Seasonal applicability of three vegetation constructed floating treatment wetlands for nutrient removal and harvesting strategy in urban stormwater retention ponds

• Urban storm water runoff was treated by using retention ponds integrated with floating wetlands (FTWs).
• Thalia dealbata FTWs exhibited the best seasonal applicability through contrasting the potentials of three FTWs.
• Thalia dealbata FTWs achieved better contaminants removal than other plants.
• The harvesting strategy of the above ground tissues of Thalia dealbata in late October or early November is recommended.

Three floating treatment wetlands (FTWs), which consist of emergent macrophytes, were constructed and planted to investigate the influence of seasonal change on contaminant removal and harvesting strategy. The investigation was carried out by treating simulated urban stormwater runoff sewage through selected aquatic plants in Jiaxing, Yangtze River Delta, China. Samples collected from the influent and effluent water of three FTWs planted with Canna indica, Thalia dealbata, and Lythrum salicaria, respectively, were analyzed for contaminant concentration in different batches. Results demonstrated that T. dealbata outperformed C. indica and L. salicaria in nutrient removal. The FTWs of T. dealbata achieved average removal efficiencies (AREs) of 71.17% ± 2.01% for chemical oxygen demand (COD), 69.96% ± 2.11% for total nitrogen (TN), and 82.40% ± 2.34% for total phosphorus (TP) in nine stages. The COD and TN concentrations in effluent water were under 20 and 1.5 mg L−1 for 20 weeks. Based on the analyses of accumulated nutrient removal in vegetation over time, the strategy of harvesting the aboveground tissues of T. dealbata and C. indica in late October or early November is recommended. However, L. salicaria aboveground tissues should be harvested in September. In Jiaxing, the constructed FTWs of T. dealbata exhibited the best seasonal applicability.