Advanced nitrogen removal without addition of external carbon source in an anaerobic/aerobic/anoxic sequencing batch reactor.

Advanced nitrogen removal without the addition of external carbon source is challenging in the conventional biological nitrogen removal processes. This study presented a novel anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A SBR) based on endogenous nitrate (NO3--N) respiration to enhance nitrogen removal. The mean effluent total nitrogen (TN) in the A/O/A SBR could be reduced to as low as 3.5 mg/L, when the average influent TN and chemical oxygen demand (COD) were 52.7 and 235.4 mg/L, respectively. This advanced nitrogen removal was attributed to the post-denitrification, since 82.7% of TN removal was achieved in the post-anoxic stage. The post-denitrification rate with nitrite (NO2--N, 0.59 mg NO2--N/gMLVSS/h) was higher than that with NO3--N (0.35 mg NO3--N/gMLVSS/h). Therefore, the post-anoxic time could be further optimized by achieving denitrification via NO2--N. The A/O/A SBR has good potential in achieving advanced nitrogen removal, especially in nitrogen-sensitive rural areas.