Aeration length phase control using on-line ammonia and dissolved oxygen feedback control at Choutrana II WWTP

Abstract

The purpose of this work was to study the impact of aeration control strategy using on-line ammonia and dissolved oxygen feedback control on energy consumption in a full-scale wastewater treatment plant. Eight identical oxidation ditches treating the same effluent and operated with conventional control aeration strategy with distinct nitrification and denitrification phases were examined. Each oxidation ditch was periodically aerated according to a fixed phase cycle and phase lengths are controlled by constant dissolved oxygen (DO) set points. To improve the plant’s energy efficiency, a new control strategy has been performed by a full-scale test to control the phase lengths by variable DO set points determined by criteria functions. Knowing the phase lengths provides flexibility to achieve easily nitrogen treatment with nitrification and dentrification processes and treatment objectives. In the test strategy, each zone was separately controlled and the DO set points were changed to avoid unnecessarily high DO levels. The results showed that the ammonium and DO feedback control method can reduce about 30% of the total airflow and lead to a significant aeration energy savings. The plant could preserve treatment efficiency, enhance simultaneous nitrification–denitrification process, and produce excellent effluent quality. A Ammonia and DO feedback controller system was implemented and compared with the actual DO control system.