Membrane-free electrical desalination
2 Jul 2013
Scientists at the University of Texas at Austin and Marburg have developed a technique that electrically removes salt from seawater.
The method, which can run on a standard household battery, works by creating an electrical field to separate the salt, without the need for a membrane.
The research team, led by Richard Crooks, believe the technique, known as electrochemically mediated seawater desalination, could be developed for commercial use.
The neutralisation reaction occurring at the electrode is key to removing the salts in seawater
Crooks, an Austin chemist, said: “The membrane-free method we’ve developed still needs to be refined and scaled-up, then one day it might be possible to provide fresh water on a massive scale using a simple, even portable, system.
The innovative method is primarily designed for water-stressed areas, which have access to seawater but no energy infrastructure or monetary funding to desalt the water.
The process involves applying a voltage of 3 volts to a plastic chip that is filled with seawater; containing a micro-channel with two branches.
An embedded electrode at the channel’s junction neutralises part of the chloride ions in the seawater, creating an ion depletion zone that increases the electric field in comparison to the rest of the channel.
This process redirects the salt into a separate branch, leaving the desalinated water to pass through into the opposite branch.
“The neutralisation reaction occurring at the electrode is key to removing the salts in seawater,” said Kyle Knust, a graduate student in Crooks’ lab and first author on the paper.
Currently, however, the research team has achieved 25% desalination, with drinking water requiring 99% desalination to be adequate for human consumption.
“We’ve made comparable performance improvements while developing other applications based on the formation of an ion depletion zone. That suggests that 99% desalination is not beyond our reach,” added Knust.
If the technique were made practical for communal or individual use, the process would have to produce many litres of desalinated water per day.
Recent efforts to produce desalinated water using the electrochemical method has resulted in the team producing 40 nanolitres per minute, with a view to dramatically scale-up the process.
