InfluenceofAdditivesonPolysulfoneBasedUltrafiltrat

1P.T.P.Aryantietal./JournalofWaterSustainability2(2013)85-96*Correspondingto:[e-mail]Polysulfone-BasedUltrafiltrationMembranePerformanceduringPeatWaterFiltrationPutuTetaPrihartiniAryanti,Khoiruddin,IGedeWenten*DepartmentofChemicalEngineering,ITB,Jl.Ganesha10,Bandung40132,IndonesiaABSTRACTTheeffectofadditivesonpolysulfonemembraneperformanceinpeatwaterfiltrationwasinvestigated.PolysulfonemembranewaspreparedbyimmersionprecipitationfromquarternarymembranesystemscontainingN,N-dimethylacetamide(DMAc)assolvent,polyethyleneglycol(PEG)andacetoneasadditives.Theperformanceofmembranewasevaluatedbypurewaterfluxandhumicacidrejection.Resultsshowthatrejectionofhumicacidinpeatwaterincreasedwiththeincreaseofacetoneconcentration.Themaximumrejectionwasachievedat8%wtacetoneconcentration.Thepresenceofacetonecontributedtothetightskinlayerformationofpolysulfonemem-brane.OtherresultssuggestthatmembranehydrophilicitycanbeimprovedbyincreasingofPEGconcentrationinmembranematrix,whichwasindicatedbytheincreaseofwaterfluxaround127LMHatthepresence25%wtofPEG.InhighPEGconcentration,thehumicacidrejectionwasdecreasedwhichmaybeattributedtomoreopenporeformedintheskinlayerofthemembraneandleadstoamoresevereirreversiblefouling.Keywords:Polysulphonemembrane;hydrophilicity;fouling;humicsubstances1.INTRODUCTIONPolysulfoneultrafiltrationmembraneshavebeenwidelyappliedinvariousindustrialfields,especiallyforwaterandwastewatertreatment.Polysulfoneasmembranematerialispreferredduetoitsseveraladvantages,suchasgoodmechanicalproperties,hightemperaturesandchemicalsresistance,processingeasiness,anditswideavailabilityinthemarket(Tweddleetal.,1983).However,thenatureofthehydro-phobicpolysulfonemembraneleadstolowwaterfluxandpronestofoulingoforganiccompounds.Inordertoovercomethisproblem,furtherresearchofpolysulfonemembranehasbeenconductedtoincreasehydrophilicityofpolysulfonemembrane,thusfurtherreducethetendencyofmembranefouling(JuckerandClark,1994;Maetal.,2001).Humicsubstance,anorganiccompound,isthemajorfoulantduringwatertreatmentpro-cess,whichgivesthewatersayellowishtobrownishcolor(WentenandWidiasa,1998).Peatwater,whereisusuallyfoundatdark-browncolour,consistsofhighlyconcen-trateddissolvedorganicmatter,particularlyhumicsubstancesandotheracidiccompound.Duringthepeatwatertreatmentusingultrafil-trationmembrane,foulingbecomesmajorproblemsthatshouldbeminimized.Themainfactorthatinfluencedthemembranefoulingmechanismisinteractionbetweenorganiccompoundsandhydro-phobicmembranesurface,whichcouldleadtosignificantreduc-tionofmembraneperfor-mance(NghiemandHawkes,2009).Asidefrommembranemate-JournalofWaterSustainability,Volume3,Issue2,June2013,85–96©UniversityofTechnologySydney&Xi’anUniversityofArchitectureandTechnology86P.T.P.Aryantietal./JournalofWaterSustainability2(2013)85-96rial,foulingtendencyisalsoinfluencedbymembraneporestructureandsurfacerough-ness,wherelargerporesizecouldleadstoporeconstrictionuptocompleteblocking,whileatightmembranetendstoformacakelayer(Costaetal.,2006;Mousa,2007).Blendingmethodwithadditiveisasimplewidelyusedmethodinpolysulfonemembranemodification.Theeffectsofadditivescon-centrationandmolecularweightonthemem-branestructureandmorphologyhavebeenreportedbyseveralresearchers(HanandNam,2002;Houetal.,1991;Khayetatal.,2002;Kimetal.,2003;Zhengetal.,2006).Com-monlyusedadditivesforthismethodarehy-drophilicpolymer,suchaspolyvinyl-pyrrol-idone(PVP)(Chakrabartyetal.,2008b;Ma-tsuyamaetal.,2003)orPEG(Chakrabartyetal.,2008a;KimandLee,1998;Maetal.,2011),whichhashighhydrophilicpropertiesandiseasilydissolvedinwater.Thepresenceofad-ditiveinmembranesolutioninfluencesther-modynamicandkineticpropertiesofmem-branesolution.Itreducesthestrengthofpol-ymer-solventinteractionandincreasessol-vent-nonsolventexchangerate,thusthepre-cipitationrateofmembranecouldbeenhanced.Theeffectofadditivesasporeformeronmembranestructurehasbeeninvestigated.Enlargedorsuppressedmacrovoidcanbeob-tainedbyvaryingadditiveconcentrationandmolecularweight.Maetal.(2011)foundthatanincreaseofPEG400additiveinmembranesolutionbetween2%-8%wtincreasedthenumberandsizeoffinger-likepores.Theex-istenceofPEGleadstohigherpolymercon-centrationandincreasestheviscosityofpol-ymer,thusmembranesolutionbecomeslessstable.DuetohydrophilicpropertiesofPEG,theincreaseofPEGconcentrationincreasestheinflowrateofwaterdiffusioninthepoly-mersolution,whichresultsinthemorede-velopedofleanphasegrowthandallowsthepossibilityofporecoalescence.TheyalsofoundthattheincreaseofPEGconcentrationalsoincreasesporosityandwaterpermeabilityofthemembrane.Highpolymerconcentrationinmembranesolutionleadstodelayedde-mixing,whichgivesanopportunityfornucle-ationandgrowthmechanismofnewporeinmembranestructure.Hanetal.(2002)investigatedtheeffectofPVPadditiveconcentrationoncorrelationbetweenthermodynamicandrheologicalpropertiesofpolysulfonemembrane.AtlowPVPconcentration,instantdemixingoccurredandcontributedtoenlargementofmembranepore.However,membranepreparedwithhighconcentrationofPVP,i.e20%wt,showedadelaydemixingduetotheincreaseofpolymersol