecasestheoveralloperationoftheplantcanbetotallycompromised.Topreventandcontrolfilamentousbulking,bothspecificandnon-specificmethodshavebeendeveloped(Martinsetal.,2004;Kotayetal.,2011).Specificmethodsarepreventivemethodsbyeliminatingthecausesfavorableforthegrowthoffilaments(Martinsetal.,2004).However,itisdifficulttofindtheappropriateenvironmentalconditionsthatwouldconsistentlyfavorthegrowthoffloc-formersbutselectivelysuppressthegrowthoffilaments(Guoetal.,2010).Moreover,systemmodificationsaresometimeslimitedbyplantdesign,treatmentcapacityandinfluentcharacteristics(Caravellietal.,2007).Theuseofnon-specificmethodscanbeoneof*Correspondingauthor.SchoolofEnvironmentalandEnergyEngineering,BeijingUniversityofTechnology,Beijing100124,China.Tel./fax:þ861067392627.E-mailaddresses:gjh@bjut.edu.cn,pyz@bjut.edu.cn(Y.Peng).Availableonlineat(2012)6531e65420043-1354/$eseefrontmatterCrownCopyrightª2012PublishedbyElsevierLtd.Allrightsreserved.firstmethodsusedtocontrolfilamentousbulking,beforethecauseleadingtosludgebulkingisidentified.Additionofbiocide(mostlychlorinebased,suchasNaClOandCl2)isoneofthemostcommonlyusedmethodsinthecontroloffila-mentousbulkingundertheacuteconditions(Jenkinsetal.,2004).Becausefilamentsprotrudefromtheflocandarethereforemoreexposedtothebiocide,itispossibletokillfilamentousorganismswithoutasimilarbiocidaleffectonfloc-formers.Thecorrectchoiceofadditionpointsandappropriateamountsofadditionshouldbecarefullydeter-mined.Recommendedvaluesare15e20mgCl2/Linordertoavoidfloc-formersdamage,andthebestdosagepointisthereturnactivatedsludge(RAS)stream(Jenkinsetal.,2004).Manysuccessfulcaseswereobtainedbyaddingchlorineinaccordancewithrecommendedconditions(Saaymanetal.,1998;Caravellietal.,2004;Jenkinsetal.,2004).Forexample,aplantinBagnuolo(Italy)sufferedseverebulkingproblemswithasecondaryclarifiersludgeblanketnormallyat10cmbelowtheeffluentlevel.Sodiumhypochlorite(NaClO)wasaddedatrateof3mgCl2/gSS/ddirectlyintotheaerationbasin.Thedilutedsludgevolumeindex(SVI)decreasedfrom500to300mL/gafteraweek.Thefilamentsweredamagedbythechlorineadditionshowingemptyspacestroughthetrichomes(DavoliandGuglielmi,1998).Successfulchlorinationhasalsobeencarriedoutinothermunicipalandindustrialactivatedsludgesystems(Lakayetal.,1988;Vanleeuwen,1992;Ramirezetal.,2000;Changetal.,2004;Caravellietal.,2006).However,casesoffailurehavealsobeenreportedintheliterature.ChlorinationhasbeenfoundineffectiveincontrollingMicrothrixparvicella.HwangandTanaka(1998)re-portedthatchlorineadditionofupto20mgCl2/gSShadnoeffectonM.parvicella,whilethisamountwashighlydetri-mentaltofloc-formers.Lakayetal.(1988)suggestedM.parvi-cellabetheleastsusceptibletochlorinationandobtainedonlyapartialeliminationofM.parvicel