05Theinfluenceofbiomasstemperatureonbiostabilizati

Theinfluenceofbiomasstemperatureonbiostabilization–biodryingofmunicipalsolidwasteFabrizioAdania,*,DiegoBaidoa,EnricoCalcaterrab,PierluigiGeneviniaaDipartimentodiProduzioneVegetale,sez.FCA,viaCeloria2,20133Milano,ItalybEcodecoS.p.a.,Loc.CassinazzadiBaselica,27010Giussago,ItalyReceived12November2000;receivedinrevisedform28November2001;accepted8December2001AbstractAlaboratorystudywascarriedouttoobtaindataontheinfluenceofbiomasstemperatureonbiostabilization–biodryingofmunicipalsolidwaste(initialmoisturecontentof410gkgwetweightðw:w:Þ1).Threetrialswerecarriedoutatthreedifferentbiomasstemperatures,obtainedbyairflowratecontrol(A¼70
C,B¼60
CandC¼45
C).Biodegradationandbiodryingwereinverselycorrelated:fastbiodryingproducedlowbiologicalstabilityandviceversa.TheproductobtainedfromprocessAwascharacterizedbythehighestdegradationcoefficient(166gkgTS10;TS10¼initialtotalsolidcontent)andlowestwaterloss(409gkgW10;W0¼initialwatercontent).Duetothehighreductionofeasilydegradablevolatilesolidcontentandpreservationofwater,processAproducedthehighestbiologicalstability(dynamicrespirationindex,DRI¼141mgO2kgVS1;VS¼volatilesolids)butthelowestenergycontent(EC¼10,351kJkgw:w:1).Conversely,processCwhichshowedthehighestwaterelimination(667gkgW10),andlowestdegradationrate(18gkgTS10)wasoptimalforrefuse-derivedfuel(RDF)productionhavingthehighestenergycontent(EC¼14,056kJkgw:w:1).Nevertheless,thelowbiologicalstabilityreached,duetopreservationofdegradablevolatilesolids,attheendoftheprocess(DRI¼1055mgO2kgVS1),indicatedthattheRDFshouldbeusedimmediately,withoutstorage.TrialBshowedsubstantialagreementbetweenlowmoisturecontent(lossesof665gkgW10),highenergycontent(EC¼13,558kJkgw:w:1)andgoodbiologicalstability(DRI¼166mgO2kgVS1),sothat,inthiscase,theproductcouldbeusedimmediatelyforRDForstoredwithminimumpollutantimpact(odors,leachesandbiogaspro-duction).2002ElsevierScienceLtd.Allrightsreserved.Keywords:Biostabilization;Calorificpower;Drying;Municipalsolidwaste;Refuse-derivedfuel;Temperatureeffect1.IntroductionThelatestEUpolicyonwastemanagement(see91/156/EEC;91/689/EEC;94/62/EU)(Gruppodepuracque,1998)recommendstherecyclingofmaterialandenergyproductsandwastetreatmentbeforelandfilldisposal.Forthisreasonthebiologicalprocessesleadingtocompostproduction,stabilizedproduct,andrefuse-derivedfuel(RDF)havecometobeconsideredofgeneralinterestandcomposting,biostabilizationandbiodryingprocesseshavebeenexhaustivelystudiedandreviewedinthepast(AA.VV,1993;WiemerandKern,1996).Inparticular,theuseofbiomassforenergypro-ductionisnowadaysregardedasofgeneralrelevance(HallandScrase,1998),aboveallinthecaseofmu-nicipalsolidwaste(MSW)(Le
aaoandTan,1998).Compostingandbiostabilizationprocessesleadtothecompletedegradationofeasilydegradableorganicmatterinordertoreachbiostabilizationandhumifica-tion(compost)(Scagliaetal.,2000).Ontheotherhand,biodryingdriesthebiomasswhilepreservingcalorificpower.Inparticular,biodrying,byreducingthewatercontentofthewaste,producesanincreaseincalorificvalueofabout30–40%(WiemerandKern,1996).Subsequentmechanicaltreatments,usedtoremovelow-caloriematerial(metals)andthefinefraction(size2mm),permittheproductionofhigh-caloriefuel(16,000–17,500kJkg1w:w:1),comparabletothecaloriecon-tentofbrowncoal(WiemerandKern,1996).Thedegreeofdrying,biostabilityandhygienizationduringanaerobicbiologicalprocesscanbevariedbycorrectmanagementoftheprocessparameters,themainBioresourceTechnology83(2002)173–179*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](F.Adani).0960-8524/02/$-seefrontmatter2002ElsevierScienceLtd.Allrightsreserved.PII:S0960-8524(01)00231-0onesbeingtemperature,oxygen,airflowrateandmois-turecontent(FinsteinandHogan,1993).Duringcompostingandbiostabilization,tempera-ture,oxygenandmoistureshouldbekeptwithinanoptimalrangeinordertoensurehighdegradationper-formance(FinsteinandHogan,1993).Ontheotherhandthebiodryingprocessshouldbemanagedinsuchawayastospeedupdryingandtoreduceorganicmatterdegradation(tosavecalorificpower).Airflowratein-fluencingbiomasstemperatureaffectdryingprocess(Haug,1986),whilethedegreeoforganicmatterde-gradation(Nellistetal.,1993)affectscalorificpowerandthedegreeofstabilityofthefinalproduct(RDF).Thispaperreportsontheinitialresultsofalabora-torytrialtoestablishhowfarbiomasstemperatureandairflowrateaffectdrying,calorificpowerandthedegreeofstabilityoftheRDFproduced.2.MethodsTrialswereperformedusinganadiabaticcompostingreactorof148lcapacity(Adanietal.,1998).Thelaboratoryreactor(CostechInternational,CernuscoS.N.,Italy;DiProVe,Milan,Italy),consistedof:(i)aninsulatedreactor;(ii)acontrolcabinet;(iii)anair-supplysystem;and(iv)abiofilter.AcylindricalPVC148-lcontainer(height800mm,externalandinternaldiametersof600and486mm,respectively)formedthereactor’sstructure.The57-mm-thickwallsofthecontainerwerefilledwithpoly-urethanefoamtoprovidethermalinsulation.Atapwasfixedtothebottomofthereactortoeliminatetheper-colatedorcondensedwater.Thetopofthereactorwasclosedbyahermeticallysealedlid.Onthelidtherewerethreeorifices:fortheair-supplytube