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.
Environ Sci Technol. 2018 Mar 20;52(6):3556-3566. doi: 10.1021/acs.est.7b05265. Epub 2018 Mar 1.
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.
正向渗透（FO）膜属于无孔膜，其假设是水和溶质的传输仅基于扩散。溶液扩散（S-D）模型已广泛用于预测它们在水力和渗透驱动力共存下的性能，该模型假定水力和渗透驱动力具有相同的性质。然而，有人提出，这些膜可能具有孔，并且质量传输可以通过对流（即体积流）以及扩散来发生，前提是膜的致密活性层由具有缺陷的非多孔结构组成，这些缺陷通过膜诱导体积流。此外，正电子湮没技术表明，活性层可能涉及相对均匀的多孔结构。因此，与水压相关的致密无孔活性层的假设是值得怀疑的。为了验证这一假设，我们已经在水传输的水力和渗透压相等但方向相反的条件下（即零压条件）测试了 FO 膜。我们还建立了一种实用有效的表征方法，该方法量化了 FO 膜对水压的脆弱性。
