Evaluation of thermally enhanced soil vapor extraction using electrical resistance heating for chlorinated solvent remediation in the vadose zone

Abstract

Soil vapor extraction (SVE) is the most popular technology for removing volatile contaminants from the vadose zone. However, SVE is limited by the contaminant vapor pressure, hydraulic conductivity and gas permeability of the vadose stratigraphy. Concentration reductions greater than 90% are hard to achieve with traditional SVE. Thermal enhancement is establishing itself as a viable method to increase the applicability and effectiveness of SVE. Heating methods include steam injection, radiowave, microwave, and electrical resistance. The appropriate method depends on site geology, soil and contaminant parameters and the maximum temperature required. Electrical resistance heating (ERH) is one promising enhancement method. ERH has been demonstrated at more than 30 sites. However, little is known about the mechanisms occurring during the heating process. Existing models are limited in scope, neglecting important aspects of heat and mass transfer.

The purpose of the research presented is to develop the basis for a general mass transfer model to simulate the SVE process during remediation of chlorinated solvents using thermally enhanced SVE in the vadose zone. A conceptual model detailing the processes occurring during vapor extraction with soil heating by electrical resistance is proposed. The conceptual model is then used to derive a set of governing equations for a general multiphase multicomponent system with an applied heat flux. This approach allows the model developed here to be extended to other thermal treatments.