A new ceramic membrane filter designed by scientists at Swansea University has shown it can remove more than 90 per cent of hydrocarbons, as well as all bacteria and particulates from contaminated water produced by fracking operations.

The filter, which is highly attracted to water or ‘superhydrophilic’, with microscale pores, was devised by researchers at the Energy Safety Research Institute (ESRI) at Swansea University, South Wales, working with colleagues at Rice University in Texas, US, and is said to "essentially eliminate" the common problem of unwanted material clogging up machinery known as fouling.

"Fracking has proved highly controversial in the UK in part as a result of the pollution generated from produced waters,” explained Darren Oatley-Radcliffe, a co-author and 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.”

The researchers’ paper in Nature’s open access Scientific Reports claims to show that one pass through the membrane at a shale oil well should clean contaminated water enough for reuse, significantly cutting the amount that has to be stored or transported.

Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea, Professor Andrew R Barron, explained: “A hydraulically fractured well uses more than five million gallons of water on average, of which only 10 to 15 per cent is recovered during the flow back stage. This makes it very important to be able to re-use this water and not every type of filter reliably removes every type of contaminant.”

Solubilised hydrocarbon molecules slip right through micro filters 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. A multistage filter that could remove all the contaminants isn't practical due to cost and the energy it would consume.

Barron continued: “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 foul, and this renders the membrane useless. In our case, 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.”

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.

Barron and his colleagues used cysteic acid to modify the surface of an alumina-based ceramic membrane, making it superhydrophilic. 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."

Rice alumnus Samuel Maguire-Boyle is lead author of the paper. Co-authors are Rice alumnus Joseph Huseman; graduate student Thomas Ainscough at Swansea University, Wales; and Abdullah Alabdulkarem, of the Mechanical Engineering Department, and Sattam Fahad Al-Mojil, an assistant professor and environmental adviser, at King Saud University, Riyadh, Saudi Arabia. In addition to his role as Sêr Cymru Chair of Low Carbon Energy and Environment, Professor Barron is also the Charles W. Duncan Jr.–Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice.

The research was supported by the Welsh Government Sêr Cymru Program, FLEXIS, which is partially funded by the European Regional Development Fund, and the Robert A. Welch Foundation.