Efficient nitrous oxide production and metagenomics-based analysis of microbial communities in denitrifying systems acclimated with different electron acceptors

Effects of electron acceptors and free nitrous acid (FNA) concentrations on the denitrification performance and nitrous oxide (N ₂ O) generation were investigated in denitrifying systems acclimated with nitrate (SBR _A ) and nitrite (SBR _I ). Denitrifying genes and functional microbial communities were also analyzed. Under the same influent organic carbon to nitrogen ratio, the nitrate removal percentage in SBR _A was 75.2%, while that of nitrite was 99.8% in SBR _I . The highest N ₂ O conversion ratio of 89.9% was obtained when nitrite was applied to SBR _A due to the insufficient electrons for N ₂ O reductase (Nos). Higher N ₂ O generation was attributed to the severe FNA inhibition on Nos when NO ₂ –N was used as the electron acceptor, rather than the relative abundance of gene nos. The dominant denitrifier was Acidovorax with the abundance of 21.9% in SBR _A , while Thauera of 11.3% in SBR _I .