Strategy for Maintaining Stable Partial Nitritation of Low-Strength Ammonia Wastewater by Hydrazine.

The primary objectives of this study were to identify the effectiveness of hydrazine on partial nitrification in a sequencing batch reactor when treating low-strength ammonia wastewater and to investigate its impact mechanism. Partial nitrification was successfully initiated and maintained by dosing with hydrazine, and the short- and long-term effects of hydrazine on partial nitrification and microbial bioactivity were investigated. The results showed that dosing with a moderate amount of hydrazine improved the nitrite accumulation rate with little effect on the ammonia conversion rate. Both the short- and long-term tests showed the optimum hydrazine dosage was 7.5 mg/L. In the long-term tests, dosing with 7.5 mg/L of hydrazine led to an ammonia conversion rate and nitrite accumulation rate of 99.10% and 93.24%, respectively. The change in the mixed liquid suspended solids (MLSS) and mixed liquid volatile suspended solids (MLVSS) in the long-term tests showed that, although dosing with hydrazine influenced the biochemical activity of the sludge, the MLVSS/MLSS increased after an initial decrease. High-throughput analysis showed that Thauera, Nitrosomonas, and Denitratisoma were the dominant bacteria in the system dosed with 7.5 mg/L of hydrazine, which may explain the high nitrite accumulation. Analysis of the mechanism showed that nitrite-oxidizing bacteria were more inhibited by hydrazine dosing than ammonium-oxidizing bacteria. [ABSTRACT FROM AUTHOR]