Effect of organic carbons on microbial activity and structure in denitrifying systems acclimated to nitrite as the electron acceptor

- Effect of acetate, propionate, peptone and starch on denitritation was examined.
- The maximum conversion ratios of produced N2O-N to denitrified NO2−-N were 17.93%, 6.51%, 37.41% and 62.67%.
- Thauera was the main denitrifying genus in the four SBRs, with ratios of 19.8%, 19.0%, 2.6% and 10.7%.

Nitrite-based nitrogen removal processes are widely used; thus, denitrification with nitrite as the electron acceptor should be characterized, including free nitrous acid (FNA) inhibition and nitrous oxide (N2O) emission. However, few studies on nitrite-based denitrification systems have been carried out. With acetate, propionate, peptone and starch as carbon sources, four denitrifying sequencing batch reactors (SBRs: SBR1, SBR2, SBR3 and SBR4) with nitrite nitrogen (NO2−-N) as the electron acceptor were used to investigate system performance and microbial communities. In particular, N2O production and emissions were also examined. The NO2−-N removal efficiencies were 99.75%, 99.92%, 85.71% and 92.47%, with NO2-N reduction rates of 102.32, 59.43, 11.79 and 6.51 mg/(g·h). The produced N2O-N concentrations peaked at 0.0200, 0.0281, 1.3772 and 5.8879 mg/L, and the maximum emitted N2O-N concentrations were 0.0122, 0.0084, 0.0182 and 0.6811 mg/L. The conversion ratios of produced N2O-N to denitrified NO2−-N were 17.93%, 6.51%, 37.41% and 62.67% at the initial FNA concentrations of 0.1161, 0.0695, 0.1258 and 0.1875 mg/L, respectively. Thauera was the main denitrifying genus in the four SBRs, with ratios of 19.8%, 19.0%, 2.6% and 10.7%. As the dominant genus containing the nosZ gene, Thauera comprised the majority in SBR1 and SBR2; Thauera, Ralstonia, Acidovorax, Paracoccus and Afipia were detected in SBR3; and Ralstonia and Thauera were the main genera in SBR4.