Temperature effects on nitrogen removal and N₂O emissions in anammox reactors

Mainstream anammox faces challenges in adapting to non-optimal temperatures and managing greenhouse gas emissions. This study investigates nitrogen removal and N₂O emissions in attached-growth anammox reactors subjected to rapid temperature shifts (15-55 °C). Temperature reductions to 15-25 °C had minimal impact on the anammox bacterial populations, with nitrogen removal rates of 0.37±0.11 gN/(L⋅d) and 0.88±0.10 gN/(L⋅d) at 15 °C and 25 °C, respectively. In contrast, increasing temperatures to 45-55 °C significantly diminished both anammox biomass and bioactivity. The reactor at 35 °C exhibited the lowest N₂O emissions (< 1.0 mgN/(L⋅d)), while emissions rose to approximately 5.0 mgN/(L⋅d) at 15 °C and 3.4 mgN/(L⋅d) at 55 °C (during 295-395 d), primarily due to denitrification performed by coexisting ammonia-oxidizing bacteria and denitrifying microbes. This study provides insights into temperature adaptability and N₂O emission risks, supporting mainstream anammox applications.