Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6b. In Situ Remediation of Petroleum Hydrocarbons

Formatted Title:

Evaluating Enhanced Biodegradation of Petroleum Hydrocarbon-Impacted Soil for Landfarming Application

Background/Objectives:

Soil and groundwater at a site located in Butte, Montana, has been impacted by petroleum hydrocarbons and heavy metals released from its industrial activities since 1885. Landfarming, also known as land treatment or land application, has been considered as a potential approach for soil remediation. Landfarming consists of spreading a thin layer of the excavated soil on the surface to promote adequate oxygen levels and stimulate bacteria activity via addition of air and/or nutrients and moisture. The objective of this study was to evaluate and enhance the potential for hydrocarbons aerobic biodegradation via simulated landfarming in site soil samples.

Approach/Activities:

A bench-scale treatability program was designed to provide proof-of-concept and evaluate effectiveness of biodegradation of petroleum hydrocarbons for landfarming. A preliminary test was conducted using soil samples from five different site locations to evaluate biomass activity against hydrocarbons and heavy metals by measuring various parameters after 24 hours of incubation, including: oxygen uptake rate (OUR), carbon dioxide (CO₂) production, adenosine triphosphate (ATP, total and dissolved), qPCR analysis of total eubacteria and the functional genes alkB and almA that encode for monooxygenase enzymes, and total petroleum hydrocarbons (TPH). After demonstrating biomass activity in the soils, a second test was conducted with one of the soil samples to evaluate hydrocarbon biodegradation in a tray setup that simulated landfarming conditions. The test included an unamended control, moisture amended, nutrient (potash and ammonium nitrate) amended, and bioaugmented (Bacillus strains) treatments, incubated for a minimum of three months. The evaluation relied on ATP, qPCR, and petroleum hydrocarbon concentrations.

Results/Lessons Learned:

Results from the preliminary test indicated strong biomass activity from CO₂ (28 mg/L), OUR (0.02 mg/L/min), total ATP (18,901 pg/mL), and total eubacteria (2x10⁹ cells/g) measurements. The highest biomass activities were presented in the sample with the highest organic carbon (49,700 mg/kg), nitrogen (366 mg/kg), and TPH (350 mg/kg) concentrations. The initial results from the long-incubation study showed a high initial concentration of total ATP (2.67x10⁵ pg/mL), total eubacteria (2.83 x10⁹ cell/g), and functional genes alkA (5.12x10⁴ cell/g) and alkB (2.95x10⁵ cell/g), with a starting moisture content of 9.91% on a weight-by-weight basis. These results implied a strong viability for biodegradation of the hydrocarbons by aerobic bacteria via landfarming. When the second study is completed, the results will demonstrate if the enhanced biodegradation measures (by moisture, nutrients, or bioaugmentation amendment) are successful and necessary to biodegrade hydrocarbons down to the remediation goal of 100 mg/Kg when compared to intrinsic conditions (unamended).

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Hyunshik Chang