Improvements in Dissolved Oxygen Control of an Activated Sludge Wastewater Treatment Process

Nowadays there is great emphasis on the optimization of wastewater treatment plants (WWTP) due to the strict regulations concerning discharged waters. The control techniques currently used in WWTPs include simple PLC-based proportional-integral-derivative control techniques. The most complex part of wastewater treatment is the activated sludge process, where the sewage is biologically treated by means of a microorganism culture in the presence of air or oxygen. This paper shows a simple way of decreasing the operational costs, together with an increase in performance and disturbances rejection by using fractional order Proportional-Integral controllers on the dissolved oxygen concentration and on the air pressure generated by the air blower. Closed loop system performance, using the fractional order Proportional-Integral controller, are compared to those obtained by using the conventional Proportional-Integral controller on the dissolved oxygen concentration. They prove the robustness of the former controller against the parameters variations. The controllers are designed and simulated on the mathematical model of the WWTP of Romanofir, Talmaciu.