Effect of wall growth on scale‐up problems and dynamic operating characteristics of the biological reactor

If inhibitory substrates are being utilized in a well‐stirred biological reactor, microbiological growth on the walls of the reactor can create a scale‐up problem. A simple model is proposed which shows that without such growth, of the three existing steady states only one is stable and nontrivial, but with wall growth the trivial, stable, steady state (washout) is impossible. In addition, wall growth reduces the region over which three steady states are feasible and reduces the minimum residence time for which there is only one steady state that corresponds to a high conversion. Thus, a laboratory process with a high surface area to volume ratio can give an over optimistic prediction of both necessary residence; time and stability of the full scale process unless wall growth is accounted for.