A Laboratory and Pilot Study of Thermally Enhanced Soil Vapor Extraction Method for the Removal of Semi-Volatile Organic Contaminants

Abstract

Laboratory and field pilot study was conducted to evaluate the effectiveness of thermally enhanced soil vapor extraction (SVE) system for the removal of semi-volatile organic contaminants (SVOCs) from soils. Several parametric studies were conducted to evaluate the effect of temperature and air flow rate on the removal of SVOCs. Column studies near ambient temperature show very little efficiency for SVOCs removal. The removal rates of SVOCs are highly dependent on temperature. Moving fronts in the effluent concentrations of contaminants are observed, according to the order of volatility of contaminant. This result is attributed to continuous changes in the liquid composition toward less volatile fractions, thus increasing the mole fraction of the less volatile fractions remaining in the liquid mixture. It is also found that increased air flow rate results in high removal rate of contaminants. However, too high air flow rate brings about the mass transfer limitation on the volatilization of the contaminants. Results from steady-state column studies show that mass transfer limitation is reduced at high temperature, possibly due to the increase in the diffusivity of contaminant in the liquid and gas phase. A field pilot study of a hot air injection method for the remediation of diesel-contaminated soil has shown advantages over the conventional SVE. Within 30 days of test operation, TPH concentrations at unsaturated soils were dramatically reduced, corresponding to more than 95% removal. However, temperature profiles and the removal rates of SVOCs near groundwater level indicate that moisture content would be a limiting factor in the real application of hot air injection.