Effect of setpoint on L-lysine fermentation

In control of a bioprocess, setpoint of fed-batch fermentation processes has a great influence on both the cost and the operating efficiency. Determination of a setpoint depends on the system and objective function. This work investigates two operating conditions for a fed-batch culture of L- lysine production. One is to maintain the reducing sugar concentration (RSC) on a constant setpoint, whereas the other has a piecewise variation of the RSC setpoint. Productivity, yield, and a cost function are employed to evaluate the performance of different setpoints on the fermentation process. Constant setpoint which is commonly used in fed-batch culture is not the best approach in L-lysine fermentation. Piecewise variation of setpoint shows that the better policy is to set the RSC at a higher concentration in the early cell growth stage then to decrease the RSC to a lower level.