Device that turns seawater into drinking water without filtration

The new device, developed by professor Jongyoon Han and colleagues at the Massachusetts Institute of Technology (MIT), produces drinking water from seawater with only a small amount of electricity.

The current version of the device is only about the size of a suitcase. The device uses a smaller amount of electricity than a smartphone charger, which can draw power from a portable solar cell in the absence of a power storage battery pack.

The electric seawater purifier weighs less than 10kg.

Instead of using a filter or distillation, the device uses an MIT-designed technology called ion-focused polarization (ICP), which was first introduced 12 years ago. The researchers pumped seawater through a narrow channel between two electrically charged membranes, one positively charged and the other negatively charged.

When water flows through the electric field between the two membranes, particles such as salt molecules, viruses and bacteria are pushed into the side water channel to be discharged. At this point, the main water channel has been purified and relatively desalinated, but may still contain some salt ions.

For the above reason, the prefiltered water will continue to flow through an electrical dialysis module. There, the last remaining salt is removed. Although this step involves passing water through an ion-exchange membrane, it helps to separate salt ions from the membrane for reuse. Finally, water comes out from the device's nozzle, which exceeds the World Health Organization's drinking water standards.

The team emphasizes that the system is a bit complicated due to the multi-stage process integration. First, water flows through a series of six ICP modules, then through three other modules and then to an electrodialysis module. The current version can produce 300 ml of drinking water per hour, with a consumption of 20 watt-hours of electricity per liter. Han and his colleagues are working to increase the capacity of the device. They published the study April 14 in the journal Environmental Science and Technology.