Exploring high charge of phosphate as new draw solute in a forward osmosis-membrane distillation hybrid system for concentrating high-nutrient sludge

Publication Type:
Journal Article
Citation:
Science of the Total Environment, 2016, 557-558 pp. 44 - 50
Issue Date:
2016-07-01
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© 2016 Elsevier B.V. For the first time, a high charge of phosphate was used as the draw solute in a forward osmosis-membrane distillation (FO-MD) hybrid system for concentrating high-nutrient sludge. A high water flux (12.5 L/m2h) and a low reverse salt flux (0.84 g/m2) were simultaneously achieved at pH 9 by using 0.1 M Na3PO4as the draw solute and deionized water as the feed solution in the FO process. The specific reverse salt flux of 0.1 M Na3PO4(Js/Jw= 0.07 g/L) was considerably less than that of 0.1 M NaCl (Js/Jw= 0.37 g/L) because the complexion between Na+and HPO42-at pH 9 led to the reduction of free Na+ions, which subsequently reduced the reverse salt diffusion substantially. Moreover, for a feed solution with an initial sludge concentration of 3500 mg/L, the sludge concentration could be concentrated to 19,800 and 22,000 mg/L in the pressure-retarded osmosis (PRO) and FO membrane orientations, respectively, after 15 h of operation. Four types of MD membranes were selected for draw solution recovery; of these, a polytetrafluoroethylene membrane with a pore size of 0.45 μm was the most effective in achieving a high water flux (10.28 L/m2h) and high salt rejection (approximately 100%) in a diluted Na3PO4draw solution.
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