Baker's yeast is to be grown in a continuous fermentation system using a fermenter volume of 20 m3 in which the flow residence time is 16 h. A 2% inoculum containing 1.2 % of yeast cells is included in the growth medium. This is then passed to the fermenter, in which the yeast grows with a steady doubling time of 2.9 h. The broth leaving the fermenter then passes to a continuous centrifuge which produces a yeast cream containing 7% of yeast, 97% of the total yeast in the broth. Calculate the rate of flow of the yeast cream and of the residual broth from the centrifuge.
The volume of the fermenter is 20 m3 and the residence time in this is 16 h so the flow rate through the fermenter must be 20/16 = 1.250 m3 h-1
Assuming the broth to have a density substantially equal to that of water, i.e. 1000 kg m-3,