A tiny device leads to portable desalination units
Photo: Patrick Gillooly/MIT
Researchers at MIT and in Korea are developing a new way to desalinate water, which could lead to small, portable units powered by solar cells or batteries that can provide fresh water to rural areas or during disaster relief.
Desalination is the process of removing salt from water. It's what sailors use to keep a stock of fresh water on hand for drinking and cleaning, and when scaled up, it's what some drought-prone cities lean on when ground water supplies run low. However, the process is incredibly energy intensive. It takes a whole lot of power to get a drop of fresh water out of seawater. That makes it impractical for use in disaster situations like post-quake Haiti. But perhaps not for long.
The new process uses ion concentration polarization, rather than reverse osmosis. The usual method of reverse osmosis requires pumps to send water through membranes that filter out the salt. The new process, however, uses an ion-selective membrane and separates salts and microbes from water electrostatically. The result is a system that doesn't need to rely on powerful pumps.
According to MIT, "The system works at a microscopic scale, using fabrication methods developed for microfluidics devices -- similar to the manufacture of microchips, but using materials such as silicone (synthetic rubber). Each individual device would only process minute amounts of water, but a large number of them -- the researchers envision an array with 1,600 units fabricated on an 8-inch-diameter wafer -- could produce about 15 liters of water per hour, enough to provide drinking water for several people. The whole unit could be self-contained and driven by gravity -- salt water would be poured in at the top, and fresh water and concentrated brine collected from two outlets at the bottom."
The researchers have already tested one of the units using seawater contaminated with plastic particles, blood and other microbes. More than 99% of the salt and contaminants were removed. That's an impressive result, though as of right now, it still required more electricity than with present systems. So the task is to maintain this level of efficiency while minimizing how much energy is required. The researchers feel that if the unit is properly engineered, the newer system would only use about as much power as a conventional light bulb.
That means the potential for a low cost, low power, highly effective desalination process for small scale relief. The researcher expect it will be about two years before the system is ready as a product.
