In the biotechnology industry, E. coli is grown aerobically to the highest possible concen...

In the biotechnology industry, E. coli is grown aerobically to the highest possible concentrations in batch or fed-batch reactors to maximize production of an intracellular protein product. To avoid substrate inhibition, glucose concentration in the initial culture medium is restricted to 100 g/dm3 in the initial charge of 80-dm3 culture medium in a 100 dm3 capacity bioreactor. After much of this glucose is consumed, a concentrated glucose feed (500 g/dm3) will be fed into the reactor at a constant volumetric feed rate of 1.0 dm3/h. When the dissolved oxygen concentration in the culture medium falls below a critical value of 0.5 mg/dm3, acetic acid is produced in a growth-associated mode with a yield coefficient of 0.1 g acetic acid/g cell mass. The product, acetic acid inhibits cell growth linearly, with the toxic concentration (no cell growth) at Cp = 10 g/dm3. Find the optimum volumetric flow rate that will maximize the overall rate cell mass production when the bioreactor is filled up and if the feed is turned on after glucose falls below 10 g/dm3. Inoculum concentration is 1 g cells/dm3.

Additional parameters:

Increase the value of the mass transfer rate (up to 1000) or the saturation oxygen concentration (up to 40 mg/dm3) to see if higher cell densities can be obtained in the fed-batch reactor.

(a) List ways you can work this problem incorrectly.

(b) How could you make this problem more difficult?

(Contributed by Professor D. S. Kompala, University of Colorado.)