Optimal control of a batch bioreactor for the production of xanthan gum

The application of an optimal control procedure to reduce the fermentation time necessary to produce a desired amount of xanthan gum is presented. This procedure computes the temperature operating policy for the culture based on the fermentation initial conditions and the desired (target) product concentration at the final lime. For that purpose, it uses biomass and product growth models proposed previously in the literature, which are dependent on the medium temperature. Computational experiments show that the optimal fermentation time to produce 15 g of gum per 1 is 16.3% shorter than the necessary time when the usual constant temperature of 28 degreesC is used, and 12% shorter than the necessary time when the two-temperature strategy of other authors is used. The results also show considerable energy savings. Rules to determine a near optimum temperature profile without applying the optimization procedure are outlined and some results are presented. These rules are based on the outcome of the optimal control procedure and only require the knowledge of the initial cell and the desired final gum concentrations. (C) 2001 Elsevier Science Ltd. All rights reserved.