Effect and Mechanism of Applying Myriophyllum Verticillatum for Reclaimed Water Purification in Urban Rivers

Reclaimed water produced via the advanced treatment of domestic wastewater has broad application prospects for reuse in urban rivers, while the nutrients in reclaimed water, especially nitrogen and phosphorus, lead to eutrophication or ecological impacts. Submerged plants are preferred as an enhanced technology used at reclaimed water recharge sites for both water quality improvement purposes and ecological conservation functions. In this study, which adopted the typical submerged plant Myriophyllum verticillatum (M. verticillatum) as its experimental object, experiments were carried out in an illumination incubator without a substrate and under hydrostatic conditions to investigate the water purification effects and mechanisms of action of M. verticillatum at different planting densities. The analysis showed that the group with a wet weight of 2.5 g L−1 had the best growth status and the best overall performance with respect to improvements in water quality indicators, including COD, nitrogen, and phosphorus, as well as demonstrating excellent uptake and synergistic effects in the process of removing nitrogen and phosphorus. The contributions of natural effects, the uptake and enrichment by M. verticillatum itself, and the synergistic effects during the nitrogen and phosphorus removal process were quantified. Furthermore, 16S rRNA gene sequencing was used to determine the surface-attached bacterial colonies of M. verticillatum, to analyze their population diversity, and to identify environmental functional genera. In conclusion, an appropriate density of M. verticillatum can improve water quality and provide a suitable environment for the survival and growth of relevant environmentally functional microorganisms, effectively removing nitrogen and phosphorus through its own absorption and synergistic effects.