Removal of Microplastics from Wastewater Treatment Plants by Coagulation

Wastewater treatment plants represent an important point source of microplastics (MPs) entering aquatic environments, raising increasing concerns regarding ecosystem integrity and potential risks to human health. Improving the removal efficiency of MPs during wastewater treatment is therefore of both environmental and technological significance. Polyaluminum chloride (PAC), polyferric sulfate (PFS), and polyacrylamide (PAM) were applied to remove MPs by coagulation, with particular emphasis on the effects of PAM type (cationic, anionic, and non-ionic). The optimal removal efficiency achieved by PAC alone for polystyrene was 55.00 ± 3.54% at a dosage of 300 mg L−1, which increased significantly to 87.50 ± 1.87% with the addition of cationic PAM. Similarly, MPs removal by PFS increased from 33.75 ± 1.77% at 160 mg L−1 to 62.50 ± 3.53% when combined with cationic PAM. Overall, PAC-based coagulation exhibited higher MPs removal efficiency than PFS, and cationic PAM outperformed anionic and non-ionic PAM, likely attributable to electrostatic interactions with negatively charged MPs in wastewater systems. In addition, PAC/PAM coagulation enabled effective removal of multiple MPs types while simultaneously enhancing phosphate removal, highlighting its potential for the integrated control of MPs and phosphate pollution in wastewater systems.