Science

Water Harvesting Breakthrough

Scientists in the US have invented a water harvester that uses sunlight to pull litres of water out of the air each day even in dry, arid conditions.

The solar-powered harvester was constructed at the Massachusetts Institute of Technology (MIT) using a special metal-organic framework produced at the University of California, Berkeley. The prototype was able to pull just under 3 litres of water from the air over a 12-hour period, at humidity levels as low as 20%.

“This is a major breakthrough in the long-standing challenge of harvesting water from the air at low humidity,” said Omar Yaghi, one of two senior authors of the paper reporting on the breakthrough. “We wanted to demonstrate that if you are cut off somewhere in the desert, you could survive because of this device. A person needs about a Coke can of water per day. That is something one could collect in less than an hour with this system.”

Metal-organic frameworks (MOF) combine metals like magnesium and aluminium with organic materials to create rigid, porous structures ideal for storing gases and liquids. Yaghi and his team created a metal organic framework that binds water vapour. He then teamed up with Evelyn Wang, a mechanical engineer at MIT, to turn the MOF into a water-collecting system.

As ambient air flows through the porous MOF, water molecules attach to the interior surfaces. Sunlight entering through a window heats up the MOF and drives the attached water toward a condenser, which is at the temperature of the outside air. The vapour condenses as liquid water and drips into a collector. “This work offers a new way to harvest water from air that does not require high relative humidity conditions and is much more energy efficient than other existing technologies,” Wang said.

Despite this revolutionary engineering breakthrough, Yaghi admits there is still room for improvement. At present, the metal-organic framework can absorb only 20 percent of its weight in water, but alternative MOF compositions could possibly absorb 40 percent or more. Additionally, the materials can be tweaked to be more effective at higher or lower humidity levels. “There is a lot of potential for scaling up the amount of water that is being harvested”, he said. “It is just a matter of further engineering now.”

Yaghi and his team are now improving their metal-organic frameworks, while Wang continues to work on the harvesting system, with an aim to produce more water.

This new invention is the start further exciting innovations on the issue of water for years to come.

Breakthroughs such as this are crucial, given the predicted scarcity of clean water and increased drought from climate change. “One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household,” said Yaghi. “To me, that will be made possible because of this experiment. I call it personalized water.”

28/04/2017

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