Supervisory control configurations design for nitrogen and phosphorus removal in wastewater treatment plants

• Published in: Water environment research
• Main Authors: Sheik, Abdul Gaffar, Seepana, Murali Mohan, Ambati, Seshagiri Rao
• Format: Journal Article
• Language: English
• Published: United States 01.08.2021
• Subjects: fuzzy control; model predictive control; Benchmark simulation model (ASM3BioP); effluent quality; supervisory control
• ISSN: 1554-7531
• DOI: 10.1002/wer.1512

Model predictive control (MPC) and Fuzzy controllers are designed in a two-level hierarchical supervisory control framework for control of activated sludge-based wastewater treatment plants (WWTP) in order to efficiently remove nitrogen and phosphorus. Benchmark simulation model No.3 with a bio-phosphorus (ASM3bioP) module is used as a working platform. The hierarchical control framework is used to alter the dissolved oxygen in the seventh reactor (DO ) to control ammonia. Lower-level PI, MPC, and Fuzzy are used to control the nitrate levels in the fourth reactor (S ) by manipulating internal recycle (Q ) and DO in the seventh tank by manipulating mass transfer coefficient (K a ). MPC and Fuzzy are designed in the supervisory layer to alter the DO set-point based on the ammonia composition in the seventh reactor (NH ). From the analysis, it is observed that the effluent quality is improved with a decrease in ammonia, TN, and TP. Though a little difference was observed in the cost for all the control strategies, a trade-off is maintained between cost and percentage improvement of effluent quality. MPC-MPC combination showed significant removal in ammonia and better effluent quality when compared to other control strategies. PRACTITIONER POINTS: Developed novel strategies in hierarchical configurations for better nutrient removal with optimal costs in an A O process. Lower level control strategies deals with dissolved oxygen in last aeration tank and nitrate in fourth anoxic tank (PI/MPC) Higher level control strategy deals with ammonia in the last aeration tank (MPC/Fuzzy). Average and violations of nutrient removal, economy and overall effluent quality for three weather conditions (Dry, Rain and Strom) are studied. A trade-off is observed between EQI and OCI.