Long-term response of anammox process to hydrazine under different exposure strategies

The enhancing effect of hydrazine (N 2 H 4 ) on anammox has been extensively studied; however, its long-term inhibitory effect remains controversial. This study aims to evaluate the susceptibility and resistance of the anammox bacteria to N 2 H 4 and to follow the dynamic changes in functional microorganisms under two different N 2 H 4 application strategies (L1-136 days; L2-344 days). In the first strategy (L1), >= 88 % of NH 4 +-N and NO 2--N were removed during the N 2 H 4 applications at <= 150 mg/L dosages. Above 150 mg/L, nitrogen treatment performance deteriorated. When 150 mg/L of N 2 H 4 was continuously fed to the bioreactor in L2, anammox bacteria performed their activity with >= 70 % removal efficiency for both NH 4 +-N and NO 2--N up to 2.74 g/L cumulative N 2 H 4 loading. During these periods in both strategies, Candidatus Kuenenia , a sole anammox genus identified in the bioreactors, was found to adapt to higher N 2 H 4 concentrations than those reported in the literature. Although nitrogen removal capacity deteriorated towards the end of the operation periods, N 2 H 4 was still utilized in the bioreactors. Therefore, this study makes an important contribution to the utilization of anammox bacteria as a potential candidate for the treatment of N 2 H 4-containing wastewaters, in addition to their current widespread applications.