Surfactant-enhanced air sparging in saturated sand

Air sparging as a subsurface remedial technique can be enhanced bythe addition of a surfactant. The effect of reduced surface tension of water on the extent of air intrusion and air saturation during air sparging in porous media was investigated. A sand column and a two-dimensional sand box were used for the experiments. The surface tension was controlled using an anionic surfactant, sodium dodecyl benzene sulfonate, and the concentration used was below the critical micelle concentration. Using the sand column, the air saturation was measured at different surface tensions and at different airflow rates. Initially water-saturated, the air saturation achieved in the column by air sparging at a surface tension of 3.42 x 10(-2) N/m was up to 5 times larger than that of water with no surfactant. Atthe same time, the rate at which the air saturation increased as a function of airflow rate was greater at reduced surface tensions. For box experiments with homogeneous sand, reduction of the surface tension caused a dramatic increase in the sparging area up to 5.2 times of that generated using water with no surfactant. A sand box experiment containing a vertical channel produced preferential flow of the air phase injected at the bottom of the channel when the surfactant was not applied. However, reducing the surface tension was found to promote airflow through the preferential channel and the finer sand surrounding the channel. These observations support the use of low concentration surfactants to improve air sparging swept zones.