Enhanced Nitrogen Removal by Anammox in Iron-Based Autotrophic Denitrification Filters

Nitrogen pollution poses significant risks to both environmental systems and human health. Iron-based autotrophic denitrification offers a green and cost-effective strategy for nitrogen removal, but is often accompanied by the accumulation of undesirable byproducts. A nitrogen removal system combining anammox with iron-based autotrophic denitrification was constructed in this study to investigate the enhancement effect of anaerobic ammonium-oxidizing bacteria (AnAOB). The results showed that during the stable operation phase, nitrate removal efficiencies reached 91.45% and 84.29% for groups A (0.5 g/L AnAOB) and B (0.1 g/L AnAOB), respectively, significantly higher than the 62.87% observed in the control group. Furthermore, the experimental groups exhibited markedly reduced accumulation of ammonium byproducts. Microbial community analysis revealed that AnAOB addition increased microbial richness and diversity, and promoted community shifts that favored nitrogen removal. Notably, even low dosages of AnAOB yielded strong performance enhancements, underscoring the economic viability of this integrated approach. Structural characterization using SEM, XRD, and XPS indicated that system performance deterioration in the later stages was primarily due to cell encrustation and iron passivation. Electrochemical analyses further demonstrated that iron passivation impaired electron transfer on the filler surface, thereby reducing denitrification efficiency, whereas extracellular polymeric substances (EPS) did not exhibit such inhibitory effects. These findings provide both mechanistic insight and practical guidance for the design and optimization of anammox-enhanced iron-based denitrification systems.