Superfund Research Program

Thermally Enhanced Soil and Groundwater Remediation

Project Leader: Kent S. Udell (University of Utah)
Grant Number: P42ES004705
Funding Period: 1995 - 2000

Project-Specific Links

Final Progress Reports

Year:   1999 

Experiments were completed and a manuscript prepared that evaluated the effects of steam injection on soil microbial activity and the potential for in situ bioremediation of contaminants following steam treatment. A bench-top steam generator was used to inject steam into a series of temperature controlled soil-packed columns. Five different soils were tested: a laboratory prepared microbially-enriched soil, two soils from petroleum contaminated field sites, one soil from a chlorinated solvent contaminated field site, and one soil from a creosote contaminated field site.

Microbial activity was evaluated directly in the soil matrix during and after steam treatment using direct epifluorescent microscopy (DEM) assays. DEM was performed using the respiratory activity dye 5-cyano-2,3, ditolyl tetrazolium chloride (CTC) in conjunction with the fluorochrome 5-(4,6-dichlorotriazinyl) aminofluorescein (DTAF) to yield a quantitative assessment of active and total microbial numbers, respectively, before and after steaming. DEM results indicate that steamed soils that were abruptly cooled exhibited microbial activity levels that were orders of magnitude below unsteamed samples. However, when soils were slowly cooled, more closely reflecting the conditions of applied SEE, the observed levels of microbial activity were comparable to presteamed soils.

The metabolic capabilities of the steamed microbial communities were also investigated by measuring cell growth in enrichment cultures on various substrates including phenanthrene. These studies provided evidence that organisms capable of degrading PAHs were among the mesophilic populations that rebounded following steam treatment. Soil stored for four months following steaming showed enrichment growth trends similar to freshly steamed soils, suggesting that the shift in microbial ecology may be long term.

A series of studies was conducted to evaluate MTBE Biodegradation in gasoline mixtures. Rubrivivax sp. PM1 had been isolated for its ability to utilize MTBE as the sole source of carbon and energy. In addition, PM1 was shown to utilize benzene (B) for growth. Mixtures of MTBE and B were readily degraded by PM1. While the presence of MTBE enhanced B degradation by MTBE-grown cells, the presence of B reduced MTBE degradation rates. The biodegradation of B and MTBE appeared to occur by two independent inducible pathways. B-grown cells did not initially consume O₂ with MTBE or its metabolic intermediates tert-butyl alcohol (TBA), 2-hydroxyisobutyric acid, 2-propanol and acetone. Further, MTBE- and TBA-grown cells did not initially consume O₂ with B or its metabolic intermediates. Results from simultaneous induction studies and enzyme assays revealed that PM1 degraded B via two successive monooxygenations of the aromatic ring followed by meta cleavage of the resulting catechol. MTBE-grown cells degraded up to 500 mg/L of MTBE with no apparent accumulation of TBA. TBA-grown cells of PM1 were not capable of degrading MTBE suggesting that the monooxygenase enzyme systems induced by MTBE and TBA are different.

Finally, a series of studies has begun to use molecular tools to characterize microbial communities capable of reductively dechlorinating TCE to ethene. In addition, laboratory and field samples were collected to evaluate the isotopic fractionation of chlorinated solvents during active reductive dechlorination.