Improving the nitrogen removal efficiency of an A²/O based WWTP by using an on-line Knowledge Based Expert System

The results obtained using an expert system to control an activated sludge process involving nutrient removal are reported. The study was conducted at a pilot plant using an Anaerobic/Anoxic/Oxic (A2/O) scheme for which a distributed control system was specially developed. The system allows various expert operational approaches to be developed with a view to minimize nitrogen levels in the outlet while using the minimum amount of energy. The proposed distributed control system is supervised by a Knowledge Based Expert System (KBES) constructed with G2© (a tool for expert system development) and permits the on-line implementation of every operating strategy of the experimental system. A set of experiments involving variable loads and flow-rates was carried out. It revealed that the amount of removed nitrogen could be increased by 11% compared to the usual operating conditions. This increase resulted in a decrease in the amount of total nitrogen and ammonium nitrogen in the outlet by 49% and 64%, respectively. These improvements were achieved with little energy cost because the performance of the treatment plant was optimised using operating rules implemented in real time. © 2002 Elsevier Science Ltd. All rights reserved.