Effect of Chemical Agents on the Diffusion Behavior of Oxygen in Groundwater Under Combined Remediation Technique of Air Sparging and Soil Flushing

Composite technique of soil flushing and air sparging was frequently used to remediate the contaminated site. During these processes, the surfactant or chelating agent is bound to affect the efficiency of air sparging. In order to study the effect of the surfactant or chelating agent on the efficiency of air sparging, experiments were performed in a self-made experimental device to test the oxygen diffusion in the surfactant or chelating agent solution. First, the liquid-side mass transfer coefficient (kL) in the surfactant or chelating agent solution was measured at a free gas-liquid interface. Then the value of the diffusion coefficient of oxygen (D) was calculated based on kL, dynamic viscosity, and density of the solution. The results showed that sodium dodecyl benzene sulfonate (SDBS), rhamnolipid (RHA), triton X-100 (TX-100), saponin (SAP), ethylene diamine tetraacetic acid (EDTA), or citric acid (CA) solution presented low kL and D values compared with deionized water. The D in the surfactant solution decreased with an increase in surfactant concentration until its CMC was reached. Among different kinds of surfactant solutions, anionic surfactant and bio-surfactant presented a relatively large impact on D. Based on these results, a correlation between the D in surfactant solution and the concentration of surfactant was adopted to predict the D in surfactant solution. Regarding the influence of the chelating agent on kL and D, it was confirmed that the D decreased with the increase of EDTA or CA concentration. This effect was related to the pH and ionic strength of the chelating agent solution.