MICROBIAL SPECIFIC GROWTH-RATE CONTROL VIA MRAC METHOD

A problematic feature in most fermentation processes is that on-line m easurement of the most important biological process variables, the con centration of the biomass and its specific growth rate, cannot be dire ctly measured. An approach for estimating these biological variables a nd for controlling the specific growth rate in a continuous flow biopr ocess of a stirred tank reactor is presented and analysed. The goal in the control is to get the specific growth rate to track the rate of a given reference model. A dynamic model for the specific growth rate i s obtained from the general growth and substrate consumption model. Th e structure of the rate model is then applied in the reference model s tructure. The methodology studied is based on two issues, joint state and parameter estimation and direct adaptive control. From the theoret ical viewpoint, this forms a combination of indirect and direct adapti ve control. The structure of the control law is justified by the struc ture of the law obtained for known fixed parameters. Convergence of th e estimation scheme and of the adaptive control scheme are demonstrate d via Lyapunov's method, and separately. The choice of the appropriate Lyapunov function results in a P1-type controller with the gains as t he parameters to be adjusted by the user. A simulation study based on Monod's model and time-varying model parameters and subject to measure ment noise shows the feasibility and robustness of the adaptive contro l methodology developed for this non-linear process.