Achieving partial nitrification by inhibiting the activity of Nitrospira-like bacteria under high-DO conditions in an intermittent aeration reactor

It is generally accepted that a low dissolved oxygen (DO) concentration is more beneficial for achieving partial nitrification than high-DO. In this study, partial nitrification was not established under low-DO conditions in an intermittent aeration reactor for treating domestic wastewater. During the operational period of low-DO conditions (DO: 0.3 ± 0.14 mg/L), stable complete nitrification was observed. The abundance of Nitrospira-like bacteria, which were the major nitrite-oxidizing bacteria, increased from 1.03 × 10⁶ to 2.64 × 10⁶ cells/mL. At the end of the low-DO period, the batch tests showed that high-DO concentration (1.5, 2.0 mg/L) could inhibit nitrite oxidation, and enhance ammonia oxidation. After switching to the high-DO period (1.8 ± 0.32 mg/L), partial nitrification was gradually achieved. Nitrospira decreased from 2.64 × 10⁶ to 8.85 × 10⁵ cells/mL. It was found that suddenly switching to a high-DO condition could inhibit the activity and abundance of Nitrospira-like bacteria, resulting in partial nitrification.