Current and future applications for nanofiltration

foodandbioproductsprocessing92(2014)161–177ContentslistsavailableatScienceDirectFoodandBioproductsProcessingjournalhomepage:filtrationtechnologyinthefoodprocessingFakhreddinSalehi∗FacultyofFoodScience&Technology,GorganUniversityofAgriculturalSciencesandNaturalResources,Gorgan,IranabstractTheincreaseinenergycostsandthedemandsforproductswithgreaternutritionalvalueandofprocessingproce-dureslesstoxictotheenvironmentareattractivefactorsfortransferringmembraneprocessingtofoodindustries.Nanofiltration(NF)technologyisstillevolving,findingmoreandmoreapplicationsinfoodprocessingandappearsasanimportantalternativetoconventionalmethods.ThepurposeofthisreviewistopresenttherecentdevelopmentandfuturepotentialofNFprocessesinthefoodindustry.RecentresearchhashighlightedthepotentialforNFuseinwideranging,includingwatersoftening,wastewatertreatment,vegetableoilprocessing,beverage,dairyandsugarindustry.NFhasbeenestablishedasgreaterseparationefficiency,successfullyreducesthewastewater,doneunderlowtemperatures,reductioninnumberofprocessingstepsandpresentsapromisingchoicetowardtheachievementofcosteffectiveprocess.NFcarriesquitedistinctivepropertiessuchasporeradiusandsurfacechargedensitywhichinfluencestheseparationofvarioussolutes.©2013TheInstitutionofChemicalEngineers.PublishedbyElsevierB.V.Allrightsreserved.Keywords:Beverage;Dairy;Drinkingwater;Sugarindustry;Vegetableoil;Wastewatertreatment1.IntroductionMembraneseparationprocessesareusedtoconcentrateorfractionatealiquidtoyieldtwoliquidsthatdifferintheircomposition.Itstandsoutasalternativestoconventionalprocessesforthechemical,pharmaceutical,biotechnologicalandfoodindustries(Cassanoetal.,2003;Baker,2004;Jiaoetal.,2004;Ravanchietal.,2009;Aroonetal.,2010;Lauetal.,2012).Inmanycasesthelowenergyconsumption,reductioninnumberofprocessingsteps,greaterseparationefficiencyandimprovedfinalproductqualityarethemainattractionsoftheseprocesses(Cheryan,1998;Baker,2004;Aroonetal.,2010;Cuartas-Uribeetal.,2010;Lauetal.,2012).NFcanalsobeappliedformorechallengingapplications,involvingfraction-ationratherthanpurification.Thenatureofthemembranecontrolswhichcomponentswillpermeateandwhichwillberetained,sincetheyareselectivelyseparatedaccordingtotheirmolarmassesorparticlesize(Cheryan,1998).ItiswellknownthatNFmembranescanbeusedforsaltfractionation∗Tel.:[phone];fax:[phone].E-mailaddress:[e-mail]28February2013;Receivedinrevisedform18August2013;Accepted24September2013sincetherejectionofmonovalentsaltsislowerthanthatofmultivalentsalts(Tanninenetal.,2006;Hilaletal.,2007).Anextremecaseofcharge-inducedseparationistheobservationofnegativerejectionsofmonovalentionsinthepresenceofmultivalentionsorpolyelectrolytes(VanderBruggenetal.,2003;Tingetal.,2007).NFappearsasanimportantalternativetoconventionalmethodsoffoodprocessing.ThisreviewsummarizestherecentdevelopmentsandfuturepotentialofNFmembraneprocessesinthefoodindus-trythatappeartohavegreatpotentialintheproductionofhighqualityfood,includingwatersoftening,wastewatertreatment,vegetableoilprocessing,beverageindustry,dairyindustryandsugarindustry.2.MembraneTheseparationperformanceofamembraneisinfluencedbyitschemicalcomposition,temperature,pressure,feedflowandinteractionsbetweencomponentsinthefeedflowandthe0960-3085/$–seefrontmatter©2013TheInstitutionofChemicalEngineers.PublishedbyElsevierB.V.Allrightsreserved.(2014)161–177membranesurface.Thefourmajorpressuredrivenmembraneprocessesareultrafiltration,reverseosmosis,microfiltrationandnanofiltration;briefgeneraldescriptionsofthemembraneprocessesusedinthefoodindustryareprovidedinthissec-tion.2.1.PressuredrivenmembraneprocessesAhydrostaticpressuregradientisthedrivingforceusedtoachievethedesiredhydrodynamicflowthroughthemem-brane(andthroughadepositedlayerthatmaydevelopduringthefiltrationprocess).Insomecases,concentrationgradientsorelectricalpotentialgradientsmayalsobeusedasadditionaldrivingforces(Cheryan,1998;Baker,2004).Fourpressuresdrivenmembraneprocessesaredistinguishedinpractice:2.1.1.Microfiltration(MF)MFisamembraneprocessthatinvolvestheuseofmembraneswithaporesizeof0.2–2m,andcanselectivelyseparatepar-ticleswithmolecularweightsof200kDa.MFusespressureslowerthan0.2MPaandseparatesmoleculesbetween0.025and10m.MFisprimarilyusedtoseparateparticlesandbacteriafromothersmallersolutes(Baker,2004;Huaetal.,2007).2.1.2.Ultrafiltration(UF)UFinvolvestheuseofmembraneswithamolecularweightcutoff(MWCO)intherangeof1–300kDaandaporesizeof∼0.01m.UFusespressuresgreaterthan1MPaandusedtoseparatecolloidslikeproteinsfromsmallmoleculeslikesug-arsandsalts(Baker,2004).2.1.3.Nanotiltration(NF)NFliesbetweentheseparationcharacteristicsofreverseosmosis(RO)andUFprocesswhichiswidelyusedforseveralapplicationssuchaswatersofteningandwastewatertreat-ment.TheporesizeoftheNFisintherangeof0.5–1nm.Itconcentrates,fractionatesorpurifiesaqueoussolutionsoforganicsoluteswithmolecularweightbetween100and1000Daandmixtureofmon