Control of the WWTP Water Line Using Traditional and Model Predictive Approaches

Wastewater treatment and resources recovery from large wastewater flowrates of the municipalities and circular bio-based economy ask for efficient control solutions. The paper presents solutions for operating the wastewater treatment plant, based on advanced process control methods aimed to merge the benefits of the cooperation between the lower-level regulatory control loops and the upper-level model predictive control strategy. The lower-level is designed to regulate the nitrification in the aerated bioreactors by controlling the Dissolved Oxygen or the ammonia concentration and to control the denitrification in the anoxic reactor by controlling the nitrates concentration. The model predictive controller either sets the setpoints of the regulatory layer or directly manipulates the air and nitrate recycle flow rates. The plant performance results obtained using the regulatory Proportional and Integral control are compared to the direct or the supervisory model predictive control outcomes. Both feedback and feedforward control configurations were considered, with the influent ammonia concentration as a representative disturbance. The WWTP control results were assessed using the Pumping and Aeration Energy, Effluent Quality, and Green House Gases emissions performance indices. They showed the advantage of the two-level control system for ammonia and nitrates concentration control with setpoints driven by the constrained model predictive controller, in association with the feedforward control.