MIT team makes clean water from the sun
An engineering team from the Massachusetts Institute of Technology headed to the deserts of New Mexico last weekend, in a high-tech showdown that could help resolve the global water crisis.
Amos Winter, an assistant professor of mechanical engineering at MIT, and doctoral student Natasha Wright squared off against four rival teams in a competition to develop better techniques to extract salt from water. The goal of the contest, sponsored by the US Agency for International Development (USAID) and the Bureau of Reclamation, is a simple, inexpensive system to provide clean water to rural communities across the developing world.
“It’s a two-billion-person problem,” Winter said. “That’s a pretty motivating problem.”
Winter and Wright work at MIT’s Global Engineering and Research Lab, or GEAR, which designs technical solutions tailored for use in developing countries. The desalination project is being backed by Jain Irrigation Systems Inc. of India and by MIT’s Tata Center for Technology and Design, which researches technologies for developing countries. The center is backed by the founding family of Tata Group, one of India’s largest corporations.
India has 16 percent of the planet’s population but just 4 percent of its fresh water. Much of this water is underground, and about 60 percent of it is brackish — not quite true seawater, but too salty to be safely consumed by plants, animals, or people. Still, Winter said about 70 percent of Indians must drink groundwater, even when it’s too salty.
This salt can be removed in several ways, but water desalination has traditionally required lots of electric power. Yet about a quarter of India’s 1.1 billion people live in rural villages of 5,000 or fewer, where for many, the availability of electricity ranges from sporadic to nonexistent.
So Wright and Winter designed a solution for people living off the grid. Most big desalination plants use reverse osmosis, a technique that uses high-pressure pumps to filter out the salt. But Winter said that osmosis wastes about 40 percent of the water.
The MIT system uses a method called electrodialysis. When salt dissolves in water, it breaks down into positively and negatively charged ions. Now they can be separated from the water by using electrically charged membranes that attract the salt ions like magnets.
“It works kind of like an electric circuit,” Wright said. “The ions get pulled out of the water toward the electrodes.” And with electrodialysis, only about 5 percent of the water is discarded.
Instead of relying on an electric utility to drive their desalination system, Wright and Winter use a bank of lead-acid batteries, similar to those found in cars and trucks. These are charged up during the day by a set of solar panels, making the system entirely self-sustaining. The total package is designed to produce enough water to irrigate a small farm or to serve the daily drinking and cooking needs of up to 5,000 people.
Glenn Vicevic, product manager at General Electric Co.’s power and water business unit in Oakville, Ontario, Canada, works on large-scale electrodialysis systems, and provided the technology used by the MIT team.
“Electrodialysis technology is well understood,” said Vicevic, who works on large-scale desalination systems. “If you combine that with properly sized solar cells and you have properly sized batteries, there’s no reason you couldn’t achieve it.”
But the system must function flawlessly if it is to be deployed in impoverished rural villages or farms. “If you take modern technology and you put it in an area where there’s no support for it,” said Vicevic, “it’s a challenge.”
During last weekend’s showdown, held at the Brackish Groundwater National Desalination Research Facility in Alamogordo, N.M., all five contestants had to run their systems nonstop for two 24-hour cycles. In each session, the MIT system desalted 2,100 gallons of water, making it fit for use in irrigation. It also ran an additional 66 gallons of water through an ultraviolet cleaning system to kill bacteria and make it safe to drink.
“Our solar array was working perfectly,” Wright said.
Wright and Winter’s competition is testing different desalination technologies: reverse osmosis, distillation, nanofiltration. They include Atlantis Technologies and EconoPure Water Systems, a pair of California water treatment companies; the Center for Inland Desalination Systems at the University of Texas El Paso; and Green Desal, a consortium of university researchers from Nepal, Jordan, Israel, Brazil and the United States.
USAID scientists will grade each contestant on various criteria, including energy consumption, ease of maintenance and, of course, water quality. The agency hopes to announce its results next week, possibly in time for Earth Day on April 22. The first-prize winner will get $125,000, with $50,000 and $25,000 for the second- and third-place teams. In addition, the top-scoring teams will be eligible for up to $400,000 in federal grants to set up their systems in a developing country, for a real-world test.