Electrodialysis recovery of reverse-fluxed fertilizer draw solute during forward osmosis water treatment

Wastewater reuse is important to address the challenge of water shortage but direct reuse could still introduce undesired contaminants to final products, e.g., via agricultural irrigation. Advanced membrane treatment such as forward osmosis can further purify the treated wastewater with recovery of high quality water. Herein, a forward osmosis – electrodialysis (FO-ED) hybrid system has been investigated by using diammonium phosphate (DAP), a common fertilizer, as a non-regeneration draw solute to achieve water reclamation and mitigation of salinity buildup. The system achieved consistent water recovery in the FO with low specific reverse solute flux for both NH₄⁺-N (0.063 g L⁻¹) and PO₄³⁻-P (0.083 g L⁻¹). Intensified fouling condition was observed when actual treated wastewater was applied as the feed, requiring periodical membrane cleaning. There were only Na⁺, Cl⁻, and small amounts of organics being presented in the recovered water (diluted draw solution of FO) at an acceptable level towards water reuse for agricultural irrigation. The ED accomplished successful recovery of 96.6 ± 3.0% reverse-fluxed DAP under 3.0 V 1-h daily operation, which could be reused in the FO. The energy consumption of the hybrid system was as low as 0.72 kWh m⁻³ or 0.45 kWh kg⁻¹ DAP. These results have demonstrated a synergy between FO and ED for creating an energy-efficient solution to enhance wastewater reuse.