Microplastics in a horizontal subsurface flow constructed wetland: A Case Study of Denizli/Türkiye

Domestic wastewater plays a critical role in the discharge of microplastics into aquatic ecosystems. Constructed wetland systems are used to treat domestic wastewater in rural areas. This study aimed to determine the microplastic concentrations and morphological properties (shape, size, and color) of microplastics in influent, effluent, and sediment samples taken from horizontal subsurface flow constructed wetland system in Denizli/Türkiye. Also, the microplastic removal efficiency was evaluated in the constructed wetland. Samples were collected during summer and winter to investigate the seasonal variations in microplastic concentrations. The findings revealed that the majority of microplastics collected in this study were fibers (winter: 67.78%, summer: 82.46%) and transparent-white colored microplastics in both periods (winter: 88%, summer: 72%). In addition, the most abundant microplastic size was obtained as 100–500 μm (winter: 92%, summer: 82%). Suspected microplastics were identified by ATR-FTIR as PES, PET, and PEVA. PEVA is the most frequently encountered type of polymer. The average removal efficiency of microplastics in summer was determined as 87.43% and in winter was 97.27%. Daily microplastic discharge from the constructed wetland was calculated as 1.365 × 10⁷ MP/day for the summer season, and 2.918 × 10⁷ MP/day for the winter season. The findings obtained in this study suggest that although the constructed wetland system adequately removes microplastics, there is a high release of microplastics in the effluent. All the data suggest that constructed wetlands are a crucial source of the release of microplastics.