By Helen Tunicliffe
FRACKING shale produces large amounts of saline wastewater, and researchers in the US and Saudi Arabia have discovered that electrolysis could be an economical method to treat it.
Water forced down into the shale during the fracking process leaches salts from the rocks it passes through, and this ‘produced water’ can be 3–6 times saltier than seawater. MIT professor John Lienhard says that electrolysis, while not a new technology, was previously thought to only be suitable for low-salinity water. The analysis carried out by his team, which includes researchers from King Fahd University of Petroleum and Minerals (KFUPM), shows otherwise.
In electrodialysis, electric currents are passed through the water, forcing the salt ions through a membrane. The researchers used several stages of electrodialysis to progressively remove the salt from the water. In the field, a filtration step would be necessary to remove any remaining traces of oil and gas, which may damage the membrane.
The salt is not completely removed, as pure water cannot conduct electricity. However, the researchers say that the point of the process is not to make the water potable, but to remove sufficient salt from the water so that it can be reused in the fracking process. This would significantly reduce the amount of fresh water needed for fracking, meaning that less would be diverted from drinking water and agriculture, something which would be of particular value in water-stressed areas like Texas in the US.
“If you can close the cycle, you can reduce or eliminate the burden of the need for fresh water,” says Lienhard.
In addition, the process would greatly reduce the amount of water from drilling sites that must be disposed of.
The researchers will now investigate the optimal salinity for fracking fluids, which they say is unclear.