Mechanism of reactive co-transport of Fe2+ and antibiotics in hyporheic zone simulated by quartz sand column

Iron redox is often coupled with the degradation and conversion of co-existing organic pollutants, however, their co-transport behavior in hyporheic zone is not clear. In this study, the characteristics and mechanism of reactive co-transport of Fe 2+ and antibiotics during groundwater discharge were revealed by quartz sand column simulation. It was found that Fe 2+ inhibited the transport of three antibiotics sulfamethoxazole (SMX), ofloxacin (OFL), and oxytetracycline (OTC) in the quartz column, and the average inhibitory intensity was OTC (∼80%) > OFL (∼20%) > SMX (∼2%). Meanwhile, the content of dissolved oxygen in the column decreased from more than 7 mg/L to 3 mg/L. Fe 2+ transport in the column was promoted with the increase of OTC and OFL concentrations (2–50 mg/L), as Fe 2+ -OTC and Fe 2+ -OFL complexes inhibited the formation of lepidocrocite and induced Fe 2+ / Fe 3+ cycling during co-transport of Fe 2+ and OTC. In contrast, the interaction between SMX and Fe 2+ was not obvious due to the electrostatic repulsion. Due to the prevalence of Fe 2+ and antibiotics in groundwater system (especially with high antibiotic contamination), this study provides a new perspective on the potential environmental impacts of Fe and pollutants co-transport during groundwater discharge.