In addressing the challenge of efficient nitrogen removal in constructed wetlands (CWs) treating low carbon-to-nitrogen (C/N) ratio agricultural runoff, researchers explored the efficacy of various amendments. The study, published in the Journal of Environmental Management, compared five CWs: one with quartz sand (control), and others with biochar, FeCl3-modified biochar (Fe-BC), iron ore, and a combination of iron ore and biochar.

Iron ore emerged as the most effective amendment, significantly enhancing total nitrogen (TN) removal. The success was attributed to the increased abundance of ammonia-oxidizing, heterotrophic denitrifying, nitrate-dependent anaerobic ferrous oxidizing (NAFO), and Feammox bacteria in the iron ore system. These microbial communities facilitated the simultaneous removal of various nitrogen compounds (NH4+-N, NO3−-N, NO2−-N).

The study’s microbial community analyses and co-occurrence network visualizations revealed a complex interplay among nitrogen and iron cycle bacteria in the iron ore system, leading to high TN removal efficiency. This cooperative mutualism among bacteria, especially those involved in nitrogen and iron cycling, was more pronounced in the iron ore system than in others.

These findings suggest that iron ore is a promising, cost-effective amendment for improving nitrogen removal in CWs, particularly for agricultural runoff with low C/N ratios. This research provides critical insights for developing more efficient and sustainable nitrogen removal strategies in wastewater treatment.