Feedback Stabilization of Fed-Batch Bioreactors; Non-Monotonic Growth Kinetics

This paper deals with the design of a feedback controller for fed-batch microbial conversion processes that forces the substrate concentration Cs to a desired setpoint C, starting from an arbitrary (initial) substrate concentration when non-monotonic growth kinetics apply. This problem is representative for a lot of industrial fermentation processes, with the bakerʹs yeast fermentation as a well-known example. It is assumed that the specific growth rate is function of the substrate concentration only. A first approach exploits the availability of on-line measurements of both the substrate and biomass concentration. A second approach is merely based on on-line measurements of the biomass concentration, which provide an estimate for the specific growth rate. After a reformulation of the substrate concentration setpoint into a specific growth rate setpoint, it is demonstrated that the fed-batch process can still be stabilized around any desired operating point along the non-monotonic kinetics.