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 & sdot;(m3 & sdot;h)-1 to 8 m3 & sdot;(m3 & sdot;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 & sdot;(m3 & sdot;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 & sdot;L- 1 to 18 mg & sdot;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.