市政污水及污泥處理英漢對照

MunicipalWastewaterandSludgeTreatmentAtmunicipalwastewatertreatmentplantsintheUnitedStates,rawmunicipalwastewaterundergoespreliminary,primary,secondary,andinsomecases,additionaltreatmenttoyieldtreatedeffluentandaconcentratedstreamofsolidsinliquid,calledsludge.Thesludgeistreatedasrequiredforutilizationordisposal,andadditionaltreatmentofeffluentmaybeneededtoaccommodatespecificwaterreuseopportunities.Thepracticeofmunicipalwastewatertreatmentevolvedprimarilytoaccommodatedischargeoftreatedeffluenttosurfacewaters,nottofacilitateuseofeffluentoncrops(seeChapter2).BecausemunicipalwastewatertreatmenttechniquesarewellestablishedintheUnitedStatesandbecauseeffluentfromsomemunicipalwastewatertreatmentfacilitiesisdischargedbothtosurfacewaterandusedtoirrigateagriculturalland,secondaryorhigherlevelsofwastewatertreatmenttypicallyprecedewastewaterreuseinagricultureintheUnitedStates.TherelationshipofmunicipalwastewaterandsludgetreatmenttocropproductionisshownschematicallyinFigure3.1.Asillustrated,reuseofwastewaterforfoodcropproductionorinotherreuseapplications,suchasgroundwaterrechargeorurbanlandscapeirrigation,typicallyoccursaftersecondarywastewatertreatmentandmaynecessitateadditionaltreatment.Treatmenttoproducereclaimedwateroftenaddscoagulation,filtration,anddisinfectiontosecondarytreatment.Figure3.1alsoillustratestheoriginandtreatmentofmunicipalwastewatersludgesappliedtocropland.Followingtreatment,sludgesmaybedisposedof(forexample,inalandfill)orusedforfoodcropproductionorinotherapplications(suchassilvicultureandnonfoodcropagriculture).Thischapterbrieflyreviewstypicalamountsandpropertiesoftreatedeffluentandsludge,thenexaminesprocessesusedinconventionalwastewatertreatment(definedaspreliminary,primary,andsecondarytreatment),processesintendedspecificallytoaccommodatewastewaterapplicationtocrops,andtypicalsludgetreatmentprocesses.QUANTITYANDQUALITYOFMUNICIPALWASTEWATEREFFLUENTANDSLUDGE狀M閱u秒n賓i紐c納i東p建a會l腦趟w蹄a風s做t衡e鳥w削a貞t校e熄r議易r燭e慈p環(huán)r每e孔s澇e驅(qū)n帽t棄s股搖t禮h矮e蔬陸s姐p結(jié)e類n訂t努獸w握a輝t狐e為r傲響s斧u港p賽p曬l拆y財任o轎f噴仗c鄙o渡m協(xié)m臉u碧n法i率t圖i頭e洗s樹.罵阿I田n米但1岸9跡9呆0萍,炕再a新v植e內(nèi)r鏟a據(jù)g芒e坊壞p房e泳r棍湊c競a崖p青i誰t伯a(chǎn)習罰u最s米a崖g近e襯襖f脆r彩o冠m耐挨p與u荷b艇l彎i祝c掙廟w傘a弦t聲e任r沈呆s悉u漠p緞p崇l撇y賠蠻s句y員s條t報e拳m撓s芳駛i鋸n奶齒t爸h信e賓夸U推n獲i旺t健e式d竿暢S妥t婚a鄉(xiāng)t尊e肉s種編w姓a粒s業(yè)管1膛8來4至身g單a雹l兆l泰o騰n前s萍避(決7動0府0孝惜l狀i荒t繁e猛r輝s柜)魚濃p愛e彎r特掌d拘a泳y鋪枝(統(tǒng)S候o引l具l終e鵲y鎖犧e編t沒菊a悄l識.烤,壟繩1泛9旨9愧3祖)治.矩校I診n復梯a伯r難i敬d學次a投r齒e冷a善s牽,伍逃m蜻u對n魔i鄭c坑i征p皺a簽l楊像w論a周s戒t俊e臟w偉a透t飾e另r攻蒙p味r蹄o鋪d夕u可c袍t拌i客o潔n洲恒i剛s便預t點y雀p犬i鋸c展a饒l國l勾y束罵l雅e貼s疏s祖韻t程h購a下n綱土t曬h桃e雪始a漢m風o同u盯n沙t圾陵w衣i梢t到h壯d烏r降a蛋w仗n送槐f瞞o結(jié)r敘挎w色a第t眨e棚r堡家s壇u蘋p軍p支l羞y窯,故涼b續(xù)u長t拋小i最n蹈杠s窄o統(tǒng)m習e堵翁a支r走e資a訪s艙,克胡w鍵a淘s程t江e咸w窮a釀t寬e潑r暢摘f盡l湊o斗w棍陳e全x心c蓮e雄e稻d抵s顆逆t悅h噸e永恭w齡a淋t誦e漏r富賤s胖u孤p打p壽l凍y校桃b播e姨c桐a白u驗s管e望圓o另f貪獸i艷n術(shù)f慢i忽l肌t跪r飽a族t蛾i待o鉗n熟賽a丈n愚d悔賞i昏n魚f眉l遺o早w蒙濫(犁e斥.沫g文.戴繁s由t蝦o累r卸m騾w梨a早t張e筋r標)隆卡i獵n掙t絮o鄰預w便a餡s摧t脖e基w艷a乎t桿e胖r棉兄c營o瞧l英l則e篩c鈴t蕉i南o束n值信s罷y趕s姿t歸e題m瓶s車.浩瓶U鞠s沿i目n竟g纖踐8柴5瓦腐p慧e寫r指c擔e移n禽t廉泥o炕f寫受w白a湖t絹e敢r極旗u唱s勢e假修a氣s構(gòu)瞞a匯n遺哀e錯s添t嬌i需m鞭a仆t溝e摘偵o痕f舉冷t謙y蛛p茫i掀c物a鉗l惜棉w鍛a稻s螞t嬸e償w逗a龍t坑e勤r咽交p墓r顫o祥d械u槐c生t映i臂o竄n值哭(第H銀e梢n始r誓y噴偶a煎n傍d百篇H暑e并i逝n賊k競e夜,激錘1群9獎8們9挖)束,蛇屠a致雜c獲i池t粒y圈o恭f訊濟2另0卷0邊,起0踢0共0偵捎p拿e令o晨p弦l完e岡誰w窄o館u險l陣d圈崗p跑r冊o穿d咬u寇c粥e腸魚a頸n尺保a鈴v礙e資r紛a尺g甜e經(jīng)閃o蒼f碼噸a范b吼o步u斬t飛魂3恐1信0博0舊0敏0券0腳0鏟朵g灶a兔l嚴/哨d慕a鄙y妹影(諸a疲b六o疫u來t村拆1迎1駕7涂0送0剩0移趨m劣/滅d鄙a妙y皺)炭胡o角f敘械r尊a訴w趟彈w的a涌s嚼t援e尖w顏a乞t牲e斥r鴿.鍵而T釘h澆e燥嫌a建m竊o戰(zhàn)u桿n因t圓伸o誓f羞趕t蜻r弱e協(xié)a曲t呆e托d制挽w鋤a詢s給t撐e尚w羊a蠢t宋e描r在扮e況f斗f的l撒u準e富n滅t視紐e茄x并t業(yè)r綁a償c倆t歲e巾d植攪i蒜s饑治n純o靜t精客a傭p倒p催r冠e罵c裂i松a削b凱l撲y右捧d摔i磁m立i護n敬i愁s笛h昆e寧d戒顛f術(shù)r竊o援m豎覽t基h競e考革o般r晝i績g沖i涼n他a搶l濫終q請u僚a臨n抗t費i姻t里y坡裂o憶f線固r絡a叢w夫量w煉a座s聾t勒e喜w匠a牢t洋e證r蘇背p偽a始r丸t渴i責c軋u榨l奸a蘇r趨l曉y衣是i延f連腔s辣l悟u淋d搞g習e賺圓i海s籮洗d贈e叔w想a伍t醫(yī)e循r猛e廳d炎,盞秩a糟s禾蘭i襯s奴趣c鄭o問m統(tǒng)m極o讀n寺.ThequalityoftreatedeffluentfromsecondarywastewatertreatmentplantsintheUnitedStatesmustcomplywiththefederalregulationofamonthlyaverageof30milligramsperliterofbiochemicaloxygendemandorBOD(ameasureoftheamountofbiodegradableorganicmaterialremaininginthetreatedwastewater)and30mg/literofsuspendedsolids(靜p添a久r送t柿i齊c任l齡e拴s奮待r上e扁m紹o谷v怖a陷b貌l鋒e割怎b混y胡墳f隔i福l霧t酷r尾a掌t堂i黎o怪n宴)毀.增簽T押y日p防i格c律a涉l己痕c揚o高n島c幫e駕n載t很r異a肯t螺i量o菜n數(shù)s屢秋o質(zhì)f淘僑o句t詠h勵e協(xié)r產(chǎn)略c晨o裕n里s駝t下i講t蝦u覺e曲n臺t菊s盲郵i諸n通腰w示a陰s祖t遍e轎w消a象t統(tǒng)e背r觀欺t壁r設e份a騙t集m中e音n主t寧樹p捕l享a煎n羨t魚奔e徐f泡f箱l荷u帝e典n憂t閥禾a增r抄e勞鋪s撞u晨m土m凈a四r雞i饅z矩e粒d市詠i就n污日C衣h根a沃p科t心e魯r查2能.坐削M晌o槐r宋e擴消d夏e釀t夜a輪i沃l邪e離d偉掩i狐n毀f走o喉r尾m難a駐t充i貧o燭n怕壯o球n碗造t耽y仔p四i奔c伏a目l蝦那e曲f災f仆l葛u晴e億n捎t推顧q綿u摩a巖l課i炕t屋y綢秤i胳s域棗p罰r肝e趣s狼e梯n字t昂e藍d禽求i釀n烤窯s姨e倒c虎t刊i沈o玉n想s脖頁o掀f托紙t艷h蜓i熄s橫璃r恭e舊p脫o材r情t斑瓶w漢h正e攤r睛e君傍p況o籌t況e籮n背t臥i信a陵l軍距e注f損f李e日c礎t竟s綢分o勞f乓涼i怨n賠d穩(wěn)i捧v無i墨d摸u章a螞l插狂c遲o乖n悠s銀t月i披t絮u舟e必n眉t仔s錘海a截r搜e船修c窩o神n頌s當i眠d池e躁r緊e幸d釘.表膽F鉛o把r閑翅e幻x貼a萬m蛋p仗l挨e納,娘偵C屠h童a勉p單t別e辣r枕殃5威稼i綿n鳴c枝l廚u偵d趴e幅s拿座i聞n覺f賴o徑r蚊m灶a殿t疏i尼o字n鎮(zhèn)幅o紗n繁蟻t腫h給e顯鄭t醉y腹p慨e倉s啞罷a籌n盟d潮范q對u撞a勿n舍t(yī)倒i請t摸i光e昏s避賠o紀f然亦p餅a端t素h烤o更g陳e動n看s弦攝t山y(tǒng)亂p江i飼c川a揭l格l禾y出屑f沈o瞇u韻n乖d踩志i森n逃烏v煤a財r稻i團o五u赴s響側(cè)w豎a篇s葉t與e沫w涉a縮t慚e撿r鼠高t遞r政e錫a尺t后m薄e紅n踏t襯寨p絲l收a念n地t韻占e喇f彈f道l布u友e悅n壇t殃s蟲.Thevolumeofmunicipalwastewatersludgeproducedbywastewatertreatmentfacilitiesisanelusivequantitybecauseitvariesasaresultoftypicalsludgetreatment(see"VolumeReductionProcesses"laterinthischapter).Sincethemassofdrysolidsisconservedduringmosttreatmentprocesses,dryweightisamoreusefulbasisforexpressingtheamountofsludgefrommunicipalwastewatertreatment.Typicalprimaryandsecondarywastewatertreatmentproducesatotalofabout1.95lbs(0.94kg)ofdrysolidsper1,000gal(3.78m3)ofwastewatertreated(MetcalfandEddy,1991).Chemicaladditiontosludgesduringconditioningandstabilizationprocesses(seelatersectionsofthischapter)canappreciablyincreasethemassofsolidsinsludges.Biologicalstabilizationactstoreducethemassofsuspendedsolidsthroughoxidationofsomeofthevolatileorganicsolidsinsludges.Forexample,ifsludgecontains80percentvolatilesuspendedsolidsand50percentofthemaredestroyedthroughoxidation,thestabilizedmassofsludgesolidswouldbereducedto60percentoftheinitialmass.Typicalsolidscontentsofsludgesatvariousstagesoftreatmentaresummarizedinthischapter.TypicalrangesofothercommonconstituentsinsludgesaresummarizedinChapter2.Aswithwastewatereffluents,moredetailedinformationaboutspecificsludgeconstituentsisfoundinsectionsofthereportwherethepotentialeffectsofthoseconstituentsarediscussed.CONVENTIONALWASTEWATERTREATMENTPROCESSESMunicipalwastewatertreatmenttypicallycomprisespreliminarytreatment,primarytreatment,andsecondarytreatment.SecondarytreatmentistheUnitedStatesnationalstandardforeffluentdischargedtosurfacewaters.Ahigherdegreeoftreatment,termedhere"advanced"or"tertiary"treatment,mayberequiredatspecificlocationstoprotecthealthorenvironmentalquality.Inthisreport,conventionalmunicipalwastewatertreatmentisconsideredtoincludescreening,gritremoval,primarysedimentation,andbiologicaltreatmentbecauseitisthemostcommonmethod(Figure3.2).ElaborationonthesetersedescriptionsmaybefoundinsourcessuchasHenryandHeinke(1989)andMetcalfandEddy(1991).PreliminaryWastewaterTreatmentPreliminarywastewatertreatmentordinarilyincludesscreeningandgritremoval.Waste-waterscreeningremovescoarsesolidssuchasragsthatwouldinterferewithmechanicalequipment.Gritremovalseparatesheavy,inorganic,sandlikesolidsthatwouldsettleinchannelsandinterferewithtreatmentprocesses.FIGURE3.2Municipalwastewaterisconventionallysubjectedtopreliminary,primary,andsecondarytreatmentintheUnitedStates.Additionaltertiaryoradvancedtreatmentmaybejustifiedbylocalconditions.Processestypicallyinvolvedineachstageoftreatmentareshown.Preliminarytreatmenteffectsminimalchangeinwastewaterquality.Primarytreatmenttypicallyremovesaboutone-thirdoftheBODandone-halfofthesuspendedsolidsindomesticwastewaters.Combinedprimaryandsecondarytreatmentisrequiredtoachieve85percentreductioninbothBODandsuspendedsolidsconcentrationtomeettheregulatorydefinitionofsecondarytreatment.Preliminarytreatmentservestopreparewastewaterforsubsequenttreatment,butiteffectslittlechangeinwastewaterquality.Theresiduesfrompreliminarywastewatertreatment,screeningsandgrit,arenotordinarilyincorporatedwithsludges,andtheyarenotconsideredfurtherinthisreport.PrimaryWastewaterTreatmentPrimarywastewatertreatmentusuallyinvolvesgravitysedimentationofscreened,degrittedwastewatertoremovesettleablesolids;slightlymorethanone-halfofthesuspendedsolidsordinarilyareremoved.BODintheformofsolidsremovablebysedimentation(typicallyaboutone-thirdoftotalBOD)isalsoremoved.AtonetimeduringtheevolutionofdomesticwastewatertreatmentintheUnitedStates,facilitiesonlypracticedprimarywastewatertreatmentandtheprimaryeffluentwascommonlydischargedtosurfacewatersofferingappreciabledilution.Now,primarytreatmentisusedasaneconomicalmeansforremovingsomecontaminantspriortosecondarytreatment.Theresiduefromprimarytreatmentisaconcentratedsuspensionofparticlesinwatercalled"primarysludge."Althoughthegoalofprimarywastewatertreatmentistoseparatereadily-removablesuspendedsolidsandBOD,wastewaterconstituentsthatexistassettleablesolidsoraresorbedtosettleablewastewatersolidsmayalsoberemoved.Thus,primarytreatmenteffectssomereductionintheeffluentconcentrationofnutrients,pathogenicorganisms,traceelements,andpotentiallytoxicorganiccompounds.Theconstituentsthatareremovedarecontainedinprimarysludge.SecondaryWastewaterTreatmentSecondarymunicipalwastewatertreatmentisalmostalwaysaccomplishedbyusingabiologicaltreatmentprocess.Microorganismsinsuspension(inthe"activatedsludge"process),attachedtomedia(ina"tricklingfilter"oroneofitsvariations),orinpondsorotherprocessesareusedtoremovebiodegradableorganicmaterial.Partoftheorganicmaterialisoxidizedbythemicroorganismstoproducecarbondioxideandotherendproducts,andtheremainderprovidestheenergyandmaterialsneededtosupportthemicroorganismcommunity.Themicroorganismsbiologicallyflocculatetoformsettleableparticles,and,followingbiologicaltreatment,thisexcessbiomassisseparatedinsedimentationtanksasaconcentratedsuspensioncalled"secondarysludge"(alsoknownas"biologicalsludge,""wasteactivatedsludge,"or"tricklingfilterhumus").Wastewaterconstituentscanbecomeassociatedwithsecondarysludgeasaresultofmicrobialassimilation,bysorptionontosettleablesolids,orbyincorporationintoagglomerateparticlesformedasaresultofbioflocculation.Someofthewastewaterconstituentsthatareincidentallyassociatedwiththebiomassfromsecondarytreatmentprocessesincludepathogens,traceelements,andorganiccompounds.TertiaryorAdvancedWastewaterTreatmentTertiarytreatmentisusedatmunicipalwastewatertreatmentplantswhenreceivingwaterconditionsorotherusesrequirehigherqualityeffluentthanthatproducedbysecondarywastewatertreatment.Disinfectionforcontrolofpathogenicmicroorganismsandvirusesisthemostcommontypeoftertiarytreatment.TheconcentrationsofsuspendedsolidsandassociatedBODintreatedeffluentcanbereducedbyfiltration,sometimeswiththeaidofacoagulant.Adsorption,ordinarilyonactivatedcarbon,canbeusedtoremovesomepersistentorganiccompoundsandtraceelements.Theconcentrationofammoniainsecondaryeffluentcanbereducedbynitrification.Tertiarytreatmenttoremovenitrogenandphosphorus,soastominimizenutrientenrichmentofsurfacewaters,iscommon;nitrogenisusuallyremovedbynitrificationfollowedbydenitrification,andphosphorusisremovedbymicrobialuptakeorchemicalprecipitation.Notalltertiarytreatmentprocessesfollowsecondarytreatment,aswasshownschematicallyinFigure3.1;nutrientremoval,forexample,canbeachievedbydesignandoperationalvariationstoprimaryandsecondarytreatmentprocesses.Theresiduesfromtertiarytreatmenttypicallybecomeincorporatedwithsludgesfromprimaryandsecondarytreatment.Therearemanyvariationstothesetreatmentpractices.Forinstance,secondarytreatmentisrarelyachievedusingphysicalandchemicalprocessesratherthanbiologicaltreatment.Primarytreatmentissometimeseliminated.Long-termretentioninlagoonsissometimessubstitutedforbothprimaryandsecondarytreatment.TREATMENTTOFACILITATECROPIRRIGATIONWITHRECLAIMEDWATERThedegreeofwastewatertreatmentrequiredpriortousingwastewatereffluentforcropproductiondependsonthecrop,localconditions,andstateregulations.Inconsideringspecificapplicationsofreclaimedwastewaterforcropproduction,tradeoffsmayexistbetweendegreeofwastewatertreatmentneededandagriculturalpractices.Specialtreatmenttoallowagriculturaluseoftreatedeffluentsisnotalwaysconsiderednecessarybystatesthatregulatethepractice(seeChapter7);effluentsfromconventionalprimaryandsecondarywastewatertreatmentareused.Indeed,historically,untreatedrawwastewaterhasbeenused,butthepracticeisnotfoundintheUnitedStatesandisnotconsideredherein.Inidentifyingappropriatewastewatertreatmentforcropapplication,itisappropriatetoconsiderprotectionofhealthandenvironmentalquality,waterqualityrequirementsofcrops,andrequirementsoftheirrigationwaterstorageanddeliverysystem(suchasavoidingodorsandclogging)(EPA,1981;WaterPollutionControlFederation,1983).Asapracticalmatter,theextentofwastewatertreatmentrequiredpriortofoodcropapplicationordinarilyisestablishedbyhealthandenvironmentalqualityconsiderations.Disinfectionandsuspendedsolidsremovalaretheprocessesmostfrequentlyusedtofurtherimproveconventionalwastewatertreatmentplanteffluentsforuseoncrops.Disinfectionoftreatedeffluentismostoftenaccomplishedbychlorination.Chlorineisaneconomicaldisinfectant,butitreactswithorganicmaterialinwastewatereffluenttoformchlorinatedorganiccompoundsthatareofpotentialconcernwithpotablereuseofreclaimedwastewater,butnotwithirrigation(seeChapter6).Alternativestochlorineasawastewaterdisinfectingagentincludeozoneandultravioletlight.Thelattertwoprocessesdonotprovidearesidualdisinfectantasrequiredbysomestateregulationsforapplyingtreatedwastewatertofoodcrops(EPA,1992).Additionally,suspendedsolidsaresometimesremovedfromconventionalwastewatertreatmentplanteffluentpriortousingtheeffluentinagriculture.Removalofsuspendedsolidsaidsincontrolofpathogenicorganismsandvirusesbymakingdisinfectionmoreeffective.Suspendedsolidremovalminimizesdepositionofsolidsontopofsoils,andreducescloggingofsomeirrigationwaterdeliverysystems.Furtherreductionofsuspendedsolidsineffluentistypicallyachievedbyaddingacoagulatingchemical,settling,andfilteringthroughgranularmedia(FallerandRyder,1991;Kuo,etal.,1994).Treatmenttechnologytoproduceanydegreeofwastewaterqualityperceivedtobenecessaryforfoodcropproductionisavailable;however,treatmentcostsescalatewithincrementalwaterqualityimprovements.Additionally,residue(sludge)managementproblemsaccompanysomeprocesses(suchasthoseusingmembranes)thatmightbeusedtoimprovetreatedwastewaterqualitybeyondthecurrentnorms.Situationsexisttodayinwhichwaterqualitydischargerequirements,thecropvalueandwaterscarcityjustifythehigherdegreesofwastewatertreatmentbeforeapplicationtofoodcrops.SLUDGETREATMENTPROCESSESPrimaryandsecondarysludgesmaybeexpectedtocontainsettleablematerialsfromrawwastewaterandtheproductsofmicrobialsynthesis.Othermaterialsarealsoremovedfromwastewatersandincorporatedintoprimaryandsecondarysludges,however.Thelargesurfaceareaofparticlesincorporatedintosludgesprovidessitesforadsorptionofconstituentsfromtheliquidphase.Non-degradedorganiccompoundsinsolutionmaypartitionintotheorganicfractionoftheparticles.Bio-flocculationmayincorporatecolloidalparticlesthatotherwisewouldnotberemovedbysedimentationintosettleableparticles.Theseandothermechanismsresultinselectiveenrichmentofwastewaterconstituentsinsludge.Additionally,wastewatersludgesaremostlywaterand,hence,wastewaterconstituentsremainingintheliquidphasealsoareincludedinsludges.Becauseprimaryandsecondarysludgeshavedifferentproperties,advantageissometimessoughtbytreatingthemseparately.Asanillustration,secondarysludgethickensbetterusingthedissolvedairflotationprocess(seefollowingsection)thanbygravitythickening,anditissometimesthickenedseparatelyfromprimarysludge.Thetwosludgesalmostinvariablyarecombinedpriortotheendofthetreatment,and,forpurposesofdiscussingtheultimateutilizationoftreatedsludge,theyarenotfurtherdistinguished.Awidevarietyofsludgetreatmentprocessesareusedtoreducesludgevolumeandaltersludgepropertiespriortodisposaloruseofthetreatedproduct.Thenatureoftheseprocessesissummarizedinthesectionsthatfollow.AdditionaldetailsmaybefoundinsourcessuchasDick(1972),Vesilind(1979),andEPA(1977),andMetcalfandEddy(1991).Sludgetreatmentisconsideredhereintocompriseengineeredprocessesforalteringsludgequalitypriortodisposalorreclamation.Whensludgeisappliedtoland,inactivationofremainingpathogenicorganismsandvirusescontinues,biologicalstabilizationofresidualorganicmaterialprogresses,andbiologically-mediatedandabioticchemicaltransformationsoccur.VolumeReductionProcessesBiologicalsludge,asproducedfromsecondarywastewatertreatmentprocesses,oftenhasasuspendedsolidscontentoflessthanonepercentbyweight;thatis,eachkgofactivatedsludgesolidsisaccompaniedbymorethan99kgofwater.Primarysludgesaremoreconcentrated,butmarginallyso;typicalcombinedprimaryandsecondarysludgemightcontainabout3percentsolidsbyweight.Becauseofthevoluminousnatureofsludges,processescategorizedhereas"thickening,""dewatering,""conditioning,"and"drying"(listedinorderofdecreasingfrequencyofapplication)arecommoninsludgemanagement.Removalofwaterfromsludgesimprovesefficiencyofsubsequenttreatmentprocesses,reducesstoragevolume,anddecreasestransportationcosts.ThickeningSludgethickeningproducesaconcentratedproductthatessentiallyretainsthepropertiesofaliquid.Gravitythickening,orconcentrationbysimplesedimentation,isthethickeningprocessmostcommonlyappliedtomunicipalsludges.Theproductofgravitysludgethickeningoftencontains5to6percentsolidmaterialbyweight.Alternativestogravitythickeningincludeflotationthickening(inwhichagasisincorporatedwithsludgesolids,causingthemtofloat),aswellastheuseofgravitydrainagebelts,perforatedrotatingdrums,andcentrifuges.DewateringSludgedewateringprocessesproducematerialwiththepropertiesofasolid,eventhoughthedewateredsludgeisstillmostlywater.Dewateredsludgecanbetransportedinadumptruck,whereasatanktruckisrequiredtotransportthickenedsludge.Dewateringmaybeaccomplishedonsanddryingbedsand,occasionally,inlagoons,wheregravitydrainageandevaporationremovesmoisture.Moreoften,largermunicipalinstallationsusemechanicalmeansfordewateringsludge.Mechanicalsludgedewateringequipmentincludesfilterpresses,beltfilterpresses,vacuumfilters,andcentrifuges.Thesolidscontentofmechanicallydewateredsludgetypicallyrangesfrom20to45percentsolidsbyweight;mostprocessesproduceconcentrationsofsolidsatthelowerendofthatrange.ConditioningSludgeconditioningprocessesdonot,inandofthemselves,reducethewatercontentofsludge.Conditioningaltersthephysicalpropertiesofsludgesolidstofacilitatethereleaseofwaterindewateringprocesses.Indeed,themechanicaldewateringtechniquesdiscussedinthepreviousparagraphwouldnotbeeconomicalwithoutpriorsludgeconditioning.Chemicaland,lessfrequently,physicaltechniquesareusedtoconditionsludge.Chemicalconditioningmostcommonlyinvolvesaddingsyntheticorganicpoly-electrolytes(or"polymers")tosludgepriortodewatering.Inorganicchemicals(mostcommonly,ferricchlorideandlimeintheUnitedStates)canalsobeused.Inorganicchemicalconditioningdosagesarelarge,andincreasethemassofthesolidphaseofsludge.Physicalconditioningtechniquesincludeheattreatmentandfreeze-thawtreatment.DryingIfcircumstancesjustifyremovalofwaterbeyondthatachievablebydewateringprocesses,dryingisneeded.Thermaldryingwithdirectorindirectdryersisusedtoachievenear-completeremovalofwaterfromsludges.Solardryingisfeasibleinsomelocations.Partialdryingalsoresultsfromheatproducedinbiochemicalreactionsduringcompostingandfromotherchemicalreactionsdescribedinthestabilizationprocessesbelow.StabilizationProcessesThepurposeofsludgestabilizationistominimizesubsequentcomplicationsduetobiodegradationoforganiccompounds.Stabilizationisusuallyaccomplishedbybiologicalorchemicaltreatmentprocesses,asdescribedbelow.ThevectorattractionreductionprovisionsofthePart503SludgeRule(EPA,1993a)concernstabilizationprocesses.Vectors,suchasflies,areorganismsthatmightbeattractedtoun-stabilizedsludgeandarecapableoftransmittinginfectiousdiseases.StabilizationprocessperformancerequirementsarespecifiedinthePart503SludgeRuleforbothbiologicalandchemicalstabilization.Whensewagesludgeisappliedtoagriculturalland,vectorattractionreductionrequirementscanalsobesatisfiedbyinjectingsludgebelowthesurfaceorincorporatingsludgeintothesoil.Stabilizationcanalsobeachievedbydryingsludgeadequatelytoimpedemicrobialactivity.Obviously,sludgecombustion,too,accomplishesthestabilizationobjective.Manystabilizationprocessescanalsocauseappreciableinactivationofpathogenicorganismsandviruses.Inactivationofpathogensinsludgesisconsideredseparatelyinasubsequentsection.BiologicalStabilizationInbiologicalstabilizationprocesses,theorganiccontentofsludgesisreducedbybio-logicaldegradationincontrolled,engineeredprocesses.Mostcommonly,domesticwastewatersludgeisbiologicallystabilizedasaliquidinanaerobicdigestersfromwhichmethanegasisabyproduct.Liquidsludgecanalsobebiologicallystabilizedinaerobicdigesterstowhichoxygen(orair)mustbeadded.Compostingisaprocessthatbiologicallystabilizesdewateredsludge.Compostingisordinarilyanaerobicprocess,andanamendmentsuchaswoodchipsorsawdustmustbeaddedtoimprovefriabilityinordertopromoteaeration.Compostingtakesplaceatthermophilictemperatures(often,about55C)becauseofheatreleasedbybiochemicaltransformations.Aerobicdigesterscanbemadetooperatethermophilicallyusingheatfromthesamesource.Anaerobicdigesterscanoperateatthermophilictemperaturesbyburningmethaneproducedfromtheprocess,buttheytypicallyoperateatmesophilictemperatures(atabout35C)intheUnitedStates.ChemicalStabilizationChemicalstabilizationofsludgesisaimednotatreducingthequantityofbiodegradableorganicmatter,butatcreatingconditionsthatinhibitmicroorganismsinordertoretardthedegradationoforganicmaterialsandpreventodors.ThemostcommonchemicalstabilizationprocedureistoraisethepHofsludgeusinglimeorotheralkalinematerial,suchascementkilndust.Sludgecanbechemicallystabilizedinliquidordewateredforms.Whendewateredsludgeisused,theexothermicreactionoflimewithwatercausesheatingwhichhelpsdestroypathogensandevaporatewater.InactivationofPathogenicOrganismsandVirusesManyoftheprocessesfordryingandstabilizingsludgescanbedesignedandoperatedtoachieveappreciableinactivationofpathogenicagents,includingbacteria,parasites,andviruses.Alternatively,sludgetreatmentprocessesspecificallyintendedtocontrolpathogenicorganismsandvirusescanbeused.Processesspecificallyintendedforinactivatingpathogensincludeirradiationandpasteurization;theseprocessescurrentlyarenotwidelyusedintheUnitedStates.InthePart503SludgeRule,(EPA,1993a)thepathogenicqualityofsludgeiscontrolledbycategorizationofsludgesaseither"ClassA"(safefordirectcontact)or"ClassB"(cropandsiterestrictionsrequired),accordingtocriteriaforthedensityofindicatorandpathogenicorganismsandbyspecificationofprocessperformance.ThePart503SludgeRuleidentifiesspecificprocesseswithregardtotheircapabilityforpathogendestruction.ProcessesthatcanbeusedtoreachtheClassBcategoryareidentifiedbyEPAas"ProcessestoSignificantlyReducePathogens."Theseincludingaerobicdigestion,airdrying,anaerobicdigestion,com-posting,andlimestabilization,oranycombinationofprocessesthatcanreducefecalcoliformlessthan2,000,000colonyformingunitspergramoftotaldrysolids.EPAidentifiesmoreeffectiveprocessesthatcanbeusedtoreachtheClassAcategorycalled"ProcessestoFurtherReducePathogens."TheseClassAprocessesincludecompostingathigher,controlledtemperatures,heatdrying,heattreatment,thermophilicaerobicdigestion,betarayirradiation,gammarayirradiation,andpasteurizationaswellashigh-levelalkalinetreatmentandotherprocessesthatcanbedemonstratedtoreducepathogenstobelowdetectablelevels.HumanhealthconcernsaboutpathogenicorganismsandvirusesinsludgeareconsideredinmoredetailinChapter5,andregulationstocontrolinfectiousdiseasetransmissionfromtheuseofsludgeincropproductionarediscussedinChapter7.OtherSludgeTreatmentProcessesAwidevarietyofprocessesareusedtotreatsludges.Thosebrieflydiscussedinthissectionordinarilyarelessrelevanttosludgemanagementschemesdirectedtowardsfoodcropproductionthanaretheprocessespreviouslydiscussed.Solidification/ImmobilizationSolidification/immobilizationprocessesinvolvetheconversionofsludgetoasolidmaterialwithload-bearingcapacityandtheincorporationofcontaminantsi