Control of Dissolved Oxygen in Stirred Bioreactors

This report discusses control of dissolved oxygen in a bioreactor where the oxygen supply is manipulated using the stirrer speed. In batch and fed-batch cultivations the operating conditions change significantly which may cause tuning problems. Analysis using a linearized process model shows that the process dynamics is mainly affected by changes in the volumetric oxygen transfer coefficient KLa. To account for the process variations, a control strategy based on PID control and gain scheduling from the stirrer speed is suggested. This approach is straightforward to implement in an industrial control system. Experimental results from a laboratory reactor are presented.