Nanoscale desalination membrane control may lead to cheaper filtration of water

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After researchers at the University of Texas at Austin and Penn State solved a complex issue that has puzzled scientists for decades – until now – the development of clean water at a lower cost could be within reach.

Desalination membranes separate water from salt and other contaminants, a process that is vital for society’s health and purifies billions of gallons of water for irrigation, development of energy and drinking.

The principle seems easy – pass through salty water and the other side comes out of clean water – but it involves complicated intricacies that scientists are still trying to understand.

Together with DuPont Water Solutions, the research team has solved an important part of this puzzle, opening the door to reducing the cost of generating clean water.

The researchers found that there is a non-uniform density and mass distribution of desalination membranes, which can affect their efficiency. At the nanoscale, uniform density is crucial to increasing the amount of clean water these membranes can create.

Manish Kumar, an associate professor in the Department of Civil, Architectural and Environmental Engineering at UT Austin who co-led the study, said, “Reverse osmosis membranes are commonly used to purify water, but there’s still a lot we don’t know about them,” “We couldn’t really tell how water moves through them, so all the improvements over the last 40 years have essentially been done in the dark.”

The results were published in Science on Dec. 31, 2020.

The work records an improvement in the performance of the tested membranes by 30-40 percent, which means they can clean more water while using substantially less energy.

For individual households and large customers alike, this could lead to better access to clean water and lower water bills.

By applying pressure to the saline feed solution on one side, reverse osmosis membranes operate.

While the water flows in, the minerals remain there.

Although it is more effective than membrane-free desalination processes, it still needs a significant amount of energy, the researchers said, and improving membrane efficiency could reduce that burden.

“Freshwater management is becoming a critical challenge around the world,” said Enrique Gomez, a Penn State chemical engineering professor who co-led the study. “Shortages, droughts – this issue is expected to become more serious with rising extreme weather.

Having clean water available, especially in low-resource areas, is important.

The research was funded by the National Science Foundation and DuPont, a company which makes many desalination products.

When DuPont researchers discovered that thicker membranes actually proved more permeable, the seed was planted.

This was a surprise, as the common wisdom was that the amount of water that could flow through the membranes was limited by thickness.

In 2015, at a “water summit” organized by Kumar, the team contacted Dow Water Solutions, now part of DuPont, eager to solve this mystery.

The research team, which includes Iowa State University researchers, created 3D reconstructions of the nanoscale membrane structure at Penn State’s Materials Characterization Lab using state-of-the-art electron microscopes.

To predict how efficiently water could be filtered based on the structure, they modeled the direction that water takes through these membranes. Greg Foss of the Texas Advanced Computing Center helped imagine these simulations, and on Stampede2, the supercomputer of TACC, most of the calculations were performed.

For more on this analysis, read Desalination Breakthrough Maximizes Flow for Cheaper Water Filtration.

Reference: ‘Internal inhomogeneity nanoscale regulation increases water transport in desalination membranes’ by Tyler E.

Biswajit Khara, Culp, Kaitlyn P.

Brickey, Michael Geitner, J. Zimudzi of Tawanda, Jeffrey D.

Wilbur, Steven D. Jons, Abhishek Roy, Mou Paul, Andrew L. Zydney, Manish Kumar, Baskar Ganapathysubramanian, and Enrique D. Gomez, 31. Science.DOI: 10.1126/science.abb851818 December 2020.

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