环境工程专业外语下.docx

环境工程专业外语下.docx

《环境工程专业外语下.docx》由会员分享，可在线阅读，更多相关《环境工程专业外语下.docx（106页珍藏版）》请在冰豆网上搜索。

环境工程专业外语下

Lesson23Sludge

Perhapsthemostpressingwatertreatmentproblematthistimehastodowithsludgecollectedorproducedduringwatertreatment.Findingasafeplacetoputthesludgeorauseforithasproventroublesomeandtheproblemisaggravatedbythegrowingnumbersofwatertreatmentsystems.

Somesludgeispresentinwastewaterandmaybecollectedfromit.Suchsludgeincludeshumanwastes,garbagegrindings,organicwastesandinorganicsiltandgritfromstormwaterrunoff,andorganicandinorganicwastesfromcommercialandindustrialsources.Therearetwomajorkindsofsludgegenerated,inawastetreatmentplant.Thefirstoftheseisorganicsludgefromactivatedsludge,tricklingfilterorrotatingbiologicalreactors.Thesecondisinorganicsludgefromtheadditionofchemicals,suchasinphosphorusremoval.

Mostcommonly,sewagesludgeissubjectedtoanaerobicdigestioninadigesterdesignedtoallowbacterialactiontooccurintheabsenceofair.Thisreducesthemassandvolumeofsludgeandideallyresultsintheformationofastabilizedhumus.Diseaseagentsarealsodestroyedintheprocess.

Followingdigestion,sludgeisgenerallyconditionedandthickenedtoconcentrateandstabilizeitandmakeitmoredewaterable.Relativelyinexpensiveprocesses,suchasgravitythickening,maybeemployedtogetthemoisturecontentdowntoabout95﹪.Sludgemaybefurtherconditionedchemicallybytheadditionofironoraluminumsalts,lime,orpolymers.

Sludgedewateringisemployedtoconvertthesludgefromanessentiallyliquidmaterialtoadampsolidcontainingnotmorethanabout85﹪water.Thismaybeaccomplishedonsludge,dryingbedsconsistingoflayersofsandandgravel.Mechanicaldevicesmayalsobeemployed,includingvacuumfiltration,centrifugation,andfilterpresses.Heatmayuseaiddryingprocess.

Someofthealternativesfortheultimatedisposalofsludgeincludelandspreading,oceandumping,andincineration.Eachofthesechoiceshasdisadvantages,suchasthepresenceoftoxicsubstancesinsludgespreadonland,orthehighfuelcostofincineration.

SomeoftheundesirablecomponentsfoundinsewagesludgeareshowninTable23.1.Thistablereferstosludgefromaprimarysettler,althoughmanyofthesamecomponentsarefoundinsecondarysettlersludges.

Richinnutrients,wastesewagesludgecontainsaround50﹪N,3%P,and0.5%Konadry-weightbasisandcanbeusedtofertilizeandconditionsoil.Thehumicmaterialinthesludgeimprovesthephysicalpropertiesandcation-exchangecapacityofthesoil.Amongthefactorslimitingthisapplicationofsludgeareexcessnitrogenpollutionofrunoffwaterandgroundwater,survivalofpathogens,andthepresenceofheavymetalsinthesludge.

Possibleaccumulationofheavymetalsisofthegreatestconcerninsofarastheuseofsludgeoncroplandisconcerned.Sewagesludgeisanefficientheavymetalsscavenger.Onadrybasis,sludgesamplesfromindustrialcitieshaveshownlevelsofupto9,000ppmZinc,6,000ppmcopper,600ppmnickel,andupto800ppmcadmium!

Theseandothermetalstendtoremainimmobilizedinsoilbychelationwithorganicmatter,adsorptiononclayminerals,andprecipitationasinsolublecompounds,suchasoxidesorcarbonates.However,increasedapplicationofsludgeoncroplandhascauseddistinctlyelevatedlevelsofzincandcadmiumbothleavesandgrainofcorn.Therefore,cautionhasbeenadvisedinheavyorprolongedapplicationofsewagesludgetosoil.Theproblemofheavymetalsinsewagesludgeisoneofthemanyreasonsfornotallowingmixtureofwastestooccurpriortotreatment.Sludgedoes,however,containnutrientswhichshouldnotbewasted,giventhepossibilityofeventualfertilizershortages.Priorcontrolofheavymetalcontaminationfromindustrialsourcesshouldgreatlyreducetheheavymetalcontentofsludgeandenableittobeusedmoreextensivelyonsoil.

TABLE23.1UndesirableComponentsCommonlyFoundinSewageSludgefromaPrimarySettler'

ComponentLevel,ppmbydryweightunlessotherwisestated

Organics

PCB0-105

DDT0-1（foundmuchlessfrequentlynow）

DDD0-0.5（foundmuchlessfrequentlynow）

dieldrin0-2

aldrin0-16

phenolsometimesencountered

Heavymetals

cadmium0-100

leadupto400

mercury3-15

chromiumupto700

copper800-1000

nickel25-400

zinc300-2000（commondeterrentuseofsludgeasasoilconditionerduetoitstoxicitytoplants）

Pathogenicmicroorganisms

humanvirusesgenerallypresent

salmonella（inrawsludge）500viablecells/100mL

salmone1la（indigestedsludge）30viablecells/100mL

fecalcoliforms（rawsludge）1×

viablecells/100mL

fecalcoliforms（digestedsludge）4×

viablecells/100mL

Asincreasingprobleminsewagetreatmentarisesfromsludgesidestreams.Theseconsistofwaterremovedfromsludgebyvarioustreatmentprocesses.Sewagetreatmentprocessescanbedividedintomainsteamtreatmentprocesses（primaryclarification,tricklingfilter,activatedsludge,androtatingbiologicalreactor）andsidestreamprocesses.Duringsidestreamtreatmentsludgeisdewatered,degraded,anddisinfectedbyavarietyofprocesses,includinggravity,thickening,dissolvedairflotation,anaerobicdigestion,aerobicdigestion,vacuumfiltration,centrifugation,belt-filterpressfiltration,sand-drying-bedtreatment,sludge-lagoonsettling,wetairoxidation,pressurefiltration,andPurifaxtreatment.Eachoftheseproducesaliquidby-productsidestreamwhichiscirculatedbacktothemainstream.Theseaddtothebiochemicaloxygendemandandsuspendedsolidsofthemainstream.

Avarietyofchemicalsludgesareproducedbyvariouswatertreatmentandindustrialprocesses].AmongthemostabundantofsuchsludgesisalumsludgeproducedbythehydrolysisofAl（III）saltsusedinthetreatmentofwater,whichcreatesgelatinousaluminumhydroxide:

（23.1）

Alumsludgesnormallyare98%ormorewaterandareverydifficulttodewater.

Bothiron（II）andiron（III）compoundsareusedfortheprecipitationofimpuritiesfromwastewaterviatheprecipitationof

.Thesludgecontains

intheformofsoft,fluffyprecipitatesthataredifficulttodewaterbeyond10or12﹪solids.

Theadditionofeitherlime,

orquicklime,CaO,towaterisusedtoraisethepHtoabout11.5andcausetheprecipitationof

alongwithmetalhydroxidesandphosphates.Calciumcarbonateisreadilyrecoveredfrom,limesludgesandcanbereca1cinedtoproduceCaOwhichcanberecycledthroughthesystem..

Metalhydroxidesludgesareproducedintheremovalofmetalssuchaslead,chromium,nickel,andzincfromwastewaterbyraisingthepHtosuchalevelthatthecorrespondinghydroxidesorhydratedmetaloxidesareprecipitated.Thedisposalofthesesludgesisasubstantialproblembecauseoftheirtoxicheavymetalcontent.Reclamationofthemetalsisattractivealternativeforthesesludges.

Pathogenic（disease-causing）microorganismsmaypersistinthesludgeleftfromthetreatmentofsewage.Manyoftheseorganismspresentpotentialhealthhazardsandthereisriskofpublicexposurewhenthesludgeisappliedtosoil.Therefore,itisnecessarybothtobeawareofpathogenicmicroorganismsinmunicipalwastewatertreatmentsludgeandtofindameansofreducingthehazardscausedbytheirpresence.

Themostsignificantorganismsinmunicipalsewagesludgeincludethefollowing:

（1）indicators,includingfecalandtotalcoliform;

（2）pathogenicbacteria,includingSalmonellaeandShigellae;（3）enteric（intestinal）viruses,includingEnterovirusandPoliovirus,and（4）Parasites,suchasEntamoebahistolyticaandAscarislumbricoides.

Severalwaysarerecommendedtosignificantlyreducelevelsofpathogensinsewagesludge.Aerobicdigestioninvolvesaerobicagitationofthes1udgeforperiodsof40to60days（longertimesareemployedwithlowsludgetemperatures）.Airdryinginvolvesdrainingand/ordryingoftheliquidsludgeforatleastthreemonthsinalayer20-25cmthick.Thisoperationmaybeperformedonunderdrainedsandbedsorinbasins.Anaerobicdigestioninvolvesmaintenanceofthesludgeinananaerobicstateforperiodsoftimerangingfrom60daysat20℃to15daysattemperatureexceeding35℃.Compostinginvolvesmixingdewateredsludgecakewithbulkingagentssubjecttodecay,suchaswoodchipsorshreddedmunicipalrefuse,andallowingtheactionofbacteriatopromotedecayattemperaturesrangingupto45-60℃.Thehighertemperaturestendtokillpathogenicbacteria.Finally,pathogenicorganismsmaybedestroyedbylimestabilizationinwhichsufficientlimeisaddedtoraisethepHofthesludge12ormore.

NewWordsandExpressions

pressingn.压（制、榨、干），冲压，榨（油），熨平；冲压件，模压制品；（同一批压制的）唱片，版样（录音）adj.紧急[迫]的，迫[恳]切的，再三要求的

havetodowith与…很有[毫无、有些]关系，与…有许多[毫无、有些]共同之处

grindingn.adj.磨削、光、碎的，研磨的，抛光的，粉碎的，费事的，难挨的

runoffn.径流（量），流量；流（溢）出，流泻；流放[放出]口；出轨

digester消化池，消化槽，煮解器

dewaterv.排[去、脱、抽]水，疏干（沼泽），浓缩，增稠，除去…的水分

thickenv.使变厚[粗、浓、深、浊、暗、稠、模糊]，使更厚[粗、浓、深、浊、暗、稠]，增稠，稠化，加多[强、深]，繁茂；复杂化，变复杂

incineration焚化，烧尽，煅烧，灰化

dieldrin狄氏剂

aldrin艾氏剂

deterrentadj.妨[阻]碍的，阻[制]止的，威慑的n.阻碍[制、止]物，威慑力量（因素）

belt-filterpress带式压滤机

fluffy松软的，蓬松的，绒毛（似）的，易碎的

dampadj.潮湿的，有湿气的v.弄[调]湿；阻尼，缓冲，抑制，衰减n.湿[潮]气，湿度，含水量；雾，水蒸气；阻尼，缓冲，减振[速]，衰减[耗]

gravel砂砾，卵石

filterpress压滤机

pathogen病原（体），细菌

survivaln.幸[生、残]存，保全，救生，继续存在；幸[生]存者，残余[存、留]物，遗物adj.活命的，保命的，安全的

fecalcoliform粪便大肠菌

reclamationn.（废料）回收，再生，修整（废品），改造；收回，恢复，要求归还；开垦[拓]，垦殖，土壤改良，填筑

enteric（intestinal）viruses肠病毒

enterovirus肠道病毒

poliovirus脊髓灰质炎病毒

underdrainn.阴[暗]沟，暗渠，地下沟道，聚水系统vt.用暗沟排水，底部排水

composting制堆肥，堆肥处理

refusev.拒绝；再熔化n.废物[品、料、渣、铸件]，渣[滓]，残渣，垃圾adj.无用的，不合格的，报废的，废料的

parasite寄生（物），废[寄生]阻力，附加

entamoebahistolytica痢疾内变形虫

lumbricoid似蚯蚓的

bulkingagent膨胀剂

assarislum