Integrated membrane systems and processes 1st edition basile

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Integrated Membrane Systems and Processes

Editors Angelo Basile • Catherine Charcosset

IntegratedMembrane SystemsandProcesses

Editedby ANGELOBASILE

InstituteonMembraneTechnology–ItalianNationalResearch Council(ITM-CNR),UniversityofCalabria,Cosenza,Italy and

CATHERINECHARCOSSET

Laboratoired’AutomatiqueetdeG ´ eniedesProc ´ ed ´ es,CNRS, Universit ´ eLyon1,VilleurbanneCedex,France

Thiseditionfirstpublished2016 ©2016JohnWiley&SonsLtd

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Includesbibliographicalreferencesandindex. ISBN978-1-118-73908-2(cloth) 1.Membranefilters.2.Filtersandfiltration.I.Basile,Angelo,editor.II.Charcosset,Catherine,editor. TP156.F5I572016 660′ .284245–dc232015024794

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ListofContributors ix

Preface xi

1Ultrafiltration,Microfiltration,NanofiltrationandReverseOsmosisin IntegratedMembraneProcesses1

CatherineCharcosset

1.1Introduction1

1.2MembraneProcesses2

1.2.1Ultrafiltration,MicrofiltrationandNanofiltration2

1.2.2ReverseOsmosis3

1.2.3MembraneDistillation3

1.2.4Electrodialysis4

1.2.5MembraneBioreactors5

1.3CombinationofVariousMembraneProcesses6

1.3.1Pressure-DrivenSeparationProcesses6

1.3.2MembraneDistillationandPressure-Driven MembraneProcesses12

1.3.3ElectrodialysisandPressure-DrivenMembraneProcesses13

1.3.4MembraneBioreactorsandPressure-Driven SeparationProcesses14

1.3.5OtherProcessesandPressure-DrivenSeparationProcesses15 1.4Conclusion17 ListofAbbreviations18 References18

2BioseparationsUsingIntegratedMembraneProcesses23

RajaGhosh

2.1Introduction23

2.2IntegratedBioseparationProcessesInvolvingMicrofiltration24

2.3IntegratedBioseparationProcessesInvolvingUltrafiltration28 2.4Conclusion31 References32

3IntegratedMembraneProcessesintheFoodIndustry35 AlfredoCassano

3.1Introduction35

3.2FruitJuiceProcessing36

3.2.1FruitJuiceClarification36

3.2.2FruitJuiceConcentration38

3.2.3IntegratedSystemsinFruitJuiceProcessing40

3.3MilkandWheyProcessing48

3.3.1IntegratedSystemsinMilkProcessing48

3.3.2IntegratedSystemsinCheesemaking51

3.3.3IntegratedSystemsinWheyProcessing52

3.4Conclusions54 ListofAbbreviations54 References55

4ContinuousHydrolysisofLignocellulosicBiomassviaIntegrated MembraneProcesses61 MohammadmahdiMalmaliandS.RanilWickramasinghe

4.1Introduction61

4.2ContinuousEnzymaticHydrolysis63

4.3IntegratedSubmergedMembraneSystem65

4.4SugarConcentration66

4.5SugarConcentrationandHydrolysateDetoxificationbyNanofiltration68

4.6StatisticalDesignofExperiments69

4.7AnalysisofVarianceusingResponseSurfaceMethodology69

4.8FutureChallenges74

4.9Conclusion75 Acknowledgements75 ListofAbbreviations75 ListofSymbols75 References76

5IntegratedMembraneProcessesforthePreparationofEmulsions, ParticlesandBubbles79 GoranT.Vladisavljevi ´ c

5.1Introduction79

5.1.1MembraneDispersionProcesses80

5.1.2MembraneTreatmentofDispersions81

5.1.3ComparisonofMembraneandMicrofluidicDrop GenerationProcesses82

5.1.4ComparisonofMembraneandConventional HomogenisationProcesses83

5.2MembranesforPreparationofEmulsionsandParticles84

5.2.1SPGMembrane84

5.2.2MicroengineeredMembranes90

5.3ProductionofEmulsionsUsingSPGMembrane92

5.4ProductionofEmulsionsUsingMicroengineeredMembranes96

5.5FactorsAffectingDropletSizeinDME98

5.5.1EffectofTransmembranePressureandFlux99

5.5.2InfluenceofPore(Channel)SizeandShearStressonthe MembraneSurface101

5.5.3InfluenceofSurfactant101

5.6FactorsAffectingDropletSizeinPME103

5.7IntegrationofMEwithSolid/Semi-SolidParticleFabrication104

5.7.1IntegrationofMEandCrosslinkingof Gel-formingPolymers104

5.7.2IntegrationofMEandMeltSolidification114

5.7.3IntegrationofMEandPolymerisation115

5.7.4IntegrationofMEandSolventEvaporation/Extraction118

5.8IntegrationofMembranePermeationandGasDispersion120

5.9IntegrationofMembraneMicromixingandNanoprecipitation121

5.10Conclusions123 ListofAcronyms123 Symbols124 Subscripts126 References126

6NanofiltrationinIntegratedMembraneProcesses141 BartVanderBruggen

6.1Introduction141

6.2PretreatmentforNanofiltration144

6.3NanofiltrationasaPretreatmentMethod146

6.4ProcessesinSeries148

6.5IntegratedProcesses150

6.6HybridProcesses153

6.7NanofiltrationCascades156

6.8Conclusions158 ListofAbbreviations159 References159

7Seawater,BrackishWaters,andNaturalWatersTreatment withHybridMembraneProcesses165 MaximePonti ´ eandCatherineCharcosset

7.1Introduction165

7.2DesalinationMarket166

7.2.1GrowthofDesalinationCapacityWorldwide166

7.2.2DesalinationTechnologies167

7.3SeawaterandBrackishWatersComposition168

7.3.1SeawaterComposition168

7.3.2BrackishWaterversusSeawater168

7.3.3ProductWaterSpecification170

7.4DesalinationwithIntegratedMembraneProcesses170

7.4.1MF/UF–RO170

7.4.2NFversusRO172

7.4.3NF–RO174

7.5NaturalWaterTreatmentUsingHybridMembraneProcesses176

7.5.1NaturalOrganicMatter178

7.5.2Arsenic183

7.5.3OtherSpecies186

7.6Conclusion190 ListofAcronyms191 References192

8WastewaterTreatmentUsingIntegratedMembraneProcesses197 JinsongZhangandAnthonyG.Fane

8.1Introduction197

8.2IMSApplicationforWastewaterTreatment:CurrentStatus198

8.2.1IMSforTextileIndustrialWastewater:Targetto ZeroDischarge198

8.2.2IntegratedPressure-DrivenMembraneProcessforMunicipal WastewaterReclamation200

8.2.3IntegratedMultipleFunctionDrivenMembraneProcessfor WastewaterReclamation212

8.3StrategicCo-locationConceptforIntegratedProcessInvolvingRO, PRO,andWastewaterTreatment219

8.4Conclusions221 Nomenclature221 ListofGreekletters222 References222

9MembraneReactor:AnIntegrated“Membrane + Reaction”System231 AngeloBasile,AdolfoIulianelliandSimonaLiguori

9.1Introduction231

9.2HydrogenEconomy232

9.2.1WhyMembraneReactors?232

9.3MembraneReactors235

9.3.1MembraneReactorsUtilization236

9.4MembranesforMembraneReactors236

9.4.1CeramicMembranes237

9.4.2ZeoliteMembranes237

9.4.3CarbonMembranes238

9.4.4MetalMembranes238

9.4.5CompositeMembranes239

9.5MassTransportMechanismsforInorganicMembranes239

9.6ApplicationsofInorganicMembraneReactors241

9.6.1RecentAdvancesonHydrogenProductioninMRsfromSteam ReformingofRenewableSources241

9.7Conclusions244

ListofSymbols245 ListofAbbreviations245 References246

10MembranesforIGCCPowerPlants255 KamranGhasemzadeh,AngeloBasile,andSeyyedMohammadSadatiTilebon

10.1Introduction255

10.2IGCCTechnologyforPowerGeneration256

10.3ApplicationofMembranesinanIGCCPowerPlants257

10.3.1HydrogenSelectiveMembranes264

10.3.2OxygenSelectiveMembranes272

10.3.3CO2 SelectiveMembranes275

10.4ConclusionandFutureTrends280 Abbreviations280 References281

11IntegrationofaMembraneReactorwithaFuelCell285 ViktorHacker,MeritBodner,andAlexanderSchenk

11.1Introduction285

11.2FuelCellBasics286

11.2.1ReactionMechanisms287

11.2.2ElectrochemicalBasicsoftheFuelCell289

11.3DifferentTypesofFuelCells292

11.3.1MethodsofClassification292

11.3.2FuelCellTypes294

11.4ContaminationsofthePEFC295

11.4.1AnodeGasStream295

11.4.2CathodeGasStream297

11.4.3ContaminationsofComponents298

11.5MethodstoAvoidPoisoning298

11.5.1IncreasingtheFuelCellTolerancetowards Contaminations299

11.5.2AvoidingContaminations300 11.6Conclusion302

ListofAbbreviations302 ListofSymbols302 References303

12SolarMembraneReactor307 KamranGhasemzadeh,AngeloBasile,andAbbasAghaeinejad-Meybodi

12.1Introduction307

12.2ConfigurationsofSolarMRSystems308

12.2.1SolarMRsforWaterandWastewaterTreatment309

12.2.2SolarMRsforHydrogenProduction312

12.3SolarMRsApplicationfromaModelingPointofView319

12.3.1WaterDecompositionLiterature319

12.3.2SteamReformingLiterature320

12.4SolarMRsApplicationfromanExperimentalPointofView322

12.4.1WaterDecompositionLiterature322

12.4.2WaterElectrolysisLiterature329

12.4.3SteamReformingLiterature331

12.5TheMainChallenges334

12.6ConclusionandFutureTrends335

ListofAbbreviations335 References336

13Membrane-AdsorptionIntegratedSystems/Processes343 SayedS.MadaeniandEhsanSalehi

13.1Introduction343

13.2AdsorptionPretreatmentforMembranes345

13.3IntegratedMembrane-AdsorptionSystems347

13.3.1LPM-AdsorptionIntegration348

13.3.2Membrane-AdsorptionBioreactors352

13.3.3MABROperatingConditions354

13.3.4MABRApplications355

13.4MembraneAdsorbents356

13.4.1Protein-AdsorbentMembranes357

13.4.2Metal-AdsorbentMembranes358

13.4.3Imprinted-MembraneAdsorbents360

13.4.4ThinMembraneAdsorbents362

13.4.5ModelingAspects362

13.4.6RegenerationandReuse365

13.5AdsorptionPost-treatmentforMembranes366 References367

ListofContributors

AbbasAghaeinejad-Meybodi,ChemicalEngineeringDepartment,SahandUniversityof Technology,Tabriz,Iran

AngeloBasile,InstituteonMembraneTechnology–ItalianNationalResearchCouncil (ITM-CNR),UniversityofCalabria,Rende(Cs),Italy

MeritBodner,InstituteofChemicalEngineeringandEnvironmentalTechnology,Graz UniversityofTechnology,Graz,Austria

AlfredoCassano,InstituteonMembraneTechnology–ItalianNationalResearchCouncil (ITM-CNR),UniversityofCalabria,Cosenza,Italy

CatherineCharcosset,Laboratoired’AutomatiqueetdeG ´ eniedesProc ´ ed ´ es,CNRS, Universit ´ eLyon1,VilleurbanneCedex,France

AnthonyG.Fane,SingaporeMembraneTechnologyCentre,NanyangTechnologicalUniversity,Singapore

KamranGhasemzadeh,ChemicalEngineeringDepartment,UrmiaUniversityofTechnology,Urmia,Iran

RajaGhosh,DepartmentofChemicalEngineering,McMasterUniversity,Ontario,Canada

ViktorHacker,InstituteofChemicalEngineeringandEnvironmentalTechnology,Graz UniversityofTechnology,Graz,Austria

AdolfoIulianelli,InstituteonMembraneTechnology–ItalianNationalResearchCouncil (ITM-CNR),UniversityofCalabria,Cosenza,Italy

SimonaLiguori,InstituteonMembraneTechnology–ItalianNationalResearchCouncil (ITM-CNR),UniversityofCalabria,Cosenza,Italy

SayedS.Madaeni,MembraneResearchCenter,ChemicalEngineeringDepartment,FacultyofEngineering,RaziUniversity,TaghBostan,Kermanshah,Iran

MohammadmahdiMalmali,RalphE.MartinDepartmentofChemicalEngineering,UniversityofArkansas,Fayetteville,AR,USA

xListofContributors

MaximePonti ´ e,L’UNAM,LaboratoryGEPEAUMRCNRS6144,Nantesuniversity, Nantes,France

EhsanSalehi,DepartmentofChemicalEngineering,FacultyofEngineering,ArakUniversity,Arak,Iran

AlexanderSchenk,InstituteofChemicalEngineeringandEnvironmentalTechnology, GrazUniversityofTechnology,Graz,Austria

BartVanderBruggen,DepartmentofChemicalEngineering,ProcESS–ProcessEngineeringforSustainableSystems,KULeuven,Belgium;FacultyofEngineeringandthe BuiltEnvironment,TshwaneUniversityofTechnology,PrivateBagX680,Pretoria0001, SouthAfrica

GoranT.Vladisavljevi ´ c,ChemicalEngineeringDepartment,LoughboroughUniversity, Leicestershire,UK

S.RanilWickramasinghe,RalphE.MartinDepartmentofChemicalEngineering,UniversityofArkansas,Fayetteville,AR,USA

JinsongZhang,SingaporeMembraneTechnologyCentre,NanyangTechnological University,Singapore

Preface

Membranescienceandtechnologyhaveshownanimpressivegrowthsincetheearly1960s withthediscoveryofaneffectivemethodforthepreparationofasymmetriccellulose acetatemembranes.Membranetechnologyisnowrecognizedforanumberofadvantagessuchasoperationalsimplicity,lowenergeticrequirements,goodstabilityundera widerangeofoperativeconditions,easycontrolandscale-up,andlargeflexibility.With theincreasingunderstandinganddevelopmentofmembranetechniques,itbecamepossibletointegratevariousoperationswiththepurposetoimproveperformanceinterms ofproductquality,plantcompactness,environmentalimpact,andenergyuse.Hybridor integratedmembraneprocessescanbeclassifiedintoseveralcategories.Insomeprocesses,adsorptionorreactionmaybeincludedinthemembraneitself,likeinmembrane reactors,ion-exchangemembranes,adsorptivemembranes,andothers.Otherhybridorintegratedmembraneprocessescombineseveralmembraneseparationsteps,onestepbeing dependentontheformerone,inamultistageconfiguration.Finally,membranefiltrationmaybeassociatedwithotherunitoperationslikeadsorptiononactivatedcarbonor ion-exchangeresins.

Thisbookissplitintotwoparts.Thefirstpartcoversseveralexamplesofintegrated membranesystemsandprocessesinthewater,food,biotechnology,andpharmaceutical fields.Chapter1(Charcosset)reviewsanddiscussesprocessesbasedontheintegration ofultrafiltration,microfiltration,nanofiltration,reverseosmosis,andothermembraneprocessessuchasmembranedistillationandmembranebioreactors.Examplesofseawater desalination,wastewatertreatment,andseparationinbiotechnologyandfoodindustries arealsogiven.Chapter2(Ghosh)reviewsdevelopmentsintheareaofintegratedmembraneprocessforbioseparations.Byusingintegratedmembraneprocesses,thenumberof separationstepsrequiredforpurificationofbiologicalmacromoleculessuchasproteins andnucleicacidscouldbesignificantlyreduced.Mostintegratedmembraneprocessesfor biologicalapplicationshavebeendevelopedbasedonmicrofiltrationandultrafiltration.In Chapter3(Cassano),themostrelevantapplicationsofintegratedmembranesystemsin specificareasoftheagro-foodproduction,suchasfruitjuice,milk,andwheyprocessing, arereviewedanddiscussed,highlightingtechnologicaladvancesandimprovementsover conventionalmethodologies.InChapter4(MalmaliandWickramasinghe),itisshown thatmembrane-basedseparationprocessesprovidetheopportunityforsignificantprocess intensificationthroughdevelopmentofacontinuoushydrolysisprocess.However,design ofacontinuoushydrolysisprocessislikelytoinvolvetheuseofmorethanonemembrane unitinseries.Chapter5(Vladisavljevi ´ c)isanoverviewofmembraneprocessesusedforthe

preparationofliquid–liquidandgas–liquidmicro-andnano-dispersions,includingdirect andpremixmembraneemulsification,membranemicromixing,andmembranemicro-and nano-bubbling.Integrationofmembraneemulsificationanddownstreamprocessingforthe preparationofstructuredmicroparticlesisalsocovered.InChapter6(VanderBruggen), integrationofnanofiltrationwithotherprocessesisdescribedonthebasisofdifferentlevelswithincreasinginterdependency:pretreatmentpriortonanofiltrationandnanofiltration asapretreatmentforfurtherprocessing,aspartofprocessesinseries,intheintegration ofprocessesandhybridization,andinmembranecascades.Itisshownthatbyintegratingprocesses,theperformanceoftheoverallsystemcanbesubstantiallyenhanced,far beyondthelimitationsofasinglemembrane.Chapter7(Ponti ´ eandCharcosset)highlights recentdevelopmentsinhybridmembraneprocessesfordesalination,suchasmembrane pre-treatmentbeforereverseosmosis,andnaturalwatertreatment,suchasactivatedcarbonadsorptionoroxidationassociatedwithultrafiltrationormicrofiltration.InChapter8 (ZhangandFane),integratedmembranesystemsforindustrywastewatertreatmentare presented,providingmoresustainablesolutionsforenergyandcost-saving,thatis,smaller footprint,approachingtozerodischarge,etc.Theconceptofintegratedmembranesystem aswellassomecasestudiesforwastewatertreatmentisintroducedanddiscussed.The secondpartconsidersvariousexamplesofintegratedmembranesystemsandprocessesin inorganicapplications,IGCCpowerplants,solarreformers,fuelcells,pervaporationsystems,aswellasadsorption-membraneintegratedprocesses.Chapter9(Basile,Iulianelli, andLiguori)pointsouttherelevanceofmembranereactortechnology.Inparticular,once appliedforhydrogengeneration,specialattentionispayedtotheconceptofamembrane reactorusedforreformingprocesses.Furthermore,anoverviewofdifferentkindsofinorganicmembranesusefulinmembranereactorapplicationsisgiven,highlightingtherole ofthePd-basedmembranesandtheirbenefitsanddrawbacks.Chapter10(Ghasemzadeh, Basile,andTilebon)reviewstheapplicationofmembranes(microporousceramic,palladiumbased,polymeric,andmixedionicandelectronicmembranes)forhydrogen,carbon dioxide,andoxygenseparationintheintegratedgasificationcombinedcycle(IGCC)power plant.Moreover,theroleofmembranetechnologyontheefficiencyofIGCCisalsodiscussed.Chapter11(Hacker,Bodner,andSchenk)investigatestheintegrationofamembrane reactorwithafuelcell.Polymerelectrolytefuelcells(PEFCs)convertthechemicalenergy intoelectricalenergy.Theinfluencesofimpuritiesoffuelandairontheperformanceand thelifetimeofPEFCsarediscussed,andtheadvantagesofthecombinationofareformer unitandamembranereactortocircumventtheselifetimelimitationsforasustainablepower productionoutofhydrocarbonfuelsareshown.InChapter12(Ghasemzadeh,Basile,and Aghaeinejad-Meybodi),anoverviewofthemainissuesdealingwiththecouplingbetween solarplantandmembranereactorispresentedasanoveltechnology,inwhichdifferentprocessessuchaswaterelectrolysis,waterdecomposition,andsteamreformingare investigated.

Chapter13(MadaeniandSalehi)dealswithadsorption-membraneintegratedsystems/ processes.Integrationofadsorptionandmembranesystemsisapromisingsolutionfor theproblemsofindividualprocesses.Membraneadsorptionbioreactorsandmembrane adsorbentsarethemostattemptedadsorption/membraneintegrationswithanimproved separationperformance.

Theeditorswouldtakethisopportunitytoparticularlythankalltheauthorsfortheir excellentworkandavailabilityinpreparingandreviewingthechaptersofthisbook.Special thanksalsotothevariousexpertsofWiley:theirspecialistichelphighlycontributedto improvethefinalpresentationofthisbook.

AngeloBasile CatherineCharcosset

Ultrafiltration,Microfiltration, NanofiltrationandReverseOsmosisin

IntegratedMembraneProcesses

CatherineCharcosset

Laboratoired’AutomatiqueetdeG ´ eniedesProc ´ ed ´ es,CNRS,Universit ´ eLyon1, VilleurbanneCedex,France

1.1Introduction

Membranescienceandtechnologyhaveknownanimpressivegrowthsincetheearly1960s whenLoebandSourirajandiscoveredaneffectivemethodforthepreparationofasymmetric celluloseacetatemembraneswithincreasedpermeationfluxwithoutsignificantchangesin selectivity.Pressure-drivenseparationtechniquessuchasmicrofiltration(MF),ultrafiltration(UF),nanofiltration(NF)andreverseosmosis(RO)havethenbeenextensivelystudied anddevelopedinindustriesincludingdesalinationandwastewatertreatment,biotechnologyandpharmaceutics,chemicalandfoodindustries.Othermembraneprocesseshave beendevelopedandfoundindustrialapplicationssuchasgasseparationandpervaporation, membranedistillation(MD),electrodialysis(ED),membranebioreactor(MBRs),andmembranecontactors.Membranetechnologyisusuallyrecognizedforthefollowingadvantages: operationalsimplicity,lowenergeticrequirements,goodstabilityunderawiderangeof operativeconditions,higheco-compatibility,easycontrolandscale-up,largeflexibility[1].

Withtheincreasingunderstandinganddevelopmentofmembranetechniques,itbecame possibletointegratevariousmembraneoperationsinthesameprocesswiththepurposeto improveperformanceintermsofproductquality,plantcompactness,environmentalimpact, andenergyuse.Theconceptofintegratedmembraneprocessesappearsclearlyattheend

IntegratedMembraneSystemsandProcesses,FirstEdition.EditedbyAngeloBasileandCatherineCharcosset. ©2016JohnWiley&Sons,Ltd.Published2016byJohnWiley&Sons,Ltd.

ofthe1990s[1]whenseveralapplicationswerereportedsuchashybridprocessNF–ED fortreatmentofpulpbleachingeffluents[2],multistagesUF,NFandROforremovalof contaminantsfromwastewatereffluents[3]andRO–MDforseawaterdesalination[4].In thefollowingyears,itbecamemoreandmoreobviousthatothercombinationscouldhave significantimpact[5],suchasMBR–ROforwastewatertreatment[6],pressure-driven membraneprocesses–MDforthetreatmentofwastewaters[7],andmultistagespressuredrivenmembraneprocessesforhigh-resolutionseparationsofbiomoleculesfromfoodand biotechnologyfeeds[8].

Inthischapter,somegeneralbackgroundsonmembraneprocessesarefirstrecalled includingpressure-drivenprocesses(MF,UF,NF,RO),andMD,EDandMBRs.Examplesofmembraneintegratedprocessesarethengivensuchasmultistagespressuredriven membraneprocessesandpressure-drivenmembraneprocessesassociatedtoMD,EDor MBRs.Applicationsconcernseawaterdesalination,wastewatertreatment,separationin biotechnologyandfoodindustriesandchemicalproduction.Thesehybridmembranetechniquesarefurtherdetailedinthefollowingchaptersofthebookaswellasotherintegrated membraneprocesses.Integratedmembraneprocessesincludinggasandvapourseparation andcatalyticmembranereactorsareconsideredinthesecondpartofthisbook.Another importantaspectofintegratedmembraneprocessesconcerntheirassociationwithprocesses otherthanmembranes.Thisisalsoconsideredinthefollowingchapters.

1.2MembraneProcesses

Variousmembraneoperationsareavailableforawiderangeofindustrialapplications. Pressure-drivenmembraneprocessesincludeMF,UF,NFandRO.Othermembraneunit operationsincludeMD,EDandMBRs.

1.2.1Ultrafiltration,MicrofiltrationandNanofiltration

UFisasizeexclusionpressure-drivenseparationprocesswhichcameintouseinthe1960s whenLoebandSourirajandiscoveredthepreparationofasymmetriccelluloseacetate membranes[9].UFmembranestypicallyhaveporesizesintherangeof10–1000 ˚ Aand arecapableofretainingspeciesinthemolecularweightrangeof300–1,000,000Da. Operatingpressuresareusuallyintherangeof0.2–4bar.Typicalrejectedspeciesinclude biomolecules,polymersandcolloidalparticles,aswellasemulsionsandmicelles.UFis foundinaverylargerangeofindustriessuchasfood,biotechnologyandpharmaceutics, chemicalsandwaterproduction.

MFisapressure-drivenseparationprocesssimilartoUFwithmembranestypically havingnominalporesizesontheorderof0.1–1.0 μm[9].MFapplicationsincludeconcentrating,purifyingorseparatingmacromolecules,colloidsandsuspendedparticlesfrom solution.MFprocessingiswidelyused,forexample,inthefoodindustryforapplications suchaswine,juiceandbeerclarification,forwastewatertreatment,andplasmaseparation frombloodfortherapeuticandcommercialuses.

NFdatesbacktothe1970swhenROmembraneswitharelativelyhighwaterflux operatingatrelativelylowpressuresweredeveloped[10,11].Suchlow-pressureRO membranesweretermedNFmembranes.NFisapressure-drivenmembraneprocess, involvingpressuresbetween5and20bar,usedtoseparateionsandmoleculesinthe

molecularweightrangeof200–2000gmol 1 .NFmembraneshaverelativelyhighcharge andaretypicallycharacterizedbylowerrejectionofmonovalentionsthanthatofROmembranes,butmaintaininghighrejectionofdivalentions.Applicationsincludepretreatment beforedesalination,watertreatment,foodindustry,chemicalprocessingindustry,pulpand paperindustry,metalandacidrecovery,etc.

1.2.2ReverseOsmosis

RObecamecommerciallyviableinthe1960swhenLoebandSourirajandiscoveredasymmetricmembranes.ROisapressure-drivenprocessthatseparatedtwosolutionswith differentconcentrationsacrossasemi-permeablemembrane[12].InRO,thepressuredifference Δp betweentheconcentratedsideandthedilutesideislargerthanacertainvalue thatdependsuponthedifferenceoftherespectiveconcentrationsandiscalledtheosmotic pressuredifference Δπ.Thedirectionofflowisreversedasobservedinosmosisandwater flowsfromtheconcentratetothediluteside.Therateatwhichwatercrossesthemembrane isthenproportionaltothepressuredifferentialthatexceeds Δπ.Inordertoovercomethe feedsideosmoticpressure,fairlyhighfeedpressureisrequired.Inseawaterdesalination itcommonlyrangesfrom55to70bar.Operatingpressuresforthepurificationofbrackish waterarelowerduetothelowerosmoticpressurecausedbylowerfeedwatersalinity.The mostcommonlyusedapplicationsofROaredesalination,brackishwaterandwastewater treatmentandconcentratingfoodandbiotechnologicalpreparations.

1.2.3MembraneDistillation

MDisathermallydrivenmembraneprocessinwhichahydrophobicmicroporousmembraneseparatesahotandcoldstreamofwater[13].Thehydrophobicnatureofthemembranepreventsthepassageofliquidwaterthroughtheporeswhileallowingthepassageof watervapour(Figure1.1).Thetemperaturedifferenceproducesavapourpressuregradient

Aqueous solution

membrane

r

Figure1.1 Schematicdiagramillustratingtheprincipleofmembranedistillation.

whichcauseswatervapourtopassthroughthemembraneandcondenseonthecoldersurface.Theresultisadistillateofveryhighpurity.MDhasbeendevelopedintofourdifferent configurations,differingbythemethodemployedtoimposethevapourpressuredifference acrossthemembrane.Thepermeatesideofthemembranemayconsistofacondensingfluid indirectcontactwiththemembrane,acondensingsurfaceseparatedfromthemembraneby anairgap,asweepinggas,oravacuum.MDhasbeenappliedforwaterdesalination,waste treatment,andfoodprocessinglikemilkandjuiceconcentration,biomedicalapplications suchaswaterremovalfrombloodandtreatmentofproteinsolutions[14].Indesalination byMD,theheatedseawaterisindirectcontactwithonesideofthemembrane.Saltsand organicmatterstayinthefeedwhilepurewaterdiffusesthroughthemembrane.

Osmoticdistillation(OD)isavariantofMDforwhichthedrivingforceisadifferencein concentration.ODusesthehydrophobicmicroporousmembranetoseparatetwoaqueous solutionshavingdifferentsoluteconcentrations:adilutesolutionononesideandahypertonicsaltsolution(concentratedbrinestripper)ontheoppositeside[15].Thehydrophobic natureofthemembranepreventspenetrationoftheporesbyaqueoussolutions,creating airgapswithinthemembrane.Thewatervapourpressuregradientacrossthemembrane determinesatransferofvapouracrosstheporesfromthehighvapourpressurephasetothe lowone.Thismigrationofwatervapourresultsintheconcentrationofthefeedanddilution oftheosmoticagentsolution.ODcanproceedatambienttemperatureandisanattractive processfortheconcentrationofsolutionscontainingthermo-sensitivecompoundssuchas fruitjuicesandpharmaceuticals.

Membranecrystallization(MCr)[16]hasbeenproposedasanextensionofMD:solutions,concentratedabovetheirsaturationlimitbysolventevaporationthroughmicroporous hydrophobicmembranes,reachasupersaturatedstateinwhichcrystalsnucleateandgrow. Thecrystallizingsolutionflowsalongthemembranefibres.Thedrivingforceoftheprocess isavapourpressuregradientbetweenbothsidesofthemembranewhichmaybeactivated byheatingthefeedsolution.MCrismainlyappliedatlaboratoryscalefortheformationof crystalswithwell-controlledpropertiesandthetreatmentofbrinedisposalfromROplants.

1.2.4Electrodialysis

ThegeneralprincipleofEDisknownsincethe1940s.Theprocessisbasedonthemovementofchargedspeciesinanelectricalfield:anionsmovetowardstheanode,whilecations areattractedbythecathode[17].Themovementoftheionsiscontrolledbyion-selective membranesbetweentheanodeandcathode.Anion-exchangemembranes(AEM)arepermeableforanions,whilecationsareheldback.Cation-exchangemembranes(CEMs)show theoppositebehaviour.TheEDstackisdividedintoseveralcellsbyAEMandCEMinan alternatingsequence(Figure1.2).ThebasicunitofanEDstackconsistsofapairofdiluted andconcentratedcompartments.Theconcentrationofionicspeciesisreducedinthediluted compartmentsandincreasedintheconcentratedcompartments.Onemajoradvantageof EDcomparedtoROisthatahigherbrineconcentrationcanbeachievedbecausethereisno osmoticpressurelimitation.Someofthemoreimportantlargescaleindustrialapplications ofconventionalEDincludebrackishwaterdesalination,wastetreatment,demineralization offoodproductsandtablesaltproduction[17].

ConventionalEDcanbecombinedwithbipolarmembranesinaprocesstermed bipolarmembraneelectrodialysis(BMED)[17].Bipolarmembranesarecomposedof

Figure1.2 Schematicdiagramillustratingtheprincipleofelectrodialysis. Source: Reproduced fromReference17withpermissionfromElsevier.

cation-andanion-exchangelayerswitha4–5nmthicktransitionlayerarrangedbetween twoelectrodes;theyareinstalledinalternatingseriesinanelectrodialysisstack.CommercialplantsofBMEDareutilizedtoproduceacidsandbasesfromthecorrespondingsalts.

1.2.5MembraneBioreactors

MBRshavebeenstudiedfromthe1980sasalternativeapproachestoclassicalmethods ofimmobilizingmicroorganisms,suchasenzymes,antibodiesandactivatedsludge.The microorganismsaresuspendedinsolutionandcompartmentalizedbyamembraneina reactororimmobilizedwithinthemembranematrixitself.Inthefirstmethod,thesystem consistsofatraditionalstirredtankreactorcombinedwithamembraneseparationunit, suchasUFandMF.Inthesecondmethod,themembraneactsbothasasupportforthe microorganismsandasaseparationunit.

Today,membranebioreactorsystemsareappliedatindustrialscaleforwatertreatment suchasindustrialwastewater,domesticwastewaterandspecificmunicipalwastewater [18,19].Conventionaltreatmentofwastewaterusuallyconsistsofathree-stageprocess: sedimentationofsolidsinthefeedwaterfollowedbyaerobicdegradationoftheorganic matterusingactivatedsludgeandthenasecondsedimentationprocesstoremovethe biomass.AnMBRcandisplacethetwophysicalseparationprocessesbyfilteringthe biomassthroughanMForUFmembrane.MBRspresentseveraladvantagescomparedto activatedsludgeplantsincludingtheircompactness(uptofivetimesmorecompactthan conventionalplants),reducedsludgeproduction,andhigherproductwaterquality[20]. ThetwomainMBRconfigurationsareimmersedandexternalconfigurationswhichare characterizedbydifferentoperatingconditions(membranematerial,filtrationmode,shear stress,etc.).Membranesareusuallyflatsheetorhollowfibres(immersedconfiguration)or multitube(externalconfiguration).

1.3CombinationofVariousMembraneProcesses

Membraneprocessescanbeassociatedintheoverallpurificationorproductionschemes inindustrialapplications.Theyoftenincludepressure-drivenmembraneprocessesaspretreatmentbeforeotherpurificationstepsorasafinaltreatment.Pressure-drivenmembrane processesmaybeassociatedwithotherprocessessuchasMD,MBRsandED.Some examplesinthefieldofwastewatertreatment,desalination,foodindustryandbiotechnology andpharmaceuticsaregiveninsection1.3.1.

1.3.1Pressure-DrivenSeparationProcesses

Duetotheirdifferentretentionproperties,pressure-drivenmembraneprocessescanbe associatedinacascadeconfigurationinapurificationscheme.Atafirststep,setting, flocculation,sandorcartridgefiltrationsservetoremoveverylargeparticles.Then,MF canbeusedtoremovelargecompounds,suchassuspendedparticles,colloidalmaterials andbacteria.TheobtainedsuspensioncanbetreatedbyUFtoseparateorremovemacromolecules,colloids,solutesinthemolecularweightrangeof300–1,000,000Da.NForRO canthenbeusedtoremoveverysmallmoleculesandsalts.Inageneralway,itcanbeseen thatdifferentmembraneprocessesinacascadearecloselylinked.Themembraneatstep n reducesfoulingofthemembraneatstep n + 1,thusincreasingthepermeationfluxand reducingthefluxdecay.Atstep n + 1,themembraneperformancedependsonsteps <n. Astheseintegratedprocessesareusedtotreatindustrialsuspensionssuchaswastewater effluentandfoodandbiologicalsuspensions,itcanbeforeseenthattheirbehaviourwillbe verydifficulttopredict.

1.3.1.1Pre-treatmentinSeawaterDesalination

Theapplicabilityofmembranesinseawaterdesalinationhasincreasedinthelast30years withmorethan2000ROinstallationsoperatingworldwide.Manydesalinationplantshave beenchangedtousemembraneprocessesbecausetheyaremuchmoreenergeticallyefficient thanthermaltechniques.InseawaterROdesalination,pre-treatmentservestoreducefoulingpotential,increasemembranelife,maintainperformancelevelandminimizescalingon theROmembranesurface[12].MostROplantsusedchemicalandphysicalpre-treatment withoutmembranetechnologies.Physicalpre-treatmentgenerallyusesflocculation,settling,sandfiltrationandcartridgefiltrationtoobtainfeedwaterwithalowsiltdensity index(SDI),whereSDIdescribesthefoulingpotentialofthefeedwaterandisdetermined infiltrationtestswithMFmembranes.Chemicalpre-treatmentincludeschlorinationto disinfectthewaterandpreventbiologicalgrowth,coagulationandflocculationagents,pH adjustment,antiscalingagentstoreduceprecipitationofsaltsontheROmembranesurface anddechlorinationpriortotheROstagetoavoiddamageofthemembranebyoxidation.

Theinterestinmembranepre-treatmentpriortoROhasbeenrecognizedformany years[21]buthasbeenlimitedbyhighcostcomparedtoconventionalpre-treatment. Withadvancesinmembranetechnologyandincreasingrequirementsonwaterquality,the useofmembranepre-treatmentpriortoROisnowasuitablealternativetoconventional pre-treatment[12].Itisgenerallyestimatedthatmembranepre-treatmentwillrapidly growinthecomingyears.BothUFandMFmembranes,usedaspre-treatmentunits,are abletoremovesuspendedparticles,colloidalmaterials,bacteria,virusandpathogenic

microorganismsfromrawwater.TheyguaranteeanSDIoftheROfeedwatergenerally below2.5evenwithstrongfluctuationofrawwaterquality,enablingoperationwitha highandstablepermeatefluxeveninlong-termoperation.Theyusuallyrequireless chemicaladditionthanconventionalpre-treatment,whichischaracterizedbyaratherhigh consumptionofchemicals.Inaddition,membranesystemsrequiresignificantlylessspace thanconventionalpre-treatment.

Membranepre-treatmentpriortoROhasbeensuccessfullyappliedatlaboratoryscale andpilotscale.Atlaboratoryscale,Kumaretal.[22]comparedMFandUFmembranes usingdead-endfiltrationbeforeROexperiments.Naturalseawaterwasfirstfilteredthrough a1 μmprefilter.MFpretreatmentwasfoundmoreeffectiveinreducingROfoulingthanconventionalfiltration.UFpretreatmentwiththe100kDamembranedidnotdecreasefouling comparedtotheMFmembrane.The20kDaUFmembraneswasthemosteffectiveinreducingfoulingbutoperatedathigherpressuresforthesamefluxastheMFand100kDaUF membranes.Atthreedifferentlocations,Vialetal.[23]operatedalong-termpilotequipped with0.1 μmhollowfibreMicrozaROmembranesforpre-treatmentofMediterraneanseawater.Dependingonthelocation,thepilotsoperatedwithorwithoutpre-treatmentusing ferricchlorideandwithorwithoutdailysodiumhypochloritebackwash.Thesystemoptimizationyieldedstable,reproduciblepermeateflowandpermeateSDIbelow1.8.Water qualityallowsROoperationathighrecovery,enhancingthetotalsystemrunningcost.

UFwasalsodemonstratedtoprovideexcellentpre-treatmenttoROatvariousdesalinationsites,forexampleinSaudiArabia,GulfofMexico,theRedSeaandtheMediterranean [24],andatQingdaoJiaozhouBay,theYellowSeainChina[25].Forexample,Pearce etal.[24]operatedUFpre-treatmenttoROdesalinationfora6-monthperiodatJeddah Port,SaudiArabia,asanalternativetoitsconventionalpre-treatmentfacility,whichcould notmeettargetedfeedwaterqualityduringperiodsofalgalbloomandstorms.Anaverage filtrateSDIof2.2wasobtained,approximatelytwounitsbetterthantheexistingconventionalpre-treatment.Xuetal.[25]utilizedUFhollowfibremembranesaspretreatment priortoROdesalinationatQingdaoJiaozhouBay,theYellowSeainChina(Figure1.3).

Figure1.3 TheUF–ROpilotsystemforseawaterdesalination.(a)Schematicdiagramofthe pilotsystem.(b)Photographofthepilotsystem. Source: ReproducedfromReference25with permissionfromElsevier.

Duringtheexperimentalperiods,theUF–ROsystemwasrunstablyandsuccessfully,withoutanychemicalsrequiredfordisinfection,flocculation,enhancedchemicalbackwashand cleaning.

TheuseofNFupstreamROisalsoapossiblealternativeaswaterhardnesscanthusbe stronglyreduced,andthemostpartofmultivalentionscanberejected[26,27].Inaddition, monovalentspeciesareretainedby10–50%,dependingontheirmolecularweightand electrostaticinteractionswiththemembrane.Asaconsequence,theosmoticpressureof ROfeedandretentatestreamsisdecreased,thusallowingthesystemtooperateathigh waterrecoveryfactorswithaconsiderabledecreaseinscaleformingcomponents.For applicationatindustrialscale,theSalineWaterConversionCorporation(SaudiArabia)has developedNFpretreatmentpriortoRO.Initialworkonapilotplantscale,resultedinits applicationinoneofthecommercialROplantsatUmmlujjinoperationsinceSeptember 2000.Al-Hajourietal.[28]detailedthelong-termoperationoftheNF–ROplantaswell asdifferentresearchprogramswhichwereundertakenandtheresultsobtained.

Thecomparisonofoverallcostsofmembranepre-treatmentandconventionalpretreatmentmaydependonsite-specificfactors[12].Fluctuationsinthefeedwaterquality intermsofturbidityandtotaldissolvedsolids(TDS)aswellasalgaebloomcancause problemsforconventionalpre-treatment,whichmightresultinadditionalcost.Membrane pre-treatmentsarelesssensitivetofluctuationsoffeedwaterqualityandsupplytheRO stagewithsuperiorwaterqualityforlong-termoperation.Membranepre-treatmentthereforemightbeabletoincreaseROmembranelifeandensurestableoperationevenunder adverseconditionsandcouldthusleadtooverallcostreductions.

1.3.1.2TreatmentofWasteEffluents

Asindustrialeffluentsareverycomplexmixturesofcontaminantssuchassuspended solids,moleculesandsalts,severalpressure-drivenmembraneprocesseswithdifferent propertiesmaybeneededtoobtainacompletetreatment.MF,UF,NFand/orROin acascadepurificationschemecanbeadequatealternativestootherprocessessuchas coagulation/flocculation,sandorcartridgefiltration,adsorption,etc.Theapplicationof membraneprocessesinthetreatmentofindustrialwastewaterscangiveareductionofthe environmentalimpact,asimplificationofcleaningproceduresofaqueouseffluents,aneasy re-useofsludge,adecreaseofdisposalcostsandasavingofchemicals,waterandenergy [5].Theseprocesseshavebeenreportedfortreatmentofseveralwasteeffluentsfromthe leather,coke,dairyoliveandoilindustries.

Intheleatherindustry,traditionallyconsideredasoneofthemostpollutingindustries, conventionalchrometanningproducesspentliquorscontainingsignificantamountsof chromiumandotherpollutingsubstances,bothorganicandinorganic.Cassanoetal.[29] recoveredandconcentratedchromiumsaltsthroughanintegratedmembraneprocessat laboratoryscale(Figure1.4).Thespenttanningliquorsweresubjectedtoapreliminary UFsteptoremovemostsuspendedsolidsandfatsubstances.Thepermeateobtainedfrom theUFtreatmentwasthensubjectedtoNFinwhichchromiumsaltswereconcentratedto afinalvalueofabout10g/L.TheUFpretreatmentreducedfoulingoftheNFmembrane, thusimprovingthepermeationfluxandreducingthefluxdecay.

Incokingindustries,thetreatmentofdesulphurizationwastewaterandtherecovery ofusablesubstancessuchassuspendedsulphur(SS)andammoniumsalts,forexample,

Figure1.4 SchemeoftheUF/NFprocessfortherecoveryofchromiumfromspenttanning effluents. Source: ReproducedwithpermissionfromReference29.Copyright2007American ChemicalSociety.

(NH4 )2 S2 O3 andNH4 SCN,isofmajorconcernandcanavoidsevereenvironmentalproblemsinthecaseofimproperdisposal.Yinetal.[30]proposedanintegratedmembrane processconsistingofUF,NFandROtotreatthewastewater.Thepermeateresultingfrom theUFtreatmentwasthenintroducedtoanNFprocessinwhichbivalentammoniumsalts wereseparatedfrommonovalentammoniumsalts.ThefinalROprocesswasrepeatedly appliedtothetreatmentoftheNFpermeatetoseparatemonovalentsaltsandwater.Both theNFandROretentateswerecirculatedinthesystemforfurtherdialysistoobtainpure saltproducts.

Thedairyindustrygeneratesalargeamountofwastewater,whichcontainshighlevels ofsuspendedsolids,ammonia,proteinandothernutrients.UF,NFandROhavebeen proposedfordairywastewatertreatmenttoproducepurifiedwaterforwaterreuseor recovernutrients.Atwo-stagemembraneprocesswithUF + NFwasinvestigatedto producewaterfordischargeandrecoverthenutrientinwastewater[31].Therecovered nutrientcouldbeusedforfeedproduction.UFoperationcouldremovetheproteininraw wastewateranddecreasethemembranefoulingintheNFprocess.ComparedwithRO operation,transmembranepressurewaslowerandthemembranefluxwashigherthanin NFoperation.

Asimplifiedintegratedmembranesystemwasalsoreportedtobesuccessfulinthe treatmentofolivemillwastewaters[32].Theintegratedmembraneprocessincludedan initialUFstepwith0.02 μmnominalporesizehollowfibremembranesfortheremoval ofsuspendedsolidsfromolivemillwastewaters.ThefirstUFpermeatewastreatedby asecondUFprocessbyusingaflat-sheetmembranehavingamolecularweightcut-off of1000Da.Finally,theresultingpermeatestreamwassubmittedtoanNFprocessto obtainaconcentratedphenolicsolution.Withthisintegratedprocess,differentfractions wereproduced:(1)aconcentratedsolutioncontainingorganicsubstancesathighmolecular

weight(retentateofbothUFprocesses),(2)aconcentratedsolution(NFretentate)enriched inpolyphenoliccompoundssuitableforcosmetic,foodandpharmaceuticalindustriesand (3)awaterstream(NFpermeate)whichcanbereusedintheoliveoilextractionprocessas processwaterorintheintegratedmembranesystemasmembranecleaningsolutionorin thediafiltrationsteptoincreasetheyieldofpolyphenolsinUFpermeates.

1.3.1.3FoodandBiotechnologyIndustries

Infoodandbiotechnologyindustries,feedsarealsocomplexandmulticomponent.Membraneprocessperformancesforbiomoleculefractionation,concentrationandpurification fromthesefeedsarethenmuchmorelimitedthanfromsimpleones.Theselastyears,a numberofsolutionshavebeenproposedtoachievehigh-resolutionseparations.Forexample,ZydneyandvanReis[33]haveexploitedanumberofdifferentstrategiestoobtain highperformancetangentialflowfiltration(HPTFF),acompleteprocedurewhichincludes: (1)properchoiceofpHandionicstrengthtomaximizedifferencesinthehydrodynamic volumeoftheproductandimpurity,(2)useofelectricallychargedmembranestoenhance theretentionoflikechargedproteins,(3)operationinthepressure-dependentregimeto maximizetheselectivityand(4)useofadiafiltrationmodetowashimpuritiesthroughthe membrane.Cascadeormultistagemembranesystemshavebeenproposedfromthemid2000sasanalternativetoachievethesehigh-resolutionseparations.MF,UFandevenNF membranes,withdifferentorsimilarproperties,canbeconsideredatthedifferentstages ofthecascade[34].Insuchsystems,themannerinwhichthedifferentflowsstreamwithin thecascade(e.g.recyclingofretentates)contributestowardsefficiencyofseparationand notmerelythenumberofstages[35].

Inthebiotechnologyindustry,separationofbiomoleculesfromfermentationbroths isacommonoperation.Zhouetal.[36]investigatedtheuseofatwo-stagetangential flowfiltrationprocessfortheseparationofhyaluronicacidfromfermentationbroth.MF membranes(0.45and0.20 μmsize)andUFmembranes(300and100kDa)wereusedto achievetheseparationinseries.Thetwo-stagemembraneprocesswasundertakenwithtwo separatingschemes:thefirstusingMFfollowedbyUFwithpurewaterasdiafiltrate,the secondsimilartothefirstexceptpermeatefrompreviousUFstageasdiafiltrateforMF stage.Thetwoschemescouldeffectivelyseparateandpurifyhyaluronicacidwithabove 77%overallyieldandabout1000purificationfactor.Thesecondschemeseemedtobe moreeffectiveforitshigheroverallyield(89%)andsavingwater.Athree-stageprocess (MF,UF,NF)wasalsodesignedforthepurificationofsweetenersfrom Steviarebaudiana Bertoni[37].Retentionsofthesweetenersforasyntheticmixtureandplantextractwere measuredincombinationwithfluxdecline.Startingfromanextractpurityof11%withthe overallprocess,apurityof37%andayieldof30%couldbereached.Itwasconcludedthat thisprocessshouldbeseenasapre-treatmentpriortootherpurificationsteps,forinstance crystallization.

Inthedairyindustry,thereiscommercialinterestintheproductionofindividualwhey proteinswithwell-characterizedfunctionalandbiologicalpropertiessuchas α-lactalbumin (α-LA)and β-lactoglobulin(β-LG).Atwo-stagetangentialflowfiltrationsystemhasbeen proposedforthepurificationofboth α-LAand β-LGfromwheyproteinisolate[8].Separationwasachievedusing100and30kDamembranesinseries.Twopurificationstrategies wereexamined(Figure1.5).InStrategyI,the100kDamembranewasusedinthefirststage

Feed

DF1 BSA WPI

Membrane 100 kD

Retentate 1

Permeate 1

α-LA, β-LG

UF-DF2

Membrane 30-kD

Retentate 2

Strategy I

β-LG

Permeate 2

α-LA

Retentate 1 DF1

Membrane 30 kD

Permeate 1

Strategy II

β-LG BSA

Feed WPI BSA

α-LA

Retentate 2 DF2

β-LG Membrane 100 kD

Permeate 2

Figure1.5 Schematicdiagramshowingtwoseparationstrategiesforthepurificationof α-LA and β-LGfromwheyproteinisolate.Eachblockrepresentsaseparatediafiltrationprocess. Source: ReproducedfromReference8withpermissionfromElsevier.

toremovebovineserumalbumin(BSA)whilecollecting α-LAand β-LGinthepermeate solution.Thecollectedpermeatewasthenusedasafeedinthesecondstagewherethe α-LAand β-LGwereseparatedusinga30kDamembrane.Themembranecombination wasreversedinStrategyII,withthe30kDamembraneusedinstageItoobtainpurified α-LAinthepermeatesolutionwhileretainingthe β-LGandBSA.Thecollectedretentate wasthenseparatedinstageIIusinga100kDamembrane.Inordertoachievehighdegrees ofpurificationandyieldduringtheproteinseparation,thefiltrationsinstagesIandII werebothperformedusingadiafiltrationprocesstoeffectivelywashthemorepermeable protein(s)throughthemembrane.Inbothcases,the α-LApurificationwasgreaterthan

10-foldat90%yield.Therecoveryof β-LGwasmorechallengingsinceitwasobtainedin thepermeatefromonestageandtheretentatefromtheother.Theauthorsconcludedthat stagedmembraneprocessesforhigh-resolutionseparationsrequirefurtherexperimental andtheoreticalinvestigationstoreachoptimalperformances[8].

1.3.2MembraneDistillationandPressure-DrivenMembraneProcesses

MDcanmakeasignificantcontributioninincreasingtheefficiencyoftheROprocess [4].InRO,theosmoticeffectoftendoesnotpermitreachingvaluesofinterest.InMD, concentrationpolarizationphenomenadonothavethesamelimitingeffect.Therefore, purewatercanbeobtainedbyMDfromhighlyconcentratedfeeds,withwhichROcannot operate.Hybridpressure-drivenmembraneprocessesandMDhavebeenimplemented mainlyindesalinationunits,inproductionofhighconcentratesolutionsinthebeverage industryandintreatmentofwastewaters.

SeawaterdesalinationbyROislimitedbytheosmoticpressure;therefore,ahighrecovery factorisnotattainable.Consequently,largevolumesofbrinearedischargedintotheseaand thepermeateflowrateislimited.Fromtheendofthe1990s[4],MDhasbeeninvestigatedto concentrateRObrineandincreasetheglobalrecoveryoftheprocess.Inthefollowingyears, aspecificattentionwaspaidtooptimizeoperatingconditionssuchasahighlypermeable membrane,highfeedtemperature,lowpermeatepressureandaturbulentfluidregime.At theseoperatingconditions,Mericqetal.[38]obtainedhighpermeateflowratesevenat averyhighsaltconcentration(300gL 1 ).Athighsaltconcentrations,scalingoccurred (mainlyduetocalciumprecipitation)buthadonlyalimitedimpactonthepermeateflux (24%decreaseforapermeate-specificvolumeof43Lm 2 forthehighestconcentration ofsalt).Aglobalrecoveryfactorof89%wasobtainedbycouplingROandMD.When MCrunitfollowsNFand/orRO,thehighlyconcentratedbrinedoesnotrepresentwastebut ratherthemotherliquorinwhichcrystalsmaynucleateandgrow.LikeMD,MCrleadsto afurtherincreaseoftheoverallwaterrecoveryfactor.BeforetheMCrunit,Ca2+ ionsare precipitatedascarbonatesbyaddingNa2 CO3 .Thisisnecessaryinordertoavoidcalcium sulphateprecipitation,whichcausesscaleanddrasticallylimitstherecoveryofmagnesium sulphate[26].

ThepossibilityofintegratingMDafterpressure-drivenmembraneprocesseshasalso beenreportedinthebeverageindustryforproducingvarioushighconcentratedfruitjuices (orange,apple,kiwifruit,passionfruit,etc.)[39,40].Separatingthesuspendedsolidsand pectinsfromjuicesbyUForMFdecreasesviscosityandincreasesfluxofROand/or OD,maximizingyieldandminimizingnutrientandflavourlosses.Forexample,Galaverna etal.[41]reportedtheproductionofconcentratedbloodorangejuiceaccordingtothe followingscheme:aninitialclarificationoffreshlysqueezedjuicebyUF;theclarified juicewassuccessivelyconcentratedbyRO,usedasapre-concentrationtechnique(up to25–30 ◦ Brix),thenOD,uptoafinalconcentrationofabout60 ◦ Brix(Figure1.6). Theintegratedmembraneprocesswaspresentedasavaluablealternativetoobtainhigh qualityconcentratedjuice,asthefinalproductshowedaveryhighantioxidantactivityand averyhighamountofnaturalbioactivecomponents.Anintegratedmembraneprocess, whichinvolvedUF,ROandODwasalsoreportedtoconcentrateanthocyanin,anatural redcolorantfromredradish[42].Theintegratedmembraneprocesshadtheadvantagesof achievinghigherconcentrationofanthocyanincomparedtothatoftheindividualmembrane

Fruit juice (10–11°Brix)

Preconcentrated juice (25–26°Brix) Concentrated juice (63–65°Brix)

Figure1.6 Schemeoftheintegratedmembraneprocessfortheproductionofconcentrated orangejuice. Source: ReproducedfromReference41withpermissionfromElsevier.

processes.Finalconcentrationof26 ◦ Brix(from1 ◦ Brix)wasachieved,withanincrease intheconcentrationofanthocyaninfrom40to980mg/100mL.

HybridmembraneprocessesincludingMF,UFandNFandMDhavealsobeenusedfor treatmentofwastewatersuchaspurificationofoilywastewater[7],drainedwastewater[43], andtextiledyebathwastewater[44].Forexample,Grytaetal.[7]performedthetreatment ofoilywastewatercollectedfromaharbourwithoutpre-treatmentbyacombinationof tubularUFandcapillaryMDasafinalpurificationmethod.Thepermeateobtainedfrom theUFprocessgenerallycontainslessthan5ppmofoil.AfurtherpurificationoftheUF permeatebyMDresultedinacompleteremovalofoilfromwastewaterandaveryhigh reductionofthetotalorganiccarbon(TOC)(99.5%)andTDS(99.9%).

1.3.3ElectrodialysisandPressure-DrivenMembraneProcesses

Fromthe1990s,pressure-drivenmembraneprocesseshavebeenproposedasapre-treatment steppriortoEDfortreatmentofdifferenttypesofwastewaters.Ahybridprocessinvolving NF–EDwasdesignedtorecoverwaterfromalkalinepulpbleachingeffluenthavingahigh contentoforganicandorganochlorinatedcompoundsandsalts[2].NFwasselectedto removeorganiccompoundsandundertakepartialdesalination.Ahigherdegreeofwater puritywasfurtherachievedusingED.Inanotherapplication,ceramicMFmembraneswere reportedasapre-treatmentsteppriortoEDforremovalofcolourandcontaminantsfrom paperindustrywastewaters[45].Thehybridpilotplantwasfoundmoreefficientthanthe singleEDprocesssincetheceramicMFmembraneeliminatedthesuspendedcolloids.