Nonlinear estimation and control schemes for a complex anaerobic digestion of microalgae with unknown kinetics and inputs

Abstract

This work addresses estimation and advanced control schemes for a complex microalgae anaerobic digestion process, used for wastewater treatment as well as for converting organic waste and biomass into biogas. The control goal is to keep the inhibitory compounds at imposed low levels despite the influent pollutant concentration and load variations. The proposed innovative control schemes work in accurate operating conditions and can cope with harsh assumptions: unknown kinetic rates, unknown feed-in pollutant concentration, unmeasurable state variables. The adaptive and robust-adaptive control laws are based on nonlinear algorithms: a sliding mode observer for the unknown inputs, kinetics parameter estimators, asymptotic and interval state observers. The tests performed under realistic conditions showed that the closed-loop bioprocess is preserved at specific operating points such that the control goal is fulfilled. The state and parameter estimators provide enough on-line information such that the control schemes can handle all the input and kinetic uncertainties.

Keywords: Anaerobic digestion process; Robust-adaptive control; Wastewater treatment.