Filtering fracking water for reuse

A SUPERHYDROPHILIC filter has been shown to remove 90% of hydrocarbons, bacteria, and particulates from contaminated water produced by fracking operations.

This means that with only one pass through the membrane, water is clean enough for reuse at a well, cutting the amount that has to be stored or transported – according to researchers led by the UK’s Swansea University and Rice University in the US.

Hydraulic fracturing, or “fracking” involves injecting an average of 20m L of water into a drilled well, to create enough pressure to force trapped gas and oil to the surface. During and after the process, some of this water flows back to the surface, heavily contaminated with hazardous hydrocarbons and bacteria.

Such waste cannot be released into the environment without difficult and expensive treatment, and so is typically either evaporated or disposed of through deep injection into abandoned wells.

Filtration as a treatment presents a range of technical challenges due to the complex nature of the contaminated water. Membranes that filter bacteria, for example, have a pore size too large to remove hydrocarbons, while filters with smaller pores can become blocked more easily.

By modifying the surface of an alumina-based ceramic membrane with cysteic acid to make it hydrophilic, or extremely attracted to water, the researchers were able to overcome such problems.

Tests on water from various fracking projects, the results of which are published in Scientific Reports, demonstrated that after a single pass through the resulting filter, more than 90% of contaminants were rejected for all samples. This included the separation of hydrocarbons smaller than the membrane’s pore size of 0.22 µm.

Andrew Barron, chair of low carbon energy and environment at Swansea, said: “In our case, the superhydrophilic treatment results in an increased flux 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 membranes also exhibited further beneficial properties. "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."

Scientific Reports: http://doi.org/cdk2