固体废弃物全过程管理

CHAPTER4PHYSICAL,CHEMICAL,ANDBIOLOGICALPROPERTIESOFMUNICIPALSOLIDWASTE,4-1PHYSICALPROPERTIESOFMSW,ImportantphysicalcharacteristicsofMSWincludespecificweight,moisturecontent,particlesizeandsizedistribution,fieldcapacity,andcompactedwasteporosity.,SpecificWeight,SpecificWeightisdefinedastheweightofamaterialperunitvolume.BecausethespecificweightofMSWisoftenreportedasloose,asfoundincontainers,uncompacted,compacted,andthelike,thebasisusedforthereportedvaluesshouldalwaysbenoted.Specificweightdataareoftenneededtoassessthetotalmassandvolumeofwastethatmustbemanaged.Unfortunately,thereislittleornouniformityinthewaysolidwastespecificweightshavebeenreportedintheliterature.Frequently,nodistinctionhasbeenmadebetweenuncompactedorcompactedspecificweights.,MoistureContent,Themoisturecontentofsolidwastesusuallyisexpressedinoneoftwoways.Inthewet-weightmethodofmeasurement,themoistureinasampleisexpressedasapercentageofthewetweightofthematerial;inthedry-weightmethod,itisexpressedasapercentageofthedryweightofthematerial.Thewet-weightmethodisusedmostcommonlyinthefieldofsolidwastemanagement.,Inequationform,thewet-weightmoisturecontentisexpressedasfollows:,ParticleSizeandsizeDistribution,Thesizeandsizedistributionofthecomponentmaterialsinsolidwastesareanimportantconsiderationintherecoveryofmaterials,especiallywithmechanicalmeanssuchastrommelscreensmagneticseparators.,Thesizeofawastecomponentmaybedefinedbyoneormoreofthefollowingmeasures:,FieldCapacity,Definition:Thefieldcapacity(场地持水量)ofsolidwasteisthetotalamountofmoisturethatcanberetainedinawastesamplesubjecttothedownwardpullofgravity.Thefieldcapacityofwastematerialsisofcriticalimportanceindeterminingtheformationofleachateinlandfills.Waterinexcessofthefieldcapacitywillbereleasedasleachate.Thefieldcapacityvarieswiththedegreeofappliedpressureandthestateofdecompositionofthewaste.Afieldcapacityof30percentbyvolumecorrespondsto30in/100in.Thefieldcapacityofuncompactedcommingledwastesfromresidentialandcommercialsourcesisintherangeof50to60percent.,PermeabilityofCompactedWaste,Thehydraulicconductivityofcompactedwastesisanimportantphysicalpropertythat,toalargeextent,governsthemovementofliquidsandgasesinalandfill.Thecoefficientofpermeabilityisnormallywrittenas,固有渗透性,水的动力黏度,渗透系数,4-2CHEMICALPROPERTIESOFMSW,InformationonthechemicalcompositionofthecomponentsthatconstituteMSWisimportantinevaluatingalternativeprocessingandrecoveryoptions.Forexample,thefeasibilityofcombustiondependsonthechemicalcompositionofthesolidwastes.Typically,wastescanbethoughtofasacombinationofsemimoistcombustibleandnoncombustiblematerials.,Ifsolidwastesaretobeusedasfuel,thefourmostimportantpropertiestobeknownare:1.Proximateanalysis2.Fusingpointofash3.Ultimateanalysis(majorelements)4.EnergycontentWheretheorganicfractionofMSWistobecompostedoristobeusedasfeedstockfortheproductionofotherbiologicalconversionproducts,theinformationwemustknow:1）themajorelements(ultimateanalysis)thatcomposethewaste,2）thetraceelementsinthewastematerials.,ProximateAnalysis,ProximateanalysisforthecombustiblecomponentsofMSWincludesthefollowingtests:1.Moisture(lossofmoisturewhenheatedto105for1h)2.Volatilecombustiblematter(additionallossofweightonignitionat950inacoveredcrucible)3.Fixedcarbon(combustibleresidueleftaftervolatilematterisremoved)4.Ash(weightofresidueaftercombustioninanopencrucible),FusingPointofAsh,definitionThefusingpointofashisdefinedasthattemperatureatwhichtheashresultingfromtheburningofwastewillformasolid(clinker)byfusionandagglomeration.Notation:Typicalfusingtemperaturesfortheformationofclinkerfromsolidwasterangefrom2000to2200(1100to1200).,UltimateAnalysisofSolidWasteComponents,UltimateAnalysisofSolidWasteComponentstypicallyinvolvesthedeterminationofthepercentC,H,O,N,Sandash(sometimeshalogen).Thepurpose:TocharacterizethechemicalcompositionoforganicmattersinMSW.,EnergyContentofSolidWasteComponents,TheenergycontentoftheorganiccomponentsinMSWcanbedetermined(1)byusingafullscaleboilerasacalorimeter,(2)byusingalaboratorybombcalorimeter(3)bycalculation,iftheelementalcompositionisknown.Becauseofthedifficultyininstrumentingafull-scaleboiler,mostofthedataontheenergycontentoftheorganiccomponentsofMSWarebasedontheresultsofbombcalorimetertests.,EssentialNutrientsandOtherElements,WheretheorganicfractionofMSWistobeusedasfeedstockfortheproductionofbiologicalconversionproductssuchascompost,methane,andethanol,informationontheessentialnutrientsandelementsinthewastematerialsisofimportancewithrespecttothemicrobialnutrientbalanceandinassessingwhatfinalusescanbemadeofthematerialsremainingafterbiologicalconversion.TheessentialnutrientsandelementsfoundintheprincipalmaterialsthatcomposetheorganicfractionofMSWarereportedinTable4-6.,4-3BIOLOGICALPROPERTIESOFMSW,theorganicfractionofmostMSWcanbeclassifiedasfollows（Excludingplastic,rubber,andleathercomponents）:1.Water-solubleconstituents,suchassugars,starches,aminoacids,andvariousorganicacids,2.Hemicellulose,acondensationproductoffive-andsix-carbonsugars,3.Cellulose,acondensationproductofthesix-carbonsugarglucose,4.Fats,oils,andwaxes(蜡),whichareestersofalcoholsandlong-chainfattyacids,5.Lignin,apolymericmaterialcontainingaromaticringswithmethoxylgroups(-OCH3),theexactchemicalnatureofwhichisstillnotknown(presentinsomepaperproductssuchasnewsprintandfiberboard),6.Lignocellulose,acombinationofligninandcellulose,7.Proteins,whicharecomposedofchainsofaminoacids.,PerhapsthemostimportantbiologicalcharacteristicoftheorganicfractionofMSWisthatalmostalloftheorganiccomponentscanbeconvertedbiologicallytogasesandrelativelyinertorganicandinorganicsolids.TheproductionofodorsandthegenerationoffliesarealsorelatedtotheputresciblenatureoftheorganicmaterialsfoundinMSW(e.g.,foodwastes).,BiodegradabilityofOrganicWasteComponents,Volatilesolids(VS)content,determinedbyignitionat550,isoftenusedasameasureofthebiodegradabilityoftheorganicfractionofMSW.TheuseofVSindescribingthebiodegradabilityoftheorganicfractionofMSWismisleading,assomeoftheorganicconstituentsofMSWarehighlyvolatilebutlowinbiodegradability(e.g.,newsprintandcertainplanttrimmings).,Alternatively,thelignincontentofawastecanbeusedtoestimatethebiodegradablefraction,usingthefollowingrelationship:,ThebiodegradabilityofseveraloftheorganiccompoundsfoundinMSW,basedonlignincontent,isreportedinTable4-7.AsshowninTable4-7,wasteswithhighlignincontents,suchasnewsprint,aresignificantlylessbiodegradablethantheotherorganicwastesfoundinMSW.Therateatwhichthevariouscomponentscanbedegradedvariesmarkedly.Forpracticalpurposes,theprincipalorganicwastecomponentsinMSWareoftenclassifiedasrapidlyandslowlydecomposable.,ProductionofOdors,Odorscandevelopwhensolidwastesarestoredforlongperiodsoftimeon-sitebetweencollections,intransferstations,andinlandfills.Thedevelopmentofodorsinon-sitestoragefacilitiesismoresignificantinwarmclimates.Typically,theformationofodorsresultsfromtheanaerobicdecompositionofthereadilydecomposableorganiccomponentsfoundinMSW.,BreedingofFlies,Inthesummertimeandduringallseasonsinwarmclimates,flybreedingisanimportantconsiderationintheon-sitestorageofwastes.Fliescandevelopinlessthantwoweeksaftertheeggsarelaid.Thelifehistoryofthecommonhouseflyfromeggtoadultcanbedescribedasfollows:,Theextenttowhichfliesdevelopfromthelarval(maggot)stageinon-sitestoragecontainersdependsonthefollowingfacts:Ifmaggotsdevelop,theyaredifficulttoremovewhenthecontainersareemptied.Thoseremainingmaydevelopintoflies.Maggotscanalsocrawlfromuncoveredcansanddevelopintofliesinthesurroundingenvironment.,4-4PHYSICAL,CHEMICAL,ANDBIOLOGICALTRANSFORMATIONSOFSOLIDWASTE,ThepurposeofthissectionistointroducethereadertotheprincipaltransformationprocessesthatcanbeusedforthemanagementofMSW.Thesetransformationscanoccureitherbytheinterventionofpeopleorbynaturalphenomena.,Solidwastecanbetransformedbyphysical,chemical,andbiologicalmeans.Onemustunderstandthetransformationprocessesthatarepossibleandtheproductsthatmayresultbecausetheywillaffectdirectlythedevelopmentofintegratedsolidwastemanagementplans.,PhysicalTransformations,Theprincipalphysicaltransformationsthatmayoccurintheoperationofsolidwastemanagementsystemsinclude(1)componentseparation,(2)mechanicalvolumereduction,(3)ment:Physicaltransformationsdonotinvolveachangeinphase(e.g.,solidtogas),unlikechemicalandbiologicaltransformationprocesses.,ComponentSeparation.,Componentseparationisthetermusedtodescribetheprocessofseparating,bymanualand/ormechanicalmeans,identifiablecomponentsfromcommingledMSW.Componentseparationisusedtotransformaheterogeneouswasteintoanumberofmore-or-lesshomogeneouscomponents.,MechanicalVolumeReduction.,Volumereduction(sometimesknownasdensification)isthetermusedtodescribetheprocesswherebytheinitialvolumeoccupiedbyawasteisreduced,usuallybytheapplicationofforceorpressure.Inmostcities,thevehiclesusedforthecollectionofsolidwastesareequippedwithcompactionmechanismstoincreasetheamountofwastecollectedpertrip.,MechanicalSizeReduction.,Sizereductionisthetermappliedtothetransformationprocessesusedtoreducethesizeofthewastematerials.Theobjectiveofsizereductionistoobtainafinalproductthatisreasonablyuniformandconsider-ablyreducedinsizeincomparisonwithitsoriginalform.Inpractice,thetermsshredding,grinding,andmillingareusedtodescribemechanicalsize-reductionoperations.,ChemicalTransformations,Chemicaltransformationsofsolidwastetypicallyinvolveachangeofphase.Toreducethevolumeand/ortorecoverconversionproducts,theprincipalchemicalprocessesusedtotransformMSWinclude(I)combustion(chemicaloxidation),(2)pyrolysis,(3)gasification.Allthreeoftheseprocessesareoftenclassifiedasthermalprocesses.,Combustion(ChemicalOxidation).,Combustionisdefinedasthechemicalreactionofoxygenwithorganicmaterials,toproduceoxidizedcompoundsac-companiedbytheemissionoflightandrapidgenerationofheat.Inthepresenceofexcessairandunderidealconditions,thecombustionoftheorganicfractionofMSWcanberepresentedbythefollowingequation:,Pyrolysis.,Pyrolysisisthetermusedtodescribetheprocess.Incontrastwiththecombustionprocess,whichishighlyexothermic,thepyrolyticprocessishighlyendothermic.Forthisreason,destructivedistillationisoftenusedasanalternativetermforpyrolysis.,Gasification.,Thegasificationprocessinvolvespartialcombustionofacarbonaceousfuelsoastogenerateacombustiblefuelgasrichincarbonmonoxide,hydrogen,andsomesaturatedhydrocarbons,principallymethane.Thecombustiblefuelgascanthenbecombustedinaninternalcombustionengineorboiler.,Whenagasifierisoperatedatatmosphericpressurewithairastheoxidant,theendproductsofthegasificationprocessare,(1)alow-Btugastypicallycontainingcarbondioxide(CO2),carbonmonoxide(CO),hydrogen(H2),methane(CH4),nitrogen(N2);(2)acharcontainingcarbonandtheinertsoriginallyinthefuel,(3)condensibleliquidsresemblingpyrolyticoil.,OtherChemicalTransformationProcesses.,Example:Thehydrolyticconversionofcellulosetoglucose,followedbythefermentationofglucosetoethylalcohol.,BiologicalTransformations,ThebiologicaltransformationsoftheorganicfractionofMSWmaybeusedtoreducethevolumeandweightofthematerial;toproducecompost,ahumus-likematerialthatcanbeusedasasoilconditioner;toproducemethane.Theprincipalorganismsinvolvedinthebiologicaltransformationsoforganicwastesarebacteria,fungi(真菌),yeasts,andactinomycetes（放线菌）.Thesetransformationsmaybeaccomplishedeitheraerobicallyoranaerobically,dependingontheavailabilityofoxygen.,AerobicComposting.,Leftunattended,theorganicfractionofMSWwillundergobiologicaldecomposition.Theextentandtheperiodoftimeoverwhichthedecompositionoccurswilldependonthenatureofthewaste,themoisturecontent,theavailablenutrients,otherenvironmentalfactors.Undercontrolledconditions,yardwastesandtheorganicfractionofMSWcanbeconvertedtoastableorganicresidueknownascompostinareasonablyshortperiodoftime(fourtosixweeks).,CompostingtheorganicfractionofMSWunderaerobicconditionscanberepresentedbythefollowingequation:,AnaerobicDigestion.,ThebiodegradableportionoftheorganicfractionofMSWcanbeconvertedbiologicallyunderanaerobicconditionstoagascontainingcarbondioxideandmethane(CH4).Thisconversioncanberepresentedbythefollowingequation:,OtherBiologicalTransformationProcesses.,Inadditiontotheaerobiccompostingandanaerobicdigestionprocesses,avarietyofotherpublicandpropri