Adaptive Control of Continuous Yeast Fermentation, Near Critical Dilution Rate

Abstract The dynamics and control of a continuous fermentation with Saccharomyces cerevisiae is investigated. A number of different sensors are evaluated for this purpose. A sensor for reducible gas concentration in the exhaust gases is selected for manipulating the substrate flow rate. Due to the timevarying nature of this process an adaptive regulator seems to be a promising tool for providing good regulatory and setpoint tracking performance. A simple third order model structure is used for a model based control design with a Linear Quadratic-LQ-regulator. At the lowest setpoint level the process is exposed to a large disturbance in substrate feed concentration and to a small setpoint disturbance. In order to investigate the process behavior around the critical dilution rate a sequence of setpoint changes is carried out. At each setpoint a closed loop identification experiment is carried out to enable identification of the process dynamics. The adaptive LQ-regulator performs well experimentally. Some interesting features are indicated concerning the adaptability of the microorganism and the possibility of multiple steady states for the fermentation process around the critical dilution rate if operated as a chemostat.