Insight Into Greenhouse Gas Emissions and Nitrogen Removal Performance: A Comparative Study on Denitrification and Anammox Under Anoxic Conditions.

Wastewater treatment is a significant source of greenhouse gas (GHG) emissions, particularly methane (CH) and nitrous oxide (NO). Denitrification acts both as a source of NO emissions and a sink for its reduction, but the direct measurement of NO reduction to N remains a challenge. In this study, an assay method was developed to monitor GHG emissions by comparing denitrification and partial denitrification coupled with anammox (PD/A), with natural isotope analysis used to track NO transformation. The results showed that the PD/A process had a higher nitrogen removal rate and decreased NO emission by 94% compared to denitrification in the treatment of domestic sewage. Both PD/A and denitrification treatments exhibited similar CH emission factors at 0.06%. In the tests of synthetic wastewater prepared with sodium acetate, both PD/A and denitrification treatments demonstrated a two-fold increase in NO -N removal rates, along with a 67%-78% reduction in NO emissions and a 67%-83% reduction in CH emissions. Isotope analysis of NO indicated that PD/A exhibited a higher N site preference and greater NO reduction rates compared to denitrification, contributing to NO mitigation. The synergy of denitrifiers (Denitratisoma and Dechloromonas) and anammox bacteria (Candidatus Brocadia) enhanced nitrogen removal rates and reduced NO emissions.