Three-quarters of a billion people around the world don't have access to clean water, a problem that is compounded by the fact that 90 percent of wastewater in developing countries flows untreated back into rivers, lakes and coastal areas. But thanks to a new device developed at MIT, removing contaminants from water has become more efficient than ever and marks an important step toward reducing water-related health problems around the world.
For the most part, polluted or brackish water is treated in one of three ways: membrane filtration, electrodialysis, or capacitive deionization. Membrane filtration uses ultrafine porous materials to strain pollutants and microorganisms from water, whereas electrodialysis and capacitive deionization remove salt from brackish water using an electric current. While these approaches work well enough, membrane filtration is expensive and not so effective when pollutants are in water in low concentrations, and electrical methods tend to require large amounts of energy.
The new device developed by MIT, however, takes advantage of electrochemical processes to remove even trace amounts of contaminants from water and its energy requirement is low enough that it could easily be solar powered. Moreover, unlike other water purification systems, this device can target the removal of specific pollutants, rather than just functioning like a catchall net.
Basically, this new system allows water to flow through to surfaces covered in a special type of material that allow them to undergo a chemical reaction and function as positive and negative electrodes. When an electrical source is applied to these surfaces, a user of the device can tune them so that they bind with specific pollutant molecules found in a given water sample—even if these molecules are only found in parts-per-million concentrations. As the researchers detailed in a recent paper in Energy and Environmental Science, they were able to successfully demonstrate this by removing ibuprofen and various pesticides from a water sample.
"Such systems might ultimately be useful for water purification systems for remote areas in the developing world, where pollution from pesticides, dyes, and other chemicals are often an issue in the water supply," said Xiao Su, a postdoctoral researcher at MIT and the lead author of the paper.
While the team's demonstration of this "highly efficient" device is impressive, one of the major challenges remaining for the team is figuring out how to scale the technology to deploy it in real-world scenarios. But so far the team is off to a promising start—their prototype was still able to function after 500 test cycles.
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