MethodsforQuantifyingLimeIncorporationintoDewatere

MethodsforQuantifyingLimeIncorporationintoDewateredSludge.I:Bench-ScaleEvaluationJasonM.North1;JenniferG.Becker2;EricA.Seagren,A.M.ASCE3;MarkRamirez4;andChristopherPeot,P.E.5Abstract:Theadditionofalkalinematerial
usuallylimetotreatedmunicipalsludgecanbeusedtoraisethepHto
12andgenerateClassAorBbiosolids.Whenlimeisaddedtodewateredsludge,itmustfirstbemadeintoaslurrybeforethepHcanbemeasuredtodemonstrateregulatorycompliance.Inthisstudy,pH12wasachievedinslurriespreparedfromlime-amendeddewateredsludge,evenwhenthelimewaspoorlyincorporatedandrelativelyhighfecalcoliformlevelsweredetected.Thus,quantitativeindicatorsoflimeincorporationareneededtocomplementslurrypHmeasurementsandensurethatsufficientcontactoccursbetweenlimeandsludgeparticlestoachieveadequatestabilization.Inthisstudy,theusefulnessofseveralpotentialmeasuresoflimeincorporation—pH,CO2consumption,distributionofcalcium,fecalcoliforms,NH3andreducedsulfurcompoundproduction,andATP—wassystematicallyevaluatedusingabench-scalesystem.SludgepHandCO2consumptionwerenotinfluencedbytheextentoflimeincorporation.Thedistributionofcalciumandfecalcoliformlevelsappeartobeusefulmeasuresoflimeincorporation.NH3andreducedsulfurcompoundemissionsandATPlevelscanalsobeusedtoassesslimeincorporationprovidedrecommendedexperimentaltechniquesareused.DOI:10.1061/
ASCE0733-9372
2008134:9
750CEDatabasesubjectheadings:Sludge;Lime;Mixing;Full-scaletests;Dewatering;pH;Laboratorytests.IntroductionIncorporationofalkalinematerial,especiallylime,intomechani-callydewateredmunicipalwastewatersludge
postlimestabiliza-tioncanbeusedtoproducematerialsthatmeettheU.S.EnvironmentalProtectionAgency
USEPAminimumcriteriaforClassBorAbiosolids
USEPA1993.TomeettheClassBPro-cessestoSignificantlyReducePathogens
PSRPrequirementforlime-stabilizedbiosolids,levelsofindicatororganismsinthesematerialsmustfallwithinmaximumallowablelimits,andthepHofthebiosolidsmustbemaintainedat12for2handat11.5foranadditional22h.AchievementofthepHcriterionisdemon-stratedbymakingmeasurementsonaslurrypreparedbyaddingwatertothelime-amendedsludgeandsubjectingittoadditionalmixing.Unfortunately,theadditionofwatertosludge–limemixturesandthesubsequenthomogenizationstepmakeitdifficulttoinferanyinformationabouttheextentoflimeincorporationintheoriginalundilutedsample.ThepHlevelsthatmeetregulatoryrequirementsforclassificationasbiosolidscouldconceivablybemeasuredinslurriesderivedfromsludgesamplesthatcontainpoorlyincorporatedlime.InthemicromorphologyanalysesshowninFig.1,differencesintheextentoflimeincorporationintobiologicalsludgesthatweregeneratedatthesamewastewa-tertreatmentplantDistrictofColumbiaWaterandSewerAu-thority’s
DCWASA’sBluePlainsadvancedwastewatertreatmentplant
BluePlainsWWTP,butweretreatedindistinctdewateringandpost-lime-stabilizationsystems,arevisuallyobvi-ous.However,thepHlevelsmeasuredinthetwosystemsweregenerallyverysimilar.TheapparentinabilityofslurrypHmea-surementstodistinguishsignificantdifferencesintheextentoflimeincorporationisimportantbecausepoorincorporationoflimecanresultinproductionofmalodors,whichinturncanleadtodecreasedpublicacceptanceofbiosolidsprocessingandlandapplicationprograms.Asaresult,thepotentialforbeneficialre-cyclingofplantnutrientsandorganicinbiosolidsmaynotbefullyrealized.Itisgenerallyrecognizedthatadequatecontactbetweenlimeandsludgeparticlesmustoccurinordertoachieveadequatein-corporationofthelimeandastableresidualsproduct
Metcalf&Eddy1991.Asaresult,mostlaboratorystudiesofpostlimesta-bilizationusedextendedmixingtimes
ontheorderofhours
e.g.,Riehletal.1952;Wongetal.2001.CountsandShuckrow
1975usedshortmixingtimes
20–30stoexaminetheeffectsoftwodifferentbench-scalemixingtypesonthepHoflime-amendedsludge.However,theirstudyinvolvedliquidsludge,ratherthandewateredcake.Theextendedmixingtimesusedinmostbench-scalestudiesmaynotbereflectiveofthemixingthatoccursinfull-scalesystems.Consequently,thereislittleinfor-1RegionalManager,NatgunCorporation,4500BlackRockRd.,Hampstead,MD21074.E-mail:[e-mail]2AssociateProfessor,Dept.ofEnvironmentalScienceandTechnology,Univ.ofMaryland,CollegePark,MD20742
correspondingauthor.E-mail:[e-mail]3AssociateProfessor,Dept.ofCivilandEnvironmentalEngineering,Univ.ofMaryland,CollegePark,MD20742.E-mail:[e-mail]4BiosolidsProcessEngineer,DistrictofColumbiaWaterandSewerAuthority
DCWASA,5000OverlookAve.SW,Washington,DC20032.E-mail:[e-mail]5BiosolidsDivisionManager,DistrictofColumbiaWaterandSewerAuthority
DCWASA,5000OverlookAve.SW,Washington,DC20032.E-mail:[e-mail]ary1,2009.Separatediscussionsmustbesubmittedforindividualpapers.ThemanuscriptforthispaperwassubmittedforreviewandpossiblepublicationonMay21,2007;approvedonAugust27,2007.ThispaperispartoftheJournalofEnvironmentalEngineering,Vol.134,No.9,September1,2008.©ASCE,ISSN0733-9372/2008/9-750–761/$25.00.750/JOURNALOFENVIRONMENTALENGINEERING©ASCE/SEPTEMBER2008J.Environ.Eng.2008.134:750-761.Downloadedfromascelibrary.orgbyBeijingUniversityOfTechon10/30/12.CopyrightASCE.F