Scientists look to batteries to cut desalination costs
Researchers at the University of Illinois in the US are exploiting the technology used in rechargeable sodium ion batteries to develop what they claim could be a "new type of device to the desalination community".Professor of mechanical science and engineering, Kyle Smith, and graduate student, Rylan Dmello, are looking to modify the process whereby sodium and chloride ions in a sodium ion battery are driven by electric current across a membrane into one electrode compartment to leave desalinated water in the other.
"We are developing a device that will use the materials in batteries to take salt out of water with the smallest amount of energy that we can," said Smith. "By publishing this paper, we're introducing a new type of device to the battery community and to the desalination community," he added.
In a press release the researchers said: "The most-used method, reverse osmosis, pushes water through a membrane that keeps out the salt, a costly and energy-intensive process. By contrast, the battery method uses electricity to draw charged salt ions out of the water."
Sodium ion batteries, contain salt water in two chambers - a positive electrode and a negative electrode - with separated by a membrane through which the ions pass. When the battery discharges, the sodium and chloride ions - the two elements of salt - are drawn to one chamber, leaving desalinated water in the other. On charging, the ions diffuse back. The Illinois researchers looked for a way to arrest ion diffusion into the pure water.
"We put a membrane that blocks sodium between the two electrodes, so we could keep it out of the side that's desalinated," said Smith.
The researchers list a number of advantages for their system over reverse osmosis. Smith claimed:
the battery device can be small or large, adapting to different applications, while reverse osmosis plants must be very large to be efficient and cost effective;
the pressure - and therefore the energy and cost - required to pump the water through the battery device is much less than in reverse osmosis because it isn't forcing fluid through a membrane; and
the rate of water flowing through the battery set up can be adjusted more easily than other desalination technologies.
Smith and Dmello have trialled their device with saline at concentrations as high as found seawater, and found that it could recover about 80% of desalinated water. They are working on experiments with real seawater.