Effect of PH on the production of N2O during denitrification process

To investigate the effect of pH on the production of N₂O during shortcut denitrification process, NaNO₂ was added into the system to ensure that the initial concentration of NO₂^--N was 40mg/L. HCl and NaOH were used to regulate pH of the system using sequencing batch reactor with volume of 2.4L. Results showed that nitrite reduction rate under different pH varied little in the shortcut denitrification system. The maximum nitrite reduction rate was 0.084mgN/(mgMLSS-h) and the minimum nitrite reduction rate was 0.071mgN/(mgMLSSh); the production of N₂O could reach 4.272mgN/L, which accounted for 10.68% of influent nitrite concentration during nitrite denitrification when pH was 6.5. The production of N₂O reached only 0.573mgN/L when pH was 8.0. The reasons of high production of N₂O under low pH during denitification process were mainly: (1) low pH had strong inhibition on N₂O reductas; (2) low pH played a role of screening strains.