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Environ Sci Technol. 2018 Mar 20;52(6):3556-3566. doi: 10.1021/acs.est.7b05265. Epub 2018 Mar 1.

Forward Osmosis Membranes under Null-Pressure Condition: Do Hydraulic and Osmotic Pressures Have Identical Nature?

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School of Earth Sciences and Environmental Engineering , Gwangju Institute of Science and Technology (GIST) , 123 Cheomdangwagi-ro , Buk-gu, Gwangju 61005 , South Korea.
UNESCO Centre for Membrane Science & Technology , School of Chemical Engineering, University of New South Wales , Sydney NSW 2052 , Australia.
Global Desalination Research Center , Gwangju Institute of Science and Technology (GIST) , 123 Cheomdanwagi-ro , Buk-gu, Gwangju 61005 , South Korea.


Forward osmosis (FO) membranes fall into the category of nonporous membranes, based on the assumption that water and solute transport occur solely based on diffusion. The solution-diffusion (S-D) model has been widely used in predicting their performances in the coexistence of hydraulic and osmotic driving forces, a model that postulates the hydraulic and osmotic driving forces have identical nature. It was suggested, however, such membranes may have pores and mass transport could occur both by convection (i.e., volumetric flow) as well as by diffusion assuming that the dense active layer of the membranes is composed of a nonporous structure with defects which induce volumetric flow through the membranes. In addition, the positron annihilation technique has revealed that the active layers can involve relatively uniform porous structures. As such, the assumption of a nonporous active layer in association with hydraulic pressure is questionable. To validate this assumption, we have tested FO membranes under the conditions where hydraulic and osmotic pressures are equivalent yet in opposite directions for water transport, namely the null-pressure condition. We have also established a practically valid characterization method which quantifies the vulnerability of the FO membranes to hydraulic pressure.

[Indexed for MEDLINE]

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