The objective of this work is to make use of methodologies and tools from nonlinear Lyapunov theory in the design of bounded control laws for the temperature stabilisation of Continuous Stirred Tank Reactors (CSTRs) with exothermic or endothermic reactions. Simple output feedback control laws, i.e. control laws that feed back o n l y t h e a vailable measurements, are designed. It is shown that these controllers yield Global Asymptotic Stability (GAS) and do not require precise knowledge of the system parameters. The capabilities of the proposed method to handle control input constraints and model uncertainty are also discussed. The work is then completed with the analysis of two case studies: the classical rst order irreversible reaction A ! B and the more complex van der Vusse reaction mechanism.

Abstract-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 up-flow 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.Index Terms-Bounded output feedback control, continuous biological reactors, input constraints, waste-water treatment plants (WWTPs).

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