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

Abstract

The enhancing effect of hydrazine (N2H4) 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 N2H4 and to follow the dynamic changes in functional microorganisms under two different N2H4 application strategies (L1–136 days; L2–344 days). In the first strategy (L1), ≥ 88 % of NH4+-N and NO2--N were removed during the N2H4 applications at ≤ 150 mg/L dosages. Above 150 mg/L, nitrogen treatment performance deteriorated. When 150 mg/L of N2H4 was continuously fed to the bioreactor in L2, anammox bacteria performed their activity with ≥ 70 % removal efficiency for both NH4+-N and NO2--N up to 2.74 g/L cumulative N2H4 loading. During these periods in both strategies, Candidatus Kuenenia, a sole anammox genus identified in the bioreactors, was found to adapt to higher N2H4 concentrations than those reported in the literature. Although nitrogen removal capacity deteriorated towards the end of the operation periods, N2H4 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 N2H4-containing wastewaters, in addition to their current widespread applications.