Influence of C/N ratio and ammonia on nitrogen removal and N2O emissions from one-stage partial denitrification coupled with anammox

Abstract

The development of low carbon treatment processes is an important issue worldwide. Partial denitrification coupled with anammox (PD/A) is a novel strategy to remove nitrogen and reduce N₂O emissions. The influence of C/N ratio and NH₄⁺ concentration on nitrogen removal and N₂O emissions was investigated in batch reactors filled with PD/A coupled sludge. A C/N ratio of 2.1 was effective for nitrogen removal and N₂O reduction; higher ammonia concentration might make anammox more active and indirectly reduce N₂O emissions. Long-term operation further confirmed that a C/N ratio of 2.1 resulted in a minimum effluent N₂O concentration (mean value of 0.94 μmol L^-1); as the influent NH₄⁺ concentration decreased to 50 mg L^-1 (NH₄⁺-N/NO₃^--N: 1), the nitrogen removal rate increased to 82.41%. Microbial analysis showed that anammox bacteria (Candidatus Jettenia and Ca. Brocadia) were enriched in the PD/A system and Ca. Brocadia gradually dominated the anammox community, with the relative abundance increasing from 1.69% to 18.44% between days 97 and 141. Finally, functional gene analysis indicated that the abundance of nirS/K and hao involved in partial denitrification and anammox, respectively, increased during long-term operation of the reactor; this change benefitted nitrogen metabolism in anammox, which could indirectly reduce N₂O emissions.

Keywords: Activity of anammox; Ca. Brocadia species; N(2)O reduction; One-stage PD/A system.