An assessment of factors controlling the biodegradation of benzene in the subsurface environment

The objectives of this research were to correlate benzene biodegradation with soil physical, chemical and biological properties, to determine if biodegradation could be predicted based on measured or observed soil properties, and to investigate the role of nutrients on benzene biodegradation in soil. Benzene disappearance over time was measured in aerobic active and control (autoclaved) microcosms prepared with previously-uncontaminated subsurface soils. Soil microcosm experiments were prepared with initial benzene concentrations of 1, 10 and 50 mg/L. For each soil, logistic, zero-, first-, and 3/2- order kinetic models were fit to benzene disappearance versus time data by regression analysis. The logistic and 3/2-order models fit the data better than zero- and first-order models for experiments prepared with initial benzene concentrations of 1 and 10 mg/L. For an initial benzene concentration of 50 mg/L, experimental data were often better fit by zero- or first-order kinetic models. To obtain predictive equations, logistic kinetic model rate constants were related to soil properties using multiple linear regression (MLR). The “best” MLR models and their regression coefficient estimates were statistically significant at p<0.05. For experiments prepared with an initial benzene concentration of 1 mg/L, the resulting predictive equation contained soil phosphorus concentration and cation exchange capacity (CEC). For experiments prepared with an initial benzene concentration of 10 mg/L, the predictive equation contained soil copper, nitrate-N and phosphorus concentrations, CEC, and % sand. A comparison was made between benzene biodegradation in unamended soil microcosms and soil microcosms amended with ammonium and potassium phosphates (11 mM nitrogen, 6 mM phosphorus and 0.6 mM potassium). Benzene disappearance over time in soil microcosms was stimulated by nutrient addition in one (11%), 6 (50%), and 5 (45%) soils at initial benzene concentrations of 1, 10 and 50 mg/L, respectively. In general, nutrient addition had the greatest affect on benzene biodegradation in low pH soils.