Predictive Control of Intermittent Aeration in Activated Sludge Processes

This paper presents a model-based predictive control for an intermittently aerated bioreactor of a medium-sized wastewater treatment plant. The main objective of the proposed method is to develop an intermittent aeration sequencing control strategy to minimize the aeration system energy consumption, with a subscription to the EU effluent standards and the plant operating constraints. A multilayer control system with two levels is implemented. The optimization level uses a model predictive control algorithm to determine the optimal value for the aeration fraction of the aeration cycle. The lower layer provides a feedback control loop of the bioreactor dissolved oxygen and secures intermittent aeration sequencing. The obtained aeration sequence guarantees that the effluent fulfills the requirements following regulatory standards for wastewater discharged. The control system demonstrates good performances for both setpoint tracking and disturbance rejection. Important energy savings are also obtained when comparing the developed control strategy to traditional control systems based on a pre-determined aeration sequence.