Removal and fate of silver nanoparticles in lab-scale vertical flow constructed wetland

Engineered nanomaterials (ENMs) are increasingly produced and consequently released into the environment. Therefore, there is a strong need to find a valid way to treat the ENMs pollution. In this study, the removal efficiencies of silver nanoparticles (AgNPs) from synthetic wastewater in lab-scale vertical flow constructed wetland (CW) systems with different operations (plant, hydraulic loading rates, bed depth) were investigated. Moreover, the environmental fate and impacts of AgNPs in CWs were also investigated. The results showed that CWs with plants were more effective in removing AgNPs than the unplanted CWs. Hydraulic loading had a significant effect on the performance of CWs in treating AgNPs, however, the influence of bed depth was negligible. AgNPs stopped in the CWs were mainly resided in the wetland substrate, indicating the main mechanism of AgNPs removal in CWs was through substrate adsorption. Although plant biomass, root activity, peroxidase activity of leaves and biofilm biomass were significantly altered following exposure to AgNPs (P < 0.05), CWs maintained constant high efficiency (63.2-93.8%) in removing AgNPs from wastewater during a continuous 2-month running. Overall, this paper suggests the feasibility and high-efficiency of using CWs to handle AgNPs contamination.