An article called Salt and Water Transport in Reverse Osmosis Membranes: Beyond the Solution-Diffusion Model was published in the December issue of Environmental Science and Technology (Environ. Sci. Technol. 2021, 55, 16665−16675). The publication is authored by researchers at Yale University in the U.S. and Wageningen University and WETSUS in the Netherlands, including Li Wang, Tianchi Cao, Jouke E. Dykstra, Slawomir Porada, P. M. Biesheuvel, and Menachem Elimelech.
This article, along with a companion publication in the Journal of Membrane Science by the same three institutions, describes an important breakthrough in how to more accurately model water and salt transport in thin film composite membranes. The Water Desalination Report, the leading industry trade communication on desalination, devoted an entire page to summarizing the findings outlined in the article.
We spoke with Professor Menachem Elimelech, Sterling Professor of Chemical and Environmental Engineering at Yale University, about the research. “Basically, I had been irritated for a long time,” he explains. “The solution-diffusion model treats membranes as a black box…dissolving and diffusing without considering the unique chemistry and pathways [for transport through real membranes]. What bothered me even more: it hinders development of water and solute transport improvements. For example, why do some membranes reject boron well and not others?”
To address the limitations of the long-standing solution-diffusion model, Elimelech and his collaborators formulated a new “solution-friction” model in which “ion transport through the membrane is described by the extended Nernst−Planck equation, with the consideration of friction between the species (i.e., ion, water, and membrane matrix). Water flow through the membrane is governed by the hydraulic pressure gradient and the friction between the water and membrane matrix as well as the friction between water and ions.” The model does an excellent job of matching experimental results using only 2 fitting parameters. Read the journal article Salt and Water Transport in Reverse Osmosis Membranes: Beyond the Solution-Diffusion Model.