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

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.