State Estimation of a Fed-Batch Baker's Yeast Fermentation

Abstract

This article gives an indirect estimation method for on-line determination of the biomass, the specific growth rate, the substrate utilization rate and the ethanol concentration of a fed-batch baker’s yeast fermentation. The method only uses measurements from established sensors such as gaseous oxygen and carbon dioxide analyzers, and an air flow meter. From these measurements the oxygen uptake rate (OUR) and the carbon dioxide evolution rate (CER) are accurately computed with a two compartment model. A measurement model has been derived from stochiometric considerations and a linear equation for ATP consumption. This model delivers on basis of CER and OUR computations, the output equations for the state variables. These equations and a simple state model for the biomass and the biomass production rate are used in an extended Kalman filter for estimation of the process variables. Experiments with a computer-coupled 100 liter pilot fermentor have confirmed the output equations especially in relation to the biomass estimation. On the other hand the results of experiments with the state model in combination with the extended Kalman filter call for further investigation.