Performance of a three-phase fluidized-bed biofilm fermenter system, which is used for the production of a secondary metabolite, is analyzed through computer simulation techniques. Penicillin fermentation was chosen for the model system. From the steady-state analysis, it was found that a complete-mixed contacting pattern is superior to a plug flow pattern in terms of productivity, since less inhibitory effect of the substrate is pronounced in that configuration. Optimum biofilm thickness for the fermenter system was found to be a function of various operating parameters, and should be determined from information on the interactions between fermenter productivity and the operating conditions.

The dynamic analysis has shown that for a given constant oxygen transfer rate in bulk phase, there exist operating conditions optimal for maximizing the volumetric productivity of the fermenter system. When a constant oxygen transfer rate with a k.e.a of 300 hr 1 was used with a complete-mixed contacting pattern, the optimum inlet substrate con- centration and mean residence time were found to be 20 (g glucose/liter) and 10 (hours), respectively. Production phase could be extended by increasing the substrate concentration in the feed stream, but the optimum increasing rate and initiation time of increase are functions of other operating parameters, such as initial inlet substrate concentration, mean residence time, and oxygen transfer rate in the fermentor. An increasing rate of 0.6 g glucose/liter/hr with the initiation time t 0 = 51 was found to be the optimal, for the operating conditions found in the dynamic analysis. The result has also shown that a high total biomass concentration and a high oxygen transfer rate in the fermentor are the most important factors to achieve a high productivity.