Scientists have developed a microchannel-based portable unit capable of separating a flow of seawater into nano-sized flows of salt and fresh water that can be used to create portable water desalination units with low energy consumption and high efficiency, as the researchers report in an article published in the online edition of the journal Nature Nanotechnology.
If the scientists succeed in developing a full-scale portable device based on their design that concentrates1600 microchannels able to fit into an area of 20 cm sq., it will be capable of removing salt and impurities from 300 ml of seawater per minute powered by an ordinary battery or solar panel.
Seawater enters the Y-shaped channel (red) on the right, and fresh water exits through the lower part on the left. The researchers, a group of scientists headed by Jongyoon Han from the Massachusetts Institute of Technology in the U.S. believe that their design will not replace the large water desalination plants used around the world and producing water for large population centers; however, it may find a use when fresh water must be obtained in field conditions or in emergency situations.
Most water desalination plants around the world use the principle of reverse osmosis in their operation, under which seawater under pressure is passed through a filter system, and at the final stage passes through a membrane that separates water molecules from the larger salt ions dissolved in it. This energy-intensive process requires the construction of large water treatment plants, since it is inefficient on a small scale.
In their work Han’s team used another principle, the so-called ion channel polarization principle. According to this design, a flow of seawater passes through a microchannel with an electric field applied at its end. This action forces the ions in the flow to move towards one side of the water flow, leaving a flow of clean fresh water on the other side of the flow. if the microflow is divided in two immediately after the section in which electrical separation of the ions from the water occurs, it is possible to obtain one flow supersaturated with salt ions and a second flow of fresh water.
In their publication, the researchers showed that by using the same electrical method, water can be purified from bacteria, viruses and other charged biological particles, and at the final purification stage it only has to pass through a charcoal filter to separate organic components not affected by the electric field.
Now the scientists are faced with the task of developing a commercially acceptable production process for microchips containing hundreds or thousands of such microchannels able to generate large flows of purified fresh water.
