Application of iron-manganese oxide fillers in bioretention facility: enhanced removal of antibiotics and conventional contaminants

Bioretention facilities are common source reduction facilities, but traditional fillers are not effective in reducing emerging contaminants such as antibiotics. Although Fe-Mn oxides have been extensively explored, their removal of emerging contaminants and application in the sponge city have not yet been addressed. Therefore, this study aims to address this limitation by developing Fe-Mn oxide fillers. In this research, the optimal preparation conditions (Fe/Mn mole ratio, polyvinyl alcohol (PVA) concentration, and filler particle size) and influencing factors (filler dosage, initial pollutant concentration, pH, temperature, and co-existing ions) were investigated using a typical antibiotic, norfloxacin (NOR), as the target contaminant. The removal mechanism of NOR was investigated by SEM, FTIR, and XPS characterizations. Subsequently, the fillers were applied to bioretention facilities with different filling modes (layered and mixed) to evaluate their effectiveness in removing NOR and conventional pollutants at different recurrence periods, drought periods, and pollutant influent concentrations. The study indicated that Fe-Mn oxide filler (Fe/Mn mole ratio of 4:1, PVA concentration of 7%, particle size of 4mm) could remove more than 70% of NOR (1~20mg/L). The NOR removal by Fe-Mn oxide filler involved adsorption and redox reactions. Notably, bioretention facilities using Fe-Mn oxide fillers have shown varying degrees of improvement in the removal of NOR and conventional pollutants compared to conventional ones. This study contributes to the application of Fe-Mn oxide filler in bioretention facilities, thus playing a crucial role in mitigating antibiotic pollution in stormwater runoff.