Heat Enhanced Bioremediation and Destruction
In situ thermal treatment through Electrical Resistance Heating (ERH) is a proven robust technology for the treatment of volatile organic compound (VOC) source zones. ERH effectively treats the subsurface by volatilizing dense non-aqueous phase liquid (DNAPL) and VOCs, recovering the vapor, and treating the vapor by conventional technologies such as granular activated carbon or thermal oxidation.
In addition to volatilization and recovery of VOCs, in situ contaminant destruction also occurs at many ERH sites and can play an important role in the overall contaminant source reduction.
TRS has completed a field study that increased the understanding of the benefits of in situ destruction mechanisms. The U.S. Environmental Security Technology Certification Program (ESTCP) funded the study that was performed at the Fort Lewis Army Base south of Seattle, WA. The overall goal of the study was to demonstrate the use of ERH to heat the treatment zone to moderate temperatures of 30°-70°C and quantify the increased efficiency of biotic and abiotic in situ degradation reactions. More specifically, the in situ destruction mechanisms were evaluated as outlined in the ESTCP submittal:
- Validate the increased rate and extent of contaminant degradation during thermally enhanced in situ bioremediation (ISB) at a temperature of approximately 35°C compared to ISB at ambient temperature
- Validate the increased rate and extent of contaminant degradation during thermally enhanced iron-based reduction at a temperature of approximately 55°C compared to ambient temperature
- Determine the relative contributions of in situ biotic and abiotic degradation at different temperatures in order to optimize each
- Collect data from a controlled field demonstration at a Department of Defense site to develop cost and performance data for the combined remedies
Data from the ESTCP demonstration suggest that thermally enhanced dechlorination activity can be sustained for 6 to 12 months after zero-valent iron injection. The average trichloroethene (TCE) dechlorination rate was 0.14 to 0.24 grams-TCE/day per m3 (about 0.12 mg/kg/day). Heating increased both desorption/dissolution and dechlorination of TCE. The dechlorination rate exceeded the desorption/dissolution rate up to temperatures of 45-50°C.