办公楼给排水毕业设计全套图纸说明书

本科毕业设计说明书外文文献及译文文献、资料题目：文献、资料来源：文献、资料发表（出版）日期：2008.3.17院（部）：专业：给水排水工程班级：姓名：学号：指导教师：翻译日期：2013.5.30外文文献：WastewaterTreatmentABSTRACT：Abioreactorsystemwith30packedgelenvelopeswasinstalledinathermalpowerplantfortheremovalofnitrogenfromammonia-containingdesulfurizationwastewater.Eachenvelopeconsistedofdouble-sidedplategelscontainingNitrosomonaseuropaeaandParacoccusdenitrificanscellswithaninternalspaceinbetweenforinjectinganelectrondonor.Theenvelopecanremoveammoniafromwastewaterinasinglestep.Whenthewastewaterwascontinuouslytreatedwiththebioreactorsystem,itremoved95.0%ofthetotalnitrogenintheinlet,andthetotalnitrogenconcentrationintheoutletwasbelow9.0mgL−1.Themaximumnitrogenremovalratewas6.0gday−1persquaremeterofthegelarea.Themaximumutilizationefficiencyoftheinjectedethanolfordenitrificationwas98.4%,andthetotalorganiccarbonconcentrationintheoutflowwasmaintainedatalowlevel.Sincethebioreactorsystemcouldusetheelectrondonoreffectively,itwasnotnecessarytouseanadditionalaerobictanktoremovetheelectrondonorandasettlingtanktosegregatethesurplussludgecontainingbacteriafromwastewater.Ourconceptofusingpackedgelenvelopeswouldbehighlyeffectiveforconstructingasimpleandefficientnitrogenremovalsystemcapableofsimultaneousnitrificationanddenitrification.1.IntroductionEutrophication,whichiscausedbyanexcessivenitrogeninflowfromdomesticandindustrialeffluents,causessevereadverseeffectsontheenvironmentofclosedwatersystem[1].InJapan,algalbloomsandredtidesoccurfrequentlyandhavecauseddamagetothewaterserviceandfishingindustryinTokyoBay,IseBay,andtheSetoInlandSea.Therefore,strictregulationswereappliedfordischargingnitrogeneffluentsintotheindustrialwastewater.Theammoniaremovalprocessusingmicroorganismshasnowbeendividedintotwokindsofbiologicalprocesses:oneisthetraditionalnitrification/denitrificationmethod[2],andtheotherisanewlydevelopedanaerobicammoniumoxidation(anammox)method[3,4].Theanammoxprocesscombinesammoniaandnitriteintonitrogengasanaerobically.Itisanattractivemethodwithgreatpromise.However,theanammoxprocessrequiresanadditionalnitrificationprocessforthepartialconversionofammoniatonitrite.Presently,nitrogen(ammonia)removalismostlycarriedoutthroughtwoconversionsteps,namely,aerobicnitrificationandanaerobicdenitrification.Thismethod,however,hasadisadvantage.Whentreatingwastewaterwithoutorganicmatters,anelectrondonorisrequiredfordenitrification.Inthiscase,itrequiresanadditionalaerobicsteptoremovesurpluselectrondonorsandasettlingsteptosegregatetheactivatedsludgecontainingbacteriafromthewastewater.Sincetherearemanystepsinthepresentnitrogenremovalsystems,acomplicatedsequenceofoperationsisnecessaryandalargeinstallationareaisrequired.Severalresearcheshavebeenconductedinanattempttocombinethetwoconversionsteps(nitrificationanddenitrification)intoasinglebioreactor[5–7].Polymericbeads,inwhichanitrifierandadenitrifierwerecoimmobilized,wereusedtoremovenitrogeninasinglestep.Nitrificationoccurredontheouterlayerofbeads,anddenitrification,inthecoreofbeads.However,theelectrondonorswereaddeddirectlytothewastewaterinthesesystems.Therefore,anadditionalaerobicstepwasrequiredfortheremovalofsurpluselectrondonors,andtheefficiencyofutilizingelectrondonorswasrelativelylow.Tosimplifythepresentsystemsusedfornitrogenremoval,wehaveproposedandinvestigatedanovelimmobilized-cellbioreactorcontainingpackedgelenvelopescapableofsimultaneousnitrificationanddenitrification[8].Thepackedgelenvelopesconsistoftwopolymericgelplateswithaninternalspacebetweenthemforinjectingtheelectrondonorfordenitrification.Anammoniaoxidizer,namely,Nitrosomonaseuropaea,andadenitrifier,namely,Paracoccusdenitrificans,arecoimmobilizedintheplategel.TheimmobilizedN.europaeaoxidizesammoniatonitriteontheoutersurfaceoftheplatethatisinaerobiccontactwiththewastewatercontainingammonia;theimmobilizedP.denitrificansreducesnitritetonitrogengasintheinsideofplatethatisinanaerobiccontactwiththeelectrondonor.Thissystemdoesnotrequireanadditionalaerobicstepbecausetheelectrondonorsarenotsuppliedtothewastewaterdirectlybuttotheinternalspaceofthegelplate.Thisresultsinanincreaseintheutilizationefficiencyoftheelectrondonorforthedenitrificationprocessandadecreaseinthequantityofsurplussludge.Inthisstudy,weinvestigatedalarge-scalebioreactorusingthinnerpackedgelenvelopesinwhichN.europaeaandP.Denitrificanscellsarecoimmobilized,treatedtheammonia-containingwastewaterfromacoal-firedthermalpowerplant,andstudiedthenitrogenremovalcapacityofthesystem.2.Materialsandmethods2.1.BacterialstrainsandculturemediumsThenitrifierN.europaeaNBRC14298andthedenitrifierP.denitrificansJCM6892wereusedinthisstudy.N.europaeawasaerobicallyculturedat30◦Cinamediumcontainingthefollowing(gL−1):(NH4)2SO4,0.5;NaCl,0.3;K2HPO4,1.0;MgSO4·7H2O,0.3;FeSO4·7H2O,0.03;phenolred,0.002(pH8.0).P.denitrificanswasaerobicallyculturedat30◦Cinamediumcontainingthefollowing(gL−1):peptone(Difco),10.0;meatextract(Difco),10.0;NaCl,5.0(pH7.2).Allnutrientsweredissolvedindistilledwater.2.2.CharacteristicsoftheactualwastewaterDesulfurizationwastewaterfromtheTakeharathermalpowerplant(TakeharaCity,HiroshimaPrefecture,Japan)wasusedinthisstudy.Themaximumoutputofthiscoal-firedthermalpowerplantwas1300MW.Theheavymetalscontainedinthisdesulfurizationwastewaterwereremovedinapreviousprocess.Theorganiccarboncontentofthewastewaterwasextremelylow.Thetotalorganiccarbon(TOC)concentrationinthewastewaterrangedbetween0.0and5.4mgL−1.Theformofnitrogeninthewastewaterwasmostlyammonia(17.6–108.4mgL−1).Moreover,nitrite(3.8–37.3mgL−1)andnitrate(0.0to26.6mgL−1)wereOftendetectedduringtheoperations.Phosphateswerenotdetected(<0.1mgL−1)inthewastewateralthoughlargeamountsofsulfatewereobserved(2412–13,176mgL−1).2.3.PackedgelenvelopeN.europaeaandP.denitrificanscellswereharvestedbycentrifugation(20,000g,10min,4◦C)andwashed3timeswithphosphatebuffercontaining9.0gL−1ofNa2HPO4·12H2Oand1.5gL−1KH2PO4(pH7.5).N.europaea(dryweight,4mgmL−1)andP.denitrificans(dryweight,3.4mgmL−1)cellsweresuspendedinphosphatebuffer.ThesuspensionwasthenmixedwiththephotocrosslinkablepolymerPVA-SbQ(SPP-H-13;ToyoGoseiKogyoCo.)intheratioof1:3.Eachpackedenvelope(envelopeI)(1100mm×1100mm×12mm)consistedofaframemadeofvinylchloride,andnonwovennetsmadeofpolyethyleneterephthalate(G2260-1S;TorayCo.)wereattachedtoboththeaspectsoftheframe(Fig.1aandb).Theabovementionedbacteria–polymermixturewasspreadonthenonwovennetoftheenvelopeandwasgelledbyirradiatingwithmetalhalidelampsfor20min(1000molm−2s−1).Asthebacteria–polymermixturepenetratedintothenonwovennetslightly,thegelwassolidifiedonthenonwovennet.Theheightandwidthofgelsheetwereboth1000mm.Thethicknessofthegelsheetonthenetwas0.5mm.Next,thesameprocedurewasfollowedfortheoppositesideoftheenvelope.Astheenvelopehadtwogelsheetsandone-sidedsurfaceofeachgelsheetcouldbecontactedwithwastewater,theareaofactiveregionwas2.00m2intheenvelopeI.ThisvaluewasusedasunitgelareaforeachenvelopeI.Inaddition,athinnerpackedenvelope(envelopeII)(1250mm×1100mm×3.5mm)wasdevelopedusingthesamenonwovennetwithoutaframe(Fig.1candd).Thebacteria–polymermixturewasspreadonthenonwovennetofopenenvelopeII,andwasgelledbysameway.Theheightandwidthofgelsheetwere1200and1050mm,respectively.Thethicknessofthegelsheetwasalso0.5mm.Aftergelation,thenonwovennetimmobilizingbacteriawasfoldedasthegelsheetoutsideandmadetoanenvelope.Theareaofactiveregionwas2.52m2intheenvelopeII.ThisvaluewasusedasunitgelareaforeachenvelopeII.Thesepackedgelenvelopescontainedinternalspacesforinjectingtheelectrondonor.Threeholesweremadeatthetopofeachenvelope,andpolyurethanetubes(outerdiameter,8mm;innerdiameter,6mm)wereattachedtotheholes.Twoholesweremadeastheoutletsfornitrogengasafterdenitrification,andonecentralholewasmadetoinjecttheelectrondonorfordenitrification.2.4.BioreactorsystemAlarge-scalebioreactorsystemwasinstalledintheTakeharathermalpowerplant.Thesystemconsistedofareactortank(1.23m×1.13m×1.50m);anoverflowtank(0.29m×1.13m×1.50m);aneutralizationtankforpHadjustment;packedgelenvelopes;pumpsforwastewatercirculation;ablowerforaeration;afeederfortheelectrondonor;metersandrecordersfortemperature,pH,anddissolvedoxygenconcentrationinthereactortank;andacontrolpanel.Fig.2showstheschematicdiagramsofthesystemduringbatchandcontinuousoperations.2.5.BatchoperationThebatchoperationswerecarriedoutovernightusing10packedgelenvelopes(envelopeI)withframescontainingN.EuropaeaandP.denitrificans(Fig.1aandb)undervariousammoniaconcentrationsbyaddingammoniumsulfate.Desulfurizationwastewater(containingmostlyammonia,andsomenitriteandnitrate)originatingfromthethermalpowerplantwastreatedintheabovementionedbioreactorsystem(workingvolume,2.3m3).For50mLof10%ethanolsolution,phosphate(Na2HPO4·12H2O,0.09gL−1andKH2PO4,0.015gL−1)andtraceelements(MgSO4·7H2O,2mgL−1;CaCl2·2H2O,0.1mgL−1;NaHCO3,5mgL−1;EDTA-Fe,0.05mgL−1;ZnSO4·7H2O,1mgL−1;MnCl2·4H2O,0.3mgL−1;H3BO3,3mgL−1;CoCl2·6H2O,2mgL−1;CuCl2·2H2O,0.1mgL−1;NiCl26H2O,0.2mgL−1;andNa2MoO4·2H2O,0.3mgL−1)wereadded;thissolutionwasinjectedintotheinternalspaceofeachenvelopeevery6h.Thewastewaterwassampledforanalysisduringthebatchoperation.2.6.ContinuousoperationThewastewaterwascontinuouslytreatedusingthedevelopedbioreactorsystem(workingvolume,1.8m3)with30thinnerpackedenvelopes(envelopeII)withoutframes(Fig.1candd)attheinflowratesof0.075(operation1)or0.45(operation2)m3h−1(averageresidencetime,24or4h)fornearlyonemontheach.Every6h,40mLof10%ethanolsolutionwasinjectedintoeachenvelope(160mLday−1foreachenvelope).Thewastewaterwassampledforanalysisevery4hfrom9:00a.m.to9:00p.m.Aheaterwasusedforwarmingthewastewaterduringwinter.2.7.AnalyticalmethodsThenitrogenconcentrationsweremeasuredasNH3–N,NO2–N,andNO3–N.Theammoniaconcentrationinthewastewaterwascolorimetricallymeasuredaccordingtoapreviouslydescribedmethod[9].Thenitriteandnitrateconcentrationsweredeterminedusinganion-chromatoanalyzer(DX-AQ;DionexCo.)withanIonPacAS12Acolumn.TheTOCconcentrationwasmeasuredusingaTOCanalyzer(TOC-650;TorayEngineeringCo.).3.Results3.1.Batchoperationusingammonia-containingwastewaterWhenthewastewatercontainingvariousconcentrationsofammoniawastreatedwith10packedgelenvelopes(envelopeI)withframescontainingN.europaeaandP.denitrificans,theammoniaconcentrationinthewastewaterdecreasedgradually(Fig.3).Asmallamountofnitratewasdetected(maximum,2.6mgL−1)duringallbatchoperations.Asaresult,thetotalnitrogenconcentration(ammonia,nitrite,andnitrate)inthewastewaterdecreasedgradually.TheTOCconcentrationinthewastewaterwasunchanged(average,2.1mgL−1).ThepHinthewastewaterrangedbetween7.9and8.4.Thetemperatureinthewastewaterrangedbetween22.0and29.0◦C.Theammoniaoxidationrate(thetransformationofammoniatonitrite)by10envelopes(envelopeI)wascalculatedbasedonthechangeinammoniaconcentrationevery2hduringbatchoperations.Thesystemyieldedammoniaoxidationratesintherangeof1.0–9.6gday−1persquaremeterofthegelareaatvariousinitialconcentrationsofammonia.Additionally,thenitrogenremovalrate(thetransformationofammonia,nitrite,andnitratetonitrogengas)wascalculatedbasedonthechangeinthetotalnitrogenconcentrationevery2hduringbatchoperations.Thesystemyieldednitrogenremovalratesintherangeof1.2–19.5gday−1persquaremeterofthegelarea.TherelationshipbetweenthenitrogenconcentrationandnitrogenremovalrateduringthebatchoperationisshowninFig.4.Therateofammoniaoxidationwasproportionaltotheammoniaconcentration.Moreover,therateofnitrogenremovalwasproportionaltothetotalnitrogenconcentration.Hence,thehigherthetotalnitrogenconcentrationinthewastewater,thehigherwasthenitrogenremovalrate.3.2.Nitrogenremovalincontinuousoperationusingammonia-containingwastewaterThegelareaofallenvelopesperworkingvolumehasaneffectonthevolumetricnitrogenremovalperformance.Newthinnerpackedgelenvelopes(envelopeII)weredevelopedusingnonwovennetsmadeofpolyethyleneterephthalatesoastoincreasethetotalnumberofthepackedgelenvelopescapableofintroducingintothereactortank,namely,thegelareaofallenvelopesperworkingvolume.Assumingthatthenitrogenremovalperformancepergelareaofeachenvelopeinthemodifiedenvelopes(envelopeII)wasequivalenttothatobtainedintheoriginalenvelopes(envelopeI),thevolumetricnitrogenremovalperformanceusingthemodifiedenvelopeswasestimatedtobetwiceashighasthatusingtheoriginalenvelopes.Sincethemodifiedenvelopesappearedpromisingfortreatinglargevolumesofwastewater,30modifiedenvelopeswereusedduringthecontinuousoperation.Thewastewaterwascontinuouslytreatedwith30modifiedpackedgelenvelopes(envelopeII)fornearlyonemontheach.Thetime-dependentchangesinthenitrogenconcentrationsintheinflowandoutflowattheinflowrateof0.075m3h−1(operation1)areshowninFig.5a.Thetotalnitrogenconcentrationintheinflow(37.6–127.1mgL−1)fluctuatedabruptlyasaresultofthesuddenvariationintheammoniaconcentrationintheinflow(17.6–108.4mgL−1).Comparedtotheammoniaconcentration,theconcentrationsofnitrite(11.9–26.0mgL−1)andnitrate(1.6–7.7mgL−1)intheinflowdidnotfluctuate.Theammoniaconcentrationintheoutflowwasmaintainedatalowlevel(average,1.3mgL−1)duringthecontinuousoperation.Theconcentrationsofnitrite(below4.9mgL−1)andnitrate(below1.9mgL−1)intheoutflowwerealsolow.Asaresult,thetotalnitrogenconcentrationintheoutflowrangedbetween0.4and9.0mgL−1(average,3.7mgL−1).Thetime-dependentchangesinthenitrogenremovalratesandefficienciesataninflowrateof0.075m3h−1(operation1)areshowninFig.5bandc.Theratesofammoniaoxidationandnitrogenremovalwerecalculatedbasedonthedifferencesbetweentheconcentrationsofammoniaandtotalnitrogenbothintheinflowandintheoutflow.Theammoniaoxidationraterangedbetween0.4and2.6gday−1persquaremeterofthegelarea,andthenitrogenremovalratewasintherange0.9–2.9gday−1persquaremeterofthegelarea(Fig.5b).Theammoniaandnitrogenremovalefficiencies,whichweredefinedastheratiosofthedifferencesbetweentheconcentrationsofammoniaandtotalnitrogenintheinflowandoutflowtotheconcentrationsofammoniaandtotalnitrogenintheinflow,werecalculatedfromtheconcentrationsofammoniaandtotalnitrogenintheinflowandoutflow.Thebioreactorwith30modifiedenvelopes(envelopeII)removedmostoftheammonia(averageremovalefficiency,97.1%)andtotalnitrogen(averageremovalefficiency,95.0%)inthewastewater(Fig.5c).TheaverageTOCconcentrationsintheinflowandoutflowwere0.4and4.8mgL−1,respectively.ThepHinthewastewaterrangedbetween7.2and8.4.Thetemperatureinthewastewaterwasmaintainedbetween25.0and32.0◦Cbyusingaheater.Theresultsrevealedthatthemodifiedenvelopescouldachievehighnitrogenremovalefficiency.However,themaximumnitrogenremovalrateataninflowrateof0.075m3h−1wasnotveryhigh,i.e.,2.9gday−1persquaremeterofthegelarea;thiswasprobablyduetothelownitrogenloadinthereactortank.Thetime-dependentchangesinthenitrogenconcentrationsintheinflowandoutflowataninflowrateof0.45m3h−1(operation2)areshowninFig.6a.Thetotalnitrogenconcentrationintheinflow(76.2–130.1mgL−1)fluctuatedabruptlyduetothesuddenvariationintheammoniaconcentrationintheinflow,whiletheconcentrationsofnitriteandnitrateintheinflowwereunchanged.Theammonia,nitrite,andtotalnitrogenconcentrationsintheoutflowvariedduetotheabruptfluctuationintheammoniaconcentrationintheinflow(43.9–104.1mgL−1).Thenitrateconcentrationintheoutflowwasunchanged.Thetime-dependentchangesinthenitrogenremovalratesandefficienciesattheinflowrateof0.45m3h−1(operation2)areshowninFig.6bandc.Themaximumammoniaoxidationrateachievedwas9.5gday−1persquaremeterofthegelarea.Thebioreactorcapableofsimultaneousnitrificationanddenitrificationachievedamaximumnitrogenremovalrateof6.0gday−1persquaremeterofthegelarea.Thismaximumrateobtainedusingthethinnerenvelopeswasequivalenttothatobtainedwiththeoriginalenvelopes.Duringthefirst5days,theaverageratesofammoniaoxidationandnitrogenremovalwere3.7and3.2gday−1persquaremeterofgelarea,respectively.Theseratesincreasedto4.9and3.5gday−1persquaremeterofthegelareainthenext5–10days,andfurtherincreasedto7.1and4.7gday−1persquaremeterofthegelareaafter10days.Theammoniaandtotalnitrogenremovalefficienciesrangedfrom24.1%to95.8%andfrom13.5%to45.0%,respectively.TheaverageTOCconcentrationsintheinflowandoutflowwere1.6and0.9mgL−1,respectively.ThepHinthewastewaterrangedbetween7.3and8.5.Thetemperatureinthewastewaterwasmaintainedbetween25.0and32.0◦Cbyusingaheater.4.Discussion4.1.NitrogenremovalperformanceunderbatchoperationThebioreactor(workingvolume,0.25L)containingeightpackedgelenvelopes(height,100mm;length,48mm;thickness,0.5mm;gelarea,0.0096m2)yieldedamaximumammoniaoxidationrateandmaximumnitrogenremovalrateof5.6and5.0gday−1persquaremeterofthegelarea,respectively,inthelaboratoryexperiment[8].Thepackedgelenvelopescapableofsimultaneousnitrificationanddenitrificationshouldbescaledupinordertotreatlargeamountofactualwastewater.Thus,thepackedgelenvelopescontainingN.europaeaandP.denitrificans(height,500mm;length,1000mm;thickness,16mm;gelarea,0.72m2)wereenlargedandthenitrogenremovalperformancewasexaminedinthepreliminaryexperiments.Whentheartificialammonia-containingwastewaterwastreatedusingalaboratorybatchsystem(workingvolume,0.35m3)withtwopackedgelenvelopes,itexhibitedamaximumammoniaoxidationrateandmaximumnitrogenremovalrateof6.9and4.6gday−1persquaremeterofthegelarea,respectively(datanotshown).Sincetheenlargedpackedgelenvelopesachievedsimilarperformance,packedgelenvelopesoffunctionalsize(envelopeI)(height,1100mm;length,1100mm;thickness,12mm;gelarea,2.00m2)weredevelopedforthescaling-upofthesysteminordertotreatlargevolumeoftheactualindustrialwastewater.Themaximumammoniaoxidationandnitrogenremovalrates,whichwerecalculatedfromthedifferencesintheammoniaandtotalnitrogenconcentrationsatthestarttimeandafter21.5h,were5.9and7.1gday−1persquaremeterofthegelarea,respectively,duringthebatchoperation.Thelargescalesystemwiththefunctionalpackedgelenvelopesexhibitedhighperformance.Particularly,thenitrogenremovalrateachievedinthisresearchwashigherthanthoseobtainedinotherexperiments,probablyduetothepresencenotonlyammoniabutalsonitriteintheinletwastewater.Theratesofammoniaoxidationandnitrogenremovalwereproportionaltotheconcentrationsofammoniaandtotalnitrogen,respectively.BecausemolecularoxygenwasnecessaryforammoniaoxidationbyN.europaea,nitrificationwascarriedoutontheoutersurfaceofthegel[10].Incontrast,thedenitrificationbyP.denitrificanswascarriedoutintheinsideofthegelsinceitrequiredananaerobicenvironment[10].Thus,fornitrification,ammoniashouldbediffusedneartheoutersurfaceofthepackedgelenvelopes.Fordenitrification,nitrite—whichpreexistedinthewastewaterandwasoxidizedfromammoniabyN.europaeaontheoutersurfaceofenvelopes—andnitrateshouldbeintroducedintotheinnerpartofthepackedgelenvelopebydiffusion.Becausetherateofdiffusionofammoniaintothepackedgelenvelopeswasproportionaltotheammoniaconcentration,theammoniaoxidationratewasthoughttobeproportionaltotheammoniaconcentration.Further,thenitrogenremovalperformanceappearedtobeproportionaltothetotalnitrogenconcentrationasthediffusionofammonia,nitrite,andnitrateintotheenvelopeswasproportionaltothetotalnitrogenconcentration.Thiswascausedbythediffusionofnitrogenintotheenvelopes.Thus,inthissystem,thediffusionofnitrogenintothepackedgelenvelopewasoneofthelimitingfactorsfornitrogenremovalperformance.Theintensityofwastewaterflowdecreasesthethicknessoftheinterfacialfilm.Thismayimprovethediffusionaffectingthenitrogenremovalperformance.4.2.UtilizationefficiencyofelectrondonorfordenitrificationAnelectrondonor(e.g.,ethanol)isrequiredfordenitrification.Thetheoreticalmaximumrateofnitrogenremovalpersquaremeterofthegelareawascalculatedasfollows:Rmax=abcA(1)whereAisthegelareaofeachenvelope(m2),aistheabsoluteethanolvolumeinjectedintoeachenvelopeperday(mlday−1),bisthepurityofethanolused,cisthenitrogenmasscapableofdenitrifyingperethanolmass(gg−1),Rmaxisthetheoreticalmaximumnitrogenremovalratepersquaremeterofthegelarea(gm−2day−1),andistherelativedensityofethanolat20◦C(gml−1).Inthiscase,thevaluesofA,b,andwere2.52m2,0.995,and0.789gml−1,respectively.Inthecontinuousoperation,since160mLofa10%ethanolsolutionwasinjectedintoeachenvelopeperday,thevalueofawas16mLday−1.Thechemicalreactionoccurringduringthedenitrificationofnitritebytheuseofethanolisasfollows:4NO2−+C2H5OH→2N2+2CO2+H2O+4OH−(2)Thus,1molofethanolcandenitrify4.0molofnitrite,andtheValueofcwas1.22gg−1.Asaresult,thetheoreticalmaximumnitrogenremovalratepersquaremeterofthegelareawascalculatedtobe6.1gm−2day−1.Inthisstudy,sincethemaximumnitrogenremovalrateachievedinthecontinuousconditionwas6.0gday−1persquaremeterofthegelarea,themaximumethanolutilizationefficiencywas98.4%.Intheactivatedsludgesystem,thenitriteoxidizedfromammoniabytheammonia-oxidizingbacteriawasfurtheroxidizedtonitratebythenitrite-oxidizingbacteria.Thechemicalreactionoccurringinthedenitrificationofnitratebytheuseofethanolisasfollows:12NO3−+5C2H5OH→6N2+10CO2+9H2O+12OH−(3)Thus,1molofethanolcandenitrifyonly2.4molofnitrate.Ontheotherhand,inthepresentsystem,therewasnonitrateaccumulationinthewastewatersincethedenitrificationofnitriteoccurreddirectly.Asaresult,theethanolrequirementinthepresentsystemwastheoretically60%ofthatintheactivatedsludgesystem.Intheactivatedsludgesystem,theamountofelectrondonorempiricallyinjectedforthedenitrificationstepwastwicethatofthetheoreticalrequirement.Thus,thepresentsystemcandecreaseethanolrequirementto30%ascomparedwiththeactualinput.Infact,thepresentsystemwiththemodifiedpackedgelenvelopes(envelopeII)couldusetheelectrondonor(e.g.,ethanol)effectivelyinthisstudy.TheTOCconcentrationintheoutflowwasmaintainedatalowlevel(averageconcentrationswere4.8and0.9mgL−1athydraulicretentiontimeof24and4h,respectively)throughthecontinuousoperation.Ontheotherhand,intheanoxicdenitrificationbioreactorcontainingpackedgelenvelopesinwhichonlyP.denitrificanscellswereimmobilized,ahighlevelofTOCwaspresentintheoutflowwhenthetotalnitrogenconcentrationwasrelativelylow[11].Thisdifferencewascausedbytheinstallationofanaerationsysteminthispilottest,indicatingthatmoderateaerationinthereactortankisconsiderablyeffectiveindecreasingtheTOCconcentrationintheoutflow.Thus,ourbioreactordoesnotrequireanadditionalaerobictanktoremovesurpluselectrondonorsreleasedfromthepackedgelenvelopesandasettlingtanktosegregatesurplussludgecontainingbacteriafromthewastewater.Thisconceptofusingthepackedgelenvelopeswouldbehighlyeffectiveforconstructingasimpleandefficientnitrogenremovalsystemcapableofsimultaneousnitrificationanddenitrification.4.3.VolumetricnitrogenremovalperformanceThemodifiedpackedgelenvelopes(envelopeII)exhibitedmaximumnitrogenremovalrateof6.0gday−1persquaremeterofthegelarea.Thisvaluecorrespondedtothevolumetricnitrogenremovalperformanceof0.252kgm−3day−1.Thevolumetricnitrogenremovalperformances(NH3→N2)ofthenitrogenremovalsystemsusingimmobilizedcellsaresummarizedinTable1.Thewater-jacketedglasscolumnreactorcouldremove80mgofnitrogen(200mLof400mgL−1ammoniamedium)forapproximately100h[7].Thevolumetricnitrogenremovalperformancewascalculatedas0.61kgm−3day−1.Thenitrogenremovalrateof5.1mmols−1percubicmeterofthegel(gelload,25%)wasachievedinabubblecolumnreactorusingdouble-layerbeadswithcoimmobilizedN.europaeaandPseudomonassp.[5].Thisratewasequivalenttothevolumetricnitrogenremovalperformanceof1.54kgm−3day−1.Ontheotherhand,thenitrogenremovalsystemusingimmobilizedmicroorganismsachievedanitrogenremo