The New A-⊘OHO process Based on DO Gradients and Load-Ratio Allocation Enabling Mainstream PN/A in Toxic Industrial...

The partial nitritation-anammox (PN/A) process offers significant benefits in energy conservation and carbon neutrality, however, its application is limited by toxic industrial pollutants and the challenge of maintaining optimal nitrogen form ratio. A novel pilot-scale coking wastewater treatment process (A-OHO process) achieved the selective accumulation of nitrogen species with different valence states within the pre-aerobic units through regulation of dissolved oxygen (DO) concentration gradients. Thermodynamic, kinetic, and SHAP analyses revealed that DO concentration and the ratio of DO to pollutants concentration (DO/COD, DO/NH₄⁺-N) play equally critical roles in nitrogen species transformations. Machine learning and the TCW-ASM3 model were integrated to optimize operating conditions and patterns under varying loads. Notably, evolving A-OHO process into A-⊘OHO (⊘O = parallel O_NH3 and O_NO2 reactor) process provided a practical strategy for mainstream PN/A. By controlling flow rates and hydraulic retention times (HRT) between two reactors, anammox was sustained without the need for external carbon sources or recirculation. When the flow ratio of the O_NH3 reactor to O_NO2 reactor was 0.4 and the HRT was 15 h/19 h, the model simulated results indicated that total nitrogen (TN) decreased from 148.20 mg/L to 28.56 mg/L, with energy consumption of 1.55 kWh/m³, saving of 3.79 kWh/m³ compared to conventional methods. This operating mode is expected to help overcome the technical barriers of PN/A in the application of high-concentration wastewater, and the modeling analysis indicates that it facilitates the control of TN emissions to extremely low levels, thereby offering a more sustainable solution for industrial wastewater management.