Specific Kinetic Rates Regulation in Multi-Substrate Fermentation Processes

The regulation of the biomass specific growth rate is an important goal in many biotechnological applications. To achieve this goal in fed-batch processes, several control strategies have been developed employing a closed loop version of the exponential feeding law, an estimation of the controlled variable and some error feedback term. Moreover, in some bioprocesses there is more than one feeding flow entering the bioreactor and supplying different nutrients or substrates. Hence, the problem of estimating multiple substrate consumption rates together with the specific growth rate of the microorganism becomes relevant. In this context, the dynamic behavior of fed-batch processes with multiple substrates and Haldane kinetics is further investigated. In particular, a nonlinear PI control law based on a partial state feedback with gain dependent on the output error is used. Then, with a recent developed algorithm for several kinetic rates estimation based on second-order sliding mode (SM) ideas, we extend the mentioned control strategy to a multi-substrate fed-batch bioprocess. The observer provides smooth estimates that converge in finite time to the time-varying parameters and allows independent design of the observer and controller dynamics. The features of the proposed estimation and control strategies are assessed by simulation in different scenarios.