Microplastics in 48 wastewater treatment plants reveal regional differences in physical characteristics and shape-dependent removal in the transition zone between North and South China

This study investigated the physical characteristics and removal efficiency of microplastics in wastewater from regions with different climatic conditions and economic development levels. Microplastics with different shapes and sizes were analyzed from the influent and effluent of 48 wastewater treatment plants in three regions of Shaanxi Province (China). Results indicated that the abundance of microplastics in the influent samples was higher in the region with less regional water resources. However, the per capita microplastics emissions was higher in the region with higher economic development level. There were less fibers and more foams and beads in the more developed region. The removal efficiency of microplastics was related to their shape and size. Particularly, the removal efficiency showed a significant negative correlation with the percentage of foams, while it had a significant positive relationship with the proportions of films and fibers. The highest removal efficiency was obtained when the size of microplastics was ranged from 0.5 to 1.0 mm. This study suggests, compared to improving the removal efficiency of microplastics, that reducing the input at source is a more scientific and promising method.