Phosphorus Removal in Constructed Treatment Wetlands: A Systematic Review

Free water surface constructed wetlands are widely used for phosphorus removal from polluted waters, yet their effectiveness varies across wetland types, designs, and environmental conditions, creating uncertainty about their broader application. Building on prior reviews, this study applies stricter screening criteria and includes the literature until 2023 to deliver a more robust and updated global assessment of phosphorus retention performance. From 71 peer-reviewed studies, statistical analysis and models are applied to identify the principal design and loading parameters governing phosphorus retention. Notably, 90% of the wetlands included exhibited net retention, efficiencies ranged from −245% to 99% (median of 43.9%). Wetland area, hydraulic loading rate, hydraulic retention time, and phosphorus loading rate significantly influenced retention. Larger wetlands (>10 ha) and those with low hydraulic loadings (<10 m/year) displayed higher and more consistent efficiencies, whereas high phosphorus loads and short retention times reduced retention and increased variability. Models indicate wetland area and phosphorus loading as key predictors of efficiency, while hydraulic and phosphorus loading are critical in driving retention rates. By integrating an updated global evidence base with robust study selection and modelling, this review demonstrates the effectiveness of well-designed wetlands, supporting their role as valuable tools for water treatment and ecosystem management.