Manipulating Moisture for Mankind?

What’s for dinner? A glass of man-made water and maybe a side of crow.

Last year, I was intrigued by various articles I read involving extracting water from the air and I posted a skeptical blog on my findings. Frankly, I thought the idea was somewhat preposterous, especially when some of the discussions mentioned extracting moisture from desert environments. After all, deserts are deserts precisely because they lack moisture. So how could moisture really be extracted from anything so dry?

Yet, here it is a year later and there’s now credible research that suggests we have the capability of doing just that – generating water from the air in even the most arid environments. Let’s take a look at some new water harvesting systems being developed.

On March 22, 2018, Science Daily reported that the Massachusetts Institute of Technology (MIT) had field tested a new water harvesting technology that “can extract clean drinking water right from the air, even in the driest of deserts.” This method uses metal-organic frameworks (MOFs) as a “high-surface area material” which allowed researchers to extract potable water from the air even when the humidity was as low as 10%, using a device solely powered by sunlight.

These results are very encouraging since most water-from-air devices require much higher humidity levels to operate and also require substantial power for water production. The MIT device was field tested at Arizona State University (ASU) in Tempe, AZ.

On the other side of the globe, Uravu – a technology start-up in Hyderabad, India is developing a residential water vapor collection device which can be placed on home rooftops. This two-part design “uses a proprietary water-absorbing material that sucks vapor from the air and uses solar thermal energy to convert it into water” without the need for electricity or moving parts.

The proprietary hydroscopic material absorbs water vapor overnight and stores it for conversion to liquid water by a solar collector the following day.  The solar collector rapidly heats the water vapor which changes it to a liquid as it cools.

The Uravu prototype produces about 50 liters (~13 gallons) of water per day and the company’s goal is to raise that to 2,000 (~ 530 gallons) liters per day.

Researchers out of Virginia Tech are exploring ways to improve the efficiency of fog harvesters.  The structure they created is called a fog harp. This mechanism is well named since it really looks like a primitive musical harp.  It’s essentially “a vertical array of parallel wires” which catches water vapor suspended in fog as the wind blows over the wires.

fog harp - Virginia Tech
“Study co-author Josh Tulkoff constructs a large prototype of the fog harp, which consists of a vertical array of 700 wires and is based on initial experimental results.” Photo Credit: Virginia Tech. 

 

The fog harp technology is a significant improvement over traditional fog nets which have been employed since the 1980’s in higher humidity areas. By using wires on the fog harp, investigators have been able to collect water vapor that may be lost when using the fog nets. Virginia Tech researchers noted a threefold increase their collection capacity using the fog harp as compared to fog nets.

Fog nets can be very finicky. The conundrum the scientists were looking to solve with the fog nets was really a spacing issue. “If the holes in the (fog net) mesh are too large, water droplets pass through without catching on the net’s wires. If the mesh is too fine, the nets catch more water, but the water droplets clog up the mesh without running down into the trough and wind no longer moves through the nets.” The use of parallel wires has seemingly solved this long perplexing puzzle.

All I can say is what a difference a year makes… any maybe, please pass the salt & pepper.

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