Indirect Control of Substrate Concentration for a Wastewater Treatment Process by Dissolved Oxygen Tracking

Abstract

Two control strategies, relying on different principles, are used in this paper for improving the performance of an Activated Sludge Process (ASP): gain scheduling PI control (GS-PI) and model predictive control (MPC). Among the numerous existing control strategy, PI control and MPC control are the most frequently ones used successfully in industrial applications. The ASP is described by a nonlinear multivariable model with two inputs and two outputs. The main objective is to obtain a substrate concentration in the effluent within the standard limits established by legislation on wastewater treatment, especially the strict EU Guideline Urban Wastewater Directive 91/271/EEC. This goal is achieved by controlling the dissolved oxygen (DO) concentration to setpoint values established by preliminary tests. Simulations are carried out on the nonlinear model to show the effectiveness of GS-PI and MPC control methods. The contribution of the paper can be summarized to the fact that the effluent substrate concentration is controlled through two different methods without using measurements of the substrate, but only measurements of the DO concentration. This is more reliable and less expensive. Additionally, the performance of wastewater treatment process is analyzed in terms of energy efficiency. This is done by considering the volume of treated water in relation to the consumed electricity.