生化工程_刘晓兰_通气与搅拌1

1、 Biochemical Engineering 主讲: Dr.1第四章 通气与搅拌第一节 细胞对氧的需求(Oxygen demand and respiration)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2Introduction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

2、 柠檬酸发酵 ：较高，110-120 rpm3 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。 4The oxygen demand of an industrial process is generally satisfied by aeration and agitation.Productivity is limited by oxygen availability and therefore it is important to the factor

3、s that affect a fermenters efficiency in supplying O2 5 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。This lecture considers the O2 requirement, quantification of O2 transfer and factors influencing the transfer of O2 into solution. 64-1 细胞对氧的需求 Oxygen demand and respiration好氧细胞:通过呼吸链获得能量(供细胞的生长 代

4、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。 74.1.1 Stoichiometry(化学计量学) of respirationTo consider the stoichiometry of respiration the oxidation of glucose may be represented as;C6H12O6 + 6O2=6H2O + 6CO2Atomic weight

5、 of CarbonHydrogenOxygen12116Molecular weight of glucose is 180How many grams of oxygen are required to oxidise 180g of glucose?Answer 192g8Solubility of OxygenBoth components oxygen and glucose must be in solution before they become available to microorganismsOxygen is 6000 times less soluble in wa

6、ter than glucoseA saturated oxygen solution contains only10mg dm-3 of oxygenImpossible to add enough oxygen to a microbial culture to satisfy needs for complete respirationOxygen must be added during growth at a sufficient rate to satisfy requirements 9Comparision of conc. and uptake rates for gluco

7、se and oxygen by yeastProblems encountered in oxygen transport can be illustrated by comparing transport of glucose vs oxygen;1% Sugar (glucose)Broth O2 sat 25oCConc. in bulk broth10,000 ppmapprox. 7 ppmCritical conc 100 ppm 0.8 ppm(growth stops)Rate of demand 2.8 mmoles/ g cells /h7.7 mmoles/ g cel

8、ls /h10The Oxygen requirements of industrial fermentationsOxygen demand dependant on convertion of Carbon (C) to biomassStoichiometry of conversion of oxygen, carbon into biomass has been elucidated(阐明)Use these relationships to predict the oxygen demand for a fermentationDarlington (1964) expressed

9、 composition of 100g of dry yeastC 3.92 H 6.5 O 1.9411O2 Requirements6.67CH2O + 2.1O2 = C 3.92 H 6.5 O 1.94 + 2.75CO2 + 3.42H2O7.14CH2 + 6.135O2 = C 3.92 H 6.5 O 1.94 + 3.22CO2 + 3.89H2Owhere CH2 = hydrocarbonCH2O = carbohydrate From the above equations to produce 100g of yeast from hydrocarbon requ

10、ires three times the amount of oxygen than from carbohydrate.124.1.2 细胞的比耗氧速率（呼吸强度）与氧浓度的关系 OXYGEN CONC. vs RESPIRATION RATE (growth rate)细胞的比耗氧速率Respiration rate (QO2 )：单位重量的细胞在单位时间内耗氧的量mmoles of oxygen consumed per gram of dry weight 。The effect of dissolved oxygen on the specific uptake rate (i.e

11、respiration or growth) is described by: Michaelis Menton 13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14Dissolved Oxygen ConcentrationQO2CcriticalEffect of dissolved O2 concentration on the QO2 of a microorganismSpecific O2 uptake increases with increase in disso

12、lved O2 levels to a certain point Ccrit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%。15Critical dissolved oxygen levels for a range of microorganismsOrganismTemperatureCritical dissolvedoCOxygen concentration(mmoles dm -3)Azotobacter sp.固氮菌300.018E. coli370.008Saccharomyces sp.300.004Penicillium chrysogen

13、um240.022Azotobacter vinelandii is a large, obligately aerobic soil bacterium which has one of the highest respiratory rates known among living organisms16 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CL Ccritical，细胞的QO2保持不变， 当CL Ccritical，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%2

14、5%。17Critical dissolved oxygen levelsTo maximise biomass production you must satisfy the organisms specific oxygen demand by maintaining the dissolved O2 levels above CcritCells become metabolically disturbed if the level drops below CcritIn some cases metabolic disturbance may be advantageousOr hig

15、h dissolved O2 levels may promote product formationAmino acid biosynthesis by Brevibacterium flavum （黄色短杆菌）18FACTORS AFFECTING OXYGEN DEMANDRate of cell respirationType of respiration (aerobic vs anaerobic)Type of substrate (glucose vs methane)Type of environment (e.g pH, temp etc.)Surface area/ vol

16、ume ratio large vs small cells (bacteria v mammalian cells)clumps, flocs, pellets etc.194.1.3 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/m3 4.1.4 氧的满足度 204.1.4 氧的满足度214.1.5 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

17、色短杆菌生产各种氨基酸时溶解氧浓度的影响。 22氧浓度对Brevibacterium flavum氨基酸生产的影响2324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% Csat 13%23%生产受抑制： CL Csat的10%20%，CL Ccritical ， CL Ccritical 254-2培养过程中的氧传递及速率4.2.1 物质传递和相的概念Mass transfer and phases Fundamental concept in fermentation technolo

18、gy is transfer of materials (e.g nutrients, products, gases etc.) through different phases (e.g gas into a liquid). 26Phases present in bioreaction/bioreactor1 = reactant supply and utilisation2 = product formation and removal27 Major problem associated with provision of oxygen to the cell - is a ra

19、te limiting step and thus serves as a model system to understand mass transfer.281) The bulk gas phase in the bubble2) The gas-liquid interphase3) The liquid film around the bubble4) The bulk liquid culture medium5) The liquid film around the microbial cells 6) The cell-liquid interphase7) The intra

20、cellular oxygen transfer resistance1234567Gas bubbleLiquid filmMicrobial cell4.2.2 氧传递过程Oxygen Mass Transfer Steps294.2.2 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。 30The rate of oxygen transfer = driving force / resistan

21、ce. 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/mol31The rate of oxygen transfer = driving force / resistance. E.g resistance to mass transfer from medium to cells are complex and may arise from: Diffusion from bulk gas to gas/liquid interfaceSolution of gas in liquid interfaceDiffusion of dissolved gas to bulk of liquidTransport of dissolved gas to regions of cellDiffusion through stagnant region of liquid surrounding the cellDi