Bioremediation is an innovative, cost-effective cleanup technology that employs microorganisms to biodegrade organic contaminants, such as petroleum hydrocarbons in soils and sediments. Unfortunately, in cases where the contaminants have been in contact with soil or sediment particles for many years, bioremediation is often unable to remove the contaminants to meet regulatory cleanup targets. Researchers at Battelle’s Marine Sciences Laboratory are looking to overcome this limitation.

Bacteria remove most hydrocarbon contamination, but leave a residual undegraded fraction behind (Figure 1). Currently, researchers believe that these aged hydrocarbons have been trapped inside the small pores of soil and sediment particles and are unavailable and inaccessible to the microorganisms (Figure 2). Battelle researchers are investigating factors that might influence the bioavailability of aged hydrocarbons to soil bacteria.

Figure 1. Bacteria leave a residual undegraded fraction of hydrocarbon contamination behind.

Figure 2. Researchers believe aged hydrocarbons are trapped inside the small pores of soil and sediment.

Battelle conducted 90 week-long slurry bioremediation experiments involving a variety of soil types that were aged for more than two years with a crude oil containing a wide range of compounds such as alkanes and polynuclear aromatic hydrocarbons.

Battelle researchers discovered that soil properties did not affect contaminant bioavailability. Using a newly developed test that measures the release of hydrocarbons from soil particles in the absence of bacteria, Battelle found that most contaminants are readily available, but that bacterial populations are either absent or too small to metabolize them.

The Battelle findings have significant practical implications. First, if contaminants are released from soil particles and are bioavailable but not metabolized by bacteria, they may pose a risk to ecological receptors or groundwater resources. Second, if bacterial populations are weakened or not present at all, it may be possible to stimulate them more effectively during bioremediation treatment. Battelle researchers are continuing to search for technological solutions to this problem.

For more information, contact Michael Huesemann (360) 681-3680, michael.huesemann@pnl.gov.