Degradation Rates for Petroleum Hydrocarbons Undergoing Bioventing at the Meso-Scale

Bioventing can be effective for the remediation of soil contaminated with petroleum hydrocarbons. However, implementing laboratory results in field scenarios is difficult due to the lack of scale-up factors. Accordingly, laboratory bioventing experiments were undertaken at the meso-scale and then compared with previously completed micro-scale tests to evaluate the important scale-up factor. The developed meso-scale system holds 4kg of soil, with bioventing conditions controlled from a nutrient, airflow, and water content perspective. Three soils were tested, and categorized as loamy sand, silt loam, and a mixture. Results over a 30-day period showed a two-stage degradation pattern that encompassed first-order degradation rates as compared with the single-stage first-order degradation rate determined in the micro-scale study. For the first stage (0-8days), the degradation rate for loamy soil was 0.598day(-1), with the silty soil at 0.460day(-1), and mixed soil at 0.477day(-1). After 8days, the degradation rate constant for the loamy soil dropped to 0.123day(-1), with the silty soil dropping to 0.075day(-1), and the degradation rate for the mixed soil dropping to 0.093day(-1). Comparison of the measured degradation rate values with the results from the micro-scale experiments gave scale-up factors varying from 1.9 to 2.7 for the types of soil considered in the current study. These differences in degradation rates between the two scales show the importance of scale-up factors when transferring feasibility study results to the field.