Bacteria may someday clean leftover frack water
In humans’ eternal quest for more energy, a relatively new oil and natural gas mining technique targets deposits locked in pockets of rock.
Called hydrofracturing, or fracking, the technique uses lots of water, which goes in clean and comes out contaminated with organic substances that render it unfit for reuse.
Purifying that water would reduce the pressure on waste disposal sites called injection wells, as well as on sites of wastewater spills. Working toward that goal are University of Minnesota microbiologists Larry Wackett and Michael Sadowsky, who have already pioneered the use of pollutant-eating bacteria against soil contamination.
Along with mechanical engineering professor Alptekin Aksan, Wackett and Sadowsky are developing a silica sponge stuffed with oil-eating bacteria. The researchers and College of Biological Sciences Dean Robert Elde—whose role is to help commercialize the work—are funded by a National Science Foundation grant.
Here’s a glimpse of the problem and the potential solution.
Fracking helps drillers reach pockets of oil and gas trapped in bubbles within impermeable rock, says U earth sciences professor E. Calvin Alexander, Jr., an expert on how water moves through rock.
"Oil companies figured out they could ‘fracture’ rock with high-pressure fluids that lifted and broke the rock," he says. "This could be done in horizontal wells extending thousands of feet. Then to get the oil [or gas] out, they reduced the pressure."
But it wasn’t that simple, because reducing the pressure allows the rock to fall back in place, closing the new fractures and blocking the flow of oil or gas. So drillers inject sand to hold the spaces in the rock open. The porous sand allows oil and gas to flow, and cocktails of organic chemicals, including soaps, are injected to lubricate the sand so it can get into cracks.
However, reducing the pressure sends some of the injected fluid—water—gushing out again. Trouble is, "it comes out with salt and other buried ugly stuff, like heavy metals, in addition to the oil or gas," says Alexander. "The secondary flowback water, [now contaminated with] the chemicals they put in to lubricate the sand, creates waste."
How much water is involved? Wackett says he’s seen up to 5-7 million gallons per frack, and one well may be fracked several times. To put it in perspective, the annual water use is about 2 percent of the amount used in agriculture, he says.
About 70 percent of the injected water gets left behind in oil- and gas-bearing rock layers after fracking. Chemicals injected with it, plus any natural chemicals released by fracking, have raised concerns about contamination of aquifers used as domestic water sources.
Earth sciences professor Calvin Alexander says: "There is remarkably little documentation of near-surface aquifers being contaminated by current practices. A study in Pennsylvania found no evidence that fracking contaminated drinking water. Many of us believe it’s a real problem, but it’s hard to document. But what if aquifers start going bad in 50 years?"
It is estimated that frack wastewater contains more than a thousand contaminants; many are organic, and so potential food for bacteria. Biochemistry professor Wackett and microbiology professor Sadowsky, both members of the U’s BioTechnology Institute, teamed up with Aksan to blend their knowledge of bacteria with his expertise in bioencapsulation.
The researchers separate out thousands of chemicals in frack water and identify them. Then, knowing the major sources of carbon in the water, they look for naturally occurring bacteria that will eat the chemicals. (Spreading genetically engineered bacteria on wastewater ponds or spill sites might result in an uncontrolled release into the environment.)
Aksan and postdoc Boris Tong have found a way to embed the bacteria within porous silicon fibers. There they are protected as they absorb oily compounds through the pores in the walls, which are thinner than the bacterial cells.
Wackett likens the spongy material to cotton candy, with bacteria trapped in the strands. A spill on a field could be treated by rolling out and spreading "what looks like a foamy, cottony material" over it," Wackett says. Treating a body of water would require pumping it through a cylinder with bacteria trapped in sturdier structures: highly porous microscopic beads.
The researchers have filed for a patent on the sponge manufacturing process.
"This work would reduce contamination of water used for industrial purposes and agriculture," says Wackett. "If it’s to be used for fracking a second well, the interest isn’t so much specific chemicals, but reducing the carbon load. When they inject water, they like pristine water because organic chemicals could promote the growth of bacteria that could quickly clog the operation."
Much work remains to scale up the technology for commercial use, but the researchers are optimistic.
"I feel very confident that good things will come out of this," Wackett says. "
Fracking is starting in China and elsewhere in the world, so I think it’s important to work on treating and recycling water. If we can find ways that water can be cleaned to the extent it can be re-used in industry, agriculture, or the oil and gas industry, there will be less demand on fresh water."