Probing the Reaction Mechanism and Properties of Shortcut Nitrification by Isotope Fractionation Techniques

Shortcut nitrification, as one of the key technologies for achieving carbon emission reduction and energy conservation, had gradually been applied in municipal wastewater treatment. To investigate nitrogen and oxygen migration-transformation characteristics during the NH₄⁺-N→NO₂⁻-N oxidation stage in urban sewage short-cut nitrification processes, an intermittent aeration strategy （aeration/rest duration ratio of 30 min:30 min） was adopted to achieve rapid start-up and stable operation of shortcut nitrification （room temperature operation with DO maintained at 1~1.2 mg/L）. Results demonstrated that the ammonia nitrogen removal efficiency exceeded 98% and nitrite accumulation rate surpassed 97% in domestic wastewater treatment. The δ¹⁵N_NO2 and δ¹⁸O_NO2 values increased with enhanced NO₂⁻-N accumulation rate, where δ¹⁸O_NO2 gradually stabilized at 11‰ while δ¹⁵N_NO2 rose from −25.79‰ to −12.51‰, indicating significantly stronger nitrogen isotope fractionation than oxygen isotope fractionation. Through artificial regulation of δ¹⁸O_H2O levels （54.34‰, 97.98‰, and 147.19‰）, δ¹⁸O_NO2 abundance was observed to substantially exceed δ¹⁸O_H2O values with increasing NO₂⁻-N accumulation rate, confirming that both O₂ and H₂O participated in NH₄⁺-N to NO₂⁻-N conversion during shortcut nitrification. The dual N and O isotope fractionation technology provided in-depth insights into the formation mechanisms of shortcut nitrification, enabled rapid assessment of the feasibility and stability of NO₂⁻-N accumulation, and offered new ideas and methods for process control and real-time monitoring in short-cut nitrification systems.