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.
Keywords: ANAMMOX; TOC/NH4+-N; denitrification; organic matter; quantitative PCR.