EDTA: a synthetic draw solute for forward osmosis

The draw solution is the driving force of the forward osmosis (FO) process; however, the solute loss of the draw solute to the feed side is a general, financial limitation for most applications. The anthropogenic amino acid ethylenediaminetetraacetic acid (EDTA) was investigated as a draw solution for FO. At concentrations of approximately 1.0 osmol/kg, EDTA demonstrated comparable water fluxes (J_v = 5.29 L/m² h) to the commonly used salt, NaCl (J_v = 4.86 L/m² h), and both produced better water fluxes than glucose (J_v = 3.46 L/m² h). EDTA showed the lowest solute loss with J_s (reverse solute loss or solute leakage) = 0.54 g/m² h. The molecular weight, degree of ionisation and charge of EDTA played a major role in this efficiency and EDTA was therefore well rejected by the membrane, showing a low J_s/J_v ratio of 0.10 g/L. Owing to the low solute loss of EDTA and its resistance to biodegradation, this compound has the potential to be used as a draw solute for FO during long periods without requiring much replenishment.