Microplastics removal and characteristics of constructed wetlands WWTPs in rural area of Changsha, China: A different situation from urban WWTPs

Abstract

Wastewater treatment plants (WWTPs) are important pathways that discharged microplastics into the natural environment, but few relevant research has been conducted in rural areas, especially with horizontal subsurface flow constructed wetlands (HSSFCWs). This study systematically investigates the removal efficiency and characteristics of microplastics in two rural WWTPs with HSSFCW in Changsha city of China and compared the microplastic pollution data of urban and rural WWTPs, to provide some advice for improving the microplastics removal efficiencies in rural WWTPs. 3 L wastewater were collected at each sampling point. Then microplastics in wastewater were extracted by density separation. The size, shape, color, and type of microplastics were analyzed and identified using the integrated microscope and FTIR. The whole experiment was carried out about a month. The results showed that the microplastics removal efficiency of rural WWTP1 was 72.38%, and that of rural WWTP2 was 68.10%, which were lower than that of most urban WWTPs. The microplastics removal efficiency of constructed wetlands in rural WWTP1 was 26.59%, and that in rural WWTP2 was 10.61%. Based on the daily discharge volume and the abundance of microplastics in the effluent of WWTPs, approximately 1.45 ∗ 107 items and 1.73 ∗ 107 items of microplastics were released each day from two rural WWTPs, separately. Fiber was the primary microplastic in both influent and effluent. The polyethylene (PE) and polystyrene (PS) were the main ingredients. The primary source of microplastics in rural WWTPs was inferred as domestic sewage. Microplastics removal efficiencies of rural WWTPs can be improved by regular maintenance, reducing the grid spacing, increasing the hydraulic stay time of biochemical pool, and increasing plant density, changing plant species, or adjusting the size and fill order of matrix in HSSFCWs, which can effectively help to prevent secondary pollution of microplastics from rural WWTPs.

Keywords: Constructed wetlands; Microplastics; Pollution; Rural; WWTPs.