Taking the salt out of brackish water
MIT engineers have invented a new desalination machine that runs on solar energy. The project began in 2013 when the engineers went to India with the hopes of helping poorer villages and townships with their drinking water.
The assumption was that they would figure out ways to rid these towns of microbes and other contaminants frequently found in poorer, older, water supplies.
“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.
The science of how the desalination system works is
similar to most, sans the power source.
The group came up with a method that uses solar panels to charge a bank of batteries. The batteries then power a system that removes salt from the water through electrodialysis. On the most basic level, that means that dissolved salt particles, which have a slight electric charge, are drawn out of the water when a small electrical current is applied. In addition to getting rid of salt (which makes water unusable for crops and for drinking), the team also applied UV light to disinfect some of the water as it passed through the system.
Solar-powered desalination projects are
not new. But the size and practicality of this project is exciting—it's won the MIT team the
USAID Desal Prize. The team will now continue testing the system against harsher and harsher conditions since the hopes are to employ these types of desalination systems throughout the world in troubled areas, similar to the ones that
inspired this work.
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.
You can look at the USAID Desal Award photos on their
flickr page.