Disturbance observer for estimation of oxygen uptake rate in an activated sludge reactor

The oxygen uptake rate (OUR) is an important quantity to the aerobic activated sludge processes. It can be used to model and to optimize the system, for monitoring the process efficiency, and as a toxicity indicator in wastewater treatment plants, among other applications. The lack of online and reliable sensors to measure this significant quantity has motivated the development of software sensors for its estimation. This paper shows the design of a discrete-time disturbance observer to be used as a software sensor to estimate the oxygen uptake rate in an activated sludge reactor. A linear model of the dissolved oxygen (DO) process is used to design a compensator to maintain the DO concentration around a reference operating point. Numerical simulations are carried out and the obtained results demonstrate the applicability of the proposed method.