2.3.2 Fed-batch cultivation at a constant specific growth rate
In this strategy, an open-loop control system was utilized to obtain a constant specific growth rate during the fed-batch phase. The feed flow rate was calculated on-line only based on initial parameter values and a process model. The fed-batch cultivation was started with an initial glucose concentration of 5 g l−1. When the initial batch phase was finished, indicated by a sudden increase in dissolved oxygen concentration, the fed-batch phase was started. During this phase, the concentration of dissolved oxygen was kept constant at 30% air saturation by adjusting the stirrer speed (50–1200 rpm).
To control the fed-batch cultivation, a process model based on the Monod model with limited substrate and for an ideal stirred tank bioreactor was developed (1), (2), (3), (4) and (5):