Waste-derived substrates in vertical-flow constructed wetlands for an efficient removal of high-concentration heavy metals.

Abstract

Contamination by heavy metals (HMs) in aquatic ecosystems is a worldwide issue. Therefore, a feasible solution is crucial for underdeveloped and developing countries. Waste-derived materials (WDMs) exhibit unique physical and chemical properties that promote diverse mechanisms for the removal of HMs in constructed wetlands (CWs). In this study, we aimed to report the removal efficiency of HMs of vertical-flow constructed wetland (VFCW) systems using different WDMs, such as clinker brick (Jhama), eggshells, and date palm fiber (DPF). Synthetic wastewater with high concentrations (3.3-61.8) mg/L of HMs (As, Cr, Cd, Pb, Fe, Zn, Cu, and Ni) was applied to the systems followed by 3 days of hydraulic retention time. The results demonstrate that removal efficiencies of HMs ranged between 94.8 and 98.7% for DPF, 95.4-98.5% for eggshells, and 79.9-92.9% for the Jhama-filled CWs, while the gravel-based systems were capable of 73-87.6% removal. Two macrophytes, Canna indica and Hymenocallis littoralis were planted in the CWs and exhibited significant accumulation of HMs in their roots. The study reports that WDMs are effective for concentrated HM removal in CWs, and macrophytes demonstrate significant phytoremediation capabilities. The findings of this study will facilitate the economically feasible and efficient design of CWs for effectively treating concentrated HMs in wastewater.