08Biostabilizationbiodryingofmunicipalsolidwasteby

Biostabilization–biodryingofmunicipalsolidwastebyinvertingair-flowMaraSugnia,EnricoCalcaterrab,FabrizioAdania,*aDipartimentodiProduzioneVegetale,sez.FCA,ViaCeloria2,20133Milano,ItalybEcodecoS.p.a.,Loc.CassinazzadiBaselica,27010Giussago,ItalyReceived1August2002;receivedinrevisedform22November2004;accepted22November2004Availableonline20January2005AbstractTheprocessofbiodryingcouldbeagoodsolutionformunicipalsolidwastemanagement,allowingtheproductionoffuelwithaninterestingenergycontent.Previouswork(Adani,F.,Baido,D.,Calcaterra,E.,Genevini,P.L.,2002.Theinfluenceofbiomasstem-peratureonbiostabilization–biodryingofmunicipalsolidwaste.BioresourceTechnology83(3),173–179)hasindicatedthatappro-priatemanagementoftheprocessingparameters(air-flowrateandbiomasstemperatures)couldachievebiomassdryinginveryshorttimes(8–9days).However,thedataofthatworkalsoevidencedthatiftheconditionsdonotconsiderpileturning,andtheair-flowisalwaysfromonedirection,temperaturegradientsarisewithinthebiomass,resultinginalackofhomogeneityinthemoistureandenergycontentofthefinalproduct.Therefore,anewlaboratorystudywasconductedonmunicipalsolidwastebiodrying–biostabilizationinanefforttoobtainhomogeneousfinalproducts.Ourproposaltosolvethislackofhomogeneityistoperiodicallyinverttheair-flowdirection.Thus,inlinewithapreviousstudy,twotrials,AandB,werecarriedout,dividingthebiomassintothreelayerstostudytemperatureandmoisturegradientsthroughouttheprocess,andathirdtrial(C)simulatingair-flowinversionatregularintervalswasintroduced.Theresultssuggestthatthedailyinversionofair-floweliminatesmarkedtem-peraturedifferencesandleadstoahomogeneousfinalproduct.
2005ElsevierLtd.Allrightsreserved.Keywords:Calorificpower;Biodrying;Municipalsolidwaste;Refuse-derivedfuel;Invertedair-flow1.IntroductionInanefforttosolveproblemsconnectedwithwastemanagement,andinlinewithnewEuropeanlegislation(91/156/EEC;91/689/EEC;94/62/EU)(Adanietal.,2002),innovativetechnologiesforwastetreatmentsuchascomposting,biostabilizationandbiodryinghavebe-comeofgeneralinterest.Aftercompostingorbiostabili-zationthefinalproductcanbeusedforagriculturalpurposes,orthebiostabilizedmaterialcanbestoredsafelyinalandfill(WiemerandKern,1996;Adanietal.,1998).Inthecaseofbiodryingtherefusecanbeusedasasourceofenergy,i.e.,fuel(Calcaterraetal.,2000;Adanietal.,2002).Althoughtherearemanystud-iesoncomposting(AA.VV.,1993)thereisverylittleintheliteratureonbiostabilizationor,especially,onbiodrying.Parameterslikebiomasstemperatureandhumidityduringaerobicprocessingwereinvestigatedinordertobetterunderstandtheirrelativeimportance,but,again,moststudiestendtoaddresscomposting(FinsteinandHogan,1993).Recently,Adanietal.(2002)reportedstudiesontheinfluenceofbiomasstemperatureandair-flowrateonthebiostabilization–biodryingofmunicipalsolidwaste.Theexperimentalresultsgaveproofofthenegative0960-8524/$-seefrontmatter
2005ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2004.11.016*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](F.Adani).BioresourceTechnology96(2005)1331–1337correlationbetweenbiodegradationandbiodrying.Infact,if,duringtheprocess,thebiomasswassubjectedtolowair-flowratesbiodegradationwasfavouredbutwatereliminationwasinadequate.Viceversa,iftheair-flowrateishigherthereisamoreconsistentwaterlossbutthedegradationrateisslower.Therefore,toachievesatisfactorywaterloss,andensurehighenergycontentinthefinalproduct(fuel),thebiodryingprocessrequiresthemaintenanceofhighair-flowratecombinedwithhightemperature.Duringtheprocess,temperaturegra-dientswereobservedthroughoutthepile;alsomoisturegradientsbecameevidentbut,whereasthetemperaturegradientsdisappearedinthecourseoftheprocessing,themoisturegradientspersistedtotheend.Thisfactresultedinalackofhomogeneityinthefinalproduct(Adanietal.,2002).Thus,itwasdecidedtoinvestigatemorefullythesegradients.Ourpurposewastoavoidhet-erogeneityinthefinalproducts.Todothisweconsidereditnecessarytoeliminatetemperaturegradientsinthepile.Theaimofthepresentexperimentationwastoinvestigate,inthelaboratory,anewprocedureforbio-dryingmunicipalsolidwaste(MSW),i.e.,inversionofair-flow,comparingitwithwhatiscommonlydoneinbiodryingplants(Calcaterraetal.,2000)andwhatwehaddoneinpreviousexperimentation(Adanietal.,2002).Thesuggestedtechnicalsolutioninvolvesvaryingtheair-flowdirectionthroughthebiomass.Infact,inbiodryingprocesses,airisusuallypumpedthroughthebiomassinjustonedirection,thewaterbeingremovedintheformofvapourbecauseofthehightemperaturesreachedduringbioticdegradation.2.MethodsThetrialswereperformedusinganadiabaticcompo-stingreactorof148Lcapacity,likethatdetailedinpre-viouswork(Adanietal.,2001).Twonon-separatedMSWsamplesweretakenfromanMSWtreatmentplantsituatedinGiussago(Pavia,Italy).Onesamplewaspartofasamplingusedinpreviousexperimentsdriedtoamoisturecontentof50gkg
1wetweight(w.w.)andstoredat4C(Adanietal.,2002),theotherwasnewandpresented,beingsampledatadiversetime,differentcharacteristicsfromthepreviousones(seeafter).Eachsampleconsistedofabout300kgofshred-dedmaterial(B50mm)collectedfromastartingamountofabou