How can we trace microplastics in wastewater treatment plants: A review of the current knowledge on their analysis approaches.

Microplastics (MPs), as an emerging pollutant derived from the human daily life and industry activities, have been widely detected in ecosystem. Wastewater treatment plants (WWTPs) play a special role in the mass flow of MPs because it is not only one of the important point sources of MPs, but also a way of collecting and removing MPs from wastewater. It is necessary to analyze the fate of MPs in WWTPs and the volume released into the environment. However, the lack of standard analytical methods of MPs in WWTPs limited the accuracy assessment of MPs and comparison between different studies. This review summarized the current knowledge on analysis approaches of MPs in WWTPs and proposed an analysis process. Specifically, the MPs sampling sites of wastewater and sludge treatment route is discussed. Moreover, various processing procedure for samples collection and pretreatment including extraction and purification, as well as identification and characterization of MPs are reviewed in great detail. Finally, as an important way to ensure accuracy of studies, quality assurance and control measures are presented. It should be pointed out that the overall analysis processes are interdependent and should be chosen and harmonized according to the aim of individual study. The lack of reliable and uniformity analysis methodology is the key challenge for present studies which needs further development.