The crucial factor for microplastics removal in large-scale subsurface-flow constructed wetlands

Abstract

Constructed wetlands (CWs) are an effective method for removing microplastics (MPs). Nevertheless, the understanding of the impact of various parameters on MPs removal within CWs remains incomplete. Through field investigations of large-scale CWs and the application of machine learning methods with an interpretable attribution technique (the Shapley Additive Explanation), we investigated the critical factors influencing MPs removal within CWs. The MPs abundance in the influent and the inlet of Z-CW (400.1±20.8 items/L and 699.6±50.6 items/kg) was significantly higher compared to that in M-CW (138.8±20.5 items/L and 166.5±36.8 items/kg), with no significant difference observed in the effluent. The primary characteristic of MPs is their fibrous and transparent appearance. The MPs removal range from 87.9–95.5%, influenced by the types and characteristics of MPs, physical and chemical parameters, biofilms, and different processes. Among these factors, dissolved organic carbon with high humic content, aromaticity, and carboxyl abundance may serve as a crucial factor in MPs removal. The results of this study highlight the significance of physical and chemical parameters for the MPs removal in CWs, providing the necessary theoretical data for the construction of future large-scale engineering applications.