1s20S0956053X12004813main戴晓虎

High-solidsanaerobicco-digestionofsewagesludgeandfoodwasteincomparisonwithmonodigestions:StabilityandperformanceXiaohuDai,NinaDuan,BinDong⇑,LinglingDaiNationalEngineeringResearchCenterforUrbanPollutionControl,SchoolofEnvironmentalScienceandEngineering,TongjiUniversity,1239SipingRoad,Shanghai200092,PRChinaarticleinfoArticlehistory:Received16February2012Accepted21October2012Availableonline21November2012Keywords:High-solidsAnaerobicdigestionDewateredsludgeFoodwasteKineticabstractSystemstabilityandperformanceofhigh-solidsanaerobicco-digestionofdewateredsludge(DS)andfoodwaste(FW)incomparisonwithmonodigestionswereinvestigated.Systemstabilitywasimprovedinco-digestionsystemswithco-substrateactingasadilutingagenttotoxicchemicalslikeammoniaorNa+.Forhigh-solidsdigestionofDS,theadditionofFWnotonlyimprovedsystemstabilitybutalsogreatlyenhancedvolumetricbiogasproduction.Forhigh-solidsdigestionofFW,theadditionofDScouldreduceNa+concentrationandhelpmaintainsatisfactorystabilityduringtheconversionofFWintobio-gas.Systemperformancesofco-digestionsystemsweremainlydeterminedbythemixingratiosofDSandFW.Biogasproductionandvolatilesolids(VSs)reductionindigestionoftheco-mixtureofDSandFWincreasedlinearlywithhigherratiosofFW.Akineticmodel,whichaimedtoforecasttheperformanceofco-digestionandtoassistreactordesign,wasdevelopedfromlong-termsemi-continuousexperiments.MaximumVSreductionforDSandFWwasestimatedtobe44.3%and90.3%,respectively,andfirstorderconstantkwasfoundtobe0.17d1and0.50d1,respectively.Experimentaldataofco-digestionwereingoodconformitytothepredictionsofthemodel.2012ElsevierLtd.Allrightsreserved.1.IntroductionSewagesludge,thebyproductofbiologicalwastewatertreat-mentprocesses,isexpectedtoincreasecontinuouslyinthenextdecade,duetoincreasingpopulationconnectedtosewagenet-works,buildingnewwastewatertreatmentplants(WWTPs)andupgradingexistingplantstomeetthemorestringentlocaleffluentregulations.InChina,over31010kgdewateredsludge(80%mois-turecontent)isgeneratedeveryyear,andalmost80%ofithasnotreachednecessarystabilization(Duanetal.,2012).Treatmentofsewagesludgeviaanaerobicdigestionhasbeencarriedoutwidely,andthetechnologyhasrecentlyreceivedincreasedinterestinmanycountriesduetotherenewableenergyitcanproduce(Chenetal.,2008).Methaneproductionofsewagesludgewasusuallyinvestigatedintraditionallow-solidsdigestionsystems.However,duetopoormanagement,unprofessionaloperation,economicallimitation,andinadequateplanning,traditionallow-solidsanaerobicdiges-tionsystemsarenotalwaysfeasibleinsmall-scaleWWTPsorthoselocatedindevelopingcountries.Forexample,amongatotalof2500WWTPsinChina,onlyabout50ofthemweredesignedwithanaerobicdigestionsystems,andonly20%anaerobicpro-cesseswerewelloperated.However,dewateringunitshaveal-readybeenimplementedinmostWWTPs,whichmakesitfavorablefordewateredsludge(DS)dischargedfromsmall-scaleWWTPstobecollectedandsenttoalarge-scaleanaerobicdigesterforcentralizedprocessing.Hence,high-solidsanaerobicdigestion,characterizedbyahightotalsolids(TS)contentofthefeedstockstypicallygreaterthan15%(w/w)(Rapportetal.,2008),couldbeoneviableoptiontosolvethesludgedisposalproblemsindevelop-ingcountrieslikeChinaorinsmall-scaleWWTPs.However,inhigh-solidsanaerobicdigestionofdewateredsludge,highammo-niaconcentrationisapotentialfactorinfluencingsystemstability(Duanetal.,2012).Analternativeistoco-digestdewateredsludgewithotherorganicwastes.Foodwaste(FW),fromresidential,commercialestablishments(suchasrestaurants),institutional(suchasschoolcafeterias)andindustrialsources(factorylunchrooms)isgeneratedatanever-increasingrate(higherthan10%everyyearinChina)duetopopu-lationgrowthandrisinglivingstandards.InChina,ofmunicipalsolidwaste(MSW),FWaccountsfor40–50%oftheweight.FW,con-taininghighmoistureandbiodegradableorganics,couldbequitebeneficialtoenergyrecoveryandMSWreductioniftreatedbyanaerobicdigestion.Highsaltcontent(mainlyNaCl)wasanothercharacteristicofFW,whichmayincreaseosmoticpressureandcausebacterialcellstodehydrate(Yerkesetal.,1997).Sincethetoxicityofsaltswasfoundtobepredominantlydeterminedbythecation(McCartyandMcKinney,1961),Na+wasconsideredapotentialfactorinfluencingFWdigestionsystems.Itwasreported0956-053X/$-seefrontmatter2012ElsevierLtd.Allrightsreserved.⇑Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](B.Dong).WasteManagement33(2013)308–316ContentslistsavailableatSciVerseScienceDirectWasteManagementjournalhomepage:(Mendézetal.,1995).McCartyreportedthatNa+concentrationsrangingfrom3500to5500mgL1tobemoderatelyand8000mgL1tobestronglyinhibitorytomethanogensundermesophilicconditions.Otherfac-torssuchasantagonisticeffect,synergisticeffectandacclimationperiodmayalsointerferewiththeinhibitoryeffectofNa+(KugelmanandMcCarty,1964;Valleroetal.,2003).HighNa+concentrationsofFWcanbedilutedbysludgeaddition.Thus,betterperformancewasexpectedinco-digestionsystems.Inad