Fragmentation of microplastics in the drinking water treatment process - A case study in Yangtze River region, China

Abstract

Microplastics (MPs) are the emerging pollutants in the fresh water and have been found in the drinking water. Drinking water treatment plant (DWTP) is an important barrier to ensure the safety and quality of drinking water, so their effectiveness in removing MPs needs to be evaluated and optimized. In this paper, the abundance, characteristics and removal performance of 5 μm-5 mm granular MPs and 100 μm-5 mm fibrous MPs in the effluent of each water treatment unit in a DWTP in China were analyzed. The results show that only 80.96% of MPs ≤ 20 μm, accounting for more than 98% in the raw water, could be removed in the DWTP, while over 99% of the removal efficiency could be achieved for MPs > 20 μm. Coagulation-sedimentation and micro-flocculation combined with sand filtration couldn't effectively remove the granular MPs ≤ 20 μm (42.8% and 25.8%, respectively), but biological activated carbon (BAC) filtration was prone to remove this part (63.8%). Significant increases of granular MPs ≤ 20 μm were observed in the effluents of biological treatment (+149.6%) and ozonation (+13.8%). According to the variation in separate MPs' size distribution, the increases in MPs were attributed to the fragmentation of MPs, on which ozonation showed a remarkable effect. The ozonation might accelerate the aging and embrittlement of MPs, and then external stresses could further break them into smaller pieces, which eventually lead to an increase in MPs. To deal with the stubborn part and fragmentation of MPs in water, the removal ability of DWTP for MPs ≤ 20 μm needs to be improved. This study provides a detailed proof for the fate of MPs in the DWTP, and the results indicate that the fragmentation of MPs and the removal rate of MPs ≤ 20 μm should draw more attention in the DWTP.