Moisture Harvesters for all?

I’m not easily impressed by reports of some newly invented uber-box, but a new paper in Science reveals an amazing little device from MIT: “Water harvesting from air with metal-organic frameworks powered by natural sunlight”

“… an efficient process for capturing and delivering water from air, especially at low humidity levels (down to 20%), has not [yet] been developed. We report the design and demonstration of a device based on porous metal-organic framework-801 [Zr6O4(OH)4(fumarate)6] that captures water from the atmosphere at ambient conditions using low-grade heat from natural sunlight below one sun (1 kW per square meter). This device is capable of harvesting 2.8 liters of water [5 British pints] per kilogram of MOF daily at relative humidity levels as low as 20%, and requires no additional input of energy.”

Sadly the Science paper is behind a paywall. But ScienceDaily has a good write-up.

At present, the device…

* is still only a working prototype. The “proof of concept harvester leaves much room for improvement”. But… “Rooftop tests at MIT confirmed that the device works in real-world conditions.”

* needs a mesh pad made… “of zirconium metal and adipic acid”.

* might work best when there’s direct sunlight to warm it.

* it looks like it would need to work with a bug screen and anti-fungals in a real-world deployment. Flies and mites can come in very small sizes, and in a dry environment would be attracted by the moisture: would a fine-meshed bug-screen let enough moisture in overnight?

Apparently zirconium cost about $14 per pound in 2010, according to figures I found, so it is not some incredibly rare metal. It’s also durable in the presence of moisture, since it’s apparently used to cap dental fillings. “Adipic acid” is also common, annually produced in the billions of pounds as a precursor in making nylon. It doesn’t melt before 152 degrees centigrade. The working device used about two pounds of the mixture in a pad. How long the pad remains viable isn’t stated, but the materials sound durable. If the pad can be made to last six months in a desert summer before gumming up its latices with microscopic fungi or other similar blockages, and the starter box costs $95, then it’ll sell like hot cakes. Or, in this case, like hot boxes.

As with all such world-changing devices, we probably want to be alert to unintended consequences of mass deployment as early in the development process as possible. Especially in terms of drinking water with a trace of zirconium or aluminium. Think: the Ancient Romans and their lead water pipes, for instance. But some nano-mesh or other would presumably filter unwanted metal traces out of the water.

But it looks good, very good. And is also well-timed, in terms of offering a simple technology that could help nudge along measures such as a green wall along the southern edge of the Sahara, or even help to water the smallholdings of the coming billions in Africa. It’s also simple like-a-bicycle, which means there should be lots of opportunities for home-brew tinkerer iterations of the sort that took humanity from the ungainly old Penny Farthing and ‘boneshaker’ bicycles to the perfected modern Safety Bicycle form we know today.