Functional state modelling approach for bioprocesses: local models for aerobic yeast growth processes

Abstract

Abstract The functional state of a process is a novel concept which helps in monitoring and control of complex processes such as bioprocesses. The concept was introduced originally by Halme. The main idea is to use a two-level hierarchy where on the top level the process is divided into macrostates, called functional states, according to behavioural equivalence. In a functional state, the process is described by a conventional type of model which is valid in this functional state — called the local model. To illustrate further the concept of functional state in fermentation processes, experimental data and simulations of an aerobic fed-batch baker's yeast fermentation are presented. It is shown how this process can be divided into functional states by considering the cell metabolism in more detail, how the local models can be obtained, and how the functional states of a fed-batch baker's yeast fermentation and recognized on-line. By simulation and comparing the results to experimental data, it is further shown how the concept works in practice. The results are also used to demonstrate an optimal substrate feed control policy.