[Effect of Different TOC to NH₄⁺-N Ratios on Nitrogen Removal Efficiency in the ANAMMOX Process]

The effect of the TOC to NH₄⁺-N ratio on nitrogen removal rate in an ANAMMOX sequencing batch reactor was studied for the short term and long term. Short-term results showed the maximum TOC/NH₄⁺-N that ANAMMOX could afford was 1.4. At the same time, the rate of nitrogen removal was 0.26 kg·(m³·d)^-1. The maximum nitrogen removal rate of 0.34 kg·(m³·d)^-1 was obtained when TOC/NH₄⁺-N was less than 0.4 in the long-term experiment. Whereas the nitrogen removal rate of the reactor decreased continuously when TOC/NH₄⁺-N exceeded 0.4, and it was difficult to recover the activity of the ANAMMOX bacteria in the short term. qPCR results showed that the amount of ANAMMOX bacteria dropped from 2.9×10¹¹ copies·mL^-1 to 3.15×10¹⁰ copies·mL^-1 with the increase of organics. When TOC/NH₄⁺-N exceeded 1.6, NH₄⁺-N could hardly be removed by the ANAMMOX bacteria, which were severely inhibited. The number of denitrifying bacteria was 3.0×10⁹ copies·mL^-1; meanwhile, most of the NO₂^--N in the reactor was removed via denitrification.