Desalinating water - removing salt from seawater to turn it into fresh water ready for drinking, was an expensive, energy-intensive process. American and German researchers, however, have just devised a way to create fresh water from salt water inexpensively, using very little electricity. Designed by Richard Crooks of the University of Texas and Ulrich Tallarek from the University of Marburg, this system, uses such a small supply of energy that it can run on a simple battery.
Desalinization is important to human health and well-being, as one-third of world's population lives in areas where fresh water is not abundant, according to the United Nations. The number of people living in such water-stressed areas is expected to double by the year 2025. It is estimated that one billion people are without any access at all to safe drinking water.
The new process is called electrochemically mediated seawater desalination, and the device itself is known as a water chip. The chip uses a pair of microchannels (each just 0.0009 inch diameter) connected by a bipolar electrode. Salt water is pushed through the two channels, and a small three-volt charge is applied to one channel, while the other remains grounded, forming an electrical potential between the two. An "ion depletion zone" is created at the junction of the channels, which acts to prevent salt from entering one channel. The difference in charges between the points in the device forces ions (the salt) into one channel, while desalinated water comes out the other branch.
"The neutralization reaction occurring at the electrode is key to removing the salts in seawater," Kyle Knust, a graduate student who was the paper's first author, said.
Current desalinization methods include boiling seawater and condensing the steam to create a fresh water supply. But, this method uses a great deal of electricity. Reverse osmosis, which involves using a membrane to filter the water, takes less energy, but the filters are expensive and ruin easily. In addition, the water to be filtered needs to be treated before the process can begin. With this new system, the only filtering of the water which is needed is to remove sand and sediment, and there is no filter to become clogged.
This new method only reduces the amount of salt in water by about 25 percent. To become water suitable for drinking, 99 percent of the salt would have to be removed.
"This was a proof of principle. We've made comparable performance improvements while developing other applications based on the formation of an ion depletion zone. That suggests that 99 percent desalination is not beyond our reach," Knust said.
This new desalinization method is detailed in the the journal Angewandte Chemie (Applied Chemistry).
