Long-term effects of acetylene on denitrifying N2O production: Biomass performance and microbial community

Maximizing production and use of N2O produced by the process of denitrification has emerged as a promising concept for energy recovery from nitrogen. Acetylene is well known as an inhibitor of N2O reductase activity, however, to date, few studies have utilized long-term cultivation with acetylene to achieve denitrifying N2O recovery. This work assessed the performance of N2O production and shifts in the denitrifying community in response to long-term exposure of acetylene during nitrite denitrification. Batch tests showed that long-term exposure to acetylene at high concentrations (volume fraction >40 %) resulted in high N2O accumulation, up to 98.6 %. High-throughput 16S rRNA gene analysis suggested that Saprospiraceae dominated the microbial community at the end of the cultivation period with its abundance increasing from the initial 3.2% to 42.2%. Metagenomic analysis revealed that after the long-term cultivation under high level acetylene, the relative abundance of nosZ in the community did not change significantly. Instead, the nosZII-harboring bacteria became dominant. Batch tests in series demonstrated that N2O reduction could be restored rapidly upon removal of acetylene. This study describes an effective method for high yield production of N2O during nitrite denitrification that can be used to enhance energy recovery and improves our understanding of the long-term effect of acetylene on the denitrifying community.