An absorbent form of silica can remove nearly all petro-chemicals from the water produced by hydraulic fracturing in shale-gas wells, Energy Department scientists announced late last week.
After field testing the modified silica, called Osorb, DOE's National Energy Technology Laboratory confirmed it can remove more than 99 percent of oil and grease from water, and more than 90 percent of benzene, toluene, ethylbenzene, and xylenes—also known as BTEX—the volatile compounds that can poison drinking water.
"These tests showed that total petroleum hydrocarbon levels were slashed from 227 milligrams per liter to 0.1 milligrams per liter," said DOE spokesman Jenny Hakun in an April 28 press release that describes Osorb as a "breakthrough technology."
Hydraulic fracturing of shale has become increasingly important for freeing vast reserves of natural gas from shale formations in the United States, such as the Marcellus Shale formation under the Appalachian Mountains. But opposition to “fracking” has mounted because water injected underground to shatter the shale carries toxic hydrocarbons back to the surface and could imperil drinking water aquifers.
"Approximately 21 billion barrels of produced water, containing a wide variety of hydrocarbons and other chemicals, are generated each year in the United States from nearly one million wells," Hakun said.
This by-product of gas drilling is much more toxic than water produced by oil wells, according to a white paper produced for the Energy Department by the Argonne National Laboratory:
Produced waters from gas production have higher contents of low molecular-weight aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX) than those from oil operations; hence they are relatively more toxic than produced waters from oil production. Studies indicate that the produced waters discharged from gas/condensate platforms are about 10 times more toxic than the produced waters discharged from oil platforms.
Drilling companies also introduce chemicals when they inject water into the shale to fracture it and free the gas. The hazards of hydraulic fracturing were highlighted by a recent spill of “fracking fluids” at a shale-gas well in Bradford County, PA.
The produced water that emerges from the well—sometimes in much greater volume than gas or oil—is usually treated, recycled, discharged into the environment, or injected back underground.
"A number of existing treatment techniques separate dispersed oils from water, taking advantage of the density difference between oil and water," Hakun said. "However, very few technologies effectively address dissolved hydrocarbons, slicking agents, and polymers that prevent flow-back water from being recycled or discharged."
A mixture of glass and polymer, Osorb rapidly expands when it encounters non-polar liquids, such as hydrocarbons, and captures them in its matrix. But it allows polar liquids, such as water, to pass unmolested. The captured hydrocarbons can be removed through heat-evaporation, and the Osorb reused.
Osorb's absorbent properties were discovered by accident in 2005 by Colleen Burkett, a student at the College of Wooster in Ohio working with associate professor of chemistry Paul Edmiston. Osorb is manufactured in a chemical reactor by Edmiston's Ohio company, ABSMaterials.
Osorb is one of several small-business technologies that have benefitted from Department of Energy initiatives to treat produced water. Earlier this month, DOE's Energy Lab announced it had tested a desalination system that successfully treated 77 percent of produced water at a Marcellus shale well, producing distilled water suitable for discharge into the environment.
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Osorb at work:
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