The American engineers who traveled to rural India two years ago believed they were going to help poor villagers get rid of microbes in their drinking water. But soon after their arrival, they began hearing about a different problem: salt.
"People kept talking about the salt in the water," recalled Natasha Wright, a doctoral candidate who was part of the team from Massachusetts Institute of Technology that made the journey in 2013. "The groundwater beneath the villages was brackish."
Those complaints inspired new technology that could some day supply water to thirsty villages and drought-stricken farms in other parts of the world. The MIT team developed a solar-powered water desalination system that uses the sun's energy to turn brackish liquid into contaminant-free water safe for drinking and for crops.
While there are dozens of different desalination systems in use around the world, MIT's is uniquely designed to be small, relatively cheap and 100-percent solar-powered, making it suitable for remote areas where the electricity supply is unreliable or non-existent, Wright said.
The panel of judges last month deemed the machine's potential so impressive that they gave the inventors the $140,000 "Desal Prize," an award sponsored by Securing Water for Food, a joint project of the U.S. Agency for International Development and the governments of Sweden and the Netherlands. Some 68 engineering teams from 29 countries competed in the contest, hosted by the Interior Department's Bureau of Reclamation in Alamogordo, N.M.
"Providing a sustainable water supply is important for the West, the country and the world," Esteva Lopez, the department's reclamation commissioner, said after the top prize was awarded to MIT and its research partner, Jain Irrigation Systems.
Wright said she and fellow engineers from MIT's Global Engineering and Research Laboratory became aware the extent of saltwater intrusion in northern and central Indian aquifers during visits to investigate solutions for widespread water contamination in India. In addition to problems with bacterial contamination, the groundwater in much of rural India is brackish, having a salt content lower than seawater but still high enough to cause problems. In some of the villages visited by the MIT researchers, locals were trying unsuccessfully to remove the salt using filters and chemicals.
"People complained about the salty taste," Wright said, "and the salt ruined their cooking pots."
Traditional desalination systems are expensive and require substantial amounts of electricity to operate, making them impractical for India's remote farming communities. Instead, the MIT researchers designed a system that removes salt through a process called electrodialysis, using a series of electrodes and membranes to remove the salt. They added solar panels and batteries to run the pumps and charge the electrodes. Then, in a final step, they installed ultraviolet light arrays to kill any microbes remaining in the water.
The finished prototype is small enough to fit in a tractor-trailer and includes photovoltaic cells to supply the electricity. The system, when fully operational, can supply the basic water needs of a village of between 2,000 and 5,000 people, MIT officials said. Although the prototype was more expensive, Wright said the team is hopes to lower the costs of a village-sized unit to about $11,000.
Such a lower-power system is useful mainly for treating brackish water and not seawater, which contains far more salt. But the prototype now being tested could handle water that contains salt concentrations of up to 4,000 parts per million, meaning it would work in about 90 percent of India's wells, Wright said. Seawater's salt concentration averages about 35,000 parts per million.
"There are places where this kind of system won't work, but the advantage is, it uses half the energy of other systems," said Wright. And, thanks to solar cells, "you can be fully off the grid."