Biodegradation of benzene in soil systems

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Virginia Tech

The inadvertent release of petroleum hydrocarbons to the subsurface can be an imminent threat to groundwater supplies. Benzene, a water-soluble, carcinogenic petroleum hydrocarbon, is often one of the primary concerns in the cleanup of these underground petroleum leaks. The purpose of this research was to investigate the effect of soil properties, nutrient addition and benzene concentration on the biodegradation of benzene in soil systems. More specifically, a primary objective was to correlate measurable soil properties with benzene biodegradation characteristics in the soil.

Benzene biodegradation was measured in seven uncontaminated Virginia soils and three contaminated soils using, laboratory microcosms. Microcosms consisted of 5 grams of soil combined with 5 mL of a sterile benzene solution. Benzene concentrations in the sterile solutions were varied at 1, 10 and 50 ppm initial benzene concentration as well as with and without nutrient supplements in the form of ammonium phosphate and potassium phosphate. Measurable physical, chemical and biological properties of each soil were then correlated with the observed benzene biodegradation characteristics, specifically an acclimation period or lag phase, a zero order biodegradation rate and a final time to degrade the substrate to less then 5 ppb benzene concentration.

Statistical analysis showed an overall increase in zero order degradation rates with the addition of nutrients in uncontaminated soils at 1, 10 and 50 ppm initial benzene concentration. Multiple linear regression analysis also indicated statistically significant relationships between several soil properties (generally pH, % sand, and % organic matter) and benzene biodegradation characteristics. These results indicate that models could be developed to predict the biodegradation of benzene and similar petroleum hydrocarbons in soils based on numerous soil physical, chemical and biological properties, rather than a single microbial degradation rate.