Anammox-synchronous zero-valent iron oxidation promoting synergistic nitrogen and phosphorus removal from wastewater

In this study, a novel process, anammox-synchronous zero-valent iron (ZVI) oxidation in which nitrate byproducts are used for in situ oxidization of ZVI was first developed to simultaneously remove nitrogen and phosphorus from wastewater. The optimal ZVI dosage of 4 g/L significantly improved the nitrogen removal efficiency to 86.02 +/- 1.98%, with the highest phosphorus removal efficiency enhanced from 39.62% to 98.97%. Several analytical techniques revealed that iron phosphate minerals formed by biologically induced mineralization promoted the phosphorus removal of the system and enhanced the settleability of granules. Candidatus Brocadia was the main anammox functional bacteria, which could promote the formation of iron phosphorus minerals. The increase of key functional genes involved in denitrification, especially narG, played a pivotal role in reducing nitrate to improve nitrogen removal performance. In addition, abundance regulation of gene fur enabled anammox bacteria always maintain high activity under different pH and ZVI dosages.