The influence zone of surfactant-enhanced air sparging in different media

This paper presents the results of a laboratory investigation of the influence zone (IZ) of air sparging (AS) in different media at different surface tension. Different kinds of media were used in two-dimensional tank experiments, designed to determine (1) the effect of surface tension reduction on the airflow pattern during AS in different air travelling modes (channels and bubbles) in homogeneous aquifer and (2) the airflow distribution and migration characteristics in heterogeneous aquifer at different surface tension during AS. The results demonstrated that in homogeneous gravel aquifer, the IZ was almost identical with or without surfactant addition into groundwater, the air saturation, however, was increased with decreasing surface tension. In homogeneous coarse sand tank saturated with 500 mg/L sodium dodecyl benzene sulphonate (SDBS) solution, the IZ was approximately 1.3 times larger than that in the same medium saturated with distilled water. In addition, the density of airflow channels was much larger in medium saturated with SDBS solution. In heterogeneous subsurface saturated with distilled water, when the permeability ratio between two adjoining layers was 8:1, air would bypass low-permeable soils. In contrast, the air would infiltrate into low-permeable soils when SDBS concentration in groundwater was 1000 mg/L. The results indicate that surfactant-enhanced air sparging can effectively improve the volatile organic compounds removal both in homogeneous and heterogeneous media.