Thermal-alkaline-solubilization-of-waste-activated-sludge-as-a-pre-treatment-stage

Thermal-alkalinesolubilizationofwasteactivatedsludgeasapre-treatmentstageforanaerobicdigestionA.G.Vlyssides*,P.K.KarlisLaboratoryofOrganicandChemicalTechnology,DepartmentofChemicalEngineering,NationalTechnicalUniversityofAthens,9HeroonPolytechniouStrasse,Zographou,15700Athens,GreeceReceived10February2003;receivedinrevisedform20May2003;accepted26May2003AbstractThisworkstudiedthehydrolysiskineticsandthesolubilizationofwasteactivatedsludgeunderamediumrangetemperature(50–90�C)andpHinthealkalineregion(8–11),asapretreatmentstageforanaerobicdigestion.Thehydrolysisrateforthesolubili-zationofvolatilesuspendedsolids(VSS)followedafirst-orderrate.Alinearpolynomialhydrolysismodelwasderivedfromtheexperimentalresultsleadingtoasatisfactorycorrelationbetweenthehydrolysisratecoefficient,pH,andtemperature.AtpH11andatemperatureof90�CtheconcentrationoftheVSSwas6.82%,theVSSreductionreached45%withintenhoursandatthesametimethesolubleCODwas70.000mg/landthetotalefficiencyformethaneproduction0.28lofCH4pergofVSSloading.�2003ElsevierLtd.Allrightsreserved.Keywords:Wasteactivatedsludge;Thermal;Pretreatment;Alkaline;Lime;Solubilization;Hydrolysis1.IntroductionSludgehandlingrepresents30–40%ofthecapitalcostandabout50%oftheoperatingcostofmanywaste-watertreatmentfacilities.Abouttwo-thirdsofthesludgeinGreeksecondarytreatmentplantsiswasteactivatedsludge(WAS).TheWAShastobestabilizedsufficientlytoreduceitsorganiccontent,odorproblems,andpathogencontaminationbeforeultimatedisposal.Anaerobicdigestionisusedasacommonmethodforprimaryandsecondarysludge(PSandWAS)stabiliza-tionleadingtoanenergyrecoverybonusintheformofmethanegasproduction.Thedemandsforhigherefficiencyprocesses,havepromptedtheneedforpre-treatmentmethodsinordertoimprovesubstratesolu-bilizationanddigestibility.MorestudiesfocusonthermalorthermochemicalprocessasapretreatmentstageofWAS.Thesestudiesincludethermalpretreat-mentinthemoderatetemperaturerangeof60–100�C(Hiraoka,1984;LiandNoike,1997),inthemediumtemperaturerangeof100–175�C(Haugetal.,1978),andinah