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”.