New device promises fresh water, water everywhere
On a cloudless day, Junghyo Joon unpacked a device at the edge of a beach and watched as it sucked water from the sea into a plastic cup, using no more power than it would take to charge a mobile phone. He drank it and said: ‘‘The taste was the same as bottled water.’’
He might have been on a desert island. Instead, he was on Carson Beach, in south Boston, a short walk from a major interstate highway. But the principle was the same.
Joon and colleagues at the Massachusetts Institute of Technology (MIT) have built a portable seawater desalination system, powered by a battery or a solar panel. It could be used by soldiers, refugees or other people in places where fresh water is scarce.
The ins and outs of the system are described in a paper published in the journal Environmental Science & Technology. It works using a technique set out 10 years ago by Jongyoon Han, a professor of electrical engineering and computer science at MIT.
While other systems have been developed to turn seawater into drinking water, they typically rely on power-hungry, highpressure pumps that force the water through filters. Han’s technique involves passing water through an electrical field, between membranes that repel positively or negatively charged particles such as salt molecules, diverting those into another stream that is discharged.
Some salts remain in the water. These are removed using a second electrical process.
Joon said a paper Han published a decade ago on the subject served ‘‘as proof of concept’’. He and his colleagues took 10 years to create the device.
The first time he tried it, a year ago, ‘‘it was really difficult’’, he said. The tide had gone out and there was a lot of mud. And he had not planned for the waves.
‘‘There were so many unexpected situations you never think of as a scientist. That was a great opportunity to understand real situations as a user of the desalination unit.’’
The unit has a plastic tube that is placed in the sea. It takes about half an hour for the device to produce a cup of water.
‘‘Production rate is directly related to power consumption,’’ Joon said. ‘‘In certain situations, the user doesn’t care about the time for desalination, but they have a problem with power supply.’’
The device is kept in a suitcase. Joon is preparing to set up a startup company that will produce a smaller and more elegant model for people on far-flung shores.