LAUSR

Abstract Sewage treatment is one of the important sources of nitrous oxide (N2O) production, understanding its microbial process is fundamental for reducing N2O emissions. In this study, the stable isotope tracer method was used to reveal the contribution of co-denitrification to the release of N2O in addition to nitrification and denitrification in subsurface wastewater infiltration system (SWIS). The effects of nitrate addition modes were also explored. The results indicated that co-denitrification, significantly affected by dissolved oxygen, pH and potential denitrification activity, had to be taken into account in N2O formation. When the addition of nitrate nitrogen changed from one-time to intermittent, the contribution of co-denitrification increased from (1.87 ± 0.3) % to (34.2 ± 3.8) %. As a result, N2O emission and conversion rate increased from (5.17 ± 1.4) × 10−3 mg/m2·h to (6.77 ± 1.7) × 10−3 mg/m2·h and from (0.17 ± 0.02) % to (0.232 ± 0.01) %, respectively. The results also suggested that, given the increasing scale of SWIS applications, more attention should be paid to the nitrogen cycle in the system. To effectively mitigate the generation and conversion of N2O, measures to reduce nitrate accumulation need to be taken.