毕业设计餐厨垃圾厌氧的外文文献Word下载.docx

毕业设计餐厨垃圾厌氧的外文文献Word下载.docx

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HIGHLIGHTS

▲Solidstateanaerobicdigestion（SS-AD）offoodwasteandyardwaste.

▲Thehighestmethaneyieldswereobtainedatfeedstock/effluent（F/E）ratio1.

▲IncreasingF/Eratiofrom1to2and3causeddecreasesinmethaneyield.

▲TheADwasupsetatF/Eratio3exceptyardwasteonly.

ABSTRACT

FoodandyardwastesareavailableyearroundatlowcostandhavethepotentialtocomplementeachotherforSS-AD.Thegoalofthisstudywastodetermineoptimalfeedstock/effluent（F/E）andfoodwaste/yardwastemixingratiosforoptimalbiogasproduction.Co-digestionofyardandfoodwastewascarriedoutatF/Eratiosof1,2,and3.ForeachF/Eratio,foodwastepercentagesof0%,10%,and20%,basedondryvolatilesolids,wereevaluated.Resultsshowedincreasedmethaneyieldsandvolumetricproductivitiesasthepercentageoffoodwastewasincreasedto10%and20%ofthesubstrateatF/Eratiosof2and1,respectively.Thisstudyshowedthatco-digestionoffoodwastewithyardwasteatspecificratioscanimprovedigesteroperatingcharacteristicsandendperformancemetricsoverSS-ADofyardwastealone.

2012ElsevierLtd.Allrightsreserved.

Keywords:

Solid-stateanaerobicdigestion，Biogas，Municipalsolidwaste，Foodwaste，Co-digestion

1.Introduction

Solid-stateanaerobicdigestion（SS-AD）hasbeensuccessfullyusedtoconvertvariouslignocellulosicbiomassfeedstockstobiogas（Lietal.,2011a）.SS-ADhasbeenthedominantADsysteminstalledinEuropesincetheearly1990sforthetreatmentofmunicipalsolidwaste（MSW）,andtypicallyoperatesat15–50%totalsolids（TS）content（Lietal.,2011b;

BaereandMattheeuws,2008;

Guendouzetal.,2010）.SS-ADprovidesmanybenefitsoverliquidADindigestinglignocellulosicbiomasssuchastreatingmoreorganicsolidsinthesamesizedigesterandproducingacompost-likefinishedorganicmaterialthatiseasiertohandleandcanbeappliedtoagriculturallandforfertilizer（Martinetal.,2003a;

Lietal.,2011b）.TheSS-ADsystemalsofeaturesfewermovingpartsandlowerenergyinputsneededforheatingandmixing（Lietal.,2011a）,andithasagreateracceptanceofinputscontainingglass,plastics,andgrit.Furthermore,SS-ADcanovercomeothercommonproblemsexistingintheliquidADprocesssuchasfloatingandstratificationoffats,fibers,andplastics（Chanakyaetal.,1999）.

Thestart-upperiodofanSS-ADsystemisconsideredthemostcriticalphaseinbatchdigestion.Thefeedstock/effluent（F/E）ratio,anoperatingparameterthatmeasurestheamountofsubstratetotheamountofinoculumonadryvolatilesolids（VS）basis,hasbeenshowntobeacriticalfactoraffectingtheperformanceofSS-AD（Lietal.,2011b）.SS-ADmayrequireupto50%ofdigestedresidueforarapidstartup,whichdecreasesreactorutilizationefficiency（Martinetal.,2003b;

Rapportetal.,2008;

Lietal.,2011b）.Ahighlyconcentratedandactiveinoculumsourceisimportanttoreducedigestiontime,improvedigesterefficacy,andincreaseTSinthefinishedproduct（Forster-Carneiroetal.,2008）.

Co-digestionofmixedsubstratesoffersmanyadvantages,includingecological,technological,andeconomicbenefits,comparedtodigestingasinglesubstrate（Rughoonundunetal.,2012）.However,combiningtwoormoredifferenttypesoffeedstocksrequirescarefulselectiontoimprovetheefficiencyofanaerobicdigestion（á

lvarezetal.,2010）.Thepurposeofco-digestionistobalancenutrients（C/Nratioandmacro-andmicronutrients）anddiluteinhibitors/toxiccompoundstoenhancemethaneproduction（Hartmannetal.,2004;

Sosnowskietal.,2003）.

XuandLi（2012）foundthatanF/Eratioof2achievedhigheraccumulativemethaneyieldsthanathigherF/Eratiosof4and6forthesamedogfoodtocornstoverratio.Thestudyalsofoundthatco-digestionimprovedmethaneyieldcomparedwithusingcornstoverordogfoodasthesolesubstrateduetoimprovementsinreactorcharacteristics.Thestudyalsoconcludedthatco-digestionofdogfoodwithcornstoverreducedstart-uptimeandvolatilefattyacid（VFA）accumulationinSS-AD.AstudybyEl-MashadandZhang（2010）foundthatinclusionoffoodwaste,atratesofupto60%offeedstockVS,withdairymanureresultedinhigherbiogasyieldsandproductionratesascomparedtothedigestionofdairymanurealone.Panichnumsinetal.（2010）examinedthepotentialofco-digestionofcassavapulpwithpigmanureusingasemi-continuouslyfed,stirredtankreactor.ThestudyfoundamaximummethaneyieldandVSremovalof306L/kgVSaddedand61%,respectfully,whenthecassavapulpaccountedfor60%ofthefeedstockVS.However,athigher（>

X%）cassavapulpratios,thereactorfailedduetorapidVFAaccumulationandinsufficientbufferingcapacity.

IntheUnitedStates,MSWsuchasyardandfoodwastes,whichareavailableyearround,areoftenlandfilled,incinerated,orcomposted.FoodwasteisthelargestwastestreaminMSW,exceptforrecyclables,andaccountedfor14.3%（34.7milliontons）ofthetotalMSWin2009（USEPA,2011）.Collectionoffoodwastefromrestaurants,grocerystores,andprocessingplants,whicharesinglelargesources,caneaselogisticalissuesandreducecollectioncostscomparedtohouseholdpickup.Yardwaste,whichincludesgrass,leaves,andvariouswoodchips,hadatotalannualavailabilityintheUnitedStatesof30.9millionmetrictons（28milliontons）（Milbrandt,2005）.Collectionofyardwastefromcitiesandtown’scollectionserviceandtreetrimmingbusinessescanprovidealargeamountofyardwasteatlowcost.Grass,leaves,andmaplewoodchipsweredeterminedtohaveC/Nratiosof17,11,and567,respectively（Micheletal.,1993;

Wongetal.,2001;

Zaguryetal.,2006）.Foodwastecollectedfromrestaurants,whichwasfoundtohaveaC/Nratioof15（Zhangetal.,2007）,couldbeaddedtobalancetheC/Nratioofyardwaste.ThefinalmixtureofliquidADeffluent,yardwaste,andfoodwasteshouldhaveaC/Nratiointherangeof20–30foroptimummicrobialperformance.Inordertomaximizebiogasproduction,thevolumetricloadingoffoodwasteshouldbemaximized.Increasingthevolumetricloadingoffoodwastecanbeaccomplishedby:

（1）increasingtheF/Eratiowithaconstantsubstratecompositionthatincludesacertainpercentageoffoodwaste,

（2）increasingthepercentageoffoodwasteinthefeedstockwhilekeepingtheF/Eratioconstant,or（3）combiningthesetwoapproaches.

Currently,therearenoreportedstudiesonsolid-stateco-digestionoffoodwastewithyardwaste.ThisstudycouldprovidebaselinedatafortheadoptionofSS-ADintheUnitedStatesusinginexpensiveandavailablefeedstocksthatcomplementeachother.Therefore,themajorobjectiveofthisstudywastodeterminemethaneyieldsandvolumetricproductivitiesforsolidstateco-digestionofdifferentfoodwastetoyardwasteratiosatdifferentF/Eratios.

2.Methods

2.1.Feedstockandinoculum

YardwastewasobtainedinJune2011fromtheOARDCWoostercampusandcontainedleavesandtreebranches.Thefeedstockwasovendriedat40_Cfor48hinaconvectionoven（PrecisionThelcoModel18,Waltham,MA）toobtainamoisturecontentoflessthan10%,andthengroundwithahammermill（Mackisik,ParkerFord,PA）topassthrougha5mmscreen,andstoredinairtightcontainersuntilused.FoodwastewascollectedinAugust2011fromthefeedinghopperofquasarenergygroup’sliquidanaerobicdigesterinWooster,Ohio,USA.ThefoodwasteoriginatedfromseveralWal-Martgrocerystoresnearby.Thefoodwastecollectedwascutandgroundupusingastandardkitchenblender.Foodwastewasstoredinair-tightbucketsat4_Cinawalk-incooleruntilused.

EffluentfromamesophilicliquidADsystemfedwithfoodwastes,fats,oilsandgreases（FOG）,andsewagesludge（operatedbyquasarenergygroupinColumbus,OH,USA）wasusedasinoculum.DuetothelowTScontent（7.7%）,theeffluentwascentrifuged（ThermoScientificSorvallLegendT+）at3500rpm（2634g）for30mintoobtaintherequiredTScontentof15%.Thedecantedliquidswereremovedfromthesolidsbyturningtheplasticcontainers（600mlforeach）upsidedownandlettingtheliquidportionrunout.ThesolidsattachedatthebottomofthecontainerwerecollectedtobeusedasinoculumforSS-AD.Effluentwaskeptinair-tightbucketsat4_Cinawalk-incooler.Priortouse,theinoculumwasstarvedfor1weekandincubatedat37_CtoreactivatemicrobiologicalactivityandremovetheeasilydegradableVS.

2.2.Solid-stateanaerobicdigestion

TheeffectofF/Eratios（1,2and3）andpercentageoffoodwaste（0%,10%,20%,basedondryVS）inthefeedstocksontheperformanceofSS-ADwasstudied.Awiderangeofvolumetricloadingratesoffoodwaste（0.0–166g/L）wasstudiedinthedigesters.Theinoculum,foodwaste,andyardwasteweremixedbyahand-mixer（Black&

Decker,250wattmixer,Towson,MD,USA）for10min.Well-mixedmaterialswereloadedintoa1Lglassreactorandincubatedinawalk-inincubationroomforupto30daysat36±

1_C.Duplicatereactorswererunforeachcondition.Inoculumwithoutanyfeedstockadditionwasusedasacontrol.Biogasgeneratedwascollectedina5LTedlargasbag（CELScientific,SantaFeSprings,CA,USA）.Thecompositionandvolumeofbiogasweremeasuredevery1–3daysduringthe30daySS-AD.

2.3.Analyticalmethods

TheStandardMethodsfortheExaminationofWaterandWastewaterwereused