Performance evaluation of Iris pseudacorus constructed wetland for advanced wastewater treatment under long-term exposure to nanosilver

The presence of nanoparticles in the wastewater treatment plants (WWTPs) effluent is a potential threat to the ecosystem due to their effective antimicrobial properties. The aim of this study was to investigate the performance of a pilot-scale vertical flow constructed wetland (VFCW) for advanced wastewater treatment under long-term exposure to silver nanoparticles (AgNPs). The migration and fate of AgNPs were also examined to explore whether the CW had a capability of nanoparticles removal. The results suggested that AgNPs (20 µg/L) showed acutely inhibitory effects on nitrogen and phosphorus removal at the initial exposure stage, followed by the persistent inhibition with time. The average removal efficiencies decreased by 16%, 11%, and 11% for NH+ 4-N, TN, and TP, respectively. For COD removal, no changes were found. The effluent of CW under AgNPs exposure could still reach the first level A of the People's Republic of China's Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002). In addition, CW showed a satisfactory AgNPs removal efficiency of 93%. The accumulation of AgNPs in different parts from high to low was soil (88.93%), effluent (7.35%), substrate (3.40%), and plant (0.32%). AgNPs enriched by plant roots were mainly transported to above ground. It demonstrated that the presence of soil layer and wetland plant Iris pseudacorus is essential for AgNPs removal. The study may provide valuable references for evaluating the ecological effects of nanoparticles.