Nonlinear MPC for optimization of recombinant Zymomonas mobilis fed-batch fermentation

Presents the development of an unstructured kinetic model incorporating the differing degrees of product and substrate inhibition on kinetic rates of alcohol fermentation by recombinant Zymomonas mobilis for growth on two substrates. Product inhibition was observed to begin to affect the specific growth rate at 20 g/L and specific productivity at about 35-40 g/L. Additionally, a mechanism for the inhibition of two competing substrates cellular uptake via membrane transport is proposed. Inhibition functions and model parameters were determined by fitting experimental data to the model. This model was utilized in a nonlinear model predictive control (NMPC) algorithm to control product concentration during fed-batch fermentation simulation to offset the inhibitory effects of product and substrate inhibition. Using this optimal feeding policy determined by the NMPC controller, the ethanol productivity was predicted in simulation to be increased 38% relative to batch operation.