Removal Effect of Coagulating Sedimentation Method on Polyethylene Microplastics in Water

Microplastic is a new kind of pollutant. It exists widely in the aquatic environment and seriously endangers the aquatic ecosystem. In this study, the coagulating sedimentation method was used to remove microplastics in water. Polyethylene (PE) was selected as the representative of microplastics, polyferric sulfate (PFS), polyaluminum chloride (PAC) and aluminum sulfate (AS) were used as coagulant, and polyacrylamide (PAM) was used as coagulant aid to study the effects of pH, coagulant concentration and sedimentation time on the removal of PE by single and composite coagulant. The results showed that when the dosage of PFS was 0.5 g/L and pH was 5.0, the removal rate could reach 82.14%, which was better than PAC and AS, indicating that PFS had better coagulation and sedimentation performance for PE; the composite coagulant of PFS+PAC+AS (1 g/L+0.2 g/L+0.2 g/L, pH was 5.0) had the highest removal rate of PE, reaching 96.06%; the removal rate of PE increased with the increase in sedimentation time, but considering that the longer sedimentation time has less contribution to the improvement of removal rate, it is recommended that 4 h is appropriate.