The development of suitable draw solutes for forward osmosis (FO) process is a big obstacle on the way of its real industrialization. In this work, a novel draw solute, ethylenediamine tetrapropionic (EDTP) acid (salt) is developed for FO application. The successful synthesis is confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high resolution mass spectrum. By optimizing the pH of EDTP solution, its composition is varied, and therefore, its water solubility and osmotic pressure are effectively improved. The effects of EDTP concentration on the osmotic pressure and FO performance are also investigated. Its outstanding osmotic pressure and big molecular size result in a high water flux of 22.69 LMH and a low salt flux of 0.32 gMH with 0.8 M EDTP draw solution (water as the feed solution, pressure retarded osmosis mode). The good stability and easy recovery by nanofiltration of EDTP solution also demonstrate its great potential as the draw solute for future FO applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1309–1321, 2015

The development of facile strategies and techniques to fabricate nanofiltration (NF) membranes with ideal molecular sieving ability has received growing attention in both academia and industry. Chitosan (CS) is deemed to be a promising renewable membrane material. However, the scalable and low-cost fabrication of pure CS membranes is severely limited by their poor solubility in organic solvents. Herein, a simple and effective film casting strategy is presented to prepare a positively charged CS-based NF membrane for effective rejection of dye and salt in textile wastewater. The penetration performance of CS membranes can be elaborately tuned by regulating the casting parameters during the fabrication process. The as-synthesized CS membranes with suitable thickness and tensile strength exhibit considerable water permeance and high rejection rates of up to 94.8% for CaCl 2 and 87.8% for MgSO 4 . Especially, the CS membrane with a molecular size cutoff of 5.015 Å (hydrated radius) shows an ultrahigh rejection rate of >99% to six kinds of conventional dyes in textile wastewater. The long-time evaluation of dye and salt separation demonstrates the superior stability of the CS membrane. This work aims to develop a facile and cost-effective solution to construct CS NF membranes with superhigh filtration capacity for dye and salt removal from actual textile wastewater.

Draw solution is one important factor to determine the separation performance in forward osmosis (FO) process. However, most draw solutions face severe reverse solute leakage and energy-intensive recovery problems, which lead to a significant performance decline. Exploration of renewable natural compounds as draw solutes may effectively break out the predicament of most current draw solution. In this work, a series of renewable, no-toxic gluconate salts are systematically investigated as draw solutes for FO applications. Their physicochemical properties are investigated systematically and related to the FO performance. The result shows that 2 M Glu-K draw solution may generate a comparable water flux (∼23.17 LMH) to that of NaCl solution, but with a significantly lower solute leakage (∼1.09 gMH), with DI water as the feed solution under PRO mode. Glu-K draw solution is further applied for juice reconcentration with a reasonable good performance achieved. Draw solution recovery by nanofiltration (NF) is also performed. This study provides useful information on using natural draw solutes in the FO process and facilitates its practical applications in the food processing field.

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