Aquifer remediation using surfactant-enhanced gas sparging applied to target the contaminant source

Abstract

The surfactant-enhanced gas sparging process designed to specifically target the source zone of an organic contaminant in an aquifer with minimal usage of injected additives was investigated using a physical model. Aqueous solutions of the anionic surfactant Sodium dodecylbenzne sulfonate (SDBS) and/or the thickener Sodium carboxymethylcellulose (SCMC) were applied in a contaminated horizontal layer in the simulated laboratory aquifer model followed by gas sparging. Fluorescein sodium salt (FSS) was added to the SDBS/SCMC solutions and represented the organic contaminant. Air and ozone were injected to generate gas sparging. A modified surfactant-enhanced ozone sparging method was also tested by applying additional air venting ports installed in the aquifer above the gas injection zone. Both non-aqueous phase liquid (NAPL) and water-dissolved TCA were applied to the SDBS-applied region to evaluate the removal of contaminants during gas sparging. A significant expansion of the de-saturated zone for the SDBS-applied region was observed during air sparging. During ozone sparging, the fluorescence by FSS in the SDBS-applied layer disappeared over a much wider range than that of the control experiment. SCMC application enhanced the performance of the SDBS-applied gas sparging process. The TCA mass removed by volatilization during air sparging from the SDBS-applied layer was 2.3 times the application in the absence of SDBS. Among five regions of injected NAPL contamination located above the single gas injection port, and during 2 h of ozone sparging, with SDBS applied, more than 50% of fluorescence in the NAPL was removed, whereas under the same conditions with no SDBS applied, less than 30% was removed. Diverted gas flow through the venting ports installed in the aquifer model induced a horizontally expanded oxidative reaction zone during ozone sparging. This study demonstrates enhanced gas sparging performance for the removal of contaminants from the aquifer with limited usage of additives applied specifically to the source zone.

Keywords: Aquifer; Contamination; Ozone; Remediation; Source zone; Surfactant.