Batter-powered, portable device may harvest water from thin air

WASHINGTON DC: Scientists are developing a lightweight, battery-powered freshwater harvester that could someday harvest as much as 10 gallons per hour from the air, even in arid locations.

The nanofibre-based method developed by researchers from University of Akron in the US could help address modern water shortages due to climate change, industrial pollution, droughts and groundwater depletion.

Harvesting water from the air has a long history. Thousands of years ago, the Incas of the Andean region collected dew and channeled it into cisterns. More recently, some research groups have been developing massive mist and fog catchers in the Andean mountains and in Africa.

To miniaturise water generation and improve the efficiency, researchers led by Shing-chung Wong from University of Akron, turned to electrospun polymers, a material they had already worked with for more than a decade.

Electrospinning uses electrical forces to produce polymer fibers ranging from tens of nanometers up to one micrometre -- an ideal size to condense and squeeze water droplets out of the air.

These nanoscale fibre polymers offer an incredibly high surface-area-to-volume ratio, much larger than that provided by the typical structures and membranes used in water distillers.

By experimenting with different combinations of polymers that were hydrophilic (attracts water) and hydrophobic (repels water), the group concluded that a water harvesting system could indeed be fabricated using nanofibre technology.

Researchers determined that their polymer membrane could harvest 744 milligrammes per square centimetre every hour, which is 91 per cent higher than similarly designed membranes without these nanofibres.

Unlike existing methods, the harvester could work in arid desert environments because of the membrane's high surface-area-to-volume ratio.

It also would have a minimal energy requirement.

"We could confidently say that, with recent advances in lithium-ion batteries, we could eventually develop a smaller, backpack-sized device," Wong said.

The design simultaneously grabs water and filters it. The electrospun fibre network can act as an anti-fouling surface, sloughing off microbes that could collect on the harvester's surface.

So the water would be "clear and free of pollutants" and immediately drinkable once it's collected, he said. Researchers hope to obtain additional funding to build a prototype of the freshwater harvester.