Desalinating seawater using electricity

 From  New Atlas    

Although there are already portable systems that create drinking water by desalinating and purifying seawater, they typically utilize filters that have to be replaced. A new MIT setup, however, just requires a small amount of electricity to get the job done.

Developed by a team led by Prof. Jongyoon Han, the current version of the device is about the size of a small suitcase. It requires less power than a mobile phone charger, meaning that it could be powered by a portable solar panel in scenarios where batteries aren't an option.

Instead of utilizing a filter or distillation, it uses an MIT-designed technique that we first heard about 12 years ago, known as ion concentration polarization (ICP). In a nutshell, this involves pumping seawater through a narrow channel between two electrically charged membranes – one is positively charged, and the other is negatively charged.

As the water passes through the electrical field between the two membranes, particles such as salt molecules, viruses and bacteria are repelled into a side channel of water which is discharged and not used. The main channel of water is now purified and relatively desalinated, but may still contain some salt ions.

For that reason, it proceeds to go through an electrodialysis module, where those last traces of salt are removed. Although this step does involve passing the water through an ion exchange membrane, trapped salt ions can be removed from that membrane, so it can be reused. The water that ends up trickling out of the device's output hose reportedly exceeds World Health Authority drinking water standards.

It should be noted that the system is a little more complex than it sounds, as it actually incorporates a two-stage process in which the water first passes through a set of six ICP modules, then through another three followed by the electrodialysis module.

The current version is capable of generating 300 ml (10 fl oz) of drinking water per hour, requiring 20 watt hours of power per liter. Han and colleagues are now working on boosting its rate of output.

A paper on the research was recently published in the journal Environmental Science and Technology. You can see first author Junghyo Yoon using the device to get drinking water from the sea at Boston’s Carson Beach, in the video below.