At disaster sites, it's not uncommon for both the water supply and electrical grid to be out of commission. That's where a new system may someday come in, as it utilizes just a small amount of electricity – which could be stored in a battery – to desalinate seawater for drinking.
Currently, reverse osmosis in the most commonly used method of desalination. In a nutshell, it works by forcing seawater through a permeable membrane that allows water molecules to pass through, but not salt (sodium chloride) molecules. It's an effective process, but it also requires a considerable amount of power in order to generate the required water-pushing pressure. Additionally, the membranes eventually get clogged with captured salt, and have to be replaced.
Developed by scientists from the UK's Universities of Bath, Swansea and Edinburgh, an experimental new system doesn't utilize pressure at all. Instead, it incorporates a vessel with a positively charged electrode at one end, a negatively charged electrode at the other, and a porous membrane between them.
When seawater is placed inside, the positively charged sodium ions in the salt molecules are drawn to the negatively charged electrode, while the negatively charged chloride ions are drawn to the positively charged electrode.
As the chloride ions pass through the membrane while moving toward the positive electrode, they also push water (H2O) molecules through that membrane. The sodium ions remain on the original side of the membrane, as they're attracted to the negative electrode.
The chloride ions are then circulated back to that side, so they can move more water molecules across. Eventually, most of the water ends up on the positive-electrode side of the membrane, completely salt-free.
So far, the system has only been tested on a few milliliters of water at a time. The researchers are thus looking for partners to help develop the technology up to the point that it can process one liter of water, so they can get a better sense of how much power a practical system would require.
"Currently reverse osmosis uses so much electricity, it requires a dedicated power plant to desalinate water, meaning it is difficult to achieve on a smaller scale," said the lead scientist, the University of Bath's Prof. Frank Marken. "Our method could provide an alternative solution on a smaller scale, and because water can be extracted without any side products, this will save energy and won’t involve an industrial scale processing plant."
The research is described in a paper that was recently published in the journal ACS Applied Materials and Interfaces.
Source: University of Bath
