How fog harvesting can revive the driest places on earth

May 28

A team of MIT and Chilean researchers is seeking to use high-efficiency fog collectors to bring water to dry regions. (Courtesy of Gareth McKinley)

For decades, scientists have been working with villagers inhabiting the driest place in the world to perfect a clever survival technique.

Erected and stretched out along a test site within the parched, mountainous region of Coquimbo in central Chile are a series of mesh-patterned nets that have been fine-tuned to efficiently trap and condense tiny droplets that make up the dense coastal fog that sweeps across the fields. As the droplets accumulate, they form heavier drops that drip into containers that, over time, fill up with potable water.

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This mesh-patterned net traps water droplets from fog. (Courtesy of Gareth McKinley)

“What’s great about fog is that nature has done the work for us in condensing the water into tiny droplets,” explains Gareth McKinley, a professor of teaching innovation at MIT. “What we’re doing with the technology we developed is simply creating a drainage system for water that’s in the air — one that doesn’t just not require power, but is scalable and modular, meaning you can set it up anywhere.”

Man-made systems that collect water from fog have been around for centuries, perhaps dating even as far back as the Byzantine Empire, when residents of the ancient city of Feodosia stacked stones to build structures thought to be air wells to draw water from the atmosphere. Currently, fog collecting systems are being used in at least 17 countries.

As a self-sufficient, low maintenance alternative, the math shows that the system the MIT team, in collaboration with researchers at the Pontifical Catholic University in Santiago, came up with would produce as much as 12 liters (3.17 gallons) a year. Scaling up the technology, they estimate, would alone produce enough fresh water for a number of settlements along the northernmost areas of the Atacama Desert, where the average annual rainfall tops off at about 0.6 of an inch. (For comparison, Las Vegas gets about 4.2 inches of rain each year).

The region also happens to be home to some of the most arid sites imaginable, such as the abandoned mining town of Yungay, which typically sees rain clouds roughly once every decade. In the coastal fishing village of Chungungo, where earlier designs were tested, residents had to rely on having drinking water trucked in from other parts of the country.

When McKinley, whose background is in chemical engineering, first got involved in the project a few years ago, the researchers had been tinkering with various mesh patterns that made it possible to dramatically increase the volume of harvested water. A series of lab tests would later determine that the optimal design was a woven mesh pattern comprised of thin, slightly-spaced apart strands of stainless steel that, from a distance, resembled a window screen. By making the gaps smaller than its predecessors, they were also able to minimize the degree in which droplets can escape while also allowing for enough spacing for the fog to pass through.

“The best examples of fog collecting can be found in nature,” McKinley points out. “Whereas flat surfaces force the wind to move around it, taking the fog along, trees like redwoods have needle-shaped leaves that collect droplets as the wind moves along.”

McKinley was then asked to develop a coating that’s sticky enough to catch tiny droplets suspended in the air while also retaining certain slippery properties that allow the accumulated drops to easily slide down towards the collection gutter before the wind blew them off the surface. The result was a design that converted 10 percent what’s available in fog into potable water, more than quadrupling the modest conversion rate (2 percent) of previous versions made using relatively inexpensive, common materials.

And under the right conditions, McKinley asserts, the systems can do even better. “I’m sure we can collect up to twice what we achieved if we keep improving the technology,” he adds.  “It’s impossible to collect all of it, but the faster the wind blows the more we can collect.”

However, other groups that have been also working to expand access to the technology, such as Canadian non-profit Fogquest, have remained skeptical, not only of efforts to incorporate high tech materials to improve upon the efficiency of such systems, but to pull it off in a manner that’s feasible. “A thousand people have wanted to try to build a better material for collecting fog droplets and no one has done it very well — yet,” FogQuest’s executive director Robert Schemenauer told CNN back in 2011. “You also have to think about the manufacturing side of it. We are using something that is used in vast amounts for another purpose, so the cost is really low.”

At the moment, the researchers are focused on making the nets durable enough to last at least a year or two with little maintenance, which, currently, involves brushing them periodically to clear away insect and other debris that tends to get lodged along the surface. And while they haven’t calculated the cost for each unit, McKinley believes that stronger nets capable of resisting wear and tear would eventually prove inexpensive enough for many underdeveloped, rural communities.

More broadly, he says, these high-efficiency fog collectors have the potential to boost water supply in dry parts of Saudi Arabia and India where westerly winds carry warm, humid air towards elevated coastal lands. McKinley even foresees a scenario not so far off in the distant future where locals in San Francisco start to look into similar methods for harvesting the thick fog cover that blankets large swaths of the bay as a way to replenish water shortages that, over the years, have become increasingly severe.

“Whether you’re living in desert villages or developed regions, climate change is real and it’s happening,” McKinley adds. “California, for instance, is suffering from a serious drought and ideas like this are going to be useful in heading off some those challenges.”

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