Effect of long-term dosage of hydrazine on mainstream anammox process: Biofilm characteristics and microbial community.

The impact of the long-term trace hydrazine (NH) exogenous supplementation on activity of the anaerobic ammonium oxidation (anammox) biofilm was investigated in a moving bed biofilm reactor (MBBR) for mainstream wastewater treatment. The results of this study demonstrated that the addition of 2-5 mg/L NH enhanced anammox biofilm activity, as evidenced by the augmented nitrogen removal rate (NRR), which increased from 113.4 g/(m·d) to 126.7 g/(m·d) with the introduction of 2 mg/L NH. However, a higher concentration of NH (10 mg/L) suppressed anammox activity, leading to a reduced NRR of 91.5 g/(m·d). Bioindicators revealed that the long-term addition of 2 mg/L NH fostered the accumulation of anammox bacteria (AnAOB) biomass, elevating the volatile suspended solids (VSS) content by 12%. Moreover, the structural composition of extracellular polymeric substances (EPS) within the biofilm was altered, resulting in enhanced biofilm strength within the reactor. The protective mechanism of the biofilm was activated, and EPS secretion was stimulated by the continuous NH supplementation. The introduction of an excess dosage of NH led to alterations in the microbial communities, ultimately resulting in a decline in the performance of the reactor. These findings collectively illustrate that NH, as an intermediate product, can effectively enhance anammox activity within the MBBR for mainstream wastewater treatment. This study contributes to the understanding of the optimization strategies for anammox processes in wastewater treatment systems.