The green footprint of anammox processes under simulated actual operating conditions: Focusing on the nitrous oxide and methane production

The anammox process has attracted increasing attention due to its advantages of low-carbon and energy-saving, nevertheless, greenhouse gas was still generated during its engineering applications process. Hence, it is vital to comprehensively understand the production characteristics and mechanisms of N2O and CH4 in anammox processes by responding to practical conditions including dissolved oxygen, temperature, and salinity. Results showed that N2O production increased by 192 %–358 %, while nitrogen removal efficiency (NRE) increased by 64.2 %–86.8 % with increasing temperature. The increased salinity inhibits 40.60 %–65.33 % N2O production with a decrease NRE of 7.85 %–18.2 %. CH4 production was the highest at 18–27 °C, reaching 3.07 ± 0.11–4.06 ± 0.16 mg·L−1, which were 1.59–2 and 1.29–1.38 times higher than that at 8–17 °C and 28–37 °C, respectively. Denitratisoma, Thauera, and Nitrosomonas were the main functional microbes for greenhouse gas production in anammox consortia. Notably, H2O2-induced intracellular Fenton reaction may be critical for the CH4 production in anammox consortia. This work provides valuable insights into achieving efficient nitrogen removal and minimizing carbon footprint in anammox systems and provides a theoretical basis for implementing the net-zero emission idea in wastewater treatment plants. [Display omitted] •N2O emission is much higher than CH4 in lab-scale anammox systems.•Higher temperatures result in more N2O emissions compared to the increased NRE.•1 % salinity inhibits NRE and reduces N2O and CH4 emissions.•Nitrosomonas and Denitratisoma are the main contributor for N2O emission.•Intracellular Fenton reaction in anammox consortia responds to the CH4 prodution.