Influence of Sub-CMC Rhamnolipid Flushing on the Mobilization and Solubilization of Residual Dodecane in Saturated Porous Media

The potential of monorhamnolipid (monoRL) biosurfactant to enhance the removal of residual dodecane from a porous medium was investigated under monoRL concentration varying from sub-CMC to hyper-CMC conditions by one-dimension column experiments. In the immiscible displacement experiment, 76% of the total volume of dodecane is removed by flushing of 150 μM monoRL solution. The solubilization of dodecane could be enhanced by rhamnolipid even at monorhamnolipid concentrations as low as 50 μM/L. The higher solubilization concentration (500 μM/L) of monoRL solution results in higher solubilized dodecane concentration (160 μM/L) due to the larger quantity of micelle formation. Compared to solubilization, immiscible displacement, or mobilization, is far more effective in removing residual dodecane. The interfacial partitioning tracer tests (IPTT) method is applied to measure the variation in specific dodecane-water interface areas (Anw). The results showed that the flushing of monoRL increased the Anw from 2.04 to 3.54 cm2/cm3. This investigation implies that low-concentration monorhamnolipid flushing and subsequent micelle solubilization is an economic method to remediate NAPL-contaminated fields.