Revealing the characteristics and nitrogen metabolism mechanism of Anammox biofilm assisted by nanoscale zero-valent iron.

Biofilm was an advanced approach to facilitating anaerobic ammonium oxidation (Anammox) application owing to high biomass retention and stable performance. The characteristics, nitrogen removal kinetics and microbial metabolic mechanism of Anammox biofilm with intermittent dosing of nanoscale zero-valent iron (nZVI) were comprehensively revealed. Anammox biofilm was acclimated efficiently with nZVI assistance within 110 days. nZVI stimulated the secretion of EPS, especially T-EPS and PN, which showed key importances in biofilm formation. The nitrogen removal kinetics were accurately described and predicted by the modified Boltzmann model. High-throughput sequencing revealed that the microbial richness and diversity gradually declined, while AnAOB were enriched from 0.12 % to 1.34 %. Furthermore, key functional genes involved in the Anammox pathway (e.g., hdh and hzsA/B/C) were enriched by 427.90-596.49 %. Anammox process was the dominant in the system, cooperating with other pathways driven by the Fe(II)/Fe(III) cycle. This study provided innovative insights into the enhanced mechanism of nZVI on Anammox.