Abstract

Ammonium is a common nitrogenous compound in wastewater, and its untreated discharge can disrupt the biogeochemical nitrogen cycle. Constructed wetlands (CWs) offer an innovative, low-cost solution for ammonium removal. In this study, three vertical CWs were designed: one control and two supplemented with iron sources, ferrihydrite (FH) and FeCl3. The two iron-supplemented CWs were bioaugmented with a preincubated inoculum enriched under high iron concentrations. Over 140 days, NH4+ removal efficiencies of 24.8% and 48.0% were achieved in the FeCl3- and FH-supplemented CWs, respectively, with FH demonstrating greater removal uniformity across the CW. Additionally, kinetic models were fitted to describe spatial and temporal trends, supporting FH as the most effective treatment for NH4+ removal. Post-operation analyses confirmed microbial genes associated with Feammox activity, such as Geobacter spp., Ferrum myxofaciens, and Acidiphilium spp. DNA sequencing revealed dominance of Proteobacteria, with Burkholderiales enriched in FH-supplemented CW and Pseudomonadales in FeCl3-supplemented CW, reflecting microbial responses to iron availability. These findings highlight the potential of CWs, particularly those supplemented with FH, as sustainable technologies for ammonium removal and nitrogen pollution control. Future studies should explore scalability and long-term system stability for broader wastewater treatment applications.