A 200-litre stirred fermenter contains a batch culture of Bacillus subtilis


A 200-litre stirred fermenter contains a batch culture of Bacillus subtilis bacteria at 28C.
Air at 20C is pumped into the vessel at a rate of 1 vvm (vvm means volume of gas per
volume of liquid per minute). The average pressure in the fermenter is 1 atm. The
volumetric flow rate of off-gas from the fermenter is measured as 189 l min21
. The exit gas
stream is analysed for oxygen and is found to contain 20.1% O2. The dissolved oxygen
concentration in the broth is measured using an oxygen electrode as 52% air saturation.
The solubility of oxygen in the fermentation broth at 28C and 1 atm air pressure is
7.8 3 1023 kg m23
.
(a) Calculate the oxygen transfer rate.
(b) Determine the value of kLa for the system.
(c) The oxygen analyser used to measure the exit gas composition was incorrectly
calibrated. If the oxygen content has been overestimated by 10%, what error is
associated with the result for kLa?​


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