Excellent Idea of the Day: Clean H2O for Navajo

Desalination equipment being tested on the roof at the University of Arizona. Chad Munich, University of Arizona
Chad Munich, University of Arizona

A low-tech desalination project could bring clean, safe water to Navajo Nation.

Roughly 80,000 Navajo lacking indoor plumbing and must travel long distances for fresh water. Arizona's largest aquifer mostly lies underneath tribal land, but that water is too brackish to drink. A low-tech solar water desalination plant under construction could finally bring fresh water to the people who need it.

"Once, twice, three times a week they're literally taking their pickup truck with a tank in the back, driving an average of about 40 miles to go to a fresh water tank," said Wendell Ela, a chemical and environmental engineering professor at the University of Arizona who is leading a Navajo desalination demonstration project in a tribal area east of Flagstaff.

Water hauling has become a costly, time-consuming routine for many Navajo, yet conventional water purification wouldn't work well there. So many live off the grid that an expensive infrastructure would have to be built first to power a new plant. Plus, a high-tech system needs constant oversight and specialized expertise to run.

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Ela, working with the U.S. Bureau of Reclamation, a solar company and several university experts on the project, took a different approach. His team created a membrane distillation system that uses hollow fiber modules to purify salty water. Resembling thin vermicelli, the modules are basically a bunch of membrane straws with a large surface area to facilitate evaporation.

To power the distillation system, they're using a trough-like solar collector that tracks the sun. Water also gets passed along the array to cool the photovoltaics. Since the solar energy also heats the water as it passes, thermal conversion jumps from 20 percent to upwards of 50 percent. Since the plant will be built entirely from off-the-shelf components, it can be maintained and repaired easily, Ela added.

The goal for the demonstration plant is to produce 1,000 gallons of potable water daily. Fully distilled water by itself is flat and tasteless, Ela pointed out, so that water will be blended with some salty water to create the right mineral balance.

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Later next month, the solar collector component is expected to be completed, with desalination starting after that. At first the water will be used for stocks so it doesn't go to waste while the group collects test data. If this demonstration proves itself, similar plants could help other rural, remote locations.

"There's nothing particularly esoteric or high-tech at all," Ela said. "And that's exactly why we like it."

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