低接种蔬菜废弃物分离重要

ShortCommunicationInitiatingmethanogenesisofvegetablewasteatlowinoculum-to-substrateratio:ImportanceofspatialseparationFanLü,LipingHao,MinZhu,LimingShao,PinjingHe⇑InstituteofWasteTreatmentandReclamation,CollegeofEnvironmentalScienceandEngineering,TongjiUniversity,1239SipingRoad,Shanghai200092,PRChinaarticleinfoArticlehistory:Received25August2011Receivedinrevisedform24November2011Accepted26November2011Availableonline2December2011Keywords:AcidificationAnaerobicdigestionFermentationGompertzmodelingStart-upabstractWiththegoalofstarting-upthemethanogenesisofeasilybiodegradablewastewithminimuminoculum,thepresentworkevaluateddifferentinoculum-to-substrateratios(rI/S)incompletelymixedsystemsandinthesystemswithspatialseparationofinoculumandwaste.Itwasfounddifficulttoinitiatemethano-genesisinthecompletelymixedsystems,evenathighrI/S1.105onavolatilesolidbasis.FermentationefficiencieswereindependentofrI/S.Inthespatial-separationsystemswithalowtotalrI/S0.053,theulti-matemethaneyield(35C,1atm)reached445mL/g-VSaddedfortheinoculum-wasteinitiallycom-pletelyseparatedsystem.Theyieldsdecreasedto285,181,and34mL/g-VSadded,respectively,forpartiallyseparatedsystemswiththeratioscontrolledat1.105,0.254,and0.113intheinoculum-contain-ingreactors.Thisdemonstratestheimportanceofsettingspatialseparationbetweeninoculumandwastewheninoculationisemployed.Anappropriateinoculationmethodwouldinitiatemethanogenesisrap-idlyevenatlowinoculum-to-substrateratios.2011ElsevierLtd.Allrightsreserved.1.IntroductionDuetoitshighbiodegradability,theanaerobicdigestionofeasilybiodegradablewaste,suchasfoodwasteandvegetablewaste,isin-clinedtobeblockedinanacidcrisis,inwhichthereactionratesofhydrolysisandacidogenesissubstantiallyexceedthatofmethano-genesis.Asaresult,methanogenesisisdifficulttobeinitiatedunderacidicconditions.Oneoftwocommonsolutionsistoreducetheor-ganicloadingofthefeedstock,withthedisadvantageofincreasingthereactorvolumerequirement.Theothersolutionistoaddalargerquantityofmicrobialinoculum,withpotentialaimsofreducingtheburdenontheunitmicrobialcell,alleviatinginhibitionbyinhibitorysubstances,shorteningthelagtimeforacclimation,orincreasingtheultimatemethaneyield,themethaneproductionrate,orthebiodeg-radationrateofthewaste.Toassesstheinoculationdemand,thera-tioofinoculumtosubstrate[rI/S,onavolatilesolid(VS)basis],representingtheratioofthequantityofbiomassaddedtothequan-tityofsubstrate,isusuallyused.Intheliterature,theeffectofrI/Sisstilluncertain(summarizedinAnnexI).ThetestedrI/Sdifferedfromzeroto10.91onaVSbasis.Significant(Pandeyetal.,2010)orinsig-nificantchanges(Raposoetal.,2006)wereobservedconcerningtheeffectsofinoculationonmethaneyieldormethaneproductionrate.ManyfactorsregulatetheeffectofrI/S,includingthesubstratechar-acteristics,theoriginoftheinoculum,thespecificmethanogenicactivityoftheinoculum,andtheconcentrationsofinhibitorysub-stances.Asaresult,itisdifficulttodetermineanoptimalvalueofrI/Ssuitableforalltreatments,andtheamountofinoculumneedstobeestimatedonacase-by-casebasis(Angelidakietal.,2009).Nevertheless,itisgenerallyobservedthatarI/Sof1orlessoreven2isinsufficientforrapidly-degradablesubstratesinabatchtest(Xuetal.,2003;Nevesetal.,2004;Wuetal.,2011).Eventhewell-knowncontinuouslyfeddryanaerobicdigestionprocessDRANCO,usuallymixesthefeedstockwastewith6–7timesofdigestateasinoculum.However,highrI/Swilldecreasetheeffectivespaceinthereactor,resultinginacorrespondingdecreaseintheorganicloadingrateofthereactor.Hence,itisimportanttofindwaystores-cueanacidifiedreactorortoacceleratetheinitiationofmethaneproductionfromeasilydegradablewasteataminimalengineeringcost,e.g.byselectinganappropriateinoculationmethod.ThepresentworkaimedtoreconsidertheroleofrI/Sontheanaerobicdigestionofeasilybiodegradablewastebycombiningwithspatialseparation,soastoassessthefeasibilityofstarting-upthemethanogenesisofeasilybiodegradablewastewithmini-muminoculumatanrI/Saslowas0.053.Therationalewastoreducetheacidloadingontheinoculumbutretaintheoverallorganicloadingofthewholeanaerobicsystemunimpaired,bymeansofregulatingthetransportrateoftheorganicacids.2.Methods2.1.SubstrateandinoculumThevegetablewastewascollectedfromasupermarketinShanghai,China.Itwasgroundtoaparticlesizeoflessthan2mmbeforefeeding.Thegranularsludgefortheinoculumwas0960-8524/$-seefrontmatter2011ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2011.11.104⇑Correspondingauthor.Tel./fax:[phone].E-mailaddress:[e-mail](P.He).BioresourceTechnology105(2012)169–173ContentslistsavailableatSciVerseScienceDirectBioresourceTechnologyjournalhomepage:flowanaerobicsludgebed(UASB)reactorwithliquidinternalrecirculationthatwastreatingpapermillwastewa-ter.Theaveragesizeofthegranularsludgewas3–5mm.Thechar-acteristicsofthevegetablewastewere:totalsolids(TS)7.5%andonadryweightbasisVS88.1%,C36.3%,N3.1%,H5.6%,starch22.4%,lignocellulose55.1%andprotein8.4%.Thecharacteristicsoftheinoculumwere:TS9.3%andonadryweightbasisVS89.4%,C41.7%,N8.1%,andH6.4%.2.2.Experimentalset-upThedigestionexper