Identification and Control During Fermentation Start-Up - a Method to Avoid Synchronous Growth in Continuous Cultures

Abstract

A control strategy is proposed to avoid development of synchronous growth in carbohydrate limited fermentations. The basic idea is to control the metabolic flux through the pathways using an ethanol measurement and substrate feed rate to keep the ethanol concentration at a low level. An adaptive and a constant parameter controller were investigated experimentally. Both were initialized at the target conditions for the continuous fermentation, where the uncontrolled process is known to be unstable. The latter fact renders it infeasible to attempt open loop operation at the critical dilution rate. The adaptive controller turned out to be superior to the non-adaptive controller. The superiority of the adaptive controller is ascribed to its ability to identify the process under varying cell activity. The experimental results demonstrate that the desired operating point is reproducibly obtainable. However, after prolonged operation under different types of disturbances the yeast seemed to adapt towards an increased respiratory activity for the same low level of ethanol in the fermentation broth.