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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.