An Optimal Operating Strategy for Fed-batch Fermentations by Feeding the Overflow Metabolite

Optimization of the fed-batch fermentation of Saccharomyces cerevisiae is analyzed. Due to the limited oxygen uptake capacity of the cells, the over ow metabolite ethanol is formed when the substrate concentration is above some critical value. This value decreases during the course of an experiment due to the reduction in dissolved oxygen concentration resulting from biomass formation. Optimal operation corresponds to regulating the substrate concentration along this time-varying critical value. This paper proposes a novel strategy to implement this optimal solution, whereby ethanol is fed along with the substrate and its concentration in the reactor regulated around the inlet concentration value. Suboptimal strategies of practical interest are also discussed and simulation results are presented.