Enhancement of hydrazine accumulation in anammox bioreactors.

The role of hydrazine (NH) in anammox metabolism has been widely studied; however, studies on NH biosynthesis by anammox bacteria are limited in the literature. In this context, the current research aims to investigate the enhancement of biological NH production in the anammox process in a long-term manner. The experimental studies started with the optimization of the operating conditions to achieve maximum NH accumulation. Under favorable conditions (pH = 8.97 ± 0.08; T = 35.5 ± 0.5 °C; initial hydroxylamine dose = 1.46 ± 0.01 mM), 17.16 ± 0.64 mg L of NH accumulated in the batch systems. The continuity of NH bioproduction was then evaluated by long-term observations. A continuous flow bioreactor was operated in four consecutive manipulated periods under optimized conditions. In the long-term operated bioreactor, 55.10 ± 0.30 mg L NH was accumulated at optimal conditions, which was 2.5 times higher than reported in the literature. Although manipulation of the bioreactor operating conditions initially resulted in a significant increase in NH bioaccumulation, it subsequently caused a severe deterioration in anammox activity. However, this could be mitigated by increasing the biomass concentration in the anammox systems. In addition, the relative abundance of Candidatus Kuenenia decreased by 1.88% throughout the long-term operation.