Continuous cultivation start-up control - an experimental investigation

A control strategy to avoid development of synchronous growth in carbohydrate limited Saccharomyces cerevisiae cultivations is proposed and experimentally investigated. The basic idea is to control the metabolic flux through the pathways by manipulating the substrate feed rate to keep the ethanol concentration at a low level.

An adaptive and a fixed parameter controller were investigated experimentally. Both controllers were initialized at the target conditions for the continuous cultivation, where the uncontrolled process is known to be marginally stable. The latter fact renders it unfeasible to attempt open loop operation at the critical dilution rate.

The adaptive controller turned out to be superior to the fixed parameter controller. The superiority of the adaptive controller is ascribed to its ability to identify the process under varying cell activity. The obtained 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 medium.