Advanced hydrophilic macromolecule and trivalent complex-based draw solution for heavy metal removal from groundwater using forward osmosis

Abstract

Forward Osmosis (FO) holds promise for treating heavy metal-contaminated groundwater, yet a suitable draw solution hinders its widespread use. This study introduced a novel draw solution (DS) for the FO process by combining hydrophilic macromolecule polyvinyl alcohol (PVA) with trivalent-charged complex EDTA-2Na. Remarkably, the incorporation of 0.7 g/L PVA into 0.3 M EDTA-2Na not only increased water flux by 24.2 %, attributed to the hydrophilic interaction between the FO membrane and the hydroxyl groups of PVA, but also significantly reduced reverse salt flux by 67.1 %, from 3.80 GMH to 1.25 GMH. This reduction can be attributed to the extended conformation of the polymer macromolecule at pH 8, acting as an effective barrier in the FO process, thereby restraining the electrophilic sodium ions of EDTA-2Na from reversing to the feed side. Moreover, the hydrophilic macromolecule coupled with the trivalent-charged complex DS has been easily regenerated by nanofiltration (NF) with a high recovery efficiency of 96 % and minimal energy input. Furthermore, the FO-NF process achieved high-quality permeate water (arsenic <0.0014 mg/L, lead <0.0029 mg/L, and iron <0.0157 mg/L) suitable for drinking water from heavy metal-contaminated groundwater. The present study therefore illustrates a facile and rational approach for integrating PVA into an EDTA-2Na solution that exhibits superior performance for heavy metal removal in groundwater via FO.