Freeport, Illinois
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In-Situ Soil Bioremediation of Petroleum Hydrocarbons
Using Aerobic DARAMEND - A Case Study from Taiwan
Soil Bioremediation Theory
Soil impacted with petroleum hydrocarbons (TPH) along with polynuclear aromatic hydrocarbons (PAHs) and pentachlorophenol (PCP) were treated at an inactive manufacturing site in Taiwan using DARAMEND soil treatment technology from ADVENTUS. DARAMEND promotes aerobic biodegradation of these compounds by providing timed-release nutrients such as nitrogen, organic carbon, phosphorus etc. as well as creating the right conditions of pH, alkalinity etc. to enhance the microbial activity of indigenous microorganisms. Oxygen for aerobic biodegradation is provided by tilling the soils periodically and moisture is provided by simple irrigation system. The benefit of in-situ bioremediation at this site allowed the treatment to occur on site avoiding the need for the often expensive off-site treatment and disposal option.
Bioremediation Operation:
There are several critical factors for effective bioremediation of hydrocarbon contaminated soil, including soil moisture content (a function of the water holding capacity (WHC)), pH, aeration of the soil via tilling, and the application rate of DARAMEND based on the concentration of contaminants. These variables must be controlled at optimum levels to realize the highest effectiveness of treatment. At the beginning of this study, baseline soil analysis was conducted to determine the concentrations of target compounds. The soil was also analyzed for pH and WHC. DARAMEND was applied at an application rate of 1% to soil mass (approximately 52 kg of DARAMEND to 5,200 kg of soil to be treated). Immediately after adding the DARAMEND, soil samples were collected and analyzed for pH, soil moisture content and WHC for both the control soil pile and the soil pile amended with DARAMEND (See Table 1). The soil pH was in the neutral range and ideal for promoting bioremediation.
Both, the control and the treatment soil piles were aerated twice a week using a tiller and irrigated to maintain moisture. Soil samples were analyzed weekly for operational monitoring (pH and moisture). The target moisture content was set at 70% of the WHC. The initial WHC of treatment soil pile was at 44.2%.
Results and Conclusion
Analytical results indicate that there was a 68% reduction in TPH-D during the first three weeks after DRAMEND was applied. No significant reductions were observed over the next four weeks suggesting that another dose of DARAMEND was required. However, soil samples collected on Dec 8, 2009 showed a sudden drop in TPH-G (almost 50% from that observed after the first three weeks). This could be due to the fact that between week 4 and week 8, the high molecular weight and long-chain TPH were being broken down to lighter intermediates but there was no net reduction in TPH. After week 9, the lighter intermediates started to mineralize. It appears that additional DARAMEND will be required to increase the removal efficiency. The final results of soil analysis of this study were successful in achieving the regulated soil TPH limits of 646 mg/kg