N2O micro-profiles in biofilm from a one-stage autotrophic nitrogen removal system by microelectrode

- N2O production from biofilm in a one-stage completely autotrophic nitrogen removal system was investigated using microelectrode technique.
- The pathways of nitrogen transformation and N2O production was characterized by concentration micro-profiles of dissolve oxygen, nitrogen compounds, and N2O in the biofilm.
- NH2OH oxidation, AOB denitrification, and HD were the pathways for N2O production from the biofilm.
- NO2− played a key role in N2O production from the biofilm.

Emission of nitrous oxide (N2O), a greenhouse gas, is of growing concern in biological wastewater treatment. N2O emission from biofilm in a one-stage completely autotrophic nitrogen removal system was investigated using microelectrodes in this study. It is indicated that the pathways of nitrogen transformation in biofilm mainly included partial nitrification and anaerobic ammonium oxidation (anammox), also included nitrification and heterotrophic denitrification (HD). Ammonium-oxidizing bacteria (AOB) denitrification and HD were the main pathways resulting in N2O production in the biofilm, and hydroxylamine (NH2OH) oxidation was a subordinate pathway. In addition, the amount of N2O emission in test in which both NH4+ and NO2− were added (NH4+-N: NO2−-N = 1:1) was about 2 times greater than that in test with NH4+ addition only. This result expressed that NO2− is an important factor affecting N2O production in the biofilm. In conclusion, the present study provides a theoretical support for reducing N2O production in one-stage completely autotrophic nitrogen removal system.