Energy Efficient Process Discovered to Turn Seawater Into Freshwater

By Nathan August, CleanTechnica

03 July 13

eawater desalination with nothing more than a small electrical field? A simple new method of creating freshwater from seawater - that uses far less energy than conventional methods do - has just been developed by researchers at the University of Texas at Austin and the University of Marburg in Germany.

The new method - electrochemically mediated seawater desalination - uses no membranes, is considerably simpler than conventional methods, and is so low-energy that it can be performed with the energy provided by store-bought batteries. Those are big improvements on all fronts - if the process can be adequately scaled up, it's a potentially revolutionary development. Freshwater scarcity is expected to become a significant problem in many regions of the world in the coming decades, but as it stands now, saltwater desalination isn't particularly economical … A cheaper, simpler method than those currently available would be of great use - one which could be used on larger scales than simple solar stills are.

The new method/technology is patent-pending and is currently in commercial development by startup company Okeanos Technologies.

"The availability of water for drinking and crop irrigation is one of the most basic requirements for maintaining and improving human health," said Richard Crooks of The University of Texas at Austin. "Seawater desalination is one way to address this need, but most current methods for desalinating water rely on expensive and easily contaminated membranes. The membrane-free method we've developed still needs to be refined and scaled up, but if we can succeed at that, then one day it might be possible to provide fresh water on a massive scale using a simple, even portable, system."

The researchers think that the new method could be of particular use to those in the world's poorer, more water-stressed regions - more than a third of the world's people live in such regions. While lacking in freshwater, the majority of these regions have access to vast seawater resources, just not an economical means to desalinate it.

"People are dying because of a lack of freshwater," said Tony Frudakis, founder and CEO of Okeanos Technologies. "And they'll continue to do so until there is some kind of breakthrough, and that is what we are hoping our technology will represent."

The University of Texas at Austin explains the method:

To achieve desalination, the researchers apply a small voltage (3.0 volts) to a plastic chip filled with seawater. The chip contains a microchannel with two branches. At the junction of the channel an embedded electrode neutralizes some of the chloride ions in seawater to create an "ion depletion zone" that increases the local electric field compared with the rest of the channel. This change in the electric field is sufficient to redirect salts into one branch, allowing desalinated water to pass through the other branch.

"The neutralization reaction occurring at the electrode is key to removing the salts in seawater," stated Kyle Knust, a graduate student and co-author on the new research paper.

"Like a troll at the foot of the bridge, the ion depletion zone prevents salt from passing through, resulting in the production of freshwater."

As of now, the best that the researchers have achieved is 25 percent desalination - drinking water requires 99 percent desalination. The researchers are confident, though, that the 99 percent goal is very achievable.

"This was a proof of principle," stated Knust. "We've made comparable performance improvements while developing other applications based on the formation of an ion depletion zone. That suggests that 99 percent desalination is not beyond our reach."

The process will also need to be scaled up - as of right now, the microchannels are about the size of a human hair, and produce about 40 nanoliters of desalted water per minute. In order for the technology to be of practical use, a device would have to produce several liters - at least - of water per day.

The researchers are confident that this can be achieved, creating "a future in which the technology is deployed at different scales to meet different needs."

"You could build a disaster relief array or a municipal-scale unit," said Frudakis. "Okeanos has even contemplated building a small system that would look like a Coke machine and would operate in a standalone fashion to produce enough water for a small village."

The new research was just published in the journal Angewandte Chemie.