Nonlinear Estimation and Adaptive Control of a Fed-Batch Fermentor

The bakers’ yeast is produced industrially in a fed-batch fermentor. The advantage of this mode of operation is that the sugar concentration in the broth is maintained at a low level to prevent ethanol formation. The yeast utilizes the sugar by two catabolic pathways under aerobic conditions: in the first pathway, the sugar is oxidized with a high energetic yield, and, in the second pathway, it is reduced with formation of ethanol as the end product with a low biomass yield. The amount of substrate reacting in each pathway depends mainly on the sugar concentration in the broth. Also, under certain conditions, the yeasts are able to oxidize the ethanol present in the broth. In order to control this process, we have to design state observers and parameter estimators because the measurement of sugar and biomass concentrations are not typically available in an industrial environment.