A recent UN report on the state of the world’s water made for some grim reading: By 2050, driven by climate change, more than 5 billion people may suffer water shortages. Although efforts are underway to attempt to mitigate this worrisome phenomenon, engineers at MIT are beavering away at a new piece of tech, one that could help communities in particularly arid regions.
Their new paper, published in Nature Communications, details a device that essentially harvests water from the air, even in dry deserts. Although this technology isn’t actually new per se, the team explain that plenty of devices that already do this aren’t particularly practical.
One way of capturing water is through so-called “fog harvesting”, which collects already liquid water straight from fog. This, however, requires humidity levels to be incredibly high, an uncommon characteristic of dry deserts.
The other, the aforementioned “dewing”, condenses water vapor and turns it into a liquid. This often requires a refrigeration-driven cooling and water condensation mechanism, which is fairly energy-intensive – but back in 2017, the MIT team showcased their own dewing device, which was far more energy efficient.
That device’s success at harvesting around 2.8 liters (0.61 gallons) of water per day was borne out of the use of a bespoke crystalline material. Water vapor gathers in the porous material like a metallic-esque sponge during the cooler nights. When the light of the Sun gently warms the device, the liquid water evaporates again, but this time it falls away from the material and into capture caches, where it condenses again and accumulates.
Compared to other dewing materials, these “metal-organic frameworks” (MOFs) capture more water and require less extreme temperature changes than their conventional cousins, like silica gels or liquid brines. It also didn’t require any moving parts, nor does it need any form of refrigerant, all of which made their device particularly energy efficient – a passive creation that works its magic using sunlight-driven temperature changes alone, independent of any artificial power source.
Back then, MIT’s device received understandable praise, although some of the hype implied it was a veritable “cure for drought”. As the authors of the 2018 study note early on, their device was merely a proof-of-concept design, and, most importantly, it had not been demonstrated to work “under representative conditions of desert/arid climates”.
This study aimed to change that. Bringing the device to Tempe, Arizona – they demonstrated that the box’s water-harvesting abilities work in arid, desert conditions, even when the relative humidity is as low as 10 percent and at sub-zero dew points.
There are still some problems, though. Sitting atop a rooftop of Arizona State University, the device appears to produce around 0.25 liters of water (0.05 gallons) per kilogram of MOF in 24 hours. That’s not really that much water as of yet, and it likely struggled in comparison to the previous test because that took place in Cambridge, Massachusetts, which had a relative humidity of around 65 percent.
The device can only operate over one 24-hour cycle at present too, and, if it continues to prove its worth, may face difficulties as the engineers begin to scale it up and make it practically useful.
Nevertheless, it’s a brilliant proof-of-concept device that’s making slow steps toward a future where water shortages and drought remain an ominous, existential threat to communities around the world.
Incidentally, this isn’t the only device that works off ambient temperature changes. Just recently, another MIT team conjured up a device that can generate small amounts of electricity based on natural, slight temperature swings – although again, scaling remains an issue here.
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