An initial study of EDTA complex based draw solutes in forward osmosis process

• Zinc, manganese, calcium, and magnesium complexes with EDTA are employed as draw solutions for FO.
• EDTA complexes are characterized for pH, conductivity, solution viscosity and osmotic pressure.
• EDTA complexes show superiority in water flux and reverse draw solute flux compared with NaCl.
• The diluted draw solution can be regenerated using a pressure-driven nano-filtration process.

The selection of appropriate draw solutes is a critical component for the development of FO technologies. Two significant concerns related to draw solution are the draw solute leakage in FO process and the intensive energy consumption in regenerating draw solute. In this study, a series of EDTA complexes (EDTA-MgNa2, EDTA-CaNa2, EDTA-MnNa2, and EDTA-ZnNa2) were systemically investigated as draw solutes for FO. Their characteristics of high solubility in water, moderate molecular size, expanded molecular structure, nontoxicity, low viscosity, and relatively high osmotic pressure can provide favorable FO performance and easy approaches in regeneration, which ensure the suitability of EDTA complexes as a new class of competent draw solutes. All EDTA complexes demonstrated higher water fluxes in PRO mode and much lower salt leakage in both FO and PRO modes when compared with conventional draw solute of NaCl, while EDTA-ZnNa2 possessed the best performance. The NF regeneration of EDTA complexes at relatively high initial concentration of 0.25 M indicated that all NF membranes performed well with the special water flux and rejection rate ranging between 0.96 and 2.0 LMH/bar, and 96 and 98%. The overall performance proves that the new concept of using EDTA complex based draw solutes in FO process is applicable.