1. 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 25 o C and 1 atm.

2. Batch Growth Kinetics Effect of factors: -Dissolved oxygen (DO) The (OTR) from the gas to liquid phase is given by: OTR = No 2 = K L a (C*-CL) K L is the oxygen transfer coefficient (cm/h), a is the gas-liquid interfacial area (cm 2 /cm 3 ) K L a is the volumetric oxygen transfer coefficient (h -1 ) C* is saturated DO concentration (mg/l); C L is the actual DO concentration (mg/l); No2 is the rate of oxygen transfer (OTR) (mgO 2 /l.h)

3. Batch Growth Kinetics Effect of factors: -Dissolved oxygen (DO) (OUR) is oxygen consumption rate by microbes. If the maintenance requirement of O 2 is negligible compared to growth, then Sufficient oxygen supply: OTR ≥ OUR When oxygen transfer is the rate-limiting step, at steady state, the rate of oxygen consumption is equal to the rate of oxygen transfer.

4. 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 k L a so that

5. Batch Growth Kinetics Effect of factors: -Temperature Temperature affects growth rate, product formation and rate- limiting step (e.g. oxygen transfer) - Psychrophiles (T opt <20 o C) - Mesophiles (20-50 o C) - Thermophiles (>50 o C) -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

6. Batch Growth Kinetics Effect of factors: -Ionic strength: affect the transport and solubility of certain nutrients: minerals I=1/2∑CiZi 2 -High substrate concentration: substrate inhibition -CO 2 -Redox potential: a function of DO, pH and other ion concentration.