Insights into air flowrate distribution and benzene removal in the heterogeneous aquifer during surfactant-enhanced air sparging

Abstract

Surfactant-enhanced air sparging (SEAS) is an effective method of remediating volatile organic compounds in groundwater. In this study, the airflow migration mechanism and benzene removal in a heterogeneous aquifer during air sparging (AS) and SEAS remediation were studied using a light transmission visualisation technology. The blocking effect of the heterogeneous geological interface on airflow clearly decreased owing to the surfactant injection. At a surfactant concentration of 800 mg/L, the ΔPe value (i.e., the air entry pressure difference of the media above and below the interface) decreased from 0.3 kPa to 0.1 kPa. After surfactant injection, there was obvious downward migration owing to gravity. Compared with AS, the lateral migration of airflow at the interface and the fingered distribution of air flowrate above the interface improved considerably during SEAS, which increased the total benzene removal rates from 0.624 to 0.979. Moreover, the spatial distribution of the surfactant changed due to prolonged AS, which decreased the zone of influence area and airflow distribution range. However, the surfactant redistribution further enhanced the rectangular distribution of air flowrate, which was beneficial for continuous benzene removal in the low-permeability zone above the interface. These findings are useful for further understanding remediation mechanisms and optimising the technological parameters of SEAS technology in layered heterogeneous aquifer.