Researchers have found a cheap way to remove the salt from the wastewater produced by fracking, helping to make the practice more environmentally friendly.
Hydraulic fracturing, or fracking, is a method used for recovering natural gas and oil from shale rock buried underground. The technique involves drilling deep into the Earth, and injecting a high-pressure water mixture containing sand and chemicals into the rock, allowing the gas to release into the well.
The water used in the mixture drains the salts from the rocks, and when it comes back to the surface, it is three to six times saltier than seawater. This salty water cannot be reused for fracking and so it is disposed into the environment.
Researchers have now shown that this salt can in fact be removed and the wastewater be reused, a discovery that substantially reduces the need for freshwater in the fracking industry.
The desalination procedure, proposed by researchers from MIT in the US, in the journal Applied Energy, involves several stages of electrodialysis, a method where salt ions move from one solution to another solution with the help of an electric current. Electrodialysis has been around for more than 50 years, but until now, it was not thought of being capable of treating such high-salinity water.
The electrodialysis process becomes less efficient as the water purifies, as its ability to conduct electricity decreases with each stage. But that's OK, because the team do not expect to purify the water to make it safe for drinking, they just want it to be able to be reused in the fracking process.
Another advantage to the system is that the researchers can control how much salt they take out of the water - they're now investigating what the optimal salinity is for the water to be reused for fracking.
"The big question at the moment is what salinity you should reuse the water at," said Ronan McGovern, lead researcher of the paper, in a press release.
This cost-effective system could dramatically lessen the amount of waste water that needs to be disposed from fracking sites, in turn, helping reduce the global problem of water scarcity.
"If you can close the cycle, you can reduce or eliminate the burden of the need for fresh water," said John Lienhard, a co-author of the study, in a press release.