FoulingbehavioursofPVDFTiO2mixedmatrixmembraneappl

Pleasecitethisarticleinpressas:Y.H.Teow,etal.,FoulingbehavioursofPVDF-TiO2mixed-matrixmembraneappliedtohumicacidtreatment,J.WaterProcessEng.(2016),(2016)xxx–xxxContentslistsavailableatScienceDirectJournalofWaterProcessEngineeringjournalhomepage:∗,B.S.Ooic,A.L.AhmadcaCentreforSustainableProcessTechnology(CESPRO),FacultyofEngineeringandBuiltEnvironment,UniversitiKebangsaanMalaysia,43600Bangi,Selangor,MalaysiabDepartmentofChemicalandProcessEngineering,FacultyofEngineeringandBuiltEnvironment,UniversitiKebangsaanMalaysia,43600Bangi,Selangor,MalaysiacSchoolofChemicalEngineering,EngineeringCampus,UniversitiSainsMalaysia,SeriAmpangan,14300NibongTebal,Penang,MalaysiaarticleinfoArticlehistory:Received20December2015Receivedinrevisedform7March2016Accepted11March2016AvailableonlinexxxKeywords:FoulingmechanismHumicacidMixed-matrixmembraneTiO2nanoparticlesUltrafiltrationabstractTheaimofthisstudywastoanalysesthefoulingmechanismofpolyvinylidenefluoride-titaniumdioxide(PVDF-TiO2)mixed-matrixmembranes(MMMs)embeddedwiththreedifferenttypesofTiO2nanoparti-cles(NPs):PC-20,P25,andX500appliedtohumicacid(HA)treatment.Althoughneatmembranehasveryoftenbeenusedinamodeladaptedtocross-flowultrafiltration(UF),MMMwithTiO2embedmenthasnotbeenstudiedbefore.TheidentificationoffoulingmechanismswasdeterminedbyfourtypicalmodesofHermia’smodelsandthecombinedblockingmodel.Thecombinedblockingmodel,whichinvolvesbothcakefiltrationandporeblocking,takingplaceatdifferentstagesofthemembranefiltrationprocess,showsthebestcorrelationwiththeexperimentaldata.Itwasshownthatthefoulingbehaviourofthemembraneisgovernedbythenatureofthemembrane,especiallymembranesurfaceroughness.ThefineandwelldispersedX500NPsonmembranepolymericmatrixwerefoundtohaveasignificanteffectonmembraneanti-foulingpropertywithareducedporeblockingparameter,lowestcakelayerresistance,andmembraneresistanceof0.3261,2.6201×106/m,and10.2182×106/mrespectively.ThisfindingisattributedtothereducedsurfaceroughnessaswellasincreasingsurfaceenergyofX500MMM.©2016ElsevierLtd.Allrightsreserved.1.IntroductionThepresenceofhumicacid(HA)intheenvironmentcanleadtodetrimentalproblemsduetotheformationofharmfuldisin-fectionby-products(DBPs)[1,2]whenitundergoesconventionalchlorinetreatmentprocesses.Progresshasbeenmadewithregardstotheextensiveuseofultrafiltration(UF)membranesasanalter-nativetechnologytoconventionaltreatmentinseparatingHAparticlesfromthewatersourcetomeetmorestringentwaterqual-ityregulations[3,4].However,despitetheexpansionandsuccessfulapplicationofmembranesystemsinthewaterindustry,adeclineinmembraneperformanceoveraperiodoftimeduetomembranefoulingisstillacriticalproblem.Itdemandsconsiderableattentionasitcausesadeclineinpermeateflux,affectsseparationproperties,andincreasestheoperationalpressure[5,6],thusconstrainingthe∗Correspondingauthorat:CentreforSustainableProcessTechnology(CESPRO),FacultyofEngineeringandBuiltEnvironment,UniversitiKebangsaanMalaysia,43600Bangi,Selangor,Malaysia.E-mailaddresses:[e-mail],[e-mail](Y.H.Teow).widespreadapplicationofmembranetechnologyforHAseparationinwatertreatmentprocesses.HAfoulingcaninvolveseveraldistinctphenomena.Yamamuraetal.[7]classifiedmembranefoulingasphysicallyreversiblefoul-ing(concentrationpolarization),whichcanbetotallyeliminatedbyphysicalcleaningorcertainpre-treatment,andphysicallyirre-versiblefouling(HAadsorptionanddeposition),whichcannotbeentirelycounteractedbyphysicalcleaningorcertainpre-treatment[8,9].VisvanathanandBenaïm[10]suggestedthatintheearlystageoffiltration,thereisasharpdeclineinpermeatefluxwhichisirreversibleforallpracticalpurposesduetotherapiddeposi-tionoffineparticlesfromsuspensiononthemembranesurfaceandsubsequentlypenetrateintotheporesandthusaccumulate.Later,aggregatesofcolloidscanformbridgesovertheporeopenings,resultinginpartialblockingofthepores.Asmallerporestructureisthenavailableforsubsequentcolloidstodeposit.Thebridgingofaggregatedcolloidsleadstotheeventualformationofafilmofcolloidsonthemembranesurface,whichimpliesthatmorethanonetypeofblockingmechanismisinvolvedinasingleprocess.ThispostulationisingoodagreementwiththefindingsofTarletonandWakeman[11]whoclaimedthatthefoulingbyparticulatesappearstobecausedbyseveralsimultaneousmechanisms.©2016ElsevierLtd.Allrightsreserved.Pleasecitethisarticleinpressas:Y.H.Teow,etal.,FoulingbehavioursofPVDF-TiO2mixed-matrixmembraneappliedtohumicacidtreatment,J.WaterProcessEng.(2016),(2016)xxx–xxxIncontrast,CaklandMikuláˇsek[12]concludedthatthefoulingmechanismishighlydependentonsoluteparticlesizeandmem-braneporesize.Theyobservedthatcakeformationtakesplaceiftheparticlesarelargerthanthepores,whereasparti