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ThestatusquoanddevelopmentofUASBanaerobicprocessAbstract:ThispaperintroducestheoriginofUASBreactor,theworkingprinciples,characteristics,thedevelopmentandapplicationofthelatestresearchprogress,pointingoutthattherecentUASBreactorresearchfocus.Keywords:UASB;anaerobictreatmentprocess;

1.Introduction:

Anaerobicbiologicaltreatmentastheuseofanaerobicmetabolismofmicroorganisms,withouttheprovisionofenergysourcesundertheconditionsoforganicmatterastoberestoredbyhydrogendonor,whilegeneratingenergyvalueofthemethanegas.Anaerobicbiologicaltreatmentappliesnotonlytohighconcentrationsoforganicwastewater,influentBODuptothehighestconcentrationoftensofthousandsofmg/l,canalsobeappliedinlowconcentrationsoforganicwastewater,suchassewage,andothercities.

Anaerobicbiologicaltreatmentprocessandlowconsumption,organicvolumeload,generally5-10kgCOD/m3.d,uptoamaximumof30-50kgCOD/m3.d;lessresidualsludge;onthenutritionalneedsoflowanaerobes,MDR-toxic,biodegradableorganicmolecularweighthighimpactresistantcapacityofstrongoutputofmethaneisakindofcleanenergy.

Inthewholeofsocietytopromotearecyclingeconomyandtheimplementationoftheconcernsoftheindustrialwasterecyclingtoday,anaerobicbiologicaltreatmentofsewageisclearlyenablestheoptimizationofresources.Inrecentyears,theanaerobicwastewatertreatmentprocessdevelopedveryrapidly,withnewtechnology,newmethodsemerging,includinganaerobiccontactmethod,theup-flowanaerobicsludgebedanaerobicstallplate,anaerobicbiologicalfilter,anaerobicexpandedbedandfluidizedbed,andthethirdgenerationofanaerobicprocessEGSBandICanaerobicreactor,developedveryrapidly.

Andtheup-flowanaerobicsludgeblanketUASB(Up-flowAnaerobicSludgeBed,Note:hereinafterreferredtoUASB)owingtotheanaerobicprocessofanaerobicfiltersandactivatedsludgecharacteristicsofthedual,ascanbetransformedintothepollutantsinthesewage10%ofrenewablecleanenergy-abiogastechnology.Thedifferentsolidcontentofthesewageadaptabilityalsostrong,anditsstructure,operationandmaintenancemanagementoperationisrelativelysimpleandrelativelylowcost,technologyisnowmature,andincreasinglysewagetreatmentindustryattention,waswidelywelcomedandApplication.

ThispaperattemptstoUASBtechnologyandtheoperationoftheUASBdesignfeatures,aswellasareasforastartbrieflydescribed.

2.TheoriginofUASB

In1971Holland(Wageningen)AgriculturalUniversityLadingge(Lettinga)Professorphysicalstructuraldesign,theuseofthegravitationalfieldoftheroleofdifferentdensitymaterialdifference,inventedthethree-phaseseparator.Theactivatedsludgewastewaterretentiontimeandstayseparated,andformedaupflowanaerobicsludgeblanket(UASB)reactorontheprototype.NetherlandsCSM1974inits6m3reactorsugarbeetprocessingwastewater,itwasfoundthattheactivatedsludgeformationmechanismofitsownfixedbiologicalpolymerstructure,granularsludge(granularsludge).Theemergenceofgranularsludge,notonlyforthepromotionofarepresentativeoftheUASBanaerobicreactor,thesecondgenerationofapplicationsanddevelopment,butalsoforthethird-generationanaerobicreactorlaidthefoundationforthebirth.Currently,theUASBprocessinEuropehasbeengenerallyformedgranularsludge,whichmakesanaerobicUASBtechnologyinEuropehavebeenquicktopopularize.Chinain1981beganUASBreactorresearch,thetechnologyinChinahasbeentheactualapplication.UASBreactoristhemostwidelyusedhigh-rateanaerobicreactor,thetechnologyathomeandabroadanaerobictreatmenthasbecomeoneofthemainstreamtechnologies.

3.UASBreactorstructureandthebasicprinciples

(1)thecompositionofUASBreactor

Figure1isaschematicdiagramoftheUASBreactor.UASBreactor,themainpartofMainlydividedintotworegions,namely,three-phasereactionzoneandtheareaofseparation.ReactionzonewhichUASBreactorforthemainwork.

(2)oftheUASBreactorprinciple

UASBsludgefromthereactionzone,thegas-liquid-solidthree-phaseseparator(includingprecipitationarea)gaschambercomposedofthreeparts.Reactionintheregionholdalargenumberatthebottomofanaerobicsludge,sludgeconcentrationscanreach50to100g/lorhigher,theprecipitationhasgoodperformanceandcohesionofthesludgeinthebottomofasludgelayer.Todealwiththesewagesludgefromtheanaerobicsludgebedatthebottomandflowsofsludgewasmixedlayercontacts,aswaterandupwardmobilityofthelargenumberofgasincreasedagitationtoformagoodnaturalrole,andpartofthesludgeintheresponsetheaboveformarelativelythinsludgesuspension,suspendedsludgeconcentrationareagenerallyfrom5to40g/lrange.Suspensionintotheareaofseparation,thefirstgaschamberwassettoenterseparation,slurrycontainingwastewaterfromenteringthesettlementroom,thesludgeinthesettlement,returnedtothereactionzonebytheslanttoclarifythewaterfromtheoverflow.Sludgeinthemicrobialdecompositionoforganicmatterinsewage,itturnedintogas.Tinygasbubblestoformtherelease,tinybubblesrisinginthecourseofthemerger,andgraduallyformlargerbubblesinthesludgebedmethanebecauseofthedisturbancetoformasludgeconcentrationinthesludgeandthintogetherwithincreasedaccesstothreewaterphaseseparator,encounteredgasseparatorplateatthebottomofreflection,thereflectionplate%forthefourweeks,andthenenterthewaterthroughthechamber,concentratedinthegaschamberwithcatheterexport,thesolid-liquidmixtureintothethree-phasereflectionSeparatorsedimentation,sewagesludgeintheflocculation,particlegraduallyincreasing,andtheroleofgravityinthesettlement.Precipitationrampstothewallofsewagequagmireobliquewallslipbackanaerobicreactorarea,thereactionregionaccumulatedalargenumberofsludge,andsludgefromthetreatedeffluentfromtheuppersedimentoverflowweirarea,andthendischargedsludgebed.

Thebasicrequirementsare:

(1)Toprovideaconducivesludgeflocculationofthephysical,chemicalandmechanicalconditions,accesstoanaerobicsludgesedimentationandmaintainagoodperformance;

(2)Goodsludgebedoftenformafairlystablebiologicalphase,andmaintainspecificprobioticsenvironment,thestrongresistancetodisturbanceforce,thelargerflocprecipitationhasgoodproperties,therebyenhancingtheequipmentsludgeconcentration;

(3)inthesludgebedequipmentthroughtheestablishmentofaprecipitationarea,thefineparticlesofsludgesedimentationinthesludgelayerfurtherflocculationandsedimentation,andthenbackintothesludgebed.

4.UASBreactor,theprocessfeatures

UASBreactoroperationofthreeimportantpremise:①reactorintheformofagoodsettlementorgranularsludgeflocsludge;②producedgasanduniformdistributionofwaterformedbymixingagoodrole③rationaldesignThethree-phaseseparator,thegoodperformanceofprecipitationcanremaininthesludgeinthereactor.(1)theuseofmicroorganismsimmobilizedcelltechnology-sludgeparticlesofUASBreactorusingbacteriaimmobilizedcelltechnology-ImplementationofthesludgeparticlesHRTandsludgeretentiontimeoftheseparation,thusprolongingthesludgesludgeage,andmaintainahighconcentrationofsludge.Anaerobicsludgeparticleswithgoodperformanceandthesettlementhigherthanmethane-producingactivity,andrelativelysmallcarrierdensitythanartificial,generatedbythesludgeandgastoachievefullaccesstotheMatrix,asavingofagitationand)forupwardmovreturntheequipmentandsludgeenergyconsumptionneednotattachedprecipitationseparationdevices.Atthesametimethereactorwithoutaddingfillersandvectorvolumeincreasedutilization.(2)fromthegasandwaterdistributionuniformityformedbymixingthenaturalgoodintheroleoftheUASBreactor,gasandwaterproductionincreasedflowandtheformationofbubblesonthereactionregionShangcuansludgeparticleshaveanimportantHierarchicalrole.Thisrolenotonlyaffecttheprocessofsludgeparticles,andalsotheformationofthegranularsludgequalitygreatlyaffected.Atthesametimetheroleofmixingthesludgeandtoachievefullaccesstothematrix.(3)therationaldesignofthethree-phaseseparatoristheapplicationofthree-phaseseparatorintheUASBreactor,themostimportantequipment.Applicationofthethree-phaseseparatordegassingsaveauxiliarydevices,canbecollectedfromthereactionzonegasseparatoratthesametimesothatthesuspensionofsedimentsdowntothegoodperformanceofprecipitationwillremaininthesludgeinthereactor.

5.UASBstateandtheflowofsludge

UASBflowpatternwithinacomplexreactionpatternontheregionandgasproductionandreactionzonehighlyrelevant,ingeneral,thereactionzoneinthelowerlayerofsludge,astheresultofgasproduction,partlythroughthemagnanimityofmoresections,formingaUnitincreasedairflow,themixtureoflead(referringtothesludgeandwaterement.Atthesametime,thisgas,andwateraroundthedownwardmovementofmedia,resultinginmixedreversethisflowpatternresultingflowofwatershort.Thisincreaseinthegasawayfromtheflowofeasytoformacorner.Inthesedeadends,butalsohasacertainproductionlevels,theformationofsludgeandwatermixedslowandweak,sothatintheformationofsludgelayervaryingdegreesofmixingzone,thesizeofthemixingzoneoftheprocessandshort.Suspensionlayerofthemixture,asgasliquidcurrencymovementsledtoahigherrateofriseandfall,astrongmixed.Gasproductionintherelativelyfewcases,andsometimessuspendedsludgelayerandtheboundarylayerisobvious,andmoregasproductioninthecircumstances,thisinterfacenotobvious.Thetrialshowedthatprecipitationintheregionwaspushingwaterflow,butthereisstillaprecipitationzonedeadzoneandmixingzone.

UASBthesludgeconcentrationandequipmentrelatedtotheorganicloadingrate.Wastewatertreatmentissugar,anddistributionofsludgeintheUASBloadrelations.AscanbeseenfromFiguresludgelayerofsludgeconcentrationofsuspendedsludgeconcentration,thesuspensionoftheupperandlowerpartsofthesludgeconcentrationdifferenceofsmaller,thatisclosetocompletelymixedflowpattern,theresponsetothedistrictawardedsludge,whenorganicloadatthehighlevelofsuspendedsludgeboundarylayerandnotobvious.Testshowsthatthesewagethroughthebottomofthe0.4-0.6mhigh,90%oftheorganicmatterisconverted.Thisshowsthatanaerobicsludgeishighlyactiveandchangedtheanaerobictreatmentforalongtimethattheconceptoftheslowprocess.Inanaerobicsludge,theaccumulationofalargenumberofhighactivityofanaerobicsludgesuchequipmentisthemainreasonforhugecapacity,whichinturnisattributabletothesludgesedimentationgoodperformance.

UASBhasahighvolumeoforganicloadingrate,mainlybecauseoftheequipment,inparticularthesludgelayerretainalargenumberofanaerobicsludge.Ofthestabilityandefficiencytoagreatextentdependonthesettlementwithexcellentperformanceandhighmethaneactivityofthesludge,especiallygranularsludge.Onthecontrary,iftheresponsetotheregion'ssludge-looseflocculationofexistence,oftenfloatingsludgelossoftheUASBnotstableunderhighloadoperation.

6.AffecttheperformanceoftheUASBreactormainfactors

(1)anaerobicwastewatertreatmenttemperaturearealsodividedintolowtemperature,hightemperatureinthethreecategoriesofmild,thetemperaturerangewiththecorrespondingmicrobialgrowthrangeshouldbe.Sofarthemajorityofanaerobicwastewatertreatmentsysteminthetemperaturerangeoperation,to30℃to40℃mostcommon,andthebesttemperatureat35℃to40℃.High-temperatureprocessinmorethan50℃to60℃ofoperation.Low-temperatureanaerobicsludgeofmoderateactivitywassignificantlylowerthanthatinhigh-temperature,thereactorloadisrelativelylow,butforsomelowertemperatureofwastewater,low-temperatureprocessisthechoiceofprogrammes.

(2)pHvalueofthepHvalueofanaerobicwastewatertreatmentisthemostimportantfactorintheimpact.Anaerobictreatment,hydrolysisandacidproducingbacteriaonthepHofagreaterrangeofadaptability,butthepH-sensitivemethanebacteriasuitableforthegrowthofpH6.5to7.8,whichisundernormalcircumstancesshouldbecontrolledbytheanaerobictreatmentofpH.

(3)nutrientandtraceelementsanaerobicbacteriafromwastewatertreatmentprocess,butitshouldmaintainagoodenvironmentforthegrowthofbacteria,thebacteriahavesufficientguaranteesofitsowncellmaterialcompounds.Basedonthechemicalcompositionofcells,whichincludenutrientsnitrogen,phosphorus,potassiumandsulfur,aswellascalcium,magnesium,iron,andothergrowthorasmallnumberofessentialtraceelements.

(4)alkalinityandvolatileacidconcentrationtoensurethattraditionaltheorythattheformationofgranularsludgereactor,alkalinityshouldbemaintainedatthe1000~5000mgCaCO3/lwithinthescopeofthereactorifthealkalinityoflessthan1000mgCaCO3/l,,PHvaluewouldleadtoitsdeclineinitsfirst-classTangstudyhasbeenconfirmedtoensurethattheUASBreactorsludgeparticlesisthealkalinityoftheminimum750mgCaCO3/l.IntheUASBreactor,theconcentrationofvolatileacidityofsecuritycontrolinthe2000mg/l(HAC)withintheVFAwhentheconcentrationislessthan200mg/l,itisthebest.

(5)theinfluentconcentrationofsuspendedsolidsinthewatertocontrolthesuspendedsolids(SS)concentrationofstrictcontrolrequirementsUASBreactorprocesswithotheranaerobictreatmentprocesssignificantlydifferent.Generallyspeaking,inthewastewaterSS/CODratioshouldbecontrolledbelow0.5.

(6)thecontroloftoxicandhazardoussubstancescontrol①ammoniaconcentration:thelevelofammoniaconcentrationonanaerobicmicroorganismsproducetwokindsofdifferentinfluences.Whenitsconcentrationinthe50-200mg/l,intheanaerobicreactorcouldstimulatemicrobialroleintheconcentrationof1500-3000mg/l,willproducesignificantlyinhibitmicrobes.Generallypreferabletocontroltheconcentrationofammoniainthe1000mg/lfollowing.②sulfate(SO2-4)concentrationcontrol:UASBreactorinthesulfateionconcentrationshouldnotexceed50mg/l,inthecourseofoperationoftheUASBCOD/SO2-4ratioshouldbegreaterthan10.③othertoxicsubstances:leadUASBreactordealwiththecausesofthefailure,inadditiontotheabove-mentionedseveralotherthanthepresenceoftoxicsubstancesmustalsobepayingverycloseattentionto,thesesubstancesaremainlythefollowing:heavymetals,alkalineearthmetals,trichloromethane,cyanides,phenols,suchasnitratesandchlorine.

7,theadvantagesanddisadvantagesofUASB

UASBthemainadvantagesare:

1,highconcentrationsofsludgeintheUASB,theaverageconcentrationofsludge20-40gVSS/1;

2,thehighorganicload,hydraulicretentiontimeisshort,whenusedinthefermentationtemperature,thevolumeloadisgenerallyaround10kgCOD/m3.d;

3,nomixerequipment,onthefermentationprocessoftheriseingascampaigntotheDepartmentofsludgebedinasuspendedstateofthesludge,thesludgelayeronthebottomthereisacertaindegreeofagitation;

4,sludgebednotavailablecarrier,costsavingsandavoidblockingfillintheproblem;

5,UASBinternalthree-phaseseparator,andarenormallynotsedimentationtanks,precipitationwasseparatedsludgeblanketreactorbacktotheregion,usuallynosludgecanbereturnedequipment.

Mainweaknessesare:

1,inthesuspensionofwaterneedtobeproperlycontrolledandshouldnotbetoohigh,generallyinthecontrolof100mg/lfollowing;

2,sludgebedshortreflowphenomenon,affectingprocessingcapability;

3,waterqualityandmoresensitivetosuddenchangesinload,impactresistanceisnotgood.

8,theAppliedResearchStatus

(1),suchasactivatedtechnologyLepistoearlierstudycarriedoutinthisrespect.TheUASBgranularsludgetechnologyisthecoreoftheformationofgranularsludgeisdirectlyrelatedtotheoperationoftheUASBreactorsuccess.Manystudiesontheanaerobicgranularsludgetrain.Sofar,thecultivationofanaerobicgranularsludgehasbeenmadealotofusefulexperience.WUYunsuchasChinatoaddtothesludgeinoculatedbentoniteandnon-ionicpolyacrylamide,beerproductionwastewatertreatment,withinfourweeksofformationofastablegranularsludgebed.Zhengequalityontheanaerobictreatmentofwastewaterpharmaceuticalactivatedtechnology.

(2)wastewatertreatmentfieldLettingaandhiscolleaguesinthelaboratory,thefirstvolumeof60LoftheUASBreactorpilotstudy.Theresultsshowthatthetreatmentplanthandlinggoodeffect,anditsorganicloadingratesashighas10KgCOD/(m3•d),thenavolumeof6m3,30m3and200m3ofsemi-productionpilotstudyontemperatureconditions,thevolumeof6m3BeetsugarprocessingdeviceswastewaterCODloadcapacityofupto36Kg/(m3•d);potatoprocessingwastewatertreatmentCODloadof15Kg/(m3•d)above,theCODremovalrateof70%-90%.Subsequently,theNetherlands,Germany,Sweden,BelgiumandtheUnitedStatesbyresearchersUASBreactorforthepotatoprocessingwastewater,broadbeansprocessingwastewater,wastewaterslaughtered,cannedproductsprocessingwastewater,wastewatermethanol,aceticacidwastewaterandwastewaterfiberboardorsmalltestproductiontest,achievingbetterresults.Accordingtoincompletestatistics,from1990,therestoftheworldhas205production-scaleUASBsystemoperational,in1993,thisfigurehadrisentomorethan400.Sofar,inEuropeUASBprocesshasbeengenerallyformedgranularsludge.UASBtechnologyapplicationinChinafromthedevelopmentsincethe1980s,moreandmoreextensiveapplications.Fromthelate1980stodealwithdistillery,brewerywastewater(UASBprocesswithasingle),tothelate1990s,andthecombineduseofothertechnology,suchastheUASB+AFwastewaterwithhighconcentrationsofpolyester,PUASBpressure,suchaspharmaceuticalwastewatertreatment.Atthesametimehasalsobeensuccessfullyappliedinurbansewagetreatmentandsewagetreatment.

9,thedevelopmenttrendofUASB

AlthoughUASBtechnologyapplicationinChinahasmadeconsiderableheadway,buttherearestillgapswithforeignstandards,shouldbefurtherstrengthenedintheUASBreactoranditsancillaryequipmentandengineeringequipmentontheexplorationandpractice.Atthesametime,inthefollowingaspects,UASBanaerobictreatmentprocessisalsoanewdevelopment:①temperatureUASBreactoroperation;②high-temperatureanaerobictreatment;③todealwiththenon-accumulationornotanewgranularsludgeUASBreactor;④treatmenttocontainhighconcentrationsoftoxicsubstancesinwastewater;⑤lowconcentrationofanaerobictreatmentofwastewater.Anaerobicprocessingsystemwithhigh-load,lowinvestmentandlowoperatingcosts,suchasenergycanberecoveredsomeadvantages,verysuitableforChina'snationalconditions.Alongwiththecontinuousdeepeningofresearchanddevelopment,andbelievethattheUASBanaerobicapplicationprocessisverybroad.UASB厌氧处理工艺的现状与发展摘要:本文介绍了UASB反应器的由来、工作原理、特点、最新开发和应用研究进展,指出了近期UASB反应器的研究重点。关键词:UASB;厌氧处理工艺；1.引言厌氧生物处理作为利用厌氧性微生物的代谢特性，在毋需提供外源能量的条件下，以被还原有机物作为受氢体，同时产生有能源价值的甲烷气体。厌氧生物处理法不仅适用于高浓度有机废水，进水BOD最高浓度可达数万mg/l，也可适用于低浓度有机废水，如城市污水等。厌氧生物处理过程能耗低；有机容积负荷高，一般为5－10kgCOD/m3.d，最高的可达30-50kgCOD/m3.d；剩余污泥量少；厌氧菌对营养需求低、耐毒性强、可降解的有机物分子量高；耐冲击负荷能力强；产出的沼气是一种清洁能源。在全社会提倡循环经济，关注工业废弃物实施资源化再生利用的今天，厌氧生物处理显然是能够使污水资源化的优选工艺。近年来，污水厌氧处理工艺发展十分迅速，各种新工艺、新方法不断出现，包括有厌氧接触法、升流式厌氧污泥床、档板式厌氧法、厌氧生物滤池、厌氧膨胀床和流化床，以及第三代厌氧工艺EGSB和IC厌氧反应器，发展十分迅速。而升流式厌氧污泥床UASB(Up-flowAnaerobicSludgeBed，注：以下简称UASB）工艺由于具有厌氧过滤及厌氧活性污泥法的双重特点，作为能够将污水中的污染物转化成再生清洁能源——沼气的一项技术。对于不同含固量污水的适应性也强，且其结构、运行操作维护管理相对简单，造价也相对较低，技术已经成熟，正日益受到污水处理业界的重视，得到广泛的欢迎和应用。本文试图就UASB的运行机理和工艺特征以及UASB的设计启动等方面作一简要阐述。2.UASB的由来1971年荷兰瓦格宁根（Wageningen）农业大学拉丁格（Lettinga）教授通过物理结构设计，利用重力场对不同密度物质作用的差异，发明了三相分离器。使活性污泥停留时间与废水停留时间分离，形成了上流式厌氧污泥床（UASB）反应器的雏型。1974年荷兰CSM公司在其6m3反应器处理甜菜制糖废水时，发现了活性污泥自身固定化机制形成的生物聚体结构，即颗粒污泥（granularsludge）。颗粒污泥的出现，不仅促进了以UASB为代表的第二代厌氧反应器的应用和发展，而且还为第三代厌氧反应器的诞生奠定了基础。目前,在欧洲的UASB工艺已普遍形成了颗粒污泥,这使得厌氧UASB工艺在欧洲迅速得到了推广和普及。我国于1981年开始了UASB反应器的研究工作,该技术在我国已得到了实际的推广应用。UASB反应器是目前应用最为广泛的高速厌氧反应器,该技术在国内外已经发展成为厌氧处理的主流技术之一。3.UASB反应器的基本构造和原理(1)UASB反应器的构成图1是UASB反应器的示意图。UASB反应器的主体部分主要分为两个区域,即反应区和三相分离区。其中反应区为UASB反应器的工作主体。(2)UASB反应器的工作原理UASB由污泥反应区、气液固三相分离器（包括沉淀区）和气室三部分组成。在底部反应区内存留大量厌氧污泥，污泥浓度可达到50~100g/l或更高，具有良好的沉淀性能和凝聚性能的污泥在下部形成污泥层。要处理的污水从厌氧污泥床底部流入与污泥层中污泥进行混合接触，由于水的向上流动和产生的大量气体上升形成良好的自然搅拌作用,并使一部分污泥在反应区的上方形成相对稀薄的污泥悬浮区,悬浮区污泥浓度一般在5~40g/l范围内。悬浮液进入分离区后,气体首先进入集气室被分离,含有悬浮液的废水进入分离区的沉降室,污泥在此沉降,由斜面返回反应区,澄清后的处理水溢流排出。污泥中的微生物分解污水中的有机物，把它转化为沼气。沼气以微小气泡形式不断放出，微小气泡在上升过程中，不断合并，逐渐形成较大的气泡，在污泥床上部由于沼气的搅动形成一个污泥浓度较稀薄的污泥和水一起上升进入三相分离器，沼气碰到分离器下部的反射板时，折向反射板的四周，然后穿过水层进入气室，集中在气室沼气，用导管导出，固液混合液经过反射进入三相分离器的沉淀区，污水中的污泥发生絮凝，颗粒逐渐增大，并在重力作用下沉降。沉淀至斜壁上的污泥沼着斜壁滑回厌氧反应区内，使反应区内积累大量的污泥，与污泥分离后的处理出水从沉淀区溢流堰上部溢出，然后排出污泥床。基本出要求有：1）为污泥絮凝提供有利的物理、化学和力学条件，使厌氧污泥获得并保持良好的沉淀性能；2）良好的污泥床常可形成一种相当稳定的生物相，保持特定的微生态环境，能抵抗较强的扰动力，较大的絮体具有良好的沉淀性能，从而提高设备内的污泥浓度；3）通过在污泥床设备内设置一个沉淀区，使污泥细颗粒在沉淀区的污泥层内进一步絮凝和沉淀，然后回流入污泥床内。4、UASB反应器的工艺特点UASB反应器运行的3个重要的前提是:①反应器内形成沉降性能良好的颗粒污泥或絮状污泥;②出产气和进水的均匀分布所形成的良好的搅拌作用;③设计合理的三相分离器,能使沉淀性能良好的污泥保留在反应器内。(1)利用微生物细胞固定化技术-污泥颗粒化UASB反应器利用微生物细胞固定化技术-污泥颗粒化实现了水力停留时间和污泥停留时间的分离,从而延长了污泥泥龄,保持了高浓度的污泥。颗粒厌氧污泥具有良好的沉降性能和高比产甲烷活性,且相对密度比人工载体小,靠产生的气体来实现污泥与基质的充分接触,节省了搅拌和回流污泥的设备和能耗;也无需附设沉淀分离装置。同时反应器内不需投加填料和载体,提高了容积利用率。(2)由产气和进水的均匀分布所形成的良好的自然搅拌作用在UASB反应器中,由产气和进水形成的上升液流和上窜气泡对反应区内的污泥颗粒产生重要的分级作用。这种作用不仅影响污泥颗粒化进程,同时还对形成的颗粒污泥的质量有很大的影响。同时这种搅拌作用实现了污泥与基质的充分接触。(3)设计合理的三相分离器的应用三相分离器是UASB反应器中最重要的设备。三相分离器的应用省却了辅助脱气装置,能收集从反应区产生的沼气,同时使分离器上的悬浮物沉淀下来,使沉淀性能良好的污泥能保留在反应器内。5.UASB内的流态和污泥分布UASB内的流态相当复杂，反应区内的流态与产气量和反应区高度相关，一般来说，反应区下部污泥层内，由于产气的结果，部分断面通过的气量较多，形成一股上升的气流，带动部分混合液（指污泥与水）作向上运动。与此同时，这股气、水流周围的介质则向下运动，造成逆向混合，这种流态造成水的短流。在远离这股上升气、水流的地方容易形成死角。在这些死角处也具有一定的产气量，形成污泥和水的缓慢而微弱的混合，所以说在污泥层内形成不同程度的混合区，这些混合区的大小与短流程度有关。悬浮层内混合液，由于气体币的运动带动液体以较高速度上升和下降，形成较强的混合。在产气量较少的情况下，有时污泥层与悬浮层有明显的界线，而在产气量较多的情况下，这个界面不明显。有关试验表明，在沉淀区内水流呈推流式，但沉淀区仍然还有死区和混合区。UASB内污泥浓度与设备的有机负荷率有关。是处理制糖废水试验时，UASB内污泥分布与负荷的关系。从图中可看出污泥层污泥浓度比悬浮层污泥浓度高，悬浮层的上下部分污泥浓度差较小，说明接近完全混合型流态，反应区内污泥的颁，当有机负荷很高时污泥层和悬浮层分界不明显。试验表明，污水通过底部0．4－0．6