4th January 2021
Scientists find way to boost desalination efficiency by up to 40%
Scientists at the University of Texas at Austin have determined that desalination membranes are inconsistent in density and mass distribution, and shown a way to increase their efficiency by up to 40 per cent.
Clean water produced at a lower cost may be possible in the near future – thanks to researchers from the University of Texas at Austin and Penn State who have solved a complex problem that baffled scientists for decades, until now.
Desalination membranes remove salt and other chemicals from water, a process critical to the health of society, cleaning billions of gallons of water for agriculture, energy production and drinking. The idea seems simple – push salty water through, and clean water comes out the other side – but contains complex intricacies that scientists are still trying to understand.
The research team, in partnership with DuPont Water Solutions, solved an important aspect of this mystery. They determined that desalination membranes are inconsistent in density and mass distribution, which can hold back their performance. Uniform density at the nanoscale is the key to increasing how much clean water these membranes can create, the team explains.
"Reverse osmosis membranes are widely used for cleaning water, but there's still a lot we don't know about them," said Manish Kumar, an associate professor in the Department of Civil, Architectural and Environmental Engineering at UT Austin, who co-led the new research. "We couldn't really say how water moves through them, so all the improvements over the past 40 years have essentially been done in the dark."
In their study, published this month in Science, the team describes how they optimised and tested new membranes with an efficiency increase of 30%-40%, meaning they can clean more water while using significantly less energy. That could lead to increased access to clean water, and lower water bills for individual homes and large users alike.
Reverse osmosis membranes work by applying pressure to the salty feed solution on one side. The minerals stay there while the water passes through. Although more efficient than non-membrane desalination processes, it still takes a large amount of energy, the researchers said, and improving the efficiency of the membranes could reduce that burden.
"Fresh water management is becoming a crucial challenge throughout the world," said Enrique Gomez, a professor of chemical engineering at Penn State who co-led the research. "Shortages, droughts – with increasingly severe weather patterns, it is expected this problem will become even more significant. It's critically important to have clean water availability, especially in low-resource areas."
The DuPont researchers made a key discovery when they calculated that thicker membranes are actually proving to be more permeable. This came as a surprise because the conventional knowledge was that thickness reduces how much water can flow through. The team developed 3D reconstructions of the nanoscale membrane structure using state-of-the-art electron microscopes at the Materials Characterisation Lab of Penn State. They modelled the path water takes through these membranes to predict how efficiently it could be cleaned, based on their structure. Greg Foss of the Texas Advanced Computing Center helped visualise these simulations, and most of the calculations were performed on the 18 petaflop Stampede2 supercomputer.
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