Dirty fracking water cleaned for reuse by superhydrophilic filtration membrane
A superhydrophilic filter has been shown to effectively reduce contaminants in water produced as a by-product from fracking operations by 90 per cent.
The filter is capable of removing not just hydrocarbons but also bacteria and other particulates that mix with the water during operations at shale oil and gas wells, according to researchers at the Energy Safety Research Institute at Swansea University.
Fracking operations typically require millions of litres of water in order to create enough pressure to force gas and oil, which is trapped underneath a layer of rock, to the surface.
Unfortunately when the water returns to the surface it is heavily contaminated and cannot be released back into nature without being put through extensive and expensive treatment processes.
The new research turns a ceramic membrane with microscale pores into a superhydrophilic filter that “essentially eliminates” the common problem of fouling.
The researchers determined one pass through the membrane should clean contaminated water enough for reuse at a well, significantly cutting the amount that has to be stored or transported and therefore lowering the amount of water required for fracking operations.
The filters keep emulsified hydrocarbons from passing through the material’s ionically charged pores, which are about one-fifth of a micron wide, small enough that other contaminants cannot pass through.
The charge attracts a thin layer of water that adheres to the entire surface of the filter to repel globules of oil and other hydrocarbons and keep it from clogging.
A hydraulically fractured well uses more than 20 million litres of water on average, of which only 10 to 15 per cent is recovered during the flow back stage, said professor Andrew R Barron who worked on the project.
“This makes it very important to be able to re-use this water,” he added.
Frac water and produced waters represent a significant challenge on a technical level. If you use a membrane with pores small enough to separate, they can foul - rendering the membrane useless.
The superhydrophilic treatment results in an increased flux (flow) of water through the membrane as well as inhibiting any hydrophobic material – such as oil – from passing through. The difference in solubility of the contaminants thus works to allow for separation of molecules that should in theory pass through the membrane.
Barron and his colleagues used cysteic acid to modify the surface of an alumina-based ceramic membrane, making it superhydrophilic, or extremely attracted to water.
The acid covered not only the surface but also the inside of the pores, and that kept particulates from sticking to them and fouling the filter.
“This membrane doesn’t foul, so it lasts,” Barron said. “It requires lower operating pressures, so you need a smaller pump that consumes less electricity. And that’s all better for the environment.”
“Fracking has proved highly controversial in the UK in part as a result of the pollution generated from produced waters,” said co-author Darren Oatley-Radcliffe, an associate professor at Swansea University. “However, with this new super-hydrophilic membrane we can clean up this waste produced water to a very high standard and recycle all of the materials, significantly improving the environmental performance of the fracking process.”
Recent research showed that the UK’s burgeoning fracking industry could face some serious roadblocks because limited space to construct wells will mean that only a quarter of the gas may be recoverable in the country’s largest reserves.