J.R. Hunt, P.A. Holden and M.K. Firestone

University of California, Berkeley, CA, 94720-1710, 510-642-0948, E-MAIL


Volatile organic chemicals present at Superfund sites preferentially partition into the soil gas and may be available for microbial degradation. A simple mass transfer model for biodegradation for volatile substrates is developed for the aerobic decomposition of aromatic and aliphatic hydrocarbons. The mass transfer analysis calculates diffusive fluxes from soil gas through water and membrane films and into the cell. The model predicts an extreme sensitivity of potential biodegradation rates to the air-water partition coefficients of the compounds. Aromatic hydrocarbons are removed rapidly while the aliphatic hydrocarbons are much slower by orders of magnitude. Furthermore, oxygen transfer is likely to limit aromatic hydrocarbon degradation rates. The model presents results that cast doubt on the practicality of using methane or propane for the cometabolic destruction of trichloroethylene in a gas phase bioreactor. Toluene as a primary substrate has better mass transfer characteristics to achieve more efficient trichloroethylene degradation. Hence, in sites where these contaminants coexist, bioremediation could be improved. The model is extended further to examine the influence of water potential on transport and transformation rates within microbial biofilms present in unsaturated soils. Water potential has multiple effects on overall VOC removal through the thickness of the biofilm, the molecular diffusivity of substrates through the biofilm, and microbial physiology.

Funding for this work was provided by the National Institute of Environmental Health Sciences Superfund grant 3P42 ES04705-08.


VOC, biodegradation, unsaturated soil, biofilms

This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.