Removal characteristics of heavy metals from polluted river water purified by hybrid constructed wetlands.

Abstract

Heavy metal pollution in urban rivers has become a global issue. In this study, hybrid constructed wetlands (HCWs) were used to comprehensively evaluate the effectiveness of field wetland projects in removing heavy metals, with evaluation metrics including seasonal variations, plant contributions, and structure compositions. The experimental results showed that the synergistic system of root-microorganism-substrate formed in the combined process well realized the high efficiency of heavy metal removal, in which the removal rate in the warm season was higher than that in the cold season. The average removal rates of Cu, Zn, Cr, and Pb were 44.62 %, 43.12 %, 40.59 % and 45.18 %, respectively. In the effluent, Zn and Cr can better meet the corresponding standards of the US, EU, and CN, and the biotoxicity of Cu and Pb was also greatly reduced. Compared to Cu, Cr, and Pb, the removal of Zn was less affected by influent loads and stable removal was achieved. In HCWs, the primary contribution to heavy metal removal is attributed to sediment deposition, subsequently followed by the uptake by plant roots and stems, with adsorption onto fillers being the least significant. These results of the study show that HCWs can effectively treat heavy metal pollution in water bodies, and are a highly efficient process for ecological remediation of urban river water. Most importantly, HCWs have demonstrated strong adaptability during the operation of actual ecological restoration projects. Additionally, HCWs can adjust the component structure according to the specific conditions of the process to realize the highest efficiency, which provides a new idea for urban river ecological restoration.