生化工程_刘晓兰_通气与搅拌1

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(Kla–measurement)•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，40~60rpm•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)ofrespirationToconsiderthestoichiometryofrespirationtheoxidationofglucosemayberepresentedas;C6H12O6+6O2=6H2O+6CO2AtomicweightofCarbonHydrogenOxygen12116Molecularweightofglucoseis180Howmanygramsofoxygenarerequiredtooxidise180gofglucose?Answer192gSolubilityofOxygen•Bothcomponentsoxygenandglucosemustbeinsolutionbeforetheybecomeavailabletomicroorganisms•Oxygenis6000timeslesssolubleinwaterthanglucose•Asaturatedoxygensolutioncontainsonly10mgdm-3ofoxygen•Impossibletoaddenoughoxygentoamicrobialculturetosatisfyneedsforcompleterespiration•OxygenmustbeaddedduringgrowthatasufficientratetosatisfyrequirementsComparisionofconc.anduptakeratesforglucoseandoxygenbyyeastProblemsencounteredinoxygentransportcanbeillustratedbycomparingtransportofglucosevsoxygen;1%Sugar(glucose)[e-mail]10,000ppmapprox.7ppmCriticalconc100ppm0.8ppm(growthstops)Rateofdemand2.8mmoles/gcells/h7.7mmoles/gcells/hTheOxygenrequirementsofindustrialfermentations•OxygendemanddependantonconvertionofCarbon(C)tobiomass•Stoichiometryofconversionofoxygen,carbonintobiomasshasbeenelucidated(阐明)•Usetheserelationshipstopredicttheoxygendemandforafermentation•Darlington(1964)expressedcompositionof100gofdryyeastC3.92H6.5O1.94O2Requirements6.67CH2O+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•LLmOOCKoCQQ)(22式中：QO2比耗氧速率molO2/kg干cell·s（QO2）m：最大比耗氧速率molO2/kg干cell·sCL：溶氧浓度mol/m3Ko：氧的米氏常数LLmOOCKoCQQ)(22DissolvedOxygenConcentrationQO2CcriticalEffectofdissolvedO2concentrationontheQO2ofamicroorganismSpecificO2uptakeincreaseswithincreaseindissolvedO2levelstoacertainpointCcrit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%。CriticaldissolvedoxygenlevelsforarangeofmicroorganismsOrganismTemperatureCriticaldissolvedoCOxygenconcentration(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•TomaximisebiomassproductionyoumustsatisfytheorganismsspecificoxygendemandbymaintainingthedissolvedO2levelsaboveCcrit•CellsbecomemetabolicallydisturbediftheleveldropsbelowCcrit•Insomecasesmetabolicdisturbancemaybeadvantageous•OrhighdissolvedO2levelsmaypromoteproductformation•AminoacidbiosynthesisbyBrevibacteriumflavum•（黄色短杆菌）FACTORSAFFECTINGOXYGENDEMANDRateofcellrespirationTypeofrespiration(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/m3·sX:细胞浓度kg/m34.1.4氧的满足度XQO2rCcriticalCL氧的满足度4.1.4氧的满足度CcriticalCL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CcriticalCL氧的满足度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：CLCsat的10%～20%，CLCsat的8%•应控制：CLCcritical，CLCcritical4-2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/bioreactorNonaqueousphaseAqueousphaseSolidphase(Reactants/products)Dissolvedreactants/productsReactionGas(O2,CO2,CH4etc)CellsLiquids(e.goils)SugarsOrganellesSolid(e.gparticlesofsubstrate)MineralsE