An advanced control strategy for biological nutrient removal in continuous systems based on pH and ORP sensors

A fuzzy logic-based control system that uses low-cost sensors for controlling and optimizing the biological nitrogen removal in continuous systems has been developed. The novelty of this control system is the use of several pH, ORP, and dissolved oxygen (DO) sensors instead of on-line nitrogen sensors/analyzers. The nitrogen control system was developed and implemented in a UCT pilot plant fed with wastewater from a full-scale plant. The developed nitrification controller allows the effluent ammonium concentration to be maintained below the effluent criteria discharge with the minimum energy consumption. The denitrification process controller allows the energy consumption derived from pumping to be minimized, as the control system only increases the internal recycle flow rate when the anoxic reactor reveals further capacity for denitrification. This advanced control strategy offers an attractive alternative to on-line, nitrogen analyzer-based control systems since it involves lower investment, maintenance, and operational costs that are derived from the instrumentation.

► pH difference indicates if the nitrification is limited by the oxygen concentration.
► pH difference is significantly similar to the monitored ammonium values.
► The controller reduces the aeration energy consumption more than an ammonium analyzer.
► Controller allows ammonium concentration to be maintained below effluent criteria.
► Recycle flow is only increased when there is further capacity for denitrification.