生物工程专业毕业设计英文翻译生物工程

High-RateContinuousProductionofLacticAcidbyLactobacillusrhamnosusinaTwo-StageMembraneCell-RecycleBioreactorSunhoonKwon,Ik-KeunYoo,WooGiLee,HoNamChang,YongKeunChangDepartmentofChemicalEngineeringandBioProcessEngineeringResearchCenter,KoreaAdvancedInstituteofScienceandTechnology,373-1Kusong-dong,Yusong-gu,Taejon305-701,SouthKorea;E-mail:hnchang@kaist.ac.krAbstractItisimportanttoproduceL(+)-lacticacidatthelowestcostpossibleforlacticacidtobecomeacandidatemonomermaterialforpromisingbiodegradablepolylacticacid.Inanefforttodevelopahigh-ratebioreactorthatprovideshighproductivityalongwithahighconcentrationoflacticacid,theperformanceofmembranecellrecyclebioreactor(MCRB)wasinvestigatedviaexperimentalstudiesandsimulationoptimization.Duetogreatlyincreasedcelldensity,highlacticacidproductivity,21.6gL−1h−1,wasobtainedinthereactor.Thelacticacidconcentration,however,couldnotbeincreasedhigherthan83g/L.Whenanadditionalcontinuousstirredtankreactor(CSTR)wasattachednexttotheMCRBahigherlacticacidconcentrationof87g/Lwasproducedatsignificantproductivityexpense.WhenthetwoMCRBswereconnectedinseries,92g/Llacticacidcouldbeproducedwithaproductivityof57gL−1h−1,thehighestproductivityamongthereportsofL(+)-lacticacidthatobtainedlacticacidconcentrationhigherthan85g/Lusingglucosesubstrate.Additionally,theinvestigationoflacticacidfermentationkineticsresultedinasuccessfulmodelthatrepresentsthecharacteristicsoflacticacidfermentationbyLactobacillusrhamnosus.ThemodelwasfoundtobeapplicabletomostoftheexistingdatawithMCRBsandwasingoodagreementwithLevenspiel’sproduct-inhibitionmodel,andtheLuedeking-Piretequationforproduct-formationkineticsappearedtobeeffectiveinrepresentingthefermentationkinetics.Therewasadistinctivedifferenceintheproductionpotentialofcells(cell-density-relatedparameterinLuedeking-Piretequation)aslacticacidconcentrationincreasesover55g/L,andthisfindingledtoamorepreciseestimationofbioreactorperformance.©2001JohnWiley&Sons,Inc.BiotechnolBioeng73:25–34,2001.Keywords:Lactobacillusrhamnosus;lacticacid;highproductivity;cellrecycle;membranebioreactor

INTRODUCTIONTheefficiencyofthemembranecell-recyclebioreactor(MCRB)wassuccessfullydemonstratedinanumberofpreviousstudiesofthehigh-volumetricproductivityoflacticacid.Withgreatlyincreaseddensityofbiocatalysts,i.e.,microbialcells,thevolumetricproductivityoflacticacidcouldgoupto160gL−1h−1asreportedinthestudyofOhleyeretal.(1985),whichismorethan20timeshigherthanthatoftheconventionalbatchandchemostatprocesses.However,thehighproductivityisnottheonlyrequirementfortheeconomicfeasibilityoftheprocess.TimmerandKromkamp(1994)foundthattheprocessmightbeprimarilyinfluencedbyproductioncapacityandproductconcentrationandtoalesserextentbythevolumetricproductivitywhenannuallacticacidproductioncapacityrosetoashighas4540metrictons.Incaselacticacidconcentrationissignificantlylow,theenergycostforwaterremovalinthedownstreamprocessoffsetsthebenefitsoftheincreasedproductivity.Fromthispoint,MCRBhasanimportantproblemtobetackled:Theconcentrationsoflacticacidaresignificantlylowwhencomparedwithbatchprocesseswherethelacticacidconcentrationabove120g/Liseasilyattainable.Exceptforareportshowing117g/LD(−)-lacticacidwithavolumetricproductivityof84gL−1h−1(MehaiaandCheryan,1987),allotherMCRBoperationsresultedinlacticacidconcentrationsoflessthan90g/Land,moreover,mostofthemhadconcentrationsbelow60g/L(Cheryan,1998;Litchfield,1996;Ohleyeretal.,1985).ThemicroorganismscannotgrowaboveacertainrangeoflacticacidconcentrationandtheMCRBsarerunundercontinuousmannerwithcontinuousbleedingofcellstopreventthelossoffluiditythatoccurswhencellconcentrationgoestoohigh.Thus,toenhancetheeconomicaladvantageoftheMCRBprocess,methodsthatincreasethelacticacidconcentrationalongwiththehigh-celldensityarerequired.Someauthors,whoconsideredthispersistentproblemoflow-productconcentration,conductedstudiestoobtainhigherlacticacidconcentrationinMCRB.Xavieretal.(1995)reportedalacticacidconcentrationof90g/Lwithaproductivityof36gL−1h−1,whileTejayadiandCheryan(1995)achieved89g/Land22gL−1h−1oflacticacidconcentationandproductivity,respectively.Atypicalapproachtoovercometheabove-mentionedproblem,alow-productconcentrationduetosevereproductinhibition,istheuseofaplug-flowreactor,whichcanbeapproximatedbyseveralcontinuous-stirred-tankreceptors(CSTRs)inseries(deGooijeretal.,1996;KellerandGerhardt,1975;LuedekingandPiret,1959b;Levenspiel,1984).TheadvantagesoftheCSTRs-in-seriesagainstasingleCSTRespeciallyinlacticacidproductionwererevealedbyothersintwo-andthree-stageCSTRs(Aeschlimannetal.,1990;Bruno-Ba´rcenaetal.,1999;Mulliganetal.,1991):increasedproductivityandconcentrationoflacticacidviapartlyseparatingcellgrowthandlacticacidproductionphases;increasedlacticacidyieldattheexpenseofbiomassformationatalatterstage;highpurityofthelacticacidisomer,L(+)-lacticacidviaincreasedpopulationoffreshcells;andreducedusageofacostlynutrient,yeastextract.Inanefforttocombinetheadvantageofboththebioreactorconfigurations—MCRBandmulti-stagedbioreactor—Kuloziketal.(1992)investigatedtheperformanceofaseven-stagedcascadereactorwithcellrecycle.Cellsintheoutflowofthelastreactorwerefivefoldconcentratedbyamicrofilterandrecycledbacktothefirstreactor.Incomparisonwithasingle-stageMCRB,thecascadereactorshowed4timeshigherproductivity,28gL−1h−1,withcompleteutilizationof100g/Llactose,inwhichthecellconcentrationsweremaintainedat20g/Landthelacticacidconcentrationswerearound72g/L.Inthisstudy,theperformanceofanewbioreactorconfiguration,twoMCRBsinseries,wasinvestigatedaimingatthehighestvolumetricproductivityeverobtainedalongwiththelacticacidconcentrationashighaspossible.Moreover,asimulationstudywasconductedtoestimatetheperformancelimitofMCRBwithanunstructuredkineticmodel,whichisvalidatedbytheexperimentresults.MATERIALSANDMETHODSMicroorganismandCultureConditionsLactobacillusrhamnosus(ATCC10863),anobligatoryanaerobichomofermentativeL(+)-lacticacidproducer,wasobtainedfromAmericanTypeCultureCollection(Rockville,MD).One-mLstockcultureswerestoredat−76°CinLactobacilliMRSmedium(Difco,Detroit,MI)with25%(v/v)glycerol.Precultureswerepreparedbytransferringastockcultureto200mLofMRSmediumandincubatedat42°Cfor12handtransferredtothemainculture.Theculturetemperaturewas42°CandtheculturepHwascontrolledat6.0withammoniawater(ca.8N).ForMCRBoperationsthebasalmediumhadthefollowingcomponentsperliter:0.2gNa3-Citrate·2H2O,1.0gKH2PO4,0.2gMgSO4·7H2O,0.03gMnSO4·H2O,0.03gFeSO4·7H2O,and0.015mLsulfuricacid.TheconcentrationsofglucoseandyeastextractwillbedescribedintheResultssection.Allthemediacomponentswereheatsterilizedtogetherat121°Cfor100minexceptforyeastextractthatwasseparatelysterilizedfor15min.Theculturevolumenotedintheresultsincludesthebrothvolumeintherecyclestream.AnalyticalMethodsCellgrowthwasmeasuredbyaspectrophotometer(PharmaciaUltrospec3000,Cambridge,UK)atawavelengthof620nm.Drycellconcentrationwascalculatedfromtheopticaldensity(OD620)withalinearcorrelationfactor(oneOD62040.32g-drycellweightperliter).Concentrationsoflacticacidandglucoseweredeterminedbyahighperformanceliquidchromatography(HPLC)systemequippedwitharefractive-indexdetector(HitachiL-6000,Tokyo,Japan).AnHPLCcolumn(Aminex87H,Bio-Rad,Richmond,CA)wasusedwith0.005Msulfuricacidasthemobilephaseatanelutionspeedof0.6mL/minwhilethecolumntemperaturewasmaintainedat50°C.Theconcentrationstandardsof1.0Mlacticacid(Fluka,Buchs,Switzerland)and10g/Lglucose(Sigma,St.Louis,MO)wereusedfortheHPLCanalysis.MembraneCell-RecycleBioreactor(MCRB)Intheexperimentsofasingle-stageMCRB,a400-mLwater-jacketedglassreactorwasemployed,thatwasequippedwithahollow-fiberfiltrationunitUFP-100-H-4X2TCA(100kNMWC,0.065m2filtrationarea;A/GTechnologyCorporation,MA).Aperistalticpump,07090-40(Cole-Parmer,IL)wasusedtocirculatetheculturebroththroughthemembraneunitwithaflowrateofca.100mL/min.Forthetwo-stageoperations,twoidenticalMCRBswereseriallyconnected.EachMCRBconsistedofa1-Lglassreactorattachedwithaplate-and-framefiltrationunit,Pellicon2BIOMAX100V(100kNMWC,0.1m2filtrationarea,Millipore,Bedford,MA),andadiaphragmpump,P-07090-40(Cole-Parmer)forcellrecyclewithaflowrateofca.600mL/min.TheMCRBwassterilizedwith50%(v/v)ethanolandwashedthoroughlywithsterilewaterbeforeinoculation.Inoperation,afreshmediumwasfedcontinuouslyintothereactorwhilefilterpermeatewassimultaneouslypumpedout.Topreventthecelldensityfromgoingoveracertainlimit,whichcausesthelossoffilterfunctionality,smallamountsofculturebrothwerecontinuouslydrawnoutfromthereactor(bleedflow).Inthetwostageoperation,thebleedandpermeateflowfromthefirstreactorwerefedtogetherintothesecond.NumericalMethodsTheleastsquaresregressionwasusedtoestimatetheparametersofthefermentationkinetics.Numericalintegrationtofindsteady-statevaluesandconstrainedmultivariableoptimizationtofindtheoptimaloperationvariableswereperformedwiththehelpofasoftwarepackage,Matlab5.0(TheMathworks,Inc.,USA).Theconstraintsutilizedintheoptimizationwerethemaximumcelldensity(Xm)andthemaximumremainingglucoseconcentration(S).DISCUSSIONToincreasethebioreactorperformancefortheproductionoflacticacid,acontinuouslacticacidfermentationsystemcoupledwithmembranecell-separationtechnique(MCRB)hasbeenstudied.Bygreatlyincreasedcelldensityinthereactorvolumetricproductivitycouldbeincreasedover10timesthantheconventionalbatchandcontinuousfermentation.However,theconcentrationoflacticacidproduced,amajorfactorforeconomicfeasibility,couldnotbeincreasedhigherthan95g/Lbeyondwhichcellgrowthisinhibitedalmostcompletely.InthepreliminaryexperimentswithsingleMCRB,lowlacticacidconcentrationsaround51g/Lwereobtainedevenwhenthecelldensitywasmaintainedathigherthan90g/L(Fig.4).WhenaCSTRwith9timeslargervolumethantheMCRBwasattached,intendingforalongerreactiontimeforthecellsintheMCRBoutflow,87g/Llacticacidcouldbeobtainedwithagreatsacrificeintheproductivity(Fig.6).Itwasconcludedthathigherlacticacidconcentrationwithhighproductivitycouldbeobtainableifthesecondreactor,CSTR,hadbeenreplacedwithanotherMCRB,whichmadeupthetwo-stagebioreactorwithcell-recycleatbothstages.WiththetwoMCRBsinseries,92g/Loflacticacidwasobtainedatahighproductivityof57gL−1h−1(Fig.12).Inconclusion,asystematicapproachwithMCRBswithmultistagedoperationcanbecarriedouttopredictoptimalperformancesoflacticacidproduction,whichexperimentallyprovedthattwostageMCRBscanproducelacticacidinahighconcentrationwithgreatlyincreasedvolumetricproductivity(typeA).References[1]AeschlimannA,StasiLD,vonStockarU.1990.ContinuousproductionoflacticacidfromwheypermeatebyLactobacillushelveticusintwochemostatsinseries.EnzymeMicrobTechnol12:926–932.[2]AmraneA,PrigentY.1999.AnalysisofgrowthandproductioncouplingforbatchculturesofLactobacillushelveticuswiththehelpofanunstructuredmodel.ProcBiochem34:1–10.[3]BerryAR,FrancoCMM,ZhangW,MiddelbergAPJ.1999.GrowthandlacticacidproductioninbatchcultureofLactobacillusrhamnosusinadefinedmedium.BiotechnolLett21:163–167.[4]BibalB,KappC,GomaG,PareilleuxA.1989.ContinuouscultureofStreptococcuscremorisonlactoseusingvariousmediumconditions.ApplMicrobiolBiotechnol32:155–159.[5]BibalB,VayssierY,GomaG,PareilleuxA.1991.HighconcentrationcultivationofLactococcuscremorisinacell-recyclereactor.BiotechnolBioeng37:746–754.[6]Bo¨rgardtsP,KrischkeW,Tro¨schW,BrunnerH.1998.Integratedbioprocessforthesimultaneousproductionoflacticacidanddairysewagetreatment.BioprocessEng19:321–329.[7]Bruno-Ba´rcenaJM,RagoutAL,CordobaPR,Sin˘erizF.1999.ContinuousproductionofL(+)-lacticacidbyLactobacilluscaseiintwo-stagesystems.ApplMicrobiolBiotechnol51:316–324.[8]CheryanM.1998.Ultrafiltrationandmicrofiltrationhandbook.Lancaster,PA:TechnomicPublishingCompany.467p.[9]deGooijerCD,BakkerWAM,BeeftinkHH,TramperJ.1996.Bioreactorsinseries:Anoverviewofdesignproceduresandpracticalapplications.EnzymeMicrobTechnol18:202–219.[10]DuttaSK,MukherjeeA,ChakrabortyP.1996.Effectofproductinhibitiononlacticacidfermentation:Simulationandmodelling.ApplMicrobiolBiotechnol46:410–413.[11]Gonc¸alvesLMD,XavierAMRB,AlmeidaJS,CarrondoMJT.1991.Concomitantsubstrateandproductinhibitionkineticsinlacticacidproduction.EnzymeMicrobTechnol13:314–319.[12]KellerAK,GerhardtP.1975.Continuouslacticacidfermentationofwheytoproducearuminantfeedsupplementhighincrudeprotein.BiotechnolBioeng17:997–1018.[13]KulozikU,Ha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利用鼠李糖乳杆菌在两级细胞膜循环生物反应器中高速连续生产乳酸——SunhoonKwon，YongKeunChang单位：韩国高等科学技术学院，化学与生物工程研究中心，E-mail:hnchang@kaist.ac.kr摘要众所周知，乳酸是可生物降解材料聚乳酸的主要原料，所以找到以一种以最低的成本来生产L（+）－乳酸的方法具有非常重大的意义。为了找到一种可以高速地生产高浓度乳酸的生物反应器，我们对膜循环生物反应器（MCRB）的性能进行了研究，并进行了实验仿真优化。由于大大增加了细胞浓度，这个反应器的乳酸生产力可达到21.6gL-1h-1。但乳酸浓度却不能超过83g/L，当额外增加一个连续搅拌反应釜（CSTR）附到MCRB旁边时，可以大幅度的提高生产速率，乳酸浓度也可以提高到87g/L，当两个MCRBs串联在一起时，乳酸的生产力速率达到57gL-1h-1，最终溶液中的乳酸浓度为92g/L，这比以前所报道的使用葡萄糖基生产L（+）乳酸浓度超过85g/L的最高的生产率还要高。此外，研究乳酸发酵动力学产生了以鼠李糖乳杆菌发酵生产乳酸为代表的成功典范，该模型被认为是适用于大多数现有的MCRBs的数据，并且很好地吻合了Levenspiel的产品抑制模型，Luedeking-Piret产品形成动力学方程似乎是有效的代表发酵动力学。然而具有生产潜力的细胞（细胞密度相关参数Luedeking-Piret方程）生产乳酸的浓度超过55g/L时，却又有一个与众不同的差异，而这一结果会让我们更进一步地精确估计生物反应器的性能。©2001JohnWiley＆Sons出版公司生物Bioeng73：25-34，2001。关键词：鼠李糖乳杆菌;乳酸;高生产力;细胞循环;膜生物反应器

1前言膜细胞循环生物反应器（MCRB）的生产效率成功地证实了一些以往关于高容积生产乳酸的研究。Ohleyer等的研究报告指出，通过大量增加生物催化剂，即微生物细胞，乳酸的生产力可高达160gL−1h−1。（1985年），这比常规批次和恒化的生产工艺高出20倍以上。然而，高生产力并不是唯一的要求，这种工艺还必须在经济上有可行性。TimmerandKromkamp（1994年）发现，这一工艺可能主要受生产能力和产品的集中的影响，在较小程度时当年这种工艺生产乳酸的产能上升到高达4540吨。如乳酸浓度显着低，能源成本中的水在去除抵消下游过程的好处，提高了生产力。从这个角度上讲，MCRB有一个重要的问题有待解决：在乳酸浓度显着低相比，间歇过程的乳酸浓度122g/L的是容易实现的。此外，还有一份报告显示以84gL−1h−1的生产速率得到的D（+）L乳酸最终浓度为117g/L（Mehaia和Cheryan，1987年），而除部分MCRB工艺生产出的乳酸浓度低于90/g/L外所有其他的大多数生产的浓度低于60g/L的（Cheryan，1998年;里奇菲尔德，1996年;Ohleyer等，1985）。微生物无法在超过一定浓度的乳酸条件下生长，因此可以通过用MCRBs工艺进行连续放出细胞，以防止损失的流动性时所产生的细胞浓度不会太高。因此，为加强MCRB工艺的经济优势的方法有，随着高密度的要求增加乳酸浓度。一些考虑到这个长期存在的低浓度产品问题的作者对他进行了研究，并通过MCRB工艺获得了较高浓度的乳酸。哈维尔等人。（1995年）和Tejayadi和Cheryan（1995年）分别发表了以36gL−1h−1的生产速率得到浓度为90g/L的乳酸和以22gL−1h−1的生产速率得到浓度为89g/L的乳酸的报道。产品的浓度低是由于乳酸菌受到了严重抑制，这里有一个很好的办法来克服上述问题，我们可以通过使用推流反应器，它类似于很多连续化搅拌式受体（CSTRs）结合在一起（日Gooijer等。996年;Keller和戈哈德，1975年;Luedeking和Piret，1959年;Levenspiel，1984年）。CSTRs的优势在一系列针对单一CSTR中特别是在乳酸生产中所揭示的其他两个和三个阶段CSTRs（艾绪里曼等人。1990年;布鲁诺-Ba'rcena等。1999年;根等。1991年）通过部分分离细胞的生长和乳酸生产阶段提高乳酸的生产力和浓度，增加乳酸产量为代价的生物形成的后期;高纯度的乳酸异构体长，L（+）乳酸菌通过增加新鲜细胞的数量;同时减少使用昂贵的养分——酵母膏。为了结合双方的优势，生物反应器的配置MCRB和多阶段生物反应器Kulozik等。（1992）进行了一项七级联反应器与细胞循环的研究。最后一个反应器中流出的细胞溶液通过收集器集中再生回到第一座反应器中，相对于单级MCRB，梯级反应器得到的生产率要高出4倍。达到28克L-1h-1，乳糖完整的利用率为100g/L，其中的细胞浓度保持在20g/L和的乳酸浓度约为72g/L。在这项研究中，对新型生物反应器的配置，即两个MCRBs串联的性能进行了研究，旨在在最高容积生产力的情况下不断得到乳酸且其浓度尽可能高。此外，对估计MCRB的性能极限与非结构化的动力学模型，进行了模拟研究，通过这个实验验证了结果。

2材料与方法2.1微生物培养法及培养条件鼠李糖乳杆菌（ATCC10863），一种同型发酵的具有极强的厌氧性的L（+）乳酸生产菌，它是从美国特种培养物保藏中心获得的（位于美国马里兰州罗克维尔市）。一毫升库乳杆菌菌种与（培养基，底特律，MI）和的25％（V/V）的甘油混合后在-76°C的条件下保存，Precultures准备通过在MRS培养基中，在42°C的条件下培养12小时，将菌株培养到200毫升，并转移到主要化。控制培养温度为42℃和通过使用氨水调节pH到6.0，MCRB工艺的培养基要有以下组成部分每升：0.2Na3-Citrate·2H2O，1.0gKH2PO4,0.2gMgSO4·7H2O,0.03gMnSO4·H2O,0.03gFeSO4·7H2O,和0.015mL硫酸。糖的浓度和酵母提取物将在结论中指出。除酵母提取物是单独灭菌15分钟外，所有培养基一起在121°C的条件下灭菌100分钟。在结论中谈到的培养体积包括循环流体培养基的体积。2.2分析方法细胞生长可通过分光光度计在波长为620纳米时测定（法玛西亚Ultrospec3000，英国剑桥）一般可由干细胞浓度与光密度（OD620）的线性相关系数（1OD62040.32克，干重每公升）计算出来。乳酸的浓度和葡萄糖含量可由配备了折射率检测器系统的高效液相色谱仪（HPLC）（日立L型6000，日本东京）测定。HPLC柱使用时（Aminex87H，酶标仪，里奇蒙，CA）以0.005M硫酸为流动相，在洗脱速度为0.6毫升/分钟，而柱温保持在50°C的浓度标准为1.0米乳酸（盐，布克斯，瑞士）和10g/L的葡萄糖（六西格玛，圣路易斯，密苏里州）用于高效液相色谱分析中。2.3膜细胞循环生物反应器（MCRB）在单级MCRB的实验中，要应用到如下实验器材：一；400毫升水套，它采用玻璃反应器并配备了中空纤维超微粒过滤装置-100-H的4X2TCA（100kNMWC，0.065平方米过滤面积;阿/g技术公司，马）。二：蠕动泵，07090-40型（科尔-Parmer，白细胞介素）CA以100毫升/分钟的速度推动发发酵液通过膜单元。在两个阶段的行动，两个相同的MCRBs是串行连接。每个MCRB包括一个1一L玻璃反应堆附有板和帧过滤单元，一个Pellicon2BIOMAX100V的（100kNMWC，0.1平方米过滤面积，超纯水，贝德福德，马）与隔膜泵，和一个P-07090-40（科尔Parmer）的细胞再生装置，其CA流速为600毫升/分钟。MCRB在接种前需要用含50％（V/V）乙醇的无菌水彻底清洗。在操作过程中，需不断向发酵罐中加入新的培养基同时排出产物。为了防止细胞密度去超过一定限度，造成过滤功能下降，需要从发酵罐中不断抽出少量的发酵液。在这两个阶段发酵过程中，从第一阶段流出的发酵液用于第二阶段中。2.4数值分析方法发酵动力学的参数可以用最小二乘回归来估算。利用Matlab5.0（MathWorks公司，公司，美国）软件进行数值积分找到稳态值和约束多变量优化以寻找到最佳操作变量。限制利用的优化是最大的细胞密度（Xm）和最大其余血糖浓度（s）。

讨论为了提高生物反应器产乳酸的性能，我们对连续乳酸发酵系统加上膜细胞分离技术（MCRB）进行了研究。大大增加在固定体积发酵罐中的细胞密度，生产率比传统的间歇和连续发酵提高了10倍以上。然而，乳酸实际生产中，最主要因素经济上的可行性，此方法乳酸浓度高于95g/L时，细胞的生长几乎完全受到抑制。在初步单MCRB实验中，即使在细胞密度保持在高于90g/L时，得到的乳酸浓度仍然很低，约51政/L，（图4）。当加入一个体积比MCRB大9的CSTR时，在放出细胞液之前如果让它在在MCRB反应器中停留更长的时间，则乳酸浓度会明显提升，会达到87g/L图6）。由此我们可以得出这样的结论：在第二个反应器CSTR与另一MCRB相连并且两个阶段的生物反应器与细胞循环同在这两个阶段前提下，可以高速生产高浓度的乳酸，如果使用两个MCRBs系列，则可以以57gL−1h−1的生产速率生产出浓度达到92g/L的乳酸（图12）。最后，通过优化多步骤MCRBs反应器，可以得到预期想得到的最优生产乳酸的方法，实验证明，利用两阶段MCRBs反应器可以高速生产高浓度的乳酸，从而使固定容积反应器的生产效率大大提高（A型）。

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