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A More Effective Remediation for Subsurface Pollutants

SOS Subsoil Bioremediation
Personnel use specialized equipment to implement bioremediation via the Solid (or Slow-releasing) Oxygen Source (SOS) method.
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Wherever subsurface soils and ground water become contaminated with pollutants, bioremediation can be an effective cleanup technology. Because the process uses microorganisms to break down contaminants into nontoxic elements, it is an attractive alternative to hazardous chemical treatments. But bioremediation performance can be limited (1) wherever the contaminated area is not readily accessible and (2) in the case of aerobic bioremediation using aerobic microorganisms (who need oxygen to live) when the oxygen supply is difficult to deliver in tight soils. To address these limitations, EPA researchers developed an advanced hydraulic fracturing technology that effectively accesses subsoil contaminants without excavation. Then they controlled the oxygen supply with the addition of an encapsulated sodium percarbonate called Solid (or Slow-releasing) Oxygen Source (SOS).

Background

In the United States, the remediation industry is a multibillion dollar enterprise. Cleaning up fuel-spill contaminants such as toluene and ethylbenzene, for example, has generated a variety of treatment technologies. Bioremediation is an attractive alternative to many conventional chemical treatments because it relies on the natural process of degradation provided by microorganisms. To overcome some of the barriers to effective biodegradation in hard-to-access sites, EPA soil scientists adapted a method of hydraulic fracturing used in the oil-drilling industry. After drilling a hole into the contaminated area, pressured water is used to gently separate the subsurface layers. Contaminant-degrading microorganisms can then be introduced into the fractures.

Because quicker-degrading aerobic microorganisms require oxygen to do their work of digesting contaminants, standard aerobic bioremediation methods introduce oxygen, either as air or as oxygenated water. However, both of these approaches usually require continual expensive energy, quickly lose oxygen, or kill off beneficial bacteria if the oxygen concentrations are too high. To correct this, EPA researchers developed SOS to provide a constant and controlled release of oxygen through the treatment zone.

In a 22-month test at a Montana site where soil and ground water were contaminated with fuel additives methyl-tertiary butyl ether (MTBE) and benzene, toluene, ethylbenzene, and xylene (BTEX), test results showed 85 percent reductions of MTBE and 99.7 percent reductions of BTEX. The study showed that the use of SOS stimulated more contaminant reduction than did conventionally supplied oxygen methods.

Combining hydraulic fracturing with the SOS process offers many advantages over standard bioremediation methods. It is a controlled, long-term treatment that can even degrade contaminants in new releases. Costs of operation and energy use are reduced because surface pumps or meters are not required. The process does not require excavation, eliminating exposure concerns and the risk of spreading pollutants. Additional oxygen can be always be added with the addition of another fracture called a “compound fracture.”

With growing concern over the use of hazardous remediation processes, bioremediation is expected to increase in importance in the United States and worldwide. The patented hydraulic fracturing SOS process will add an effective and environmentally friendly technology to the array of bioremediation treatment options.

Visit the U.S. Patent record for a complete description and discussion of the SOS method.

Contact

Cindy Kirchmer, Office of Public Affairs (513) 569-7737

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See EPA's PDF page to learn more.

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