Rapid Biological Clean-Up of Soils Contaminated with Lubricating Oil

An experimental program assessed which mechanisms control the rapid biodegradation of used lubricating oil which contaminates soils. The ultimate goal is to effect a rapid biodegradation before the contaminants in the oil are leached into the groundwater or carried into surface waters with runoff. Large amounts of lubricating-oil-degrading bacteria could be grown in liquid culture, as long as a dispersant was applied to form and maintain an oil-in-water emulsion. Application of the oil-degrading bacteria (up to 4.9 × 10⁸/g soil) significantly increased the initial rate of oil degradation in soil plots. However, the long-term rate of degradation slowed as the more available or more biodegradable components of the oil were removed. The fastest removal rates were obtained when the oil-contaminated soil was put into a water-soil slurry and was inoculated with microorganisms and dispersant. Improved microorganism contact and dispersant effectiveness apparently were responsible for the rapid rates in slurry reactors. The increased rates demonstrated the potential value of adding a large, acclimated inoculum and providing good mixing and dispersion to make the oil more available to the microorganisms.