Electrically charged forward osmosis: Promoting reverse salt flux to enhance water recovery and struvite precipitation

Agricultural wastewater contains high concentrations of nitrogen and phosphorus. There is a growing interest in recovering these nutrients. In this study, an electrically charged forward osmosis (eFO) system was developed to recover struvite and water from synthetic livestock wastewater. By applying a voltage near the surface of the FO membrane, magnesium migrated reversely into the feed chamber and reacted with the ammonium and phosphate in the feed solution to form struvite. As a result of electrical charging, the recovery of struvite and water was enhanced by 77% and 39%, respectively. The enhancement might be because dilutive and concentrative polarization was alleviated on the draw and feed side of the FO membrane during ion migration. High external voltage, high draw concentration, and alkaline/neutral draw pH favored water recovery and struvite precipitation. This study provides insights into harnessing reverse salt flux to improve the recovery of nutrients and water in FO systems.