Determination of the optimal periodic waveform for a continuous fermentation process

Forced bioreactors may lead to better performances with respect to stationary schemes as it is widely reported in the literature. In this work, we investigate the impact of the forcing waveform on the process productivity of a continuous bioreactor governed by an unstructured, non-linear kinetic model. The (periodic) forcing is applied on the substrate concentration in the feed. An analytical/numerical approach is used. The analytical step is based on the -criterion that gives useful information for small amplitudes. The extension to larger amplitudes, when significant improvements are expected, is performed through a continuation-optimization procedure. It is found that the choice of the specific waveform has an impact on the performance of the process and there is no unique best forcing for any process condition but its choice depends on the operating parameters.The influence of the waveform functions on the wash-out conditions are extensively examined. The analysis shows that all the waveforms examined in this work lead to a significant enlargement of the non-trivial regime with respect to a steady state operation. In particular, the maximum extension is predicted for a square-wave forcing.