N2O profiles in the enhanced CANON process via long-term N2H4addition: minimized N2O production and the influence of exogenous N2H4on N2O sources

Production of the greenhouse gas nitrous oxide (N2O) from the completely autotrophic nitrogen removal over nitrite (CANON) process is of growing concern. In this study, the effect of added hydrazine (N2H4) on N2O production during the CANON process was investigated. Long-term trace N(2)H(4)addition minimized N2O production (0.018% +/- 0.013% per unit total nitrogen removed) and maintaining high nitrogen removal capacity of CANON process (nitrogen removal rate and TN removal efficiency was 450 +/- 60 mg N/L/day and 71 +/- 8%, respectively). Ammonium oxidizing bacteria (AOB) was the main N2O producer. AOB activity inhibition by N(2)H(4)decreased N2O production during aeration, and the N(2)H(4)concentration was negatively correlated with N2O production rate in NH(4)(+)oxidation via AOB, whereas N2O production was facilitated under anaerobic conditions because hydroxylamine (NH2OH) production was accelerated due to anammox bacteria (AnAOB) activity strengthen via N2H4. Added N(2)H(4)completely degraded in the initial aeration phases of the CANON SBR, during which some N(2)H(4)intensified anammox for total nitrogen removal to eliminate N2O production from nitrifier denitrification (ND) by anammox-associated, while the remaining N(2)H(4)competed with NH2OH for hydroxylamine oxidoreductase (HAO) in AOB to inhibit intermediates formation that result in N2O production via NH2OH oxidation (HO) pathway, consequently decreasing total N2O production.