Specific Growth Rate Estimation in Bioreactors Using Second-Order Sliding Observers*

This paper addresses the estimation of specific growth rate of microorganisms in bioreactors. In particular, a second-order sliding observer based on biomass concentration measurement is proposed. Differing from other proposals that only guarantee bounded errors, the observer provides a smooth estimate that converges in finite time to the time-varying parameter. Further, the observer exhibits very robust properties since no model of the kinetics is used for its design. In addition, the off-surface coordinate of the sliding observer is useful to determine the convergence time as well as to identify sensor faults and unexpected behaviors. The features of the proposed observer are assessed by numerical and experimental data.