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

Abstract

Wastewater treatment is a significant source of greenhouse gas (GHG) emissions, particularly methane (CH₄) and nitrous oxide (N₂O). Denitrification acts both as a source of N₂O emissions and a sink for its reduction, but the direct measurement of N₂O reduction to N₂ 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 N₂O transformation. The results showed that the PD/A process had a higher nitrogen removal rate and decreased N₂O emission by 94% compared to denitrification in the treatment of domestic sewage. Both PD/A and denitrification treatments exhibited similar CH₄ 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 NO₃ ^--N removal rates, along with a 67%-78% reduction in N₂O emissions and a 67%-83% reduction in CH₄ emissions. Isotope analysis of N₂O indicated that PD/A exhibited a higher ¹⁵N site preference and greater N₂O reduction rates compared to denitrification, contributing to N₂O mitigation. The synergy of denitrifiers (Denitratisoma and Dechloromonas) and anammox bacteria (Candidatus Brocadia) enhanced nitrogen removal rates and reduced N₂O emissions.