Design of supervisory fuzzy control for enhanced energy saving in a sequencing batch reactor-based wastewater treatment plant

Humankind has been grappling with wastewater treatment for centuries. To ensure optimal operation and control of a wastewater treatment plant (WWTP), suitable advanced control strategies are required as they are inherently nonlinear in nature and subjected to different influent conditions. This paper proposes a novel supervisory control scheme for sequencing batch reactor (SBR)-based WWTP. It integrates hierarchical fuzzy control, based on ammonia and nitrate observations, in the presence of lower-level proportional integral (PI) and fractional-order PI (FPI) controllers, with the dual goal of aeration cost reduction and effluent quality enhancement. A modified ASM2d (activated sludge model No. 2d) framework is used as a model for SBR. In the hierarchical control system, variable dissolved oxygen (DO) trajectories are generated by the supervisory fuzzy logic controller and passed to the lower-level controller, according to ammonia and nitrate profiles within SBR. It is crucial to adjust this element properly in order to maximize wastewater treatment efficiency and reduce plant costs, especially for the aeration system. A notable aspect of nitrate-based hierarchical control scheme is to curtail the fresh oxygen use since nitrate (S NO ), a product of nitrification, is utilized for limiting aeration costs. Six distinct control techniques are implemented of which PI and FPI controllers for control of DO at the lower level. Four types of hierarchical ammonia and nitrate-based controllers employing intelligent fuzzy control are deployed. Addition of fuzzy controller contributes to an airflow reduction of 40.08% for ammonia control and 31.58% for nitrate control strategies. This study highlights the superiority of the ammonia-based control strategy, particularly coupled with lower-level FPI controller, based on its ability to minimize airflow without affecting effluent quality. These findings offer helpful insights for advancing the field of wastewater treatment, improving efficiency, and promoting cost-effective and sustainable practices in SBR.