Swansea filter could help reduce environmental impact of fracking

Fracking, the hydraulic fracturing process by which shale oil and gas is removed from the ground, uses huge volumes of water. According to Swansea University’s Prof Andrew Barron, a hydraulically fractured well uses more than 5 million gallons of water on average and only 10 to 15 per cent is recovered during the flow back stage.

Currently this recovered water tends to heavily contaminate and often unsuitable for re-use. However, the new membrane, developed in collaboration with researchers from Rice University in the US is claimed to be able to remove more than 90 per cent of hydrocarbons, as well as all bacteria and particulates from contaminated water.

The work by Prof Andrew R Barron and his colleagues turns a ceramic membrane with microscale pores into a superhydrophilic (i.e extremely attracted to water) filter that is claimed to eliminate the problem of fouling. A paper on their research is published in Nature's open-access Scientific Reports.

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.

The superhydrophilic properties result from the use of cysteic acid to modify the surface of an alumina-based ceramic membrane. 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.

According to Barron, the filter has a number of advantages over other filtration methods. Solubilised hydrocarbon molecules slip through microfilters designed to remove bacteria. Natural organic matter, like sugars from guar gum used to make fracking fluids more viscous, require ultra or nanofiltration, but those foul easily, especially from hydrocarbons that emulsify into globules. Whilst, a multistage filter that could remove all the contaminants isn't practical due to cost and the energy it would consume.

In tests with fracking produced water that contained guar gum, the new alumna membrane showed a slow initial decrease in flux - a measure of the flow of mass through a material - but it stabilized for the duration of lab tests. Untreated membranes showed a dramatic decrease within 18 hours.

The researchers theorised the initial decrease in flow through the ceramics was due to purging of air from the pores, after which the superhydrophilic pores trapped the thin layer of water that prevented fouling.

"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.”