Some Considerations About Control of Multispecies Anaerobic Digestion Systems

Abstract

AbstractThis paper presents a brief evaluation of a start-up strategy for multispecies anaerobic digestion systems modelled as two-step reaction systems, in which acidogenesis is described by Monod kinetics while the methanogenesis is described by Haldane kinetics. The start-up policy has been developed originally for single species systems with the aim of maximizing the biogas outflow rate. It consists of switching the dilution rate from minimum to maximum and then to the optimal value in order to bring the system from an arbitrary initial condition to the optimal setpoint. This start-up strategy is applied to the multispecies system using an averaged model, which is usually the only model that can be identified for a multispecies system, as measuring individual biomasses is quite difficult in practice. This study shows that the start-up policy leads to an efficient ecosystem, characterized by high outflow rate of biogas, even in the case of an inaccurate averaged model. It can be viewed as a robustness evaluation of the single species start-up strategy, as the process changes from the averaged kinetics to the kinetics of the winning species during species selection.