Effects of Polystyrene Microplastics on Multiple Tetracycline Removals by Ferrate

Water treatment processes typically focus on eliminating organic pollutants in wastewater but often overlook the presence of coexisting microplastics. In this study, we examined the effects of polystyrene microplastics on removing three tetracyclines using ferrate. The presence of polystyrene microplastics influenced the efficiency of oxidation, adsorption, coagulation, and complexation, leading to varying degrees of tetracycline removal by ferrate. Our results showed that unaged polystyrene microplastics increased tetracycline removal by 29.2%, while three aged polystyrene microplastics showed an increased removal ratio, and ten soaked polystyrene microplastics inhibited tetracyclines removal by up to 41.6%. The breakdown of polystyrene microplastics also released small molecules and contributed to a 7.4% increase in total organic carbon. The carbonyl index of polystyrene microplastics also rose to 1.68, and specific functional groups, including C–O, C═O, Fe–O, and C–N–C, appeared on the surface. While polystyrene microplastics weakened the oxidation capacity of ferrate in removing tetracyclines, their increased surface area and pore volume aided in tetracyclines adsorption. Furthermore, polystyrene microplastics acted as support sites for Fe3+ and Fe(OH)3, facilitating the formation of polystyrene-Fe-tetracycline complexes, which aided in tetracycline removal via complexation. Fe(OH)3 helped with the adsorption and coagulation removal of tetracyclines. The potential adverse effects of polystyrene microplastics are widespread and require more attention in removing pollutants when microplastics coexist in aquatic environments.