Air stripping of hydrocarbon‐contaminated soils: Investigation of mass transfer effects

Bench‐scale experiments were carried out to simulate air stripping of soil contaminated with a semi‐volatile hydrocarbon, n‐octane. The experiments were conducted in an 8‐cm diameter glass column, packed with two types of packings: glass beads to represent non‐adsorbing materials and soil particles to represent adsorbing materials. Effects of gas superficial velocity, particle size and soil organic matter on the column outlet concentration and temperature profile were studied. Nitrogen adsorption/desorption experiments were performed to establish the desorption characteristics of the soil sample. Additionally, a mathematical model is presented which treats the interphase contaminant transport as a mass transfer rate‐limited process. The predictions from the mathematical model are shown to be in good agreement with the experimental results. Most importantly, the numerical results show that, contrary to the common assumption of local equilibrium, the interphase contaminant transport (from the sorbed to the vapour phase and/or from the liquid to the vapour phase) is mass transfer controlled.