Set-point regulation of an anaerobic digestion process with bounded output feedback

This work addresses the robust output feedback tracking problem for a biological wastewater treatment process in the presence of input constraints and limited knowledge on the process parameters. The considered process is an anaerobic upflow fixed bed biological reactor within a semi-industrial scale pilot plant for the treatment of industrial wine distillery wastewater. A mathematical model describing the dynamic behavior of the biological process is considered and nonlinear control techniques are used to design a bounded output feedback control law. Local asymptotic stability and local set-point tracking of the resulting closed-loop system is proved when the dilution rate is selected as the manipulated variable and the output methane gas flow-rate as the measured and controlled variable. Finally, the implementation of the nonlinear output feedback control law is described and experimental results are reported. It is observed that the proposed controller yields set-point regulation, rejects disturbances and preserves stability despite uncertainty on the kinetic parameters.