Effects of aeration conditions on nitrogen removal performance and N2O emissions in a biofilm CANON reactor

The complete autotrophic nitrogen removal over nitrite (CANON) process offers significant nitrogen removal benefits, but N₂O emissions remain a concern. This study used a sequencing batch biofilm reactor (SBBR) to examine how different aeration conditions (aeration rates and strategies) affect N2O emissions during CANON. In the experiment, N₂O emissions were collected and calculated every 30 min, with nitrogen removal efficiency (NRE) maintained between 81 % and 92 %. The results showed that under continuous aeration conditions, as the aeration rate increased from 1 m³·(m³·h)⁻¹ to 8 m³·(m³·h)⁻¹, N₂O emissions significantly increased from 2.99 mg to 20.23 mg, and the emission proportion increased from 1.53 % to 9.74 %. Under intermittent aeration conditions, when the aeration rate was maintained at 8 m³·(m³·h)⁻¹ and the initial aerobic phase was shortened by 30 min, the system rapidly shifted from aerobic to anaerobic conditions, reducing N₂O emissions from 16.16 mg to 12.69 mg, with the emission proportion dropping from 7.94 % to 6.1 %. At this point, the concentration of NO₂^--N decreased from 27.77 mg·L⁻¹ to 18 mg·L⁻¹. The study suggests that the aeration rate influences N₂O generation by regulating dissolved oxygen (DO) concentration and NO₂^--N accumulation, and affects its release through the gas stripping effect. Appropriately shortening the duration of both the aerobic and anaerobic phases can effectively reduce N₂O emissions.