The effect of S/N ratio on NO and N2O accumulation during sulfide autotrophic denitrification

Nitro oxide (NO) and Nitrous oxide (N₂O) are inevitable intermediates of sulfide autotrophic denitrification (SAD) process, and have huge environmental hazard. This study investigated the produce mechanism and accumulation characteristic of NO and N₂O in SAD process under different S/N ratios. The results showed that the lower S/N ratio, the higher NO accumulation. Which was due to the strong reducing effect of S²- and the electronic competition between nitrogen reductase. And under S/N ratio = 2, N₂O level reached its peak, which was caused by electronic competition. When the S/N ratio = 1, although the electronic competition was more intense, the total amount of electrons was less, thus the N₂O produced is lower than that produced when S/N=2. Microbial community analysis showed that Thiobacillus sp. (62.44%) was the predominant genus, and conducted the suldide-oxiding autotrophic denitrification process.