MULTILAYER ADAPTIVE-CONTROL OF CONTINUOUS BIOPROCESSES USING OPTIMIZING CONTROL TECHNIQUE - CASE-STUDY - BAKERS-YEAST CULTURE

High costs associated with many fermentation processes in an increasin gly competitive industry make any prompt application of modern control techniques to industrial bioprocesses very desirable. However, this i s often hampered by the lack of adequate mathematical models, on the o ne hand, and by the absence of continuous, on-line measurement of the most relevant process variables, on the other hand. This paper address es these problems and offers a new strategy to control continuous biop rocesses using a hierarchical structure such that neither structured p rocess models nor continuous measurement of all relevant variables hav e to be available. The control system consists of two layers. The lowe r layer represents a dynamic adaptive follow-up control of a continuou sly measured output - in our case dissolved oxygen concentration. This variable is supposed to be strongly correlated with the key output va riable - in our case cellular concentration which is not continuously available for measurement. The higher layer is then designed to mainta in a desired profile of the process key output using a set-point optim ising control technique. The Integrated System Optimisation and Parame ter Estimation method used operates on an appropriately chosen steady- state performance criterion. A prerequisite for successful application of the proposed approach is an approximate steady-state model, descri bing the relationship between the measured output and the process key output variable. Furthermore, occasional in situ, off-line or laborato ry measurement values of the key output variable are needed. Promising simulation results of the biomass concentration control, by manipulat ing the air flow-rate in the continuous bakers' yeast culture are pres ented.