QFT Robust Control of a Wastewater Treatment Process

The paper deals with the wastewater treatment process control using QFT (Quantitative Feedback Theory) techniques. The aim of the control is to obtain an effluent having the substrate concentration within the standard limits established by law (under 20 mg/l). It has been admitted variable operating regimes in large limits. Three main regimes have been taken into account: rain, normal, and drought. In these conditions two aspects were considered: a QFT controller designed to assure good properties for the three regimes mentioned before; a control structure that adjusts the dissolved oxygen setpoint as a function of the influent regime. The purpose is to stabilize the operating regime with respect to the quality variable (the effluent substrate concentration) and the command variable (the dilution rate).