Recycled water purification performance of a subsurface flow constructed wetland in the Yongding River

To safeguard water quality for ecological water replenishment in the Yongding River and address the potential water quality non-compliance issues caused by direct recycled water discharge, a subsurface flow constructed wetland was established within Beijing Yongding River Leisure Forest Park, aiming for advanced purification of recycled water. Based on daily water quality monitoring data throughout a complete water supply period (Mar. to Nov.) in 2022, this study systematically evaluated the continuous purification efficiency of the subsurface flow constructed wetland on recycled water. Results demonstrate that the subsurface flow constructed wetland effectively purified the quality of recycled water, with chemical oxygen demand (COD) and pollutant concentrations, including suspended solids (SS), total nitrogen (TN) and total phosphorus (TP), were significantly reduced (p<0.001) compared to the influent. The treated effluent water also exhibited greater stability. The removal rates for SS and TP were particularly high, reaching 68.35% and 57.78%, respectively, while removal rates for COD and TN were 29.49% and 15.29%, respectively. In terms of purification mechanisms, pollutant removal in this system primarily relied on filtration and adsorption by the substrate, whereas plant uptake and microbial decomposition played a more limited role. To address existing issues, future improvements can prioritize the construction of surface flow wetland units to optimize hydraulic condition, the selection of highly efficient purifying plants to establish diverse communities, and the inoculation of functional microorganisms to enhance biodegradation performance. These multidimensional strategies will strengthen the water purification capacity of the subsurface flow constructed wetland, enabling it to better support ecological restoration of the Yongding River.