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Batch Growth Kinetics

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.

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Batch Growth Kinetics

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  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. Critical oxygen concentration: the 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.

  2. Batch Growth Kinetics Effect of factors: • Dissolved oxygen (DO) The rate of oxygen transfer (OTR) from the gas to liquid phase is given by: 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)

  3. Batch Growth Kinetics Effect of factors: • Dissolved oxygen (DO) Oxygen Uptake Rate (OUR) is oxygen consumption rate by microbes. If the maintenance requirement of O2 is negligible compared to growth, then When oxygen transfer is the rate-limiting step, at steady state, the rate of oxygen consumption is equal to the rate of oxygen transfer. Sufficient oxygen supply: OTR ≥ OUR

  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 kLa 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 (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

  6. 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.

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