Effect of exogenous hydrazine on metabolic process of anammox bacteria.

The effect of N 2 H 4 (hydrazine) on AnAOB (anaerobic ammonia oxidizing bacteria) metabolic pattern is unknown. Therefore, the main purpose of this paper was to explore the effects of exogenous N 2 H 4 on the SAA (specific anammox activity), characteristics and metabolic pathway of AnAOB. The results showed that low N 2 H 4 concentration (1–5 mg/L) continuous dosing can promote SAA. The promoting effect was found to be more obvious within the dosage of 3–5 mg/L N 2 H 4. It was also indicated that high N 2 H 4 concentration dosing (5–10 mg/L) can trigger the self-protection mechanism of AnAOB granular sludge by secreting a large amount of B-PN (binding polymeric protein). Intermittent addition of N 2 H 4 at low concentration is conducive to the long-term stable operation of anammox process. Exogenous N 2 H 4 can be directly oxidized by AnAOB to promote the consumption of NO 2 −-N and NH 4 +-N. In addition, excess electrons can also drive the process of NO 3 −-N reduction and NO 2 −-N disproportionation. Theoretically, these reaction processes need two and ten extra electrons respectively, which is not easy to occur compared with the anammox process. [Display omitted] • High N 2 H 4 concentration triggered excessive secretion of binding polymeric protein. • The oxidation of N 2 H 4 enhanced the nitrite reduction and anammox process. • N 2 H 4 drive the nitrate reduction and nitrite disproportionation process. • Low-frequency supplement of N 2 H 4 was beneficial for anammox stable operation. [ABSTRACT FROM AUTHOR]