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Yale scientists developing method to distill sea water

Posted August 7

— Removing salt from seawater to create distilled water is not a new phenomenon.

But using solar power to make the incredibly energy-intensive process potentially viable for a household or a small, remote community is new.

Historically, desalination, or the removal of salt and minerals from water to make it drinkable or usable for watering crops, typically requires a large amount of energy, according to Menachem Elimelech, a professor of environmental and chemical engineering at Yale University. Now however, with a combination of the sun and nanoparticles, Elimelech knows it doesn't have to be.

"Any place that is off-grid, this (technology) can be useful," Elimelech said.

Elimelech and Ashkay Deshmukh, a Yale doctoral candidate, are working in collaboration with scientists at Rice University, the University of Texas in El Paso, and Arizona State University on this project. So far, there is only proof that the concept will work, Elimelech said, and this is not yet a product being produced for the market.

In the group's new approach to desalination, salt water rests above a layer of nanoparticles that help heat the water to between 40 and 60 degrees Celsius (104 to 140 Fahrenheit) when hit with rays from the sun, Deshmukh said. The water then evaporates, leaving salt and other contaminants behind, and moves to another container through a porous membrane.

The salt and other contaminants do not evaporate and therefore do not move through the membrane, Deshmukh said.

Deshmukh describes the layer of nanoparticles as acting "like a Gortex rain coat that doesn't let the rain in but will let sweat out."

Some minerals would have to be added back to the purified water that results from the desalination process, Elimelech said, so it would be good to drink.

What is new about this research, Deshmukh said, is the use of a renewable energy source to make the desalination work.

"Desalination overall can be very energy intensive," he said, as it requires heat generation and pumps for the water. This method does not require pumps, and the heat source is renewable, he said.

Usually, to remove the salt from 1,000 liters of seawater, you would need the energy of about 30 100-watt light bulbs turned on for one hour, Elimelech said. That may not seem like a lot, "But when you think about major, large-scale desalination for millions of people, it's a lot of energy," Elimelech said.

Elimelech said that his goal is for the solar-powered desalination to be used in remote, rural areas of undeveloped countries or for a single household. He said he does not believe this technology could be used on a large scale for an entire city of millions of residents at this time.

But he also said he hopes that the technology could be expanded to include cleaning up the waste water generated from hydraulic fracturing, which is the process of removing natural gas from underground shale deposits, and is more commonly known as fracking. Waste water from fracking is typically five to six times saltier than seawater, he said.

Desalination of that water would be a better alternative than pumping the waste water into the ground, as is typically done for disposal today, Elimelech said.

For now, though, the group of scientists continues to hone and improve the technology.

"This is an off-grid idea," Deshmukh said. "It doesn't need very expensive technology."

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Online: http://bit.ly/2uzEohb

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