Given our knowledge so far we now need to evaluate if it is feasible to run the process in the designed vessel. We therefore need to compare the oxygen uptake rate and the oxygen transfer rate. It is essential that the transfer rate exceeds the uptake rate by quite a margin but remember we are evaluating the worst case senario so we need to consider the result carefully.

In Section Two we calculated the maximum oxygen uptake rate of the culture for the conditions specified. We also need to check that the level of oxygen in the outlet gas is satisfactory for effective performance:

(i) Evaluate the exit gas oxygen concentration at the maximum oxygen uptake rate given that the vessel will probably operate with an over pressure of 0.25 bar g. The final test is to evaluate if the required biomass consumption can be achieved in the vessel. If we assume that at the maximum oxygen uptake rate and the oxygen transfer rate are just matching we can evaluate the likely minimum dissolved oxygen tension that will be attained at this point. We can then determine if this is acceptable.

(ii) Calculate the minimum dissolved oxygen tension likely to occur under the conditions described. Give reasons for any assumptions you make.