ADSORPTION OF VOLATILE ORGANIC-COMPOUNDS ON SOIL AND PREDICTION OF DESORPTION BREAKTHROUGHS

Vapor extraction of volatile organic compounds from soil was investiga ted by performing adsorption and desorption experiments of trichloroet hylene, trichloroethane, and chlorobenzene on soil particles. The adso rption breakthrough curves were obtained using a dynamic response tech nique based on frontal analysis chromatography. The shape of the break through curves indicated that the adsorption process was close to an i deal adsorption system of no mass transfer resistance, no axial disper sion, and infinitesimal width of mass transfer zone. The adsorption is otherms 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 de creasing profiles of chlorobenzene. The desorption profiles of trichlo roethylene and trichloroethane were simulated using a local equilibriu m theory which indicated that desorption behavior was independent of t he number of adsorption layers on soil. For chlorobenzene, the monolay er desorption was the rate-controlling step of the overall desorption process. The effect of moisture on desorption efficiency was significa nt for chlorobenzene, which showed more unfavorable desorption behavio r than trichloroethylene and trichloroethane.