It is not uncommon at a disaster site for both the water supply and the electrical grid to fail. A new system may one day be useful in this regard, using only a small amount of electricity that can be stored in batteries to desalinate seawater for drinking.
Currently, the most commonly used desalination method is reverse osmosis. Simply put, it works by forcing seawater through a permeable membrane that allows water molecules to pass through but not salt (sodium chloride) molecules. This is an efficient process, but it also requires considerable energy to create the required pushing water pressure. Additionally, the membrane eventually becomes clogged with trapped salt and must be replaced.
An experimental new system developed by scientists at the Universities of Bath, Swansea and Edinburgh in the UK does not use pressure at all. Instead, it houses a container with a positively charged electrode on one end and a negatively charged electrode on the other, with a porous membrane in between.
When seawater is placed in it, the positively charged sodium ions in the salt molecules are drawn into the negatively charged electrode, while the negatively charged chloride ions are drawn into the positively charged electrode. As chloride ions move across the membrane toward the positive electrode, they also push water (H2O) molecules across the membrane. The sodium ions are attracted to the negative electrode and remain on the original side of the membrane. The chloride ions are then recycled back to this side so they can push more water molecules through. Eventually, most of the water flows to the positive electrode side of the membrane, which is completely free of salt.
So far, the system has only been tested with a few milliliters of water at a time. So the researchers are looking for partners to help develop the technology so that it can process a liter of water, so they can better understand how much power a practical system would require.
Lead scientist Professor Frank Marken from the University of Bath said: "Currently, reverse osmosis is very power-intensive and requires a dedicated power plant to desalinate the water, which means it is difficult to implement on a smaller scale. Our method could provide an alternative solution on a smaller scale, which would save energy as water can be extracted without any by-products, and does not involve industrial-scale processing plants."
A paper on this research was published in the recently published journal "ACS Applied Materials and Interfaces".