Long-term Performance of Single-stage Partial Nitritation, Anammox and Denitrification Process (SPNAD) Applying With Multi-section Declined Aeration

To solve the problem that partial nitritation is difficult to maintain stable in the integrated system of single-stage partial nitritation, anammox and denitrification (SPNAD) process, and the effluent of partial shortcut nitrification is unstable, the study was conducted based on 60-day aeration control experiment fed with constant sewage, 80 mg/L of ammonium mass concentration and 150 mg/L of chemical oxygen demand (COD). Results show that with the control of dissolved oxygen (DO) in the range of 0.3-0.5 mg/L, three DO jump points, marked as T_a, T_b, and T_c, respectively, appear during the continuous aeration stage. T_b can be regarded as the end point of COD degradation while T_c can be viewed as the end point of aeration. At the point of T_c, the mass concentrations of ammonium and nitrite were 20.11 mg/L and 22.83 mg/L, respectively, and the mass concentration ratio of nitrite/ammonium was in the range of 0.93-1.37, which is feasible for Anammox. Besides, Δρ(DO)/Δt≥0.04 mg/(L·min) was set for decreasing aeration and stopping aeration. Afterwards, the aeration pattern was applied in the SPNAD system fed with real sewage (41.4-75.5 mg/L ammonium for 81 days. 96.7% of total nitrogen removal ratio (NRR) was achieved and nitrogen in effluent was 2.11 mg/L in average. Based on nearly a 150-day experiment, a novel multi-section declined aeration control strategy was put forward and applied in SPNAD system fed with real sewage. Results show that the system can adapt to the fluctuation of low ammonium concentration and low ρ(COD)/ρ(TN) sewage and achieve a much better effluent quality, which meets standard of the class A sewage discharge.