Transport and fate of microplastics in constructed wetlands: A microcosm study

Constructed wetlands (CWs) are commonly used for the treatment of wastewater. However, the removal of microplastics in CWs are poorly understood. In this work, the fate and behavior of microplastics of different shapes (film, fragment, and fiber) and sizes (0.5-1 mm and 2-4 mm) were studied. Results showed that the microplastic removal rate was 81.63% in surface flow constructed wetlands (SF-CWs) and 100% in horizontal subsurface flow constructed wetlands (HSF-CWs). Fragments and fibers with 2-4 mm sizes flowed out preferentially from SF-CWs. Retained microplastics accumulated dominantly near the inlet area. Biofilm attachment and physical filtration played an important role in the retention of microplastics. The microplastics' morphological features and the apertures of the substrate related to the transport of microplastics in the substrate. We observed the formation of holes, cracks, and weeny fibers on the surface of the microplastics extracted from the microcosms with a scanning electron microscope (SEM), but we detected no oxidation based on the Fourier transform infrared spectra. Our results suggest that CWs, especially HSF-CWs, are efficient for the removal of microplastic pollution. However, microplastics are persistent in CWs. The potential impacts of microplastics on the function of CWs should be further assessed.