Effect of weathering behavior of polyethylene microplastics in water on coagulation process

Polyethylene (PE) microplastics with high abundance in surface water were used as the research object to conduct adsorption and coagulation experiments. Based on the study regarding the organic matter adsorption capacity of PE microplastics, the effect of weathering behavior of PE microplastics on the coagulation process was further explored by using photoaged PE microplastics with xenon lamp to simulate weathering behavior of microplastics under natural conditions. The results showed that PE microplastics with particle size 50-200 mesh could adsorb 310-350 mg/g (calculated by carbon) organic matter, indicating that the microplastic size would not significantly influence the adsorption performance of PE microplastics. In coagulation, compared with no PE microplastics conditions, the addition of unweathered PE microplastics was prone to decrease the organic matter removal rate, while the addition of weathered PE microplastics was able to obviously increase the removal efficiency of organic matter. Furthermore, the removal rate of weathered PE microplastics was remarkably higher than that of unweathered PE microplastics in coagulation, which suggested that the weathering behavior was beneficial to PE microplastics removal during the coagulation process. According to the floc properties in coagulation, it was notable that both unweathered and weathered PE microplastics would not influence floc average size in coagulation, but significantly increased the growth rate of flocs in this process.