Laboratory evaluation of surfactant-enhanced air sparging for perchloroethene source mass depletion from sand

Abstract

Surfactant-enhanced air sparging (SEAS) was evaluated in this laboratory-scale study to assess: (i) the removal efficiency of volatile contaminant from an aquifer model contrasted to conventional air sparging; and (ii) the effect of mass removal of dense non-aqueous phase liquid (DNAPL) during air sparging on the changes in aqueous flux of dissolved DNAPL. We conducted sparging experiments to remove perchloroethene (PCE) sources from laboratory flow chambers packed with sand. PCE was emplaced in rectangular zones at three locations within the flow chamber. The resident water was supplemented with the anionic surfactant, sodium dodecylbenzene sulfonate (SDBS), to reduce the surface tension of water, and then sparged with nitrogen gas at a constant flow rate of 0.12 L/min. It was found that SEAS was significantly more efficient than conventional air sparging for removing PCE. For SEAS, about 78% and 75% of total PCE mass was depleted from the flow chamber at a surface tension of 52.2 dynes/cm (350 mg/L SDBS) and 63.1 dynes/cm (150 mg/L SDBS), respectively, whereas only 38% was removed at 72.5 dyne/cm (no SDBS added). Before and after sparging, PCE mass flux in the aqueous phase during steady water flow through the chamber was measured in the flow chambers. Post-SEAS PCE fluxes were reduced, but not in direct proportion to the reduction in PCE mass.