It is a simple act that we take for granted multiple times a day and 365 days a year, but what would we do if it suddenly wasn’t there? What I am talking about is water, clear, cool water. I’ve been through minor water outages and they are not very pleasant. We really don’t think about all of the things for which we need water until the tap is dry. What if the tap was dry with no chance of it producing fresh running water at all?
An article published May 3, 2018 in Engadget.com titled “Atmospheric harvesters will enable arid nations to drink from thin air” brought this serious issue to the forefront of my mind. The author, Andrew Tarantola, was writing about the serious water shortage problem in Cape Town South Africa. Severe droughts have plagued Cape Town since 2015 making them question when the water might actually run out.
Quoting the story “Cape town narrowly avoided Zero Day earlier this year, when the city’s taps were projected to run dry, but the city is expected to face another critical shortage in 2019. The situation has become so dire that officials are seriously considering importing icebergs to augment the water supply. But why try to tow 70,000 tons of ice 1,200 miles up from Antarctica when modern technology can suck the humidity we need out of thin air?” Zero Day is the projected day when their water supply would be dried up and no water would flow through the city’s public works water system.
The iceberg towing idea isn’t as farfetched as you might think. The United Arab Emirates has a plan in place to tow an iceberg from Antarctica to the eastern emirtate of Fujairah near the shore sometime this year. The company that plans to do the towing,The National Advisor Bureau Limited, estimates they could get more than 20 million gallons of fresh water from just one iceberg. That is the average amount of water contained in an iceberg according to the experts. Now back to the new technology.
The Engadget.com article reported that the Incas actually collected water from the air with “fog fences” that collected dew from the air. Scientists say our atmosphere holds about 13 trillion liters of water vapor at any given time. That’s equal to approximately 10 percent of all of the surface fresh water on the planet, but, as you can see, it’s not a very efficient means of collecting drinking water for large masses of people. That’s why this research is so very important. According to the article “The current state-of-the-art dew-harvesting refrigeration based machines operate by lowering the temperature of the surrounding air below the dew point and then collecting the vapor. Unfortunately, as the relative humidity drops below 50 percent, the efficiency of these machines nosedives too, requiring untenable amounts of electrical power to operate the refrigeration units.” The newly developed technology, however, still operates well even when the relative humidity falls as low as 10 percent.
Scientists from MIT and UC Berkeley teamed up to develop this process. The device uses a metal-organic framework (MOFs) to control which gasses will bind to the MOF. Professor Omar Yagi, a chemistry professor at UC Berkeley, invented the material back in the 1990s developing over 20,000 types of MOFs in 20 years. The specific one used in this case (shown above) is called MOF-81 or Zr6O4(OH)4(fumarate)6 which they say works better than conventional sorbents like zeolite or silica gel.
Here’s how it works. “The device itself is a simple design with two main parts: the absorption layer (aka the MOF) and an enclosed, an air-cooled condenser. The backside of the MOF is painted black to operate as a solar absorber. At night, the enclosure walls are opened to enable airflow past the MOF and it becomes saturated with vapor. Once morning rolls around, the enclosure is buttoned upland the black side of the MOF is covered with an ‘optically transparent thermal insulator’ (OTTI). When the MOF is is exposed to sunlight, it heats up, causing its organic molecules to release their hold on their water molecules, which condense at ambient temperatures for collection.” They make it sound so simple, right.
The team performed an experiment last year testing the MOF on the roof of a building on the University of Arizona. They extracted .75g of water using 3g of MOF. That amount fit the protocol they set up to validate their model. Much more work will have to be done, however, to produce sufficient quantities of water to make the production of water by this method feasible and cost effective. They also need to produce much larger quantities of water for public use. I’m sure this isn’t the last we’ll hear about this process.
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