Fate and removal of microplastics in unplanted lab-scale vertical flow constructed wetlands

[EN] Many studies have reported conventional wastewater treatment plants as one of the main sources of microplastics (MPs). However, constructed wetlands (CWs) as a nature-based wastewater treatment system have received little attention. This study investigated the influence of biofilm, media type and earthworms on the fate and removal of MPs in a short-term (45d) experiment with unplanted lab-scale vertical flow CWs (VFCWs). In sand-filled VFCWs, MPs were retained in the first 10 cm, and the removal efficiency was 100%, regardless of the presence of a biofilm. When gravel was used as filling material, the removal efficiency of MPs was stable at 96%, but the MPs were distributed throughout the 80 cm high VFCWs. In the presence of earthworms, the maximum depth that MPs reached within sand-filled VFCWs increased from 10 to 15 cm. Furthermore, the MPs concentration at a depth of 3-6 cm and 6-10 cm increased 2 and 10 fold respectively compared to the same VFCWs without earthworms. Although no MPs were detected in the sand from deep layers (15-80 cm), transport of MPs from top to the bottom by earthworms was found, and a few MPs were detected in the effluent, leading to a removal efficiency of 99.8%. This study indicated that both a higher media grain size and the presence of earthworms have a small effect on the removal efficiency of MPs in VFCWs, but the effect on the distribution of MPs was considerably. Longer-term studies in full-scale CWs are advised to perform under the influence of more practical factors. Qintong Wang is financially supported by the China Scholarship Council by a PhD grant (Ref. 201906690045) . Carmen HernandezCrespo had a "Jose Castillejo" mobility grant (CAS19/00114) from the Spanish Ministry of Science, Innovation and Universities (State Program for the Promotion of Talent and its Employability in R&D, State Mobility Subprogramme, of the State R&D Plan) . Benben Du was financially supported by the China Scholarship Council (Ref. 201908330708) and the province of WestFlanders as an exchange student. Finally, the authors would like to thank Hafiz Khan for the construction of labscale VFCWs, and Boyi Huang for the help with English grammar. Wang, Q.; Hernández Crespo, C.; Du, B.; Van Hulle, SW.; Rousseau, DP. (2021). Fate and removal of microplastics in unplanted lab-scale vertical flow constructed wetlands. Science of The Total Environment. 778:1-9. https://doi.org/10.1016/j.scitotenv.2021.146152