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Batch Growth Kinetics Effect of factors: aerobic growth is more efficient. - Dissolved oxygen (DO) - aerobic fermentation requires oxygen - oxygen gas is sparingly soluble in water - specific growth rate may be limited by DO if DO is below a critical oxygen concentration. : growth rate becomes independent of DO concentration. bacteria and yeast: 5%-10% of the saturated DO mold: 10%-50% of the saturated DO The saturated DO in aqueous solution is 7 ppm at 25oC and 1 atm. Batch Growth Kinetics Effect of factors: - Dissolved oxygen (DO) The given by: (OTR) from the gas to liquid phase is OTR = No2 = KLa (C*-CL) KL is the oxygen transfer coefficient (cm/h), a is the gas-liquid interfacial area (cm2/cm3) KLa is the volumetric oxygen transfer coefficient (h-1) C* is saturated DO concentration (mg/l); CL is the actual DO concentration (mg/l); No2 is the rate of oxygen transfer (OTR) (mgO2/l.h) Batch Growth Kinetics Effect of factors: - Dissolved oxygen (DO) (OUR) is oxygen consumption rate by microbes. If the maintenance requirement of O2 is negligible compared to growth, then OUR qo2 X g X YX / O2 (mg O2 /h) qo2 is the specific rate of O 2 consumptio n (mg O 2 /g dw cells - h) When oxygen transfer is the rate-limiting step, at steady state, the rate of oxygen consumption is equal to the rate of oxygen transfer. g X YX / O2 k L a(C * C ) Sufficient oxygen supply: OTR ≥ OUR Batch Growth Kinetics Effect of factors: - Dissolved oxygen (DO) Question: Oxygen is to be supplied for yeast production. If oxygen uptake rate (OUR) is 15g/l medium-h for a required yeast growth, and the oxygen transfer rate (OTR) is 10 g/l medium-h. Is such oxygen transfer rate sufficient to maintain the required yeast growth? If the required growth has to be maintained, how to improve the oxygen transfer rate? Answers: OUR=15g/l medium-h > OTR=10 g/l medium-h insufficient oxygen supply rate. Oxygen transfer rate is limiting. Increase kLa so that g X YX / O2 k L a(C * C ) Batch Growth Kinetics Effect of factors: - Temperature Temperature affects growth rate, product formation and ratelimiting step (e.g. oxygen transfer) - Psychrophiles (Topt<20oC) - Mesophiles (20-50oC) - Thermophiles (>50oC) - pH - Affects the activity of enzymes and therefore growth rate. optimum pH for bacteria: 3-8, yeast: 3-6, molds, 3-7, plant 5-6, animal 6.5-7.5 Batch Growth Kinetics Effect of factors: - Ionic strength: affect the transport and solubility of certain nutrients: minerals I=1/2∑CiZi2 - High substrate concentration: substrate inhibition - CO2 - Redox potential: a function of DO, pH and other ion concentration.