Modeling of air sparging of VOC-contaminated soil columns

Air sparging is a remediation technology currently being applied for the re storation of sites contaminated with volatile organic compounds (VOCs). Att empts have been made by various researchers to model the fate of VOCs in th e gas and liquid phase during air sparging. In this study, a radial diffusi on model with an air-water mass transfer boundary condition was developed a nd applied for the prediction of VOC volatilization from air sparging of co ntaminated soil columns, The approach taken was to use various parameters s uch as mass transfer coefficients and tortuosity factors determined previou sly in separate experiments using a single air channel apparatus and applyi ng these parameters to a complex system with many air channels. Incorporate d in the model, is the concept of mass transfer zone (MTZ) where diffusion of VOCs in this zone was impacted by the volatilization of VOCs at the air- water interface but with negligible impact outside the zone. The model pred icted fairly well the change in the VOC concentrations in the exhaust air, the final average aqueous VOC concentration, and the total mass removed. Th e predicted mass removal was within 1% to 20% of the actual experimental ma ss removed. The results of the model seemed to suggest that air-sparged soi l columns may be modeled as a composite of individual air channels surround ed by a MTZ, For a given air flow rate and air saturation, the VOC removal was found to be inversely proportional to the radius of the air channel. Th e-approach taken provided conceptual insights on mass transfer processes du ring air sparging operations. (C) 2000 Elsevier Science B.V. All rights res erved.