Theeffectofpolymeradditionongranulationina

WaterResearch36(2002)933–943Theeffectofpolymeradditionongranulationinananaerobicbaffledreactor(ABR).PartI:processperformanceS.Uyanik,P.J.Sallis*,G.K.AndersonEnvironmentalEngineeringGroup,DepartmentofCivilEngineering,UniversityofNewcastleuponTyne,ClaremontRoad,NewcastleuponTyneNE17RU,UKReceived15May2000;receivedinrevisedform10May2001;accepted12June2001AbstractThestabilityandperformanceofananaerobicbaffledreactor(ABR)treatinganice-creamwastewateratseveralorganicloadingrateshavebeeninvestigated.Specifically,itwasdeterminedwhetheranABRwouldpromotephaseseparationandifapolymeradditivewascapableofenhancinggranuleformationinanABR.Inordertoachievethesegoals,twoABRs,havingidenticaldimensionsandconfigurations,wereusedtostudytheaboveobjectivesusingasyntheticice-creamwastewater.TheABRprovedtobeanefficientreactorconfigurationforthetreatmentofahigh-strengthsyntheticice-creamwastewater.Anorganicloadingrateofaround15kgCODm
3d
1wastreatedwitha99%CODremovalefficiency.Fromthejartestandinhibitionassay,itwasconcludedthatKymeneSLX-2wasthemosteffectiveandleastinhibitorypolymertested.Themethaneyieldwashigherinthepolymer-amendedreactorcomparedtothecontrolreactor.Inaddition,polymeradditionresultedinaconsiderablyhigherdegreeofbiomassretentionandlowersolidswashoutfromtheABR.Consequently,itdemonstratedthattherewasaconsiderablepotentialforsludgeconditioninginABRsbyfacilitatingbetterbiomassretentionwithinthereactorwhichinturnledtobetterprocessperformance.GranulationwasachievedinbothABRswithin3months.However,thegranulesfromthepolymer-amendedreactorappearedearlierandweregenerallylargerandmorecompact,althoughthiswasnotquantifiedindetailduringthepresentstudy.ThemainadvantageofusinganABRcomesfromitscompartmentalisedstructure.ThefirstcompartmentofanABRmayactasabufferzonetoalltoxicandinhibitorymaterialinthefeedthusallowingthelatercompartmentstobeloadedwitharelativelyharmless,balancedandmostlyacidifiedinfluent.Inthisrespect,thelattercompartmentswouldbemorelikelytosupportactivepopulationsoftherelativelysensitivemethanogenicbacteriaandpartlyexplainswhythebestgranulesandthehighestmethaneyieldwereobtainedinCompartment2.Itisunlikelythatacompleteseparationofphases(acidogenicandmethanogenic)occurredwithintheABRssincemethaneproductionwasobservedinallcompartments,althoughthiswaslow(B40%ofallgascomposition)inCompartment1,becominghigher(B70%)inthefollowingcompartments.r2002ElsevierScienceLtd.Allrightsreserved.Keywords:Anaerobicbaffledreactors(ABR);Ice-creamwastewater;Polymeraddition;Partialphaseseparation;Granulation1.IntroductionSincetheearlyattemptstoexploitanaerobicbiotech-nologyforwastewatertreatment,manydevelopmentshavetakenplaceinreactordesignandoperationthathaveenhancedboththeefficiencyandreliabilityofthetechnology.First,itbecameevidentthatthetreatmentefficiencyofananaerobicreactorwascloselyrelatedtotheconcentrationofactivebiomassretainedwithinthesystem,andconsequentlymuchresearchhasbeenconductedintomodificationstotheconfigurationofthebasicanaerobicdigestionchamberinordertoproducehigh-ratedesigns.Thisworkhasalsoprovidedagreaterunderstandingoftherelationshipbetweenoperationalconditions,reactordesign,andtheformationofgranularsludgewithinreactors.Granula-tionimpliestheimmobilisationofactiveanaerobic*Correspondingauthor.Tel.:[phone].E-mailaddress:[e-mail](P.J.Sallis).0043-1354/02/$-seefrontmatterr2002ElsevierScienceLtd.Allrightsreserved.PII:S0043-1354(01)00315-3sludgeintodiscretemacroscopicaggregates.Theseexhibitenhancedsettlingcharacteristicsandarethere-forelesspronetobeingwashed-outofthereactor.TheconsequencesofgranulationanditsinfluenceonthephysiologyofanaerobicbacteriahavebeenreviewedbyCallejaetal.[1].TheadvantagesofgranularbiomassoverflocculentbiomasshavebeenbrieflystatedbyWirtzandDague[2].Thesecanbesummarisedasfollows:granulation*allowshighbiomassconcentrationsincontinuousreactors,*leadstointernalphysicochemicalgradientswithintheaggregates,*leadstoheterogeneousstructuredpopulationsofsyntrophicmicro-organisms,*allowsreactorstobeoperatedcontinuouslybeyondnormalwashoutflowrates,*allowsthemanipulationofbiomassasasinglephase,*affectsoverallstoichiometry,ratesofgrowthandmetabolism,*allowsthemanipulationofgrowthrateindependentofthedilutionrateand*generatesareactoreffluentwithlowsuspendedsolids.However,despiteitsobviousadvantage,granulationdoesnotoccurinalltypesofanaerobicreactororwitheverytypeofwastewaterbeingtreated.Upflowanaero-bicsludgebed(UASB)reactorsaregenerallyconsideredtobethebestdesignforpromotinggranulationforawiderangeofwastewaters,withhighcarbohydratecontainingwastewatersbeingmostlikelytoachievereliablegranuleformation.However,certainindustrialeffluentscontaininghighlevelsoffattymatter,suchasdairywasteandice-creamwastewater,aremoredifficulttotreatinUASBreactorsonaccountofthelowpropensityforgranuleformation.Inaddition,sincetheyarestrongwastewaterscontaininghighorganicload,significantamountsoflong-chainfattyacidscandevelopfromthepartialdegradationoffatsandthesecaninhibitthemethanogenicpopulationsinthereactor.Long-chainfattyacidsdonothavesuchanadverseeffectontheaci