Adaptive extremum-seeking control applied to productivity optimization in yeast fed-batch cultures

Abstract

In this study, we consider the problem of optimizing the productivity of fed-batch cultures of S. cerevisiae, which are characterized by strongly nonlinear kinetic models based on the bottleneck assumption of Sonnleitner and Käppeli [1986] and ethanol inhibition resulting from the fermentation of a possible excess of substrate feeding. In contrast with most published studies where the critical substrate level is assumed constant, we investigate the situation where this critical substrate level depends on the yeast respiratory capacity, and in turn on the oxygen and etahnol concentration in the culture medium. The challenge is thus to maintain the process at a high level of productivity by avoiding the accumulation of ethanol. To this end, an adaptive extremum seeking control scheme, coupled to an asymptotic observer, is developed based on Lyapunov stability arguments.