Nonlinear offset free MPC for self-optimizing control in wastewater treatment plants

This paper describes the application of an offset free nonlinear model predictive controller (NMPC) to regulate the self-optimizing variables and active constraints in a wastewater treatment plant, particularly the activated sludge process using the benchmark simulation model No. 1 (BSM1). A set of terminal constraints have been added to the NMPC formulation in order to ensure stability. The procedure to find the self-optimizing variables as the best controlled variables in an economic sense, has also been described briefly, considering the most important measurements of the process. This methodology provides the optimum combination of measurements to keep constant with minimum economic loss. The simulation results show good reference tracking for typical average load disturbances.