Energy

New Filter Removes Contaminates From Fracking Wastewater

Millions of gallons of wastewater are produced during the fracking process, but this device could help reduce the oil and gas sector’s environmental impact.

A ceramic filter that can clean wastewater from hydraulic fracturing without clogging could help ease one of the environmental problems associated with that petroleum-extracting process — and maybe ease the shakes that have hit the US oil patch.

Fracking uses a high-pressure stew of water, chemicals, sand, and other particles to break up underground rock formations and free oil and natural gas locked inside. A typical well drilled that way uses up to 5 million gallons (20 million liters) of fluid, and up to 15 percent of that flows back to the well. And once a well starts producing oil, a much bigger volume of salt-rich wastewater comes up with it.

Being able to re-use that water instead of just shooting it back underground, which is the usual way drillers get rid of it now, would help reduce the environmental footprint of the practice. So a team of researchers at Houston’s Rice University set about finding a better way of filtering out the particles and oily residue that comes up with that wastewater.

“Ceramic filters themselves are durable, but the problem with frack water or produced water from the oil and gas industry, you can’t filter that because the filters block up. They get fouled,” Andrew Barron, a Rice professor of chemistry and engineering at Rice, told Seeker. “Our filters don’t do that.”

Barron and his colleagues designed a long, tubular filter with pores a fifth of a micron wide — a few millionths of an inch. That screens out most contaminants, but they would tend to build up in the pores and clog them.

But coating the filter with cysteic acid creates a surface that draws a microscopically thin layer of water to cover the pores. That prevents oily fluids from building up and clogging the filter, he said.

The filters themselves are tubular structures about a meter (3.25 feet) long and about 5 centimeters (2 inches) across, filled with small passages. At the drill site, they would be bundled together in arrays up to the size of a shipping container. Water is pumped into the tubes, with the treated product emerging from the sides. The remaining concentrated mix of contaminants can also be sent to a refinery to extract the oil products inside, he said.

“Your disposal becomes a fraction of what you had before, and the hydrocarbon has a value,” Barron said, adding that the filter he developed is an economically viable solution, with a commercial unit under construction “as we speak.”

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The findings were published this week in the research journal Scientific Reports.  Barron said the filtered water remains too salty to be drinkable, but it’s clean enough to be re-used at the well — and if treated further through reverse osmosis to remove the salt, it would be safe for human consumption. “We have demonstrated that’s possible,” he said.

Currently, most wastewater is disposed of by injecting it deep underground, far below the water table. But in the southern Great Plains, particularly in Oklahoma, the practice has been blamed for a surge of hundreds of small to moderate earthquakes a year. Barron said the process his team developed could reduce the amount of wastewater enough to calm those shakes.

“Essentially you would get to the point where you wouldn’t need to do deep-well injection,” he said.