生化工程刘晓兰通气与搅拌

生化工程BiochemicalEngineering,主讲:Dr.刘晓兰齐齐哈尔大学,第四章通气与搅拌,第一节细胞对氧的需求(Oxygendemandandrespiration)第二节培养过程中的氧传递和速率第三节氧传递速率与细胞呼吸的关系第四节Kla的测定(Klameasurement)第五节反应器搅拌轴功率的计算第六节Kla与设备参数及操作变数之间的关系式第七节反应器中的Kla与其调节,Introduction,搅拌的作用：（1）混合均匀(需功率小)，（2）打碎气泡，有助溶氧（需功率大）。实例：醪液浓度啤酒发酵：较小，产生的二氧化碳使发酵液循环。乳酸发酵：高，4060rpm柠檬酸发酵：较高，110-120rpm,所以，对好氧培养系统，除了均匀混合需要搅拌之外，搅拌的作用是强化溶氧。氧在水中的溶解度很低，培养液溶氧浓度更低，所以搅拌的更重要功能在于:打碎气泡，增加气液接触面积，提高传氧效率。,Theoxygendemandofanindustrialprocessisgenerallysatisfiedbyaerationandagitation.ProductivityislimitedbyoxygenavailabilityandthereforeitisimportanttothefactorsthataffectafermentersefficiencyinsupplyingO2,本章的内容是讨论有关溶氧和搅拌之间的问题，目的是做到既满足细胞对氧的需求，又能尽量降低能量消耗。ThislectureconsiderstheO2requirement,quantificationofO2transferandfactorsinfluencingthetransferofO2intosolution.,4-1细胞对氧的需求Oxygendemandandrespiration,好氧细胞:通过呼吸链获得能量(供细胞的生长代谢使用),需要有分子态的氧作为呼吸链末端的电子受体;此外，氧还直接参与一些生物反应，对于这些细胞，供氧不足就会抑制细胞的生长代谢。兼性厌氧微生物:如酵母菌和乳酸菌，在无氧条件下通过酵解来获得能量。绝对厌氧微生物：其它代谢途径获得能量，氧是一种有害物质。,4.1.1Stoichiometry(化学计量学)ofrespiration,Toconsiderthestoichiometryofrespirationtheoxidationofglucosemayberepresentedas;,C6H12O6+6O2=,6H2O+6CO2,AtomicweightofCarbonHydrogenOxygen,12116,Molecularweightofglucoseis180,Howmanygramsofoxygenarerequiredtooxidise180gofglucose?,Answer192g,SolubilityofOxygen,BothcomponentsoxygenandglucosemustbeinsolutionbeforetheybecomeavailabletomicroorganismsOxygenis6000timeslesssolubleinwaterthanglucoseAsaturatedoxygensolutioncontainsonly10mgdm-3ofoxygenImpossibletoaddenoughoxygentoamicrobialculturetosatisfyneedsforcompleterespirationOxygenmustbeaddedduringgrowthatasufficientratetosatisfyrequirements,Comparisionofconc.anduptakeratesforglucoseandoxygenbyyeast,Problemsencounteredinoxygentransportcanbeillustratedbycomparingtransportofglucosevsoxygen;1%Sugar(glucose)BrothO2sat25oCConc.inbulkbroth10,000ppmapprox.7ppmCriticalconc100ppm0.8ppm(growthstops)Rateofdemand2.8mmoles/gcells/h7.7mmoles/gcells/h,TheOxygenrequirementsofindustrialfermentations,OxygendemanddependantonconvertionofCarbon(C)tobiomassStoichiometryofconversionofoxygen,carbonintobiomasshasbeenelucidated(阐明)UsetheserelationshipstopredicttheoxygendemandforafermentationDarlington(1964)expressedcompositionof100gofdryyeastC3.92H6.5O1.94,O2Requirements,6.67CH2O+2.1O2=C3.92H6.5O1.94+2.75CO2+3.42H2O7.14CH2+6.135O2=C3.92H6.5O1.94+3.22CO2+3.89H2OwhereCH2=hydrocarbonCH2O=carbohydrateFromtheaboveequationstoproduce100gofyeastfromhydrocarbonrequiresthreetimestheamountofoxygenthanfromcarbohydrate.,4.1.2细胞的比耗氧速率（呼吸强度）与氧浓度的关系OXYGENCONC.vsRESPIRATIONRATE(growthrate),细胞的比耗氧速率Respirationrate(QO2)：单位重量的细胞在单位时间内耗氧的量mmolesofoxygenconsumedpergramofdryweight。Theeffectofdissolvedoxygenonthespecificuptakerate(i.erespirationorgrowth)isdescribedby:MichaelisMenton,式中：QO2比耗氧速率molO2/kg干cells（QO2）m：最大比耗氧速率molO2/kg干cellsCL：溶氧浓度mol/m3Ko：氧的米氏常数,DissolvedOxygenConcentration,QO2,Ccritical,EffectofdissolvedO2concentrationontheQO2ofamicroorganism,SpecificO2uptakeincreaseswithincreaseindissolvedO2levelstoacertainpointCcrit,这时的DO值称为临界溶氧浓度。,微生物的临界溶氧浓度大约是饱和浓度的1%25%。,Criticaldissolvedoxygenlevelsforarangeofmicroorganisms,OrganismTemperatureCriticaldissolvedoCOxygenconcentration(mmolesdm-3),Azotobactersp.固氮菌300.018E.coli370.008Saccharomycessp.300.004Penicilliumchrysogenum240.022Azotobactervinelandiiisalarge,obligatelyaerobicsoilbacteriumwhichhasoneofthehighestrespiratoryratesknownamonglivingorganisms,虽然氧在培养液中溶解度很低，但在培养过程中不需要使溶氧浓度达到或接近饱和值，而只要超过某一临界溶氧浓度即可。当CLCcritical，细胞的QO2保持不变，当CLCcritical，细胞的QO2下降，细胞处于半厌氧状态，代谢活动受到影响。微生物的临界溶氧浓度约是饱和浓度的1%25%。,Criticaldissolvedoxygenlevels,TomaximisebiomassproductionyoumustsatisfytheorganismsspecificoxygendemandbymaintainingthedissolvedO2levelsaboveCcritCellsbecomemetabolicallydisturbediftheleveldropsbelowCcritInsomecasesmetabolicdisturbancemaybeadvantageousOrhighdissolvedO2levelsmaypromoteproductformationAminoacidbiosynthesisbyBrevibacteriumflavum（黄色短杆菌）,FACTORSAFFECTINGOXYGENDEMAND,RateofcellrespirationTypeofrespiration(aerobicvsanaerobic)Typeofsubstrate(glucosevsmethane)Typeofenvironment(e.gpH,tempetc.)Surfacearea/volumeratiolargevssmallcells(bacteriavmammaliancells)clumps,flocs,pelletsetc.,4.1.3摄氧率r,摄氧率：单位体积培养液在单位时间内消耗氧量称为摄氧率。r：摄氧率molO2/m3sX:细胞浓度kg/m34.1.4氧的满足度,4.1.4氧的满足度,4.1.5溶氧浓度对细胞生长和产物生成影响的不一致性,很多时候培养的目的不是为了取得细胞而是为了获得代谢产物，而溶氧浓度对细胞生长和产物生成的影响可能是不同的，即对于细胞生长的最佳氧浓度不一定就是生成产物的最佳氧浓度。Hirose等考查了黄色短杆菌生产各种氨基酸时溶解氧浓度的影响。,氧浓度对Brevibacteriumflavum氨基酸生产的影响,微生物次级代谢产物生产与氧浓度的关系,微生物的次级代谢产物生产也有类似的情况。例如Feren等发现：头孢菌素卷须霉素临界氧浓度：Csat的0%7%Csat13%23%生产受抑制：CLCcritical，CLCcritical,4-2培养过程中的氧传递及速率,4.2.1物质传递和相的概念MasstransferandphasesFundamentalconceptinfermentationtechnologyistransferofmaterials(e.gnutrients,products,gasesetc.)throughdifferentphases(e.ggasintoaliquid).,Phasespresentinbioreaction/bioreactor,1=reactantsupplyandutilisation2=productformationandremoval,Majorproblemassociatedwithprovisionofoxygentothecell-isaratelimitingstepandthusservesasamodelsystemtounderstandmasstransfer.,1)Thebulkgasphaseinthebubble2)Thegas-liquidinterphase3)Theliquidfilmaroundthebubble4)Thebulkliquidculturemedium5)Theliquidfilmaroundthemicrobialcells6)Thecell-liquidinterphase7)Theintracellularoxygentransferresistance,4.2.2氧传递过程,氧传递（从气相传递到细胞内）要克服一系列的阻力。阻力大小决定于液体流体力学性质、温度、细胞的活性和浓度，液体的组成，界面特性等。氧传递过程的总推动力就是气相与细胞内的氧分压之差，这一总推动力消耗在从气相到细胞内的各项传递阻力上。,Therateofoxygentransfer=drivingforce/resistance.当氧的传递达到稳定时，总的传递速率与串联的各步传递速率相等NO2氧的传递通量mol/m2s：各阶段的推动力（分压差）Pa：各阶段的传递阻力m2sPa/mol,Therateofoxygentransfer=drivingforce/resistance.E.gresistancetomasstransferfrommediumtocellsarecomplexandmayarisefrom:Diffusionfrombulkgastogas/liquidinterfaceSolutionofgasinliquidinterfaceDiffusionofdissolvedgastobulkofliquidTransportofdissolvedgastoregionsofcellDiffusionthroug