Enhanced biological nitrogen removal under low dissolved oxygen in an anaerobic-anoxic-oxic system: Kinetics, stoichiometry and microbial community

A lab-scale anaerobic-anoxic-oxic system was used to investigate the nitrogen removal mechanism under low dissolved oxygen (DO) conditions. When DO was decreased from 2 to 0.5 mg L-1, chemical oxygen demand (COD) and NH4+ removals were not influenced, while total nitrogen removal increased from 69% to 79%. Further batch tests indicated that both the specific nitrification rate and denitrification rate greatly increased under low DO conditions. When DO was decreased from 2 to 0.5 mg L-1, the oxygen half saturation constant value for ammonia oxidizing bacteria (AOB) decreased from 0.39 to 0.29 mg-O2 L-1, and for nitrite oxidizing bacteria (NOB), it reduced from 0.29 to 0.09 mg-O2 L-1. Correspondingly, the observed yield coefficients increased from 0.05 to 0.10 mg-cell mg(-1)-N for AOB, and from 0.02 to 0.06 mg-cell mg(-1)-N for NOB. High-throughput sequencing revealed that the relative abundances of AOB increased from 6.13% to 6.54%, Nitrospira-like NOB increased from 3.67% to 6.50%, and denitrifiers increased from 2.84% to 7.04%. Improved simultaneous nitrification and denitrification under low DO conditions contributed to the enhanced nitrogen removal. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study found that specific nitrification and denitrification rates increased under low dissolved oxygen conditions, with a decrease in the oxygen half saturation constant for both ammonia oxidizing bacteria and nitrite oxidizing bacteria. The observed yield coefficients also increased, along with higher relative abundances of AOB, NOB, and denitrifiers detected through high-throughput sequencing. Improved simultaneous nitrification and denitrification under low DO conditions contributed to enhanced nitrogen removal.