Rapid achievement of partial nitrification process by adopting the combined strategy of anoxic starvation and free ammonia inhibition

Partial nitrification (PN) is a prerequisite step for the short-cut nitrogen removal process, which is crucial to provide stable nitrite accumulation for subsequent units. The present study innovatively proposed a new strategy for the rapid establishment of PN by adopting short-term anoxic starvation combined with high free ammonia inhibition. The sludge obtained from the secondary sedimentation tank of a municipal wastewater treatment plant was starved for 7 days under anoxic conditions, and then wastewater with high ammonia nitrogen (400 mg L⁻¹) was introduced. Within 17 days, stable nitrite accumulation was achieved in the sequencing batch reactor, and the nitrite accumulation rate reached more than 95.0%. The activity of ammonia monooxygenase enzyme increased from 0.0364 ± 0.0074 to 0.1275 ± 0.0021 μg NO₂⁻-N·mg⁻¹ protein min⁻¹, while that of hydroxylamine oxidoreductase enzyme increased from 1.5350 ± 0.0208 to 6.3852 ± 0.0400 EU g⁻¹ SS. The relative abundance of <i>Nitrosomonas</i> increased from 0.10% to 25.90%, while that of <i>Nitrospira</i> consistently remained below 0.04%. And the relative abundance of short-cut denitrifying bacteria, including <i>Truepera</i>, <i>OLB8</i>, and <i>OLB13</i> all increased. The results proved that the short-term anoxic starvation combined with high free ammonia inhibition was an effective strategy for rapid establishment of PN.