Adsorption of Volatile Organic Compounds on Soil and Prediction of Desorption Breakthroughs

Abstract

Vapor extraction of volatile organic compounds from soil was investigated by performing adsorption and desorption experiments of trichloroethylene, trichloroethane, and chlorobenzene on soil particles. The adsorption breakthrough curves were obtained using a dynamic response technique based on frontal analysis chromatography. The shape of the breakthrough curves indicated that the adsorption process was close to an ideal adsorption system of no mass transfer resistance, no axial dispersion, and infinitesimal width of mass transfer zone. The adsorption isotherms were BET Type I for trichloroethylene and trichloroethane, and BET Type II for chlorobenzene. Two types of desorption profiles were observed depending on the compounds, i.e., the continuously decreasing profiles of trichloroethylene and trichloroethane and the stepwise decreasing profiles of chlorobenzene. The desorption profiles of trichloroethylene and trichloroethane were simulated using a local equilibrium theory which indicated that desorption behavior was independent of the number of adsorption layers on soil. For chlorobenzene, the monolayer desorption was the rate-controlling step of the overall desorption process. The effect of moisture on desorption efficiency was significant for chlorobenzene, which showed more unfavorable desorption behavior than trichloroethylene and trichloroethane.