Deciphering Iron Interactions with Anaerobic Ammonia Oxidation: Nitrogen Removal Performance, Iron Transformation, and Microbial Community Succession

Abstract

In this study, the mechanism including Fe3+ is involved in the Fe-N cycle and influences Anammox microbial metabolism was investigated. The results revealed that concentrations corresponding to the highest nitrogen removal efficiency (NRE) for short-term dosing differed from those for long-term dosing. The highest NRE of 80.15% was achieved during the first 10 d when Fe3+ concentration was 40 mg/L. The concentration of Fe3+ was 20 mg/L on 65 d, the NRE reached the highest and remained stable at 93.15%, with the accumulation of insoluble iron compounds at 1295.48 mg/L. Then, the NRE gradually decreased with the increase of Fe3+ concentration, and it eventually collapsed to a minimum of 3.72% when 110 mg/L Fe3+ was added. Microbial community results revealed that the abundance of Candidatus_Brocadia gradually decreased from 24.24% to 5.75%. Meanwhile, the abundance of denitrifying bacteria genera (OLB13 & Bosea) and nitrate-dependent Fe2+ oxidation (NDFO) bacteria genera (Comamonas, Thermomonas, Bdellovibrio, and Mizugakiibacter) increased from 0.31% to 13.36%. In conclusion, soluble trivalent iron salts played an active role in constructing the anammox-Feammox-NDFO hybrid nitrogen removal system, and controlling the Fe3+ dosing concentration was the key to improving the NRE and avoiding system degradation.

Keywords: anaerobic ammonia oxidation(Anammox), anaerobic ferric ammonia oxidation(Feammox), Nitrogen removal performance, Sludge morphology, Microbial community