An average of more than five million gallons of water are used in a hydraulically fractured well, and only a small portion, around 10 to 15 percent of this water is recoverable during the backflow process.
“This makes it very important to be able to re-use this water,” Rice University chemist Andrew Barron said. Researchers from Rice University have developed a superhydrophilic, which means extremely attracted to water, alumina-based ceramic microfilter that can eliminate more than 90% of the impurities without the fouling produced during the filtration process.
The alumina-based ceramic filter has small pores, around 200 nanometers in diameter. Its surface and pores are treated with cysteic acid to make them ionically charged and thus, rendering them as superhydrophilic. The ionic charges attract a thin layer of water, which in return prevents the passage of the hydrophobic, which means repellant to water, or oily hydrocarbon molecules.
Barron further explains, “The superhydrophilic treatment results in an increased flux (flow) of water through the membrane and inhibits 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.”
A single pass of the contaminated water through the superhydrophilic microfilter has been proven by the team to be sufficient enough to clean the fracking water for reuse. This reduces significantly the amount of water that has to be stored or transported. Nanofiltration systems are known to generate foul odors, but this superhydrophilic microfilter eliminates this fouling problem.
“If you use a membrane with pores small enough to separate [the hydrocarbons], they foul, and this renders the membrane useless. This membrane doesn’t foul, so it lasts. It requires lower operating pressures, so you need a smaller pump that consumes less electricity. And that’s all better for the environment,” said Barron.