ON-LINE ANALYSIS AND CONTROL OF FERMENTATION PROCESSES

Abstract

This paper gives a brief account on the results using mini-computer for on-line, real-time followup and control of fermentation processes. Data indicate that the status of a microbiol culture can be characterized if the available direct sensor signals are further analyzed. Such an analysis gives insight into the physico-chemical, physiological and biochemical conditions of the culture. In particular, the gas exchange conditions (oxygen uptake, CO? release rates and especially respiratory quotient (RQ)) were found sensitive indicators of the culture's status. Using the process status analysis capability of the computer optimum environmental conditions were searched by means of perturbation testing of the culture. For example, a C/N ratio was found in C. utilis culture which resulted in near perfect oxidation (RQ close to 1.0) which coincided with enhanced cell growth rate and suppressed ethyl alcohol formation. During these tests interactions between the environmental factors and the cellular metabolism were also detected. Analysis of these interactions is a prerequisite to develop control techniques for microbiological processes. Information on the interactions between the cells and environment as well as on the process status made it possible to establish a culture milieu in which the C. utilis cells metabolism was shifted in the direction of protein synthesis with simultaneous decrease in ETOH production. This operation was implemented using a double control loop strategy in which the setpoints of the individual controlled variables (composite of which creates the environment) were adjusted according to the physiological state of the culture.