Robust state observers for biological wastewater treatment processes with activated sludge

The paper deals with the applying of two robust estimation techniques to a biological wastewater treatment processes: Sliding-Mode Observer and Extended H_∞ Filter. The sliding-mode observer was designed on the basis of the equivalent control method. For the observer implementation it is necessary a state transformation that needs to bring the process to the observable canonical form. The behavior of the two observers has been studied in the presence of the parameter´s uncertainties and when the state variables are affected by noise. Based on the results obtained through numerical simulation some conclusions have been drawn regarding the performances of the two robust state observers. A biological wastewater treatment process with activated sludge having as objective the removal of the organic substrate has been considered as case study.