Critical micelle concentration remediation

Enhanced HOC solubility in surfactant systems generally has been quantified by a distribution coefficient that only considers HOC partitioning to surfactant micelles that exist above the critical micelle concentration (CMC). Although surfactants can form a mobile micellar pseudophase that leads to the facilitated transport of solubilized HOCs, they also can be adsorbed by the solid matrix and thereby lead to HOC partitioning to immobile sorbed surfactants and, thus, enhanced HOC retardation. Therefore, the effectiveness of a remediation scheme utilizing surfactants depends on the distribution of an HOC between immobile compartments (e.g., subsurface solids, sorbed surfactants) and mobile compartments (e.g., water, micelles). 

Finally, remediation by solubilization is a robust process, relatively independent of the type of surfactant used, and has little impact on the movement of liquid contaminants. The critical micelle concentration (CMC) of the surfactant, however, does determine the quantity of the surfactant used (see Table 15.1 for CMCs of surfactants used in aquifer remediation). 

For enhanced oil recovery (EOR) and environmental remediation, an important property of any surfactant is its critical microemulsion concentration, or CfiC, because this is the minimum surfactant concentration needed to achieve ultralow interfacial tensions (<0.1 mN/m) [37, 38]. Recently, it has been determined that for rhamnolipids with a CMC of 10 mg/1, the C/rC is close to 100 mg/1 [39], which is approximately 10 times lower than the C/rC of anionic surfactants [38]. The study of the C/rC for rhamnolipids and other biosurfactants obtained from waste sources has not been performed yet. The work of Nguyen et al. [39] on the formulation of microemulsions with rhamnolipids also suggests that they are relatively hydrophilic (i.e. tend to form micelles but not reverse micelles), and that it is best to use them in combination with other surfactants. 

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