Model based substrate set point control of yeast cultivation processes based on FIA measurements

In this contribution a model based substrate control system for Saccharomyces cerevisiae fed batch cultivations is presented. The intention is to keep the concentration of the substrate glucose at a fixed selected set point during the process run. Set points of 0.07 g L−1 and 0.5 g L−1 are chosen, as the cells change their metabolism from pure oxidative to oxidative–reductive depending on the glucose concentration. The precise control of glucose concentration during cultivations still poses a challenge as the analysis with available on-line measurement systems still has the problem of noise and a time delay of at least 6 min. To compensate these effects a control system based on an ordinary FIA system for glucose measurements complemented by an extended Kalman filter is employed. The Kalman filter could handle the dynamics of the process accurately. Based on the glucose measurement every 3 min it estimated the biomass and glucose concentration as well as the growth rate factor and the volume of the culture broth. Utilising the estimated values of the process variables a feed forward controller was complemented by a PI controller to adjust the glucose concentration at the desired set points. During the control phase the standard deviation of the measurements are 0.002 g L−1 and 0.022 g L−1 for the set points of 0.07 g L−1 and 0.5 g L−1, respectively.