Simultaneous removal of Microcystis aeruginosa and microplastics by oxidation enhanced coagulation

The composite pollution is an increasingly severe challenge in the field of water treatment. Especially, microplastics (MPs) contamination and Microcystis aeruginosa (M. aeruginosa) were verified that they could synergistically pose a serious threat to safety of drinking water. Therefore, developing effective removal technology is an urgent task. In this study, the simultaneous removal of M. aeruginosa and polystyrene (PS, a typical plastic matter) was investigated by H₂O₂ enhanced Fe(II) coagulation. The results demonstrated that the removal rate of both algae and PS can reach over 90%. It was also demonstrated that the PS removal efficiency increased from 23.3% to 97.3% with the increase of M. aeruginosa biomass from 0 cells/mL to 0.5 × 10⁶ cells/mL. The possible reason might be that the addition of algal cells raises the number of contaminant particles, which greatly increases the floc size during the coagulation process. It makes MPs easier to be trapped by sweep flocculation in this process. Additionally, naturally weathered polystyrene (NWPS) exhibited higher removal rate than virgin PS, due to more original functional groups, larger particle size (d₅₀ 9.75 μm-11.25 μm), and a lower absolute zeta potential (-34.15 mV to -30.1 mV). Furthermore, low Fe residue level and AOM (algal organic matter) control was simultaneously achieved in this process (TOC <1 mg/L, MCs <1 μg/L). Therefore, this study suggests that the H₂O₂-Fe(II) process is an efficient and green technology for the removal of M. aeruginosa and PS composite pollutants without secondary pollution, which is promising technology in drinking water treatment plant.