Remediation of saturated Shanghai sandy silt contaminated with p-xylene using air sparging

Abstract

Air sparging is an effective technique for the remediation of soil and groundwater polluted by volatile organic compounds. In this paper, this technique was investigated by conducting air-sparging test in the laboratory on the Shanghai sandy silt that was artificially contaminated with p-xylene. A test tank was designed for this purpose. During the air-sparging process, aqueous p-xylene solutions were extracted from the observation holes, and their concentrations were quantified by the spectrophotometric detection method. The mechanism of mass transfer process of p-xylene in the vicinity of sparging well and the remediation of the contaminated groundwater by air sparging were explored. The results showed that the removal zone of the p-xylene was mainly located within a radius of about 20 cm around the air injection well, with 90 % p-xylene removed after 20-day air sparging. Within the initial 5-day sparging, the concentration of p-xylene decreased rapidly in the mass transfer zone. By contrast, in the area far from the injection well, the p-xylene concentration decreased evenly and slowly. Thus, the remediation of contaminated soil and groundwater by air sparging is space–time dependent. For further analysis, the adsorption of silt was taken into account, and the distribution coefficient, Kd, was introduced to the modified Shackleford’s mass transfer model. The comparison between the simulated and measured results indicates that the modified model can satisfactorily describe the p-xylene mass transfer observed in this study.