Enhanced removal of microplastics from wastewater treatment plants by a novel magnetic filter

Microplastics (MPs) discharged from wastewater treatment plants (WWTPs) have emerged as serious pollutants in aquatic environments. Herein, a new magnetic filter (MFA) was prepared using an acidification-magnetization method with fly ash (FA) as the base material. The filter specifically targeted the removal of 1-μm polystyrene microspheres (PSMPs) because of the challenges they pose in filtration processes. The findings demonstrated that MFA filter exhibited superior PSMPs removal efficiency, with increases of 219%, 250%, and 288% compared to FA at flow rates of 1, 3, and 5 mL min, respectively. Scanning electron microscopy and other characterizations provided insights into the removal mechanisms of PSMPs using the MFA filter, which combined electrostatic attraction, π-electron conjugation, hydrogen bonding, and complexation. Environmental variables, such as solution pH, ionic strength, and dissolved organic matter, were identified as considerable influences in the removal process of PSMPs. The practical application confirmed that the MFA filter considerably promoted the elimination of MPs from the secondary treatment effluent of WWTPs without having any toxic effects on freshwater fish. Thus, this study provides a new approach to the resource utilization of FA, which would prominently promote its application prospects in MPs immobilization and removal from wastewater effluent.