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

Qintong Wang; Carmen Hernández-Crespo; Benben Du; Stijn W H Van Hulle; Diederik P L Rousseau

doi:10.1016/j.scitotenv.2021.146152

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

Sci Total Environ. 2021 Jul 15:778:146152. doi: 10.1016/j.scitotenv.2021.146152. Epub 2021 Mar 4.

Authors

Qintong Wang¹, Carmen Hernández-Crespo², Benben Du³, Stijn W H Van Hulle⁴, Diederik P L Rousseau⁵

Affiliations

¹ Laboratory for Industrial Water and Ecotechnology (LIWET), Department of Green Chemistry and Technology, Ghent University Campus Kortrijk, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium. Electronic address: Qintong.Wang@UGent.be.
² Laboratory for Industrial Water and Ecotechnology (LIWET), Department of Green Chemistry and Technology, Ghent University Campus Kortrijk, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium; Research Institute of Water and Environmental Engineering (IIAMA), Instituto de Ingeniería del Agua y del Medio Ambiente, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain. Electronic address: carhercr@upv.es.
³ Laboratory for Industrial Water and Ecotechnology (LIWET), Department of Green Chemistry and Technology, Ghent University Campus Kortrijk, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium; Laboratory of Environmental Science and Engineering, College of Environment, Zhejiang University of Technology, Hangzhou 310032, PR China. Electronic address: 15868828994@163.com.
⁴ Laboratory for Industrial Water and Ecotechnology (LIWET), Department of Green Chemistry and Technology, Ghent University Campus Kortrijk, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium. Electronic address: Stijn.Vanhulle@UGent.be.
⁵ Laboratory for Industrial Water and Ecotechnology (LIWET), Department of Green Chemistry and Technology, Ghent University Campus Kortrijk, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium. Electronic address: Diederik.Rousseau@UGent.be.

PMID: 33714826
DOI: 10.1016/j.scitotenv.2021.146152

Abstract

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.

Keywords: Biofilm; Constructed wetlands; Earthworms; Media; Microplastics.