Dynamic Optimization of Fed-batch Fermentation Processes for Ethanol Production from Lignocellulose

This paper presents the design of optimal control policies for a fed-batch process of simultaneous saccharification and co-fermentation to produce ethanol from lignocellulose using enzymes and recombinant strain Saccharomyces yeast 1400 (pLNH33). The goal of the optimal design herein is to find the optimal feed rate, fed lignocellulosic concentration, and fermentation time that maximizes the ethanol production rate under the constraints of operational restrictions. We applied Arrhenius relationship to each rate constant to express temperature effect on the kinetic model for both saccharification and fermentation. Good bioreactor performance is not only defined as the maximum production rate yielded, but also considers follow-up separation specifications as the constraints for the optimization problem. Additional restrictions were also considered in the optimization problem to cope with operating costs and environmental impact. From sensitivity analysis, we observed that the fed lignocellulosic concentration and the first feed rate action are the most sensitive decision variable with respect to the production rate. However, the temperature increasing was less influential to the production rate, but was significant to each residual sugar concentration.