啤酒废水处理再利用 47页

Thetreatmentofbrewerywastewaterforreuse:StateoftheartGeoffreyS.Simatea,⁎,JohnCluetta,SunnyE.Iyukea,EvansT.Musapatikaa,SehliseloNdlovua,LubindaF.Walubitab,AllexE.AlvarezcaSchoolofChemicalandMetallurgicalEngineering,UniversityoftheWitwatersrand,Johannesburg,P/Bag3,Wits2050,SouthAfricabTTI-TexasA&MUniversitySystem,CollegeStation,TX,USAcDepartmentofCivilEngineering,UniversityofMagdalena,SantaMarta,Magdalena,ColombiaabstractarticleinfoArticlehistory:Received25October2010Receivedinrevisedform11February2011Accepted12February2011nKeywords:BrewerywastewaterBiologicaloxygendemandChemicaloxygendemandPretreatmentTreatmentReuseThebeerbrewingprocessoftengenerateslargeamountsofwastewatereffluentandsolidwastesthatmustbedisposedoffortreatedintheleastcostlyandsafestwaysoastomeetthestrictdischargeregulationsthataresetbygovernmententitiestoprotectlife(bothhumanandanimal)andtheenvironment.Itiswidelyestimatedthatforeveryoneliterofbeerthatisbrewed,closetotenlitersofwaterisused;mostlyforthebrewing,rinsing,andcoolingprocesses.Thereafter,thiswatermustbedisposedofforsafelytreatedforreuse,whichisoftencostlyandproblematicformostbreweries.Asaresult,manybrewersaretodaysearchingfor:(1)waystocutdownonthiswaterusageduringthebeerbrewingprocess,and/or(2)meanstocost-effectivelyandsafelytreatthebrewerywastewaterforreuse.Basedontheavailabledocumentedliterature,thispaperprovidesareviewassessmentofthecurrentstatusofthebrewerywastewatertreatmentprocessesincludingpotentialapplicationsforreuse.Keychallengesforbothbrewerywastewatertreatmentandreusearealsodiscussedinthepaperandincluderecommendationsforfuturedevelopments.©2011ElsevierB.V.Allrightsreserved.Contents1.Introduction..............................................................2362.Legislationandenvironmentalmanagementsystems...........................................2363.Conventionalmethodsofpretreatingbrewerywastewater........................................2363.1.Physicalmethods........................................................2373.2.Chemicalmethods.......................................................2373.3.Biologicalmethods.......................................................2373.3.1.Aerobic........................................................2373.3.2.Anaerobic.......................................................2394.Treatmentofbrewerywastewaterforreuse...............................................2394.1.Membranefiltration.......................................................2404.2.Non-thermalquenchedplasma..................................................2414.3.Membranebioreactor......................................................2424.4.Combinedanaerobicandaerobictreatment............................................2424.5.Theuseofcarbonnanotubes...................................................2434.5.1.Nanosorbents......................................................2434.5.2.Nanofilters.......................................................2444.6.Electrochemicalmethods....................................................244n4.7.Microbialfuelcells.......................................................2444.8.Carbon.............................................................2445.Discussionandsynthesisoffindings..................................................2445.1.Comparisonofprocessesandtechnologies............................................2445.2.Integrationofprocessesandtechnologies.............................................245Desalination273(2011)235–247⁎Correspondingauthor.Tel.:+27117177570,+27761126959(Cell);fax:+27117177599.E-mailaddress:simateg@yahoo.com(G.S.Simate).0011-9164/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.desal.2011.02.035ContentslistsavailableatScienceDirectDesalinationjournalhomepage:www.elsevier.com/locate/desal6.Summary...............................................................245Disclaimer.................................................................246References..................................................................2461.IntroductionDespitedischarginglargevolumesofhighlypollutingeffluentsthroughouttheyear[1,2],thebrewingindustryconstituteanimportanteconomicsegmentofanycountry[3,4].Infact,beeristhefifthmostconsumedbeverageintheworldbehindtea,carbonates,milkandcoffee[3].Beerbrewinginvolvestwomainsteps,i.e.,brewingandpackagingofthefinishedproduct[5].Theby-products(e.g.,spentgrainsfrommashing,yeastsurplus,etc)generatedfromthesestepsareresponsibleforpollutionwhenmixedwitheffluents[5].Inaddition,cleaningoftanks,bottles,machines,andfloorsproduceshighquantitiesofpollutedwater[5].Itisestimatedthatfortheproductionof1Lofbeer,3–10Lofwasteeffluentisgenerateddependingontheproductionandspecificwaterusage[1,3,6].Inotherwords,verylargequantitiesofwaterareconsumedduringthebeerbrewingprocess.Similarlyandbecauseofvoluminouswaterusage,thebreweryindustrydischargeslargevolumesofhighlypollutingeffluentsthroughouttheyear[1,2].Itmustalsobenotedthateffluentsfromindividualprocessnstepsarevariable.Forexample,bottlewashingresultsinalargewastewatervolume,butitcontainsonlyaminorpartofthetotalorganicsdischargedfromthebreweryprocesses.Ontheotherhand,effluentsfromfermentationandfilteringarehighinorganics/biochemicaloxygendemand(BOD),butgenerallylowinvolume,accountingforabout3%ofthetotalwastewatervolumebut97%oftheBOD[7].Wastewaterfromabreweryplantmaybedischargedinseveralwaysincludingthefollowing[8,9]:(1)directlyintoawaterway(oceans,rivers,streams,orlakes),(2)directlyintoamunicipalsewersystem,(3)intothewaterwayormunicipalsewersystemafterthewastewaterhasundergonesomepretreatment,and(4)intothebrewery'sownwastewatertreatmentplant.Thedisposalofuntreated(orpartiallytreated)brewerywastewaterintowaterbodiescanconstitutepotentialorseverepollutionproblemstothewaterbodiessincetheeffluentscontainorganiccompoundsthatrequireoxygenfordegradation[10].Forexample,ifwaterofhighorganicmattercontentvalueflowsintoariver,thebacteriaintheriverwilloxidizetheorganicmatterconsumingoxygenfromthewaterfasterthantheoxygendissolvesbackintheriverfromtheair.Furthermore,asregulationsbecomemoreandmorestringentandthecostofwaterincreases,thecallforwaterrecyclingiscurrentlygainingalotofmomentum.Therearemanypapers,suchasthosereviewedbyFillaudeauetal.[3],dealingwithseveralaspectsofbrewerywastewatertreatment.However,areviewofthisliteratureshowsthatonlyinlateryearshasinformationbecomeavailableonwatertreatmentforreuse.Itmustbenoted,however,thatwastewaterreuseisnotcommoninthistypeoftheindustryduetopublicperceptionandthepossibleproductqualitydeteriorationproblems[11].However,thefuturereuseofbrewerywastewaterseemstobeunavoidable,astheissueofwatershortagehasbecomeaseriousglobalandenvironmentalproblem.Thisisparticularlyverycriticalinmostdevelopingcountriessuchasthesub-Saharanregionwheredroughtsareperpetual,thuseverydropofwatermustbepreciouslyconserved.Inthispaper,thepotentialopportunitiesthatmaybeavailablefortreatingbrewerywastewaterforreuseintwoapplicationsarereviewed,namely:(a)primarywaterusedintheproductionofbeer,and(b)secondarywaterthatdoesnotcomeincontactwithbeer;e.g.utilitiescooling,waterusedinthepackagingprocessandgeneralcleaningwater.Oncetechnologyimprovesandthepercep-tionshavechangedregardingtheuseofrecycledwater,beertowaterratiosisperceivedmaybereducedtotheratioofabout1:2.Pertinentchallengesasrelatedtobrewerywastewaterreuse(orrecycling)arealsodiscussedinthepaper.nThetreatment,recoveryandapplicationsofvariousbreweryby-products(e.g.,spentgrains,spenthops,surplusyeast,kieselghursludge,trubandwastelabels)havebeenextensivelydocumentedelsewhere[3,6,8,12–14],thusarenotdiscussedinthispaper.Accordingly,thepaperisorganizedasfollows:abackgroundofthelegislationandenvironmentalmanagementsystemsispresentedfirst,followedconsecutivelybybrewerywastewaterpre-andtreatment-methods.Challengesandfutureprospectsareincludedinthediscussiontowardstheend.Asummaryisthenprovidedtoconcludethepaper.2.LegislationandenvironmentalmanagementsystemsLikeanyotherindustry,thebrewingindustryissubjecttoextensivegovernmentregulations.Someoftheregulationsimposedinvolveproduction,distribution,labeling,advertising,tradeandpricingpractices,credit,containercharacteristics,andalcoholiccontentrequirements[9].Governmentalentitiesalsolevyvarioustaxes,licensefeesandothersimilarchargesandmayrequirebondstoensurecompliancewithapplicablelawsandregulations.Furthermore,themanagementofenvironmentalissuesisofgrowinginterestnowadays.Thereisaneedtounderstandtheimportantenvironmentalimpactsonthecommunityandthenconsidertheadvantagesanddisadvantagesassociatedwithvariouslevelsofenvironmentalmanagement[15].Thismeansthatthebrewingindustrymustalsocomplywithnumerousenvironmentalprotectionlaws.Infact,thebrewingindustryhasshownincreasingawarenessforenvironmentalprotectionandtheneedofsustainableproductionprocesses[16].Furthermore,mostnationalgovernmentswheretheseindustriesoperatehavesignedandratifiedtheKyotoProtocolaimedatreducinggreenhousegasemissions[17].Throughenvironmentalmanagementsystems(EMS)suchas,(1)ISO14001,(2)Eco-ManagementandAuditScheme(EMAS),and(3)Interna-tionalSafetyRatingSystem(ISRS),breweriesshouldbeabletoproactivelymanagetheirimpactsontheenvironment.Infact,EMSsshouldhelpbreweriesfocusoneffectiveandefficientmanagementofbothcurrentandfutureenvironmentalimpacts.TheInternationalFinanceCorporation(IFC)alsohasenvironmental,healthandsafety(EHS)guidelinesforbreweries[18].3.ConventionalmethodsofpretreatingbrewerywastewaterBrewerywastewatertypicallyhasahighchemicaloxygendemand(COD)fromalltheorganiccomponents(sugars,solublestarch,ethanol,volatilefattyacids,etc)[9].Itusuallyhastemperaturesnrangingfrom25°Cto38°C,butoccasionallyreachingmuchhighertemperatures.ThepHlevelscanrangebetween2and12[9]andareinfluencedbytheamountandtypeofchemicalsusedincleaningandsanitizing(e.g.,causticsoda,phosphoricacid,nitricacid,etc.)[9,16,19].Sanitizingchemicalswhichincludechlorinecompoundsensurethatthesurfacesarefreeofanymicroorganismsharmfultothebrewingindustryandthepublicconsumingthebeer.Nitrogenandphosphoruslevelsaremainlydependentonthehandlingofrawmaterialandtheamountofyeastpresentintheeffluent[9,16,19].Table1isanexampleofthephysicochemicalcharacteristicsofbrewerywastewaterfromtheUnitedBreweriesinIndia[20].236G.S.Simateetal./Desalination273(2011)235–247Infact,thebrewerywastewaterischaracterizedbylargevariationsintheparametersmentionedinTable1[21].Asaresult,mostlargebreweriesrequiresomedegreeofwastewaterpretreatment.Incaseswherethebrewerydoesnotdischargetothemunicipalsewer,thenprimaryandsecondarytreatmentoftheeffluentisrequired.However,ifthebreweryispermittedtodischargeintoamunicipalsewer,pretreatmentmayberequiredtomeetmunicipalbylawsand/ortolessentheloadonthemunicipaltreatmentplant.Insomecases,sewerdischargefeesimposedoneffluentvolume,andonthesuspendedandorganicloads,bythemunicipalitymayencouragethebrewerytoinstallitsowntreatmentfacility.Pretreatmentismeanttoalterthephysical,chemical,and/orbiologicalpropertiesoffeedwater[22],thusimprovingtheperformanceofupstreamprocesses.Therefore,pretreatmentisdonebyphysical,chemical,orbiologicalmethods,orbyacombinationofallthesemethods.Table2liststheunitoperationsincludedwithineachcategory,anddetailedschematicrepresentationofaconventionalwastewatertreatmentprocessescanbefoundinSpellman'sStandardHandbookforWastewaterOperators[23].Table3isasummaryofthegenericadvantagesanddisadvantagesofvariouswastewatertreatmentprocessesasshowninliterature[24].Thesecharacteristics(Table3)generallyrelatetothecostofconstructionandeaseofoperation.Generally,thecomplexityandcostofwastewatertreatmenttechnologiesincreasewiththequalityoftheeffluentproduced.Infact,thewatermanagementandwastedisposalinthebreweryindustryareconsideredassignificantcostfactorsandimportantaspectsintheoperationsofabreweryplant[25,26].3.1.PhysicalmethodsAmongthefirsttreatmentmethodsusedarephysicalunitoperations,inwhichphysicalforcesareappliedtoremovecontaminants.Physicalnmethodsremovecoarsesolidmatter,ratherthandissolvedpollutants.Itmaybeapassiveprocess,suchassedimentationtoallowsuspendedpollutantstosettleoutorfloattothetopnaturally.Ingeneral,thesemethodshaveyieldedlittlesuccess;mostoftenresultinginincompletecontaminantremovaland/orseparation.Forexample,sedimentationhasbeenfoundtobeunsatisfactoryevenwiththeadditionofcoagulantsandotheradditives[27].3.2.ChemicalmethodsDifferentchemicalscanbeaddedtothebrewerywastewatertoalterthewaterchemistry[22].ChemicalpretreatmentmayinvolvepHadjustmentorcoagulationandflocculation.Theacidityoralkalinityofwastewateraffectsbothwastewatertreatmentandtheenvironment.LowpHindicatesincreasingaciditywhileahighpHindicatesincreasingalkalinity.ThepHofwastewaterneedstoremainbetween6and9toprotectorganisms.WasteCO2maybeusedtoneutralizecausticeffluentsfromclean-in-places(CIP)systemsandbottlewashers[28].ThewasteCO2canalsobeusedasacheapacidifyingagentfordecreasingthepHofalkalinewastewatersbeforetheanaerobicreactor,thusreplacingtheconventionallyusedacids[20].NeutralizationwithH2SO4andHClacidsisusuallynotrecommendedbecauseoftheircorrosivenatureandsulfateandchloridedischargelimitations[29],whichmayaddtothecostofeffluenttreatmentoperations[20].Coagulationandflocculationarephysicochemicalprocessescommonlyusedfortheremovalofcolloidalmaterialorcolorfromwaterandwastewater.Inwaterandwastewatertreatment,coagu-lationimpliesthestepwhereparticlesaredestabilizedbyacoagulant,andthismayincludetheformationofsmallaggregatesbyBrownianmotion(perikineticcoagulation).Ontheotherhand,thesubsequentprocessinwhichlargeraggregates(flocs)areformedbytheactionofshearisthenknownasflocculation[30].Aftersmallparticleshaveformedlargeraggregates,colloidalmaterialcanthenbemoreeasilyremovedbyphysicalseparationprocessessuchassedimentation,flotation,andfiltration.3.3.BiologicalmethodsBiologicalwastetreatmentprocessesplayacentralroleinthewaysocietymanagetheirwastewaters.Itisbasedontheactivityofawiderangeofmicroorganisms,convertingthebiodegradableorganicpollutantsinthewastewaters.Infact,breweryeffluentshavingbothchemical(withveryhighorganiccontent)andmicrobialcontaminantsaregenerallytreatedbybiologicalmethods[31].Therefore,afterthebrewerynwastewaterhasundergonephysicalandchemicalpretreatments,thewastewatercanthenundergobiologicaltreatment.Comparedtophysicochemicalorchemicalmethods,biologicalmethodshavethreeadvantages[32]:(1)thetreatmenttechnologyismature,(2)highefficiencyinCODandBODremoval,rangingfrom80to90%,and(3)lowinvestmentcost.However,thoughbiologicaltreatmentprocessesareparticularlyeffectiveforwastewatertreatment,theyrequireahighenergyinput[33].Biologicaltreatmentofwastewatercanbeeitheraerobic(withair/oxygensupply)oranaerobic(withoutoxygen)[9].TheaerobicandanaerobicprocessesareshowngraphicallyinFig.1[34].Theseprocessesarediscussedinmoredetailsinthesubsequentsections.Generally,aerobictreatmenthassuccessfullybeenappliedforthetreatmentofbrewerywastewaterandrecentlyanaerobicsystemshavebecomeanattractiveoption[9].Table4presentsageneralcomparisonbetweenanaerobicandaerobicbiologicaltreatmentsystemssuchasactivatedsludge.3.3.1.AerobicAerobicbiologicaltreatmentisperformedinthepresenceofoxygenbyaerobicmicroorganisms(principallybacteria)thatmetabolizetheorganicmatterinthewastewater,therebyproducingmoreTable1Characteristicsofbrewerywastewater[20].ParameterValuepH3–12Temperature(°C)18–40COD(mgL−1)2000–6000BOD(mgL−1)1200–3600COD:BODratio1.667VFA(mgL−1n)1000–2500PhosphatesasPO4(mgL−1)10–5TKN(mgL−1)25–80TS(mgL−1)5100–8750TSS(mgL−1)2901–3000TDS(mgL−1)2020–5940Table2Wastewatertreatmentunitoperationsandprocesses.Physicalunitoperations-Screening-Comminution-Flowequalization-Sedimentation-Flotation-Granular-mediumfiltrationChemicalunitoperations-Chemicalprecipitation-Adsorption-Disinfection-Chlorination-OtherchemicalapplicationsBiologicalunitoperations-Activatedsludgeprocesses-Aeratedlagoons-Tricklingfilters-Rotatingbiologicalcontactorsn-Pondstabilization-Anaerobicdigestion-Biologicalnutrientremoval237G.S.Simateetal./Desalination273(2011)235–247microorganismsandinorganicend-products(principallyCO2,NH3andH2O).Aerobictreatmentutilizesbiologicaltreatmentprocesses,inwhichmicroorganismsconvertnon-settle-ablesolidstosettle-ablesolids.Sedimentationtypicallyfollows;allowingthesettle-ablesolidstosettleandseparateout.Threeoptionsinclude:Activatedsludgeprocess.Intheactivatedsludgeprocess,thewastewaterflowsintoanaeratedandagitatedtankthatisprimedwithactivatedsludge.Thiscomplexmixturecontainingbacteria,fungi,protozoans,andothermicroorganismsiscollectivelyreferredtoasthebiomass.Inthisprocess,thesuspensionofaerobicmicroorganismsintheaerationtankismixedvigorouslybyaerationdevices,whichalsosupplyoxygentothebiologicalsuspension.Attachedgrowth(biofilm)process.Thesecondtypeofaerobicbiologicaltreatmentsystemiscalled“attachedgrowth(biofilm)process”anddealswithmicroorganismsthatarefixedinplaceonasolidsurface.This“attachedgrowthtype”aerobicbiologicaltreatmentprocesscreatesanenvironmentthatsupportsthewastewaterAerobicprocesssludgeElectronacceptor:O2,1-2mg/LAnaerobicprocessHeatnsludgemethaneElectronacceptor:SO4,PO4,organics50%50%90%10%Fig.1.Anillustrationofaerobicandanaerobicprocesses[34].Table3Genericadvantagesanddisadvantagesofconventionalandnon-conventionalwastewatertreatmenttechnologies[24].TreatmenttypeAdvantagesDisadvantagesAquaticsystemsStabilizationlagoons–LowcapitalcostRequiresalargeareaofland–Lowoperationandmaintenancecost–Mayproduceundesirableodors–LowtechnicalmanpowerrequirementsAeratedlagoonsRequiresrelativelylittlelandarea–Requiresmechanicaldevicestoaeratebasins–ProducesfewUndesirableodors–ProduceeffluentsWithahighsuspendedsolidsconcentrationTerrestrialsystemsSeptictanks–Canbeusedbyindividualhouseholds–Providesalowtreatmentefficiency–Easytooperateandmaintain–Mustbepumpedoccasionally–Canbebuiltinruralareas–RequiresalandfillforperiodicdisposalofsludgeandseptageConstructedwetland–Removesupto70%ofsolidsandbacteria–Remainslargelyexperimentaln–Minimalcapitalcost–Requiresperiodicremovalofexcessplantmaterial–Lowoperationandmaintenancerequirementsandcosts–BestusedinareaswheresuitablenativeplantsareavailableMechanicalsystemsFiltrationsystemsMinimallandrequirements–Requiresmechanicaldevices–Relativelylowcost–Canbeusedforhouseholdscaletreatment–EasytooperateVerticalbiologicalreactors–Highlyefficienttreatmentmethod–Highcost–Requireslittlelandarea–Complextechnology–Applicabletosmallcommunitiesforlocalscaletreatmentandtobigcitiesforregionalscaletreatment–Requirestechnicallyskilledmanpowerforoperationandmaintenance–Needssparepartsavailability–HasahighenergyrequirementActivatedsludge–Highlyefficienttreatmentmethod–Highcost–Requireslittlelandarea–Requiressludgedisposalarea(sludgeusuallyland-spread)–Applicabletosmallcommunitiesforlocalscaletreatmentandtobigcitiesforregionalscaletreatment–Requirestechnicallyskilledmanpowerforoperationandmaintenancerequirement238G.S.Simateetal./Desalination273(2011)235–247growthofmicroorganismsthatprefertoremainattachedtoasolidmaterial.Tricklingfilterprocess.Inthetricklingfilterprocess,thewastewaterissprayedoverthesurfaceofabedofroughsolids(suchasgravel,rock,orplastic)andisallowedto“trickledown”throughthemicroorgan-ism-coveredmedia.nBiofiltrationtowers.Avariationofatricklingfiltrationprocessisthebiofiltrationtowerorotherwiseknownasthebiotower.Thebiotowerispackedwithplasticorredwoodmediacontainingtheattachedmicrobialgrowth.Rotatingbiologicalcontactorprocess.Therotatingbiologicalcontactorprocessconsistsofaseriesofplasticdisksattachedtoacommonshaft.Lagoons.Theseareslow,cheap,andrelativelyinefficient,butcanbeusedforvarioustypesofwastewater.Theyrelyontheinteractionofsunlight,algae,microorganisms,andoxygen(sometimesaerated).Sludgetreatmentanddisposal.Ingeneral,aerobictreatmentsystemsliketheactivatedsludgesystemproducerelativelylargequantitiesofsludge,whichrequiresdisposal.Thesludgecanundergoadewateringtreatmenteitherbyreconsolidatedcentrifugation,vacuumfiltration,orinapressurefilter.3.3.2.AnaerobicAnaerobicwastewatertreatmentisthebiologicaltreatmentofwastewaterwithouttheuseofairorelementaloxygen.Anaerobictreatmentischaracterizedbybiologicalconversionoforganiccompoundsbyanaerobicmicroorganismsintobiogas,whichcanbeusedasafuel;mainlymethane55–75vol%andcarbondioxide25–40vol%withtracesofhydrogensulfide[35].Inbreweries,directutilizationofbiogasinaboilerisusuallythepreferredsolution.Thereasonforthisisthatinvestmentcostsforacombinedheatandpowerunit(CHP)arehigherandmoreextensivebiogastreatmentisrequired[36].Inthecontextofdecreasingfossilfuelreserves,anaerobicwastewatertreatmentmakesabrewerymoreindependentfromexternalfuelsupply.Furthermore,itcontributestoamoresustainablebrewingprocess.UpflowAnaerobicSludgeBlanket.OneofthemostpopularanaerobicprocessesistheUpflowAnaerobicSludgeBlanket(UASB).IntheUASBreactor,thewastewaterentersaverticaltankatthebottom.Thewastewaterpassesupwardsthroughadensebedofanaerobicsludgewherethemicroorganismsinthesludgecomeintocontactwithwastewatersubstrates[34].Thissludgeismostlyofagranularnature(1–4mm)havingsuperiorsettlingcharacteristics(i.e.,atarateofmorethan50mh−1n).Theorganicmaterialsinthesolutionareattackedbythemicrobes,whichreleasebiogas.Asthebiogasrises,itcarriessomeofthegranularmicrobialblanket.AtthetopoftheUASBreactor,asocalledthree-phaseseparatorseparatesthebiomassfromthebiogasandwastewater[16].Thethree-phaseseparatorisalsoknownasthegas–liquid–solid-separator[34].Fig.2showsagraphicalillustrationoftheUASBprocess[34].FluidizedBedReactor.InaFluidizedBedReactor(FBR),wastewaterflowsinthroughthebottomofthereactor,andupthroughamedia(usuallysandoractivatedcarbon)thatiscolonizedbyanactivebacterialbiomass.Themediaprovidesagrowthareaforthebiofilm.Thismediais“fluidized”bytheupwardflowofwastewaterintothevessel,withthelowestdensityparticles(thosewithhighestbiomass)movingtothetop.4.TreatmentofbrewerywastewaterforreuseThedischargedwastewaterfromthebiologicalpretreatmentprocess-escanbefurthertreated.InthissectionvariousmethodsthatmaybeusedbiogasgascapSludgebedbafflesgasbubblessludgegranulesinfluenteffluentthreephaseseparatornFig.2.UASBanaerobicprocess[34].Table4Anaerobictreatmentascomparedtoaerobictreatment[16].AerobicsystemsAnaerobicsystemsEnergyconsumption-High-LowEnergyproduction-No-YesBiosolidsproduction-High-LowCODremoval(%)-90–98-70–85Nutrients(N/P)removal-High-LowSpacerequirement-High-LowDiscontinuousoperation-Difficult-Easy239G.S.Simateetal./Desalination273(2011)235–247totreatbrewerywastewaterforreuseareexplored.Itmustbenoted,however,thatrecyclingofregeneratedwaterasbrewingwaterisconsideredinappropriateandwouldrequirethatdrinkingwaterstandardsarecompliedwith[1].Table5showsthemostimportantstandardsforrinsing,coolinganddrinkingwater[1].AmongtheparametersinTable5,themostimportantparameterforrecyclingwaterorrequiredtobemeasuredistheCOD[1,37].CODisameasureoftheoxygenequivalentoftheorganicmattercontentofasamplethatissusceptibletooxidationbyastrongoxidant[38].TheCODisconsideredanappropriateindexforshowingtheamountoforganicsinwater[39].TheCODvalueofawastewatermainlyrepresentsthebiodegradableandnon-biodegradableorganiccomponents(Fig.3),althoughinorganiccom-poundsmaybesignificantincertaincases[37].However,ingeneral,breweryeffluentsareeasilybiodegradablewithBOD/CODratiointherange0.6–0.7[19,20,36].Theorganiccomponentsinthebreweryeffluent(expressedasCOD)consistofsugars,solublestarch,ethanol,volatilefattyacids,etc[1,36].4.1.MembranefiltrationTheseparationbyporousmembranesisofgreatinterestinenvironmentalandchemicalengineeringprocesses[40–42].Infact,filtrationtechnologyisconsideredasanintegralcomponentofdrinkingwaterandwastewatertreatmentapplications[43].Membranefiltrationcanbedividedintofourcategories,dependingontheeffectiveporesizeofthemembrane,andhencethesizeoftheimpuritiesremoved.Inorderofndecreasingporesize,theyareasfollows:microfiltration,ultrafiltration,nanofiltration,andhyperfiltration.Table6summarizestheessentialfeaturesoftheseprocesses,suchasporesizeandoperatingpressure[30].However,thecharacteristicslistedinTable6arenotexhaustive,thusdifferentrangesmaybequotedelsewhere.Fig.4showstwowaysofoperatingamembranefilter,i.e.,deadendfiltrationandcross-flowfiltration.Indead-endfiltration,allofthefeedwaterflowsthroughthemembrane(aspermeate)sothatallimpuritiesthataretoolargetopassthroughtheporesaccumulateinthefiltermodule.Somemeansofremovingtheseisnecessary.Cross-flowfiltrationinvolvesflowingthefeedwaterparalleltothemembranesurface,withonlyaproportionpassingthroughthemembrane.Theretainedimpuritiesremainintheretentate,whichisnormallyrecirculated.Membranescanbeclassifiedaccordingtotheirmaterialofconstruction[34].Thereisavarietyofmaterialsthatareusedforthemanufactureofmembranefilters,e.g.,ceramicsandpolymers[30,44].Polymermaterialsusedformembranemanufactureare,forinstance,celluloseacetate,polyamides,polypropylene,andpolysulfone[34].Ceramicmembranesareusuallymanufacturedfrommetaloxides,suchasalumina,oftenusingsomeformofasol–gelprocess.Inwastewatertreatment,theuseofnanofiltration/reverseosmosisfororganic/saltremovalisnormallypracticed[45].Nanofiltration(NF)isactuallyarelativelyrecentmembranefiltrationprocessusedmostoftenwithlowtotaldissolvedsolidswatersuchassurfacewaterandfreshgroundwater,withthepurposeofsoftening(polyvalentcationremoval)andremovalofdisinfectionby-productprecursorssuchasnaturalorganicmatterandsyntheticorganicmatter[46].Thenominalporesizeofthemembraneistypicallyabout1nm.However,nanofiltermembranes(justlikeothermembranes)aretypicallyratedbynominalmolecularweightcut-off(MWCO)ratherthannominalporesize.TheMWCOisanexpressionoftheretentioncharacteristicsofthemembraneintermsofmoleculesofknownsizes[44].ThenominalMWCOofthemembranemaybedefinedastherelativemolecularmassofthecomponentthatisrejectedby90%[47].Inotherwords,MWCOisanattributeoftheporesizeandisrelatedtotherejectionofasphericalsoluteofagivenmolecularweight[48].Thereasonthattheword‘nominal’isusedisthattheshapeandchargeonthemoleculewillinfluenceitsrateofmigrationthroughthemembrane[44].TheMWCOistypicallylessthan1000atomicmassunits(daltons).TheNFisacross-flowfiltrationtechnologywhichliesnsomewherebetweenultrafiltration(UF)andreverseosmosis(RO)(Table6).Thesemembranesareabletoremoveparticlesbelow100nminsize.Inaddition,thetransmembranepressure(pressuredropacrossthemembrane)required(upto3MPa)isconsiderablylowerthantheoneusedforRO,thusreducingtheoperatingcostsignificantly.Braekenetal.[1]usedNFinanattempttotreatbrewerywastewaterforrecycling.TheresultsofthisstudyshowedthattheremovalofCOD,Na+,andCl−(averaging100%,55%and70%removal,respectively)withNFwassufficientforthebiologicallytreatedwastewater,whereastheotherthreewastewaterstreams(bottlerinsingwater,rinsingwaterofTable5Qualitystandardsforrinseandcoolingwater,andaimedvaluefordrinkingwater[1].QualitystandardrinsingwaterQualitystandardcoolingwaterQualitystandarddrinkingwaterCOD(mgO2L−1)0–20–20–2Na+(mgLn−1)0–200/20Cl−(mgL−1)50–25/25pH6.5–9.56.5–9.56.5–9.5Conductivity(μscm−1)//400/:Notspecified.Non-oxidisableNon-biologicallydegradableTotalOrganicCarbon(TOC)Chemicallyoxidisable(COD)Biologicallydegradable(BOD)Fig.3.Therelationshipbetweentheorganiccarbonfractionsinwastewater.Table6Typicalcharacteristicsofmembraneprocesses[30].ProcessOperatingpressure(bar)Poresize(nm)nMolecularweightcut-offrangeSizecut-offrange(nm)Microfiltrationb4100–3000N500,00050–3000Ultrafiltration2–1010–2001000–1,000,00015–200Nanofiltration5–401–10100–20,0001–100Reverseosmosis(hyperfiltration)15–150b2b200b1240G.S.Simateetal./Desalination273(2011)235–247thebrightbeerreservoir,andrinsingwaterofthebrewingroom)werenotsuitableforrecyclingusingNF.Theseresultsclearlyshowtheimportanceofpretreatmentprocesses.Thoughnanofiltrationisvitalforthetreatmentofwastewaters,themajorlimitationisfouling.However,coagulation/flocculationcanbeusedtoenhancenanofiltrationperformancetowardswaterreuseandminimizationoffouling[49].Thisisbecausecoagulation/flocculationreducetheconcentrationofimpuritiesandhenceimprovethepermeatefluxaftersedimentation.Asmentionedearlier,ROisnormallypracticedfortheremovaloforganic/saltinwastewaters[45].TheROisthetightestpossiblemembraneprocessinliquid/liquidseparationandthereforeproducesthehighestwaterqualityofanypressuredrivenmembraneprocess[34].TheROmembranesareclassifiedbypercentagerejectionofNaClandrangesfrom95to99.5%[34].ThesuccessofROinlarge-scaledesalinationandmunicipalwastewatertreatmenthasledmanyindustriestoviewthistechnologyasameansofpollutionabatementandcostsavingsthroughreuse[50].InfactwastewatertreatmentusingROhavebeenemployedinchemical,textile,petrochemical,electrochemical,pulpandpaper,andfoodindustriesaswellasformunicipalwastewater[51].MadaeniandMansourpanah[39]reviewedseveralstudiesofROapplicationsandfoundthatROmaydecreasetheCODoftheeffluentbymorethan90%orcompletely.Infact,teststoreduceCODvaluesshowedthatROisthebestmethodtoseparateorganicsfromwater.ROisalsousuallycombinedwithotherphysicalseparationtechniques,aswellasbiologicalandphysiochem-nicaltreatment,toproduceeffluentssuitableforreuse.Forexample,acombinationofultrafiltration(UF)andROhaveproducedhighqualitywater[52,53].InstudiesbyMadaeniandMansourpanah[39],biologicallytreatedwastewaterfromanalcoholmanufacturingplanthavingCODintherangeof900to1200mgL−1wastreatedbyvariouspolymericROandNFmembranes.ThepolyethyleneterphetalateROmembraneyieldedoutstandingresultswithhigherflux(33kgm−2h−1)andextremeCODremoval(100%).Inanotherstudy,brewerybio-effluentwasobtainedusinganinternalaerobicmembranebioreactor(internalMEMBIOR)[54].Inthisstudy,theCODofbrewerywastewatervariedstronglyfrom1500to3500mgL−1,butaftertheinternalMEMBIORtheCODwasaround30mgL−1regardlessoftheCODfluctuationsoftheinfluent.Thesuspendedsolidswerecompletelyretainedbytheflatplatemembrane.Thismadetheeffluentperfectlysuitedforre-useviareverseosmosisasprocesswater,omittingtheneedforexpensivepretreatmentmethods.Insummary,areviewofseveralliteratureshasshownthatROisapreferredconditioningmethodforthebrewingindustrybecauseofitsenvironmentallyfriendlyapplications,itssimplicityregardingautomation,itsuser-friendlyaspects,andthesmallamountofspaceitnrequires.Furthermore,itrequiresnoregeneratingchemicals,whichmeansnoadditionalsaltshavetobeaddedforwastewaterneutralization.4.2.Non-thermalquenchedplasmaPlasmaisahighlyionizedgasthatoccursathightemperatures.Theintermolecularforcescreatedbyionicattractionsandrepulsionsgivethesecompositionsdistinctproperties;forthisreason,plasmaisdescribedasafourthstateofmatter[55].Likegas,plasmadoesnothaveadefiniteshapeoradefinitevolumeunlessenclosedinacontainer;unlikegas,intheinfluenceofamagneticfield,itmayformstructuressuchasfilaments,beamsanddoublelayers.Somecommonplasmasarestarsandneonsigns.Insummary,aplasmausuallyresultsfromtheincreaseoftheenergyofagasprovidedbyvarioussources,suchaselectric,magnetic,mechanical(shockwavesandultrasound),thermalorevenoptical(laser)sources[56].Apartofthegaseousmatteristhuschangedfromthestartingmoleculesoratomstoanelectricallyneutralmixtureofions(anionsandcations)andelectrons,involvingotherheavyspeciesandphotons[56].Doublaetal.[5]reportedtheuseofhumidairplasmacreatedbyanelectricglidingarcdischargeinhumidairtolowerorganicpollutantsinbrewerywastewater.Theglidingarcdischargeinhumidairgenerates.NOand.OHradicals,whichhavestrongoxidizingcharacteristics.The.OHradicalisaverypowerfuloxidizingagent[E0(.OH/H2O)=2.85V/NHE]andthusresponsibleforoxidationreactionswithorganictargets,bothduetoitsownpropertiesandtoitsderivativeand/orparentmoleculeH2O2asshowninEq.(1)[5]:nH2O2↔2OHð1ÞInitially,NOleadstotheformationofnitriteinneutralmediums,butisfurtheroxidizedtonitrateionsasstablespecies.Additionally,thehighstandardoxidation-reductionpotentialsoftheHNO2/NO(1.00V)andNO3−/HNO2(1.04V)systemsreflecttheoxidizingpowerofthenitrateion[5].Inotherwords,thenitrateionsparticipateintheoxidizingcharacteristicsofthehumidairplasma.InthestudybyDoublaetal.[5],theBODremovalefficiencyoftheprocesswithbreweryindustrialwatersofBODvaluesof385and1018mgL−1were74and98%,respectively.ThealkalinewastewaterswerealsorapidlyneutralizedduetopHloweringeffectoftheplasmatreatmentemanatingfromtheproductionofnitrateions[56].Thisprocesscanbecoupledwithbiologicalprocesstreatmentstofurtherlowertheorganicpollutantconcentrationmoreeasilyandrapidlytoanacceptablelevelforreuse[5].pressurepermeatemembranesfeedpressureretentatenpermeateFiltecaker(a)(b)Fig.4.Twoformsofmembranefiltration,(a)dead-endand(b)cross-flowfiltration.241G.S.Simateetal./Desalination273(2011)235–2474.3.MembranebioreactorDepletionofwaterresources,increasingwaterprice,andstringentregulationhascausedthedevelopmentofvariouscombinationsofmembraneswithotherconventionaltreatmentcomponents[45].Membranebioreactor(MBR)isbecomingoneofsuchflourishingtechnologyinwaterandwastewatertreatmentfields[45].TheMBRcombinestwoproventechnologies,i.e.,enhancedbiologicaltreatmentusingactivatedsludge,andmembranefiltrationasshowninFig.5[57].Dependingonhowthemembraneisintegratedwiththebioreactor,twoMBRprocessconfigurationscanbeidentified:side-streamandsubmerged(Fig.6).Inside-streamsMBRs,membranemodulesareplacedoutsidethereactor,andthereactormixedliquorcirculatesoverarecirculationloopthatcontainsthemembrane.InsubmergedMBRs,themembranesareplacedinsidethereactor,submergedinthemixedliquor.Theside-streamMBRsaremoreenergyintensivecomparedtosubmergedMBRs[34,58]duetohigheroperationaltransmembranepressures(TMP)andtheelevatedvolumetricflowrequiredtoachievethedesiredcross-flowvelocity[58].However,submergedMBRsusemoremembraneareaandoperateatlowerfluxlevels[34].TheMBRhasbeenstudiednotonlyforwastewaterbutalsofordrinkingwatertreatment[59,60],andisappliedtomunicipalwastewatertreatmentatfullscale[61].LiandChu[59]foundthatnearly60%ofinfluenttotalorganiccarbon(TOC)wasremovedbyMBR,accompaniedbymorethan75%reductionintrihalomethanesformationpotential(THMFP).TheMBRtechnologyisalsoappliedtothebrewerywastewaterforreuse[32].TheCODreductioninMBRinfluent(i.e.,UASBreactoreffluentrangingfrom500to1000mgO2L−1n)ofuptoanaverageof96%wasreportedbyDaietal.[32].Brewerywastewaterwasalsoconductedbyvariousotherresearchers[62–64].Inmostofthesestudies,significantamountsofCODremovals(~90%)werereported.Withthesepromisingresults,itcanbeconcludedthattheMBRprocessisanattractiveoptionforthetreatmentandreuseofindustrialandmunicipalwastewaters.Table7showstheoperatingparametersandsomeoftheresultsoftheanaerobicdigestion-ultrafiltrationprocess[45].Justlikeothermembraneseparationprocesses,membranefoulingisthemostseriousproblemaffectingsystemperformanceofMBRsand,thereforeneedtobecleanedfrequently[34].Membranefoulingcanbeclassifiedasreversibleandirreversible[65].Itresultsfrominteractionbetweenthemembranematerialandthecomponentsoftheactivatedsludgeliquor,whichincludebiologicalflocsformedbyalargerangeoflivingordeadmicroorganismsalongwithsolubleandcolloidalcompounds.Foulingleadstoasignificantincreaseinhydraulicresistance,manifestedaspermeatefluxdeclineorTMPincreasewhentheprocessisoperatedunderconstant-TMPorconstant-fluxconditionsrespectively.Theorganicfoulingofthemembraneismainlydependentonseveralfactorsincludingthefollowing[65]:(1)thecomponentsoforganicmattersuchascolloidalfractionanddissolvedfraction,(2)organiccharacteristicssuchashydrophobicityandmolecularsizeandconfiguration,(3)solutionchemistrysuchaspH,divalentionsconcentrationandionicstrength,and(4)membranepropertiessuchasporesizeandsurfaceroughness.Inpractice,membranefoulingcanbecontrolledbytwotypesofapproaches,i.e.,(1)periodicalairscouring,backwashingandchemicalcleaning[67],and(2)theadditionofadsorbentsandpretreatmentbycoagulation[68,69].Arecentstudyhasshownthatdirectadditionofacoagulantinthebioreactorwasabletomitigatemembranefouling[66].TheintegrationofcoagulationintoMBRistermedmembranecoagulationbioreactor(MCBR).Infact,themostimportanttrendinthedevelopmentofmembranefiltrationforwatertreatmentistheintegrationofdifferentpretreatmentstrategiestoimprovetheperformanceoflowpressuremembranes[22].4.4.CombinedanaerobicandaerobictreatmentAnaerobicandaerobictreatmentsareoftencombinedinbrewerywastewatertreatment[16,70,71].AsshowninFig.7,thereareessentiallyfourtypesofintegratedanaerobic–aerobicbioreactors[72].TheattributesFig.5.SimplifiedschematicdescriptionoftheMBRprocess[57].npermeatemembraneunitbioreactorwastewaterbioreactorpermeatewastewaterSide-streamMBRSubmergedMBRFig.6.Membranebioreactorconfigurations[57].Table7Meanoperatingcriteriaofanaerobicdigestion-ultrafiltrationplantstreatingvariousindustrialeffluents[45].Operatingparameter/resultsBreweryWinedistilleryMaltingEggprocessMaizeprocessVolumeofdigester(m3)0.052.43.0802610Operationalperiod(month)3185836FeedCOD(kg/L)6.7373.584–15PermeateCOD(kg/L)0.180.260.800.350.30nCODremoval(%)9793779597Spaceloadrates(kgCOD/m3·d)17.012.05.06.03.0Sludgeloadrate(kgCOD/kgVSS·d)0.70.580.50.330.24HRT(day)0.83.30.81.35.2Temperature(°C)3535353035MLSS(kg/m3)30–50501010–3023Membranearea(m2)0.441.759.6200800Flux(L/m2·h)10–4040–8020–4015–3010–70Inletpressure(kPa)340400500500600Crossflowvelocity(m/s)1.52.01.81.81.6Tubediameter(mm)9.012.79.012.79.0242G.S.Simateetal./Desalination273(2011)235–247ofintegratedanaerobic–aerobicbioreactorsareasfollows[36]:Firstly,intheanaerobicreactorthebulkoftheCOD,70–85%,isconvertedintobiogasonasmallsurfacearea.Secondly,inanaerobic/anoxicpost-treatmentstep,upto98%oftheCODandnutrientsareremoved.Furthermore,someoftheimportantadvantagesofcombinedaerobic/anaerobictreatmentofbreweryeffluentovercompleteaerobicincludeapositiveenergybalance,reduced(bio)sludgeproductionandsignificantlowspacerequirements[16].Recentdevelopmentoftallslenderanaerobic(e.g.,internalcirculationreactors)andaerobic(e.g.,airliftreactors)reactorsallowsforextremecompacteffluenttreatmentplantdesignstillmeetingstringentrequirementsofsurfacewaterquality[16].4.5.TheuseofcarbonnanotubesSincethe‘rediscovery’ofcarbonnanotubes(CNTs)in1991[73]byIijima[74],severalresearchersworldwidecuttingacrossalldisciplineshaveembarkedonstimulatingresearchtoutilizethemyriaduniquepropertiesofthesenanomaterials.TheCNTsconsistofhoneycombnstructuresofgraphenesheetsrolledupintocylinderswithadiameterofafewnanometers,butlengthofmanymicronorevencentimeters[75,76].Alotofmethodsandcarbonsourcesforthegrowthofcarbonnanotubeshavebeenactivelypursuedinthepastfewyears,andthesehavebeenoutlinedinseveralreviewpapers[77–82].TherearetypicallytwoformsofCNTsaccordingtothenumberofrolledupgraphenelayersthatformthetube,i.e.,single-walledcarbonnanotubes(SWCNT)andmulti-walledcarbonnanotubes(MWCNT).Themodelrepresentationsofmulti-walledCNTandsingle-walledCNTareshowninFig.8[83,84].TheuniquepropertiesofCNTsarisefromtheirspecialatomicandelectronicstructures[85].Owingtotheiruniquestructural,mechanical,andelectronicproperties,CNTspossessgreatpotentialinalargevarietyofpromisingapplicationssuchaschemicalsensors,fieldemissionmaterialsandcatalystsupports[75,78,81,86].SomeoftheimportantapplicationsofCNTswithrespecttowatertreatmentarediscussedbelow.4.5.1.NanosorbentsCarbonnanotubeshaveshownexceptionallygoodadsorptioncapabilityandhighadsorptionefficiencyforvariousorganicpollu-tants[87–91]andinorganicpollutantssuchasfluoride[92].TheCNTshavealsobeenfoundtobesuperiorsorbentsforheavymetals[89,93,94].TheCNTsareparticularlyattractiveassorbentsbecause,onthebasisofmass,theyhavelargersurfaceareasthanbulkparticles,andcanbefunctionalizedwithvariouschemicalgroupstoincreasetheiraffinitytowardstargetcompounds[95].TheCNTsalsohavesmallsize,andhollowandlayeredstructures,whichareveryimportantcharacteristicattributesforadsorption[96].TheabilityoffunctionalizedCNTstoadsorbvariousimpuritiesfromwastewatercanbeextendedtotheremovalofCODfrombrewerywastewater.AreviewoftheliteraturehasshownthatalthoughCNTshavebeenproventopossessgoodpotentialassuperioradsorbents,tothebestoftheauthors'knowledgenopublishedworkisavailableregardingtheiruseascoagulantsand/orflocculants.However,itcanbetheorizedthatifCNTscanadsorbonseparatecolloidalparticles,thentheparticlescanbedrawntogether;aphenomenonknownasbridgingfloccula-tion.Furthermore,theadsorptionofCNTsontoparticlesurfacescanalsoresultinchargeneutralization,resultinginanearzeronetcharge.Oncethesurfacechargehasbeenneutralized,theionicclouddissipatesandtheelectrostaticpotentialdisappearssothatthecontactamongcolloidalparticlesoccursfreely.Chargeneutralizationniseasilymonitoredandcontrolledusingzetapotential[97].Fromthetwophenomenaabove(adsorptionandcoagulation),itcanbeascertainedthatforthetreatmentofwastewaters(includingbrewerywastewaters)containingbothdissolvedandsuspendedorganics,CNTsmaywellbeappliedtoremovedissolvedorganicsbyadsorption,andsuspendedsolidorganicbyheterogeneouscoagulation(bridgingandneutralization),atthesametime.However,alotofchallengesariseinattemptingtouseCNTsintheirpresentstateascoagulantsorflocculants.Firstly,theCNTslackdispersionandsolubility.However,therehavebeenseveralsuccessfulattemptstopreparewatersolublecarbonnanotubesbyvarioustechniques[98–100],andimprovementsintheirdispersivitythroughIntegratedbioreactorswithphysicalseparationofanaerobic-aerobiczoneIntegratedbioreactorswithoutphysicalseparationofanaerobic-aerobiczoneAnaerobic-aerobicSequencingBatchReactor(SBR)Combinedanaerobic-aerobicculturesystemAnaerobic-aerobicsystemusinghighratebioreactorsConventionalanaerobic-aerobicsystemIntegratedanaerobic-aerobicbioreactorsnAnaerobic-aerobictreatmentFig.7.Typesofcombinedanaerobic-aerobicsystem[71].Fig.8.Modelsandrepresentationofmulti-walledCNTandsingle-walledCNT[82,83].243G.S.Simateetal./Desalination273(2011)235–247functionalization[101].Secondly,theCNTsareveryexpensive,thustheyrequiretoberegeneratedafteruse.IftheCNTsareappliedintheformofslurry,anefficientseparationprocessdownstreamsuchasmembranefiltrationisneededtoretainandrecycletheCNTs.Retentionofnanomaterialsiscriticalnotonlybecauseofthecostassociatedwithlossofnanomaterials,butalso,andmoreimportantly,becauseofthepotentialimpactsofnanomaterialsonhumanhealthandecosystems[102–104].4.5.2.NanofiltersThesuccessfulfabricationofcarbonnanotubefiltershavebeenreported[105].Thesefiltrationmembranesconsistofhollowcylinderswithradiallyalignedcarbonnanotubewalls.Srivastavaetal.[105]efficientlycarriedoutfiltrationofheavierhydrocarbonspecies,CmHn(mN12),fromhydrocarboneceousoilforexample,petroleumCmHn(n=2m+2,m=1to12),andintheremovalofEscherichiacolifromdrinkingwaterandfiltrationofthenanometer-sizedpoliovirus.ThehighorganiccontentofbreweryeffluentisclassifiedashighstrengthwasteintermsofCOD,from1000mgL−1to4000mgL−1andBODofupto1500mgL−1[6].ThismakesbrewerywastewateragoodcandidatefortreatmentwiththeseCNTfilters.nMembranesthathaveCNTsasporescouldbeusedindesalinationanddemineralization.Billionsofthesetubesactastheporesinthemembrane.Amembranefilterpossessingbothsuper-hydrophobicityandsuper-oleophilicitywassynthesizedfromvertically-alignedmulti-walledcarbonnano-tubesonastainlesssteelmeshforthepossibleseparationofoilandwater[106].Bothsuper-hydrophobicityandsuperoleophilicitycouldbeobtainedduetothedual-scalestructure,needle-likenano-tubegeometryonthemeshwithmicro-scalepores,combinedwiththelowsurfaceenergy[106].Thenano-tubefiltercouldseparatedieselandwaterlayers,andevensurfactant-stabilizedemulsions.Thesuccessfulphaseseparationofthehighviscositylubricatingoilandwateremulsionswasalsocarriedout.Theseparationmechanismcanbereadilyexpandedtoavarietyofdifferenthydrophobicandoleophilicliquidssuchasbrewerywastewater.4.6.ElectrochemicalmethodsElectrochemicalmethodofwastewatertreatmentcameintoexistencewhenitwasfirstusedtotreatsewagegeneratedonboardbyships[107].Thereafter,theapplicationofelectrochemicaltreatmentwaswidelyreceivedintreatingindustrialwastewatersthatarerichinrefractoryorganicsandchloridecontent[108,109].Theelectrochemicalmethodoftreatmentiswell-suitedfordegradingbiorefractoryorganicpollutants,becauseitispossibletoachievepartialorcompletedecompositionoftheorganicsubstances.Theelectrochemicalmethodsoftreatmentarefavored,becausetheyareneithersubjecttofailureduetovariationinwastewaterstrengthnorduetothepresenceoftoxicsubstancesandrequirelesshydraulicretentiontime.Vijayaraghavanetal.[108]developedanovelbrewerywastewatertreatmentmethodbasedoninsituhypochlorousacidgeneration.Thegeneratedhypochlorousacidservedasanoxidizingagentthatdestroyedorganiccompoundspresentinthebrewerywastewater.AninfluentCODvalueof2470mgL-1wasreducedto64mgL−1(over97%reduction).Thehypochlorousacidwasgeneratedusingagraphiteanodeandstainlesssteelsheetasacathodeinundividedelectrolyticreactor.Initially,duringelectrolysis,chlorinewasproducedattheanodeandhydrogengasatthecathode.Sincetheanodeandcathodewerekeptinanundividedelectrolyticreactor,thechlorinenthatwasgeneratedundergoesadisproportionationreaction,resultinginhypochlorousacid[108]asindicatedinEq.(2)below:Cl2þH2O→HOClþHClð2ÞFurtherdisproportionofOCl−toClO3−wasacceleratedathightemperature(75°C)andunderalkalineconditions(Eq.(3)).3OCl−→ClO−3þ2Cl−ð3Þ4.7.MicrobialfuelcellsRecently,brewerywastewaterhasbeensimultaneouslytreatedwhilegeneratingelectricityfromorganicmatterinwastewater[33,110–112].Thisdevicethattreatswastewaterandgenerateselectricityatthesametimeistermedmicrobialfuelcell(MFC)[113,114].TheMFCisacombinedsystemwithanaerobicandaerobiccharacteristics.Theyaredesignedforanaerobictreatmentbybacteriainthesolutionneartheanode,withthecathodeexposedtooxygen(oranalternativechemicalelectronacceptor).Electronsreleasedbybacterialoxidationoftheorganicmatteraretransferredthroughtheexternalcircuittothecathodewheretheycombinewithoxygentoformwater[33].Consequently,acombinationofanaerobic–aerobicnprocessescanbeconstructedusingadouble-chamberMFC,inwhichtheeffluentoftheanodechambercouldbeuseddirectlyastheinfluentofthecathodechambersoastobetreatedfurtherunderaerobicconditionstoimprovethewastewatertreatmentefficiency[112].Fengetal.[33]foundthatwithaninfluentCODofbrewerywastewaterof2250±418mgL−1,theCODremovalefficiencywas85%and87%at20°Cand30°C,respectively.Performanceofsequentialanode-cathodeMFCachievedCODremovalefficiencyofmorethan90%(e.g.,CODof1250±100mgL−1wasreducedto60mgL−1)[112].Furthermore,upto94%CODremovalhasalsobeenreportedbyotherresearcherswiththismethod[111].SincehighCODremovalefficiencieswereachievedinthesestudies,itcanbeconcludedthatMFCs,particularly,sequentialanode–cathodetype,canprovideanewapproachforbrewerywastewatertreatmentwhileofferingavaluablealternativetoenergygeneration.4.8.CarbonThecharacteristicsofawatertreatmentplanthaveagreatinfluenceonthecharacteristicpropertiesoftheendproduct.Evenwhentheincomingprocesswaterisfromamunicipaldrinkingwatersource,thewatermaycontainresidualtastes,odors,disinfectionby-products,andfreeandcombinedchlorine.Moleculeswithcarbon–sulfurbondsoftensmellandtastebad,buttheseareoftenpreferentiallyadsorbedoncarbon.Thesameistrueofmoleculesnwitharomaticrings.Carbon'sde-chlorinatingcapabilityresultsfromitsabilitytoactasareducingagentthatreactswithstrongoxidizingagentssuchashypochlorousacidorchlorinedioxide.Thetreatmentoftannicacidforflavorandodorremovalisaprocessapplicationinbrewingwherecarbonadsorptionisused.Carbonisalsousedtoremovecolorfrommaltsforuseinclearbeersandotherflavoredmaltbeverages.Severalgranularandpowderedproductscanbeusedforthistypeofapplication.Activatedcarbonsareaneffectivetreatmenttoassurewaterthatiscontaminant,taste,andodorfree.5.DiscussionandsynthesisoffindingsThissectionprovidesadiscussionandsynthesisofthereviewfindingsofthispaper.Thisdiscussionincludesacomparisonandpossibleintegrationoftheprocessesandtechnologies.Inanutshell,thediscussionprimarilyaddressesthefollowingtwofundamentalquestions:(a)Howdotheprocessesandtechnologiescomparewitheachother?(b)Cantheybeintegratedwitheachother,andifso,whatarethepotentialchallengesandbenefits?5.1.ComparisonofprocessesandtechnologiesThisreviewhighlightedtheneedfortreatmentofbrewerywastewater,andlookedatvariousmethodsthatmaybeusedtosafelyandcost-effectivelytreatbrewerywastewaterforreuse.Inaddition,somechallengesassociatedwiththesemethodswerediscussed.Itshouldbenotedandemphasizedhereinthatthetreatmentofbrewerywastewatereffluentisacostlyandrelatively244G.S.Simateetal./Desalination273(2011)235–247complexactivity;particularlywiththeneedtomeetgovernmentalregulationsandenvironmentalfriendliness[6,115].Conventionalseparationmethodssuchascoagulation/flocculation,centrifugation,andgravityseparationexhibitshortcomingsincludingincompleteCODremoval.Thesemethodsaregenerallyassociatedwithlowseparationefficiency,highoperationcosts,largesetupsize,andthegenerationofsecondarypollutants.Itwasalsonoticedthatbiologicaltreatmentiswidelyappliedasapretreatmentmethod.Generally,aerobictreatmenthasbeenappliedforthetreatmentofbrewerywastewaterandrecently,anaerobicsystemshavebecomeanattractiveoption,amongotheradvantages,becauseoftheirhighCODcontentremoval.Thoughthesebiologicalmethodshavefoundwidespreadapplicationforthetreatmentofthecharacteristicallyhighnorganiccontentofthebrewerywastewater,furthertreatmentisrequiredforwaterreuse.Nevertheless,thisreviewhasshownsomepromisingresultswithquenchedplasma,MBR,electrochemicalmethods,andmicrobialfuelcells.Thesemethodshavegreatpotentialtobeusedtotreatbrewerywastewaterforreuseandneedstobefurtherinvestigatedwithrespecttodifferentchallengesandopportunitiesinvolved.Forexample,beerbrewerywastewatermightbeagoodsourceforelectricitygenerationinMFCsduetoitsnatureofhighcarbohydratesandlowammonium–nitrogenconcentration.Theauthorshavealsonotedthatrecentadvancessuggestthatmanyoftherecentproblemsinvolvingwaterqualitycouldbesolvedorgreatlyamelioratedusingcarbonnanotubesassorbents.Therefore,itisexpectedthatthebreweryindustrywillalsobenefitfromthesediscoveries.However,theknowledgerequiredforthelarge-scaledesignandapplicationoftheprocessesdiscussedinthisreviewisperhapsstilllacking.Itisfurtherrecommendedtocarryoutsomestudiestoestablishestimatedcapitalcostsofthesepromisingprocesses.Ontheotherhand,theapplicationofmembranefiltration(e.g.,NFandRO)todrinkingwatertreatmentandwastewaterreuse,thoughwellestablished,hasundergoneaccelerateddevelopmentinthepastdecadewiththeimprovementinmembranequalityandthedecreaseinmembranecost.Averyimportanttrendinthedevelopmentofmembranefiltrationforwatertreatmentistheintegrationofdifferentpretreatmentstrategiestoimprovetheirperformance.TheRO,inparticular,hasbeenshowntobeanefficientandcosteffectiveprocessforthetreatmentofbrewerywastewaterforreuse.Table8showsasummaryofsomeofthestudiesconductedonbrewerywastewater,showingtheCODreductions,andwhethertheeffluentissuitableasaprimaryorsecondarywaterbasedonthecriterialistedinTable5.Itmustbenoted,however,thatthesestudieshaddifferentexperimentaldesigns.5.2.IntegrationofprocessesandtechnologiesItcanbebeenseeninTable8thatnoneofthemethods(apartfromRO)canbeusedindividuallyinbrewerywastewatertreatmentapplicationswithgoodeconomicsandhighdegreeofenergyefficiency.Couplingtheseprocessestogetherastwoorthreestageprocesseswouldbemoreappropriate.Subsequently,differentprocesscombinationsareproposedanddiscussed.nThedemandforrenewableenergyinoursocietyiseverincreasing[111].Therefore,theMFCsisrecommendedtobethefirstpretreat-mentstageofeveryintegratedprocessparticularlywithfiltrationtechniques.MFCshaveoperationalandfunctionaladvantagesoverthetechnologiescurrentlyusedforgeneratingenergyfromorganicmatter[111].First,thedirectconversionofsubstrateenergytoelectricityenableshighconversionefficiency,unlikethebiologicalprocessesreactorswherethemetabolizedproducts(e.g.,NH3)havetobeusedinboilersforenergygeneration.Second,MFCsoperateefficientlyatambienttemperature.Third,anMFCdoesnotrequiregastreatmentbecausetheoff-gassesofMFCsareenrichedincarbondioxideandnormallyhavenousefulenergycontent.Fourth,MFCsdonotneedenergyinputforaerationprovidedthecathodeispassivelyaerated[116].Fifth,MFCshavepotentialforwidespreadapplicationinlocationslackingelectricalinfrastructuresandcanalsooperatewithdiversefuelstosatisfyenergyrequirements.ThehighCODremovalefficiency(seeTable8)couldalsoreducetheloadinothercoupledstages.Theusesofothertechniquesasfirststagesinanintegratedprocessdonotofferanyforeseeablebenefits.Electrochemicalmethodscanbewellsuitedtobecoupledinthelatterstagesoftheintegratedprocess.Sanitizingagents(oftencalleddisinfectants)whicharepresentinbrewerywastewatercontainchlorinecompounds.Thesecompoundsproducechlorineduringelectrolysisand,thereafter,chlorinegenerateshypochlorousacidwhichoxidizesorganiccompounds.Chlorineisoneofthemostwidelyuseddisinfectants.Itisveryapplicableandveryeffectiveforthedeactivationofpathogenicmicroorganisms.Therefore,electrochem-icalmethodsifcoupledinthelatterstagescanserveasanorganicoxidationanddisinfectingstage.Plasmamethodsthoughveryeffective(seeTable8),theprocessisexpensivebecauseofthehighenergyrequirementsbythegas,andthecostofenergysourcessuchaslaser.Therefore,ifcoupledwithothermethods,theprocessescanbeveryexpensive.CNTshaveshownremarkableadsorptionpower.CombiningCNTswithUFwillresultinsubstantialremovaloforganics.However,theadditionofCNTswouldrapidlyincreasethetransmembranepressurerapidlyduetotheformationofCNTcakeonthemembranesurface.Inthiscase,CNTsmayneedtobeoflargeenoughdiameterstoreducethetransmembranepressureeffect.AsfortheMBRorfiltrationingeneral,foulingmitigationcanpotentiallybedonebycouplingcoagulationandflocculationtotheprocess[117].6.SummarynWaterisacommonelementinthelivesofallpeopleandsocieties.Waterhasbeenthefoundationandsometimes,theundoingofmanyTable8Summaryofbrewerywastewatertreatmentprocesses.ProcessInitialCOD(mg/L)FinalCOD(mg/L)CODreduction(%)PotentialuseReferencePrimary(processwater)Secondary(non-processwater)Quenchedplasma1018a18a98NoNo[5]UASB(*1)1947–3079Notgiven73–91NoNo[21]AerobicreactorNotgivenNotgiven90–98NoNo[16]Combinedbioreactor(*1)NotgivenNotgiven98NoNo[36]Membranebioreactor500–10004096NoNo[32]Electrochemicalmethod24706497NoNo[107]Microbialfuelcells(*2)171010594NoNo[110]Nanofiltration369214396NoNo[1]Reverseosmosis8500100YesYes[39]aBODfigures;(*1)hasaddedvalueofenergyproductionfrombiogas;(*2)hasaddedvalueofelectricityproduction.n245G.S.Simateetal./Desalination273(2011)235–247greatcivilizations.Today,watercontinuestobeessentialforlifesustenance(bothhumanandanimals),agricultural,economicandindustrialactivitiesthathelpsocietytodevelop.Lessthanacenturyago,itwaswidelyassumedthattherewereenoughfreshwatersuppliesintheworldforeveryone.Yettoday,increaseduseoffreshwaterforindustrial,agricultural,anddomesticusehascreatedacutewatershortagesinsomeareasoftheworld,particularlythedevelopingcountries.Theseshortagesarestimulatingorworseninginternationalconflictsoverwater,whichhasjoinedoilasamajorcommoditytriggeringwars.Thepresenceofpollutantsinrawwaterduetohumanactivitieshasalsoexacerbatedthesituation.Ontheotherhand,wastewaterreclamationandreusehasbecomeanimportantoption,sinceindustrializationandurbanizationhaveacceleratedenvironmentalwaterpollution,makingitalimitedresourceforwatersupply[118].Whenproperlytreatedandrecycled,wastewatercanbeanalternativewatersourcethatcanbeneficiallyandcost-effectivelyreducethedemandsforfreshwater.Itcanbeconcludedthat,alongwiththegrowingworldpopulationandindustrialactivitiescoupledwithstringentenvironmentalrequirements,thecostofwaterisincreasing.Asaresult,thedemandforwaterreuseinthebreweryindustryisexpectedtoincreaseatanunprecedentedrate.Consequently,anincreasingneedofprocessescapableofachievinganefficienttreatmentunderextremeoperationalconditionsthatsimultaneouslyoptimizeoperationalcostscanbeexpectedinthefuture.Informationobtainedfromthisreviewshowsthatinordertoremoveimpuritiesefficiently,integrationofdifferentprocessesisrecommended.DisclaimerThecontentsofthispaperreflecttheviewsoftheauthorswhoareresponsibleforthefactsandaccuracyofthedatapresentedhereinanddonotnecessarilyreflecttheofficialviewsorpoliciesofanyagencyorinstitute.Thispaperdoesnotconstituteastandard,specification,norisitintendedfordesign,construction,bidding,contracting,orpermitpurposes.References[1]L.Braeken,B.VanderBruggen,C.Vandecasteele,Regenerationofbrewerywastenwaterusingnanofiltration,WaterResearch38(13)(2004)3075–3082.[2]W.Parawira,I.Kudita,M.G.Nyandoroh,Astudyofindustrialanaerobictreatmentofopaquebeerbrewerywastewaterinatropicalclimateusingafull-scaleUASBreactorseededwithactivatedsludge,ProcessBiochemistry40(2)(2005)593–599.[3]L.Fillaudeau,P.Blanpain-Avet,G.Daufin,Water,wastewaterandwastemanagementinbrewingindustries,JournalofCleanerProduction14(2006)463–471.[4]L.Fillaudeau,B.Boissier,A.Moreau,P.Blanpain-Avet,S.Ermolaev,N.Jitariouk,A.Gourdon,Investigationofrotatingandvibratingfiltrationforclarificationofroughbeer,JournalofFoodEngineering80(2007)206–217.[5]A.Doubla,A.Laminsi,A.Nzali,E.Njoyim,J.Kamsu-Kom,J.-L.Brisset,Organicpollutantsabatementandbiodecontaminationofbreweryeffluentsbyanon-thermalquenchedplasmaatatmosphericpressure,Chemosphere69(2007)332–337.[6]K.Kanagachandran,R.Jayerantene,Utilisationpotentialofbrewerywastewatersludgeasanorganicfertilizer,JournaloftheInstituteofBrewing112(2)(2006)92–96.[7]InstituteofBrewingandDistilling,Examinersreports2005to2009,DiplomainBrewingModuleOne,2005–2009.[8]N.J.Huige,Breweryby-productsandeffluents,in:F.G.Priest,G.G.Stewart(Eds.),HandbookofBrewing,CRCPress,BocaRaton,2006.[9]T.Goldammer,TheBrewers'Handbook,2ndeditionApexPublishers,Clifton,2008.[10]Y.Sarfo-Afriye,1999,AStudyofIndustrialWasteManagementinKumasi(CaseStudy),KumasiBreweriesLimited,TheCoca-ColaBottlingCompanyofGhana,2009.[11]T.Janhom,S.Wattanachira,P.Pavasant,Characterisationofbrewerywastewaterwithspectrofluorometryanalysis,JournalofEnvironmentalManagement90(2009)1184–1190.[12]W.Fischer,Reprocessingordisposalofkieselguhr?BrauweltInternational1(1992)60–65.[13]G.Hrycyk,Therecoveryanddisposalofdiatomaceousearthinbreweries,MBAATechnicalQuarterly34(1)(1997)293–298.[14]V.I.Kaur,Incorporationofbrewerywasteinsupplementaryfeedanditsimpactongrowthinsomecarps,BiosourceTechnology91(2004)101–104.n[15]D.Norman,Normanenvironmentalmanagementsystems,GlassTechnology38(5)(1997)146–149.[16]W.Driessen,T.Vereijken,Recentdevelopmentsinbiologicaltreatmentofbreweryeffluent,TheInstituteandGuildofBrewingConvention,Livingstone,Zambia,March2–7,2003.[17]UN,KyotoProtocoltotheUnitedNationsFrameworkConventiononClimateChange,19928http://unfccc.int/resource/docs/convkp/kpeng.html.[18]IFC,Environmental,HealthandSafetyGuidelinesforBreweries,20078http://www.ifc.org/ifcext/enviro.nsf/AttachmentsByTitle/gui_EHSGuidelines2007_Breweries/$FILE/Final+−+Breweries.pdf.[19]A.G.Brito,J.Peixoto,J.M.Oliveira,J.A.Oliveira,C.Costa,R.Nogueira,A.Rodrigues,Breweryandwinerywastewatertreatment:somefocalpointsofdesignandoperation,in:V.Oreopoulous,W.Russ(Eds.),UtilisationofBy-productsandTreatmentofWasteintheFoodIndustry,Vol.3,Springer,NewYork,2007.[20]A.G.Rao,T.S.K.Reddy,S.S.Prakash,J.Vanajakshi,J.Joseph,P.N.Sarma,pHregulationofalkalinewastewaterwithcarbondioxide:acasestudyoftreatmentofbrewerywastewaterinUASBreactorcoupledwithabsorber,BioresourceTechnology98(2007)2131–2136.[21]C.Cronin,K.V.Lo,AnaerobictreatmentofbrewerywastewaterusingUASBreactorsseededwithactivatedsludge,BioresourceTechnology64(1998)33–38.[22]H.Huang,K.Schwab,J.G.Jacangelo,Thepretreatmentforlowpressuremembranesinwatertreatment:areview,EnvironmentalScienceandTechnology43(9)(2009)3011–3019.[23]F.R.Spellman,Spellman'sStandardHandbookforWastewaterOperators,Vol.1,TechnomicPublishers,Lancaster,1999.[24]UnitedNationsEnvironmentProgramme,SourceBookofAlternativeTechnol-ogiesforFreshWaterAugmentationinLatinAmericaandtheCaribbean,OrganisationofAmericaStates,WashingtonDC,19978http://www.oas.org/DSD/publications/Unit/oea59e/ch25.htm.[25]K.Unterstein,Energyandwatergotomakebeer,BrauweltInternational18(5)(2000)368–370.[26]M.Perry,G.DeVilliers,Modelingtheconsumptionofwaterandotherutilities,nBrauweltInternational5(3)(2003)286–290.[27]G.J.Sheehan,P.F.Greenfield,Utilisation,treatmentanddisposalofdistillerywastewater,WaterResearch14(1980)257–277.[28]L.Lampinen,F.Quirt,Effluentneutralizingwithfluegas,TechnicalQuarterlyMasterBrewersAssociationoftheAmericas24(3)(1987)86–89.[29]T.Lom,Anewtrendinthetreatmentofalkalinebreweryeffluents,TechnicalQuarterlyMasterBrewersAssociationoftheAmericas14(1977)50–58.[30]J.Gregory,ParticlesinWater:PropertiesandProcesses,IWAPublishing/CRCPress,London,2006.[31]Degrémont,WaterTechnicalHandbook,9thedition,Degrémont,Paris,1989.[32]H.Dai,X.Yang,T.Dong,Y.Ke,T.Wang,EngineeringapplicationofMBRprocesstothetreatmentofbeerbrewingwastewater,ModernAppliedScience4(9)(2010)103–109.[33]Y.Feng,X.Wang,B.E.Logan,H.Lee,Brewerywastewatertreatmentusingair-cathodemicrobialfuelcells,AppliedMicrobiologyandBiotechnology78(2008)873–880.[34]M.Seneviratne,APracticalApproachtoWaterConservationforCommercialandIndustrialFacilities,El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