Rapid start-up and metabolic evolution of partial denitrification/anammox process by hydroxylamine stimulation: Nitrogen removal performance, biofilm characteristics and microbial community

Enhanced nitrogen removal by hydroxylamine (NH OH) on anammox-related process recently received attention. This study investigated the impact of NH OH on the partial-denitrification/anammox (PDA) biosystem. Results show that NH OH (≤10 mg N/L) immediately induced nitrite accumulation and provided sufficient NO to anammox, achieving a 18.1 ± 4.3 % increase of nitrogen removal efficiency compared to the absence of NH OH. Long-term exposure to NH OH accelerated the functional microbial community transformation to PDA. Thauera was highly enriched (6.1 % → 26.9 %) along with Candidatus Brocadia increased in the biofilms, which mainly favor the coupling process of nitrate reduction and anammox. Although the migration mechanism of anammox and denitrifier revealed by CLSM-FISH alleviates the adverse effects of NH OH, the anammox was inhibited when NH OH exceeding 15 mg N/L through destroying the inner reduction of NO . These results suggested appropriate NH OH addition favors the synergy between denitrifying and anammox bacteria, providing a promising option for wastewater treatment.