Solubilization of a multicomponent nonaqueous phase liquid using a nonionic surfactant

Polycyclic aromatic hydrocarbons (PAHs) and nonaqueous phase liquids (NAPLs) are contaminants of environmental interest. These compounds are very persistent in the subsurface due to their hydrophobicity and low aqueous solubility. Conventional pump-and-treat remediation technology has been quite unsuccessful to treat these contaminants. Therefore, surfactant-enhanced remediation techniques are being explored. Often, PAHs are found in mixtures with nonaqueous phase liquids (NAPLs). The components in a multicomponent system often behave differently than the individual components. This study focused on the solubilization behavior of the three PAHs, naphthalene, phenanthrene, and anthracene dissolved in a transformer oil (Univolt 60). The principal objective of this research was to study the solubilization efficiency of oil and PAHs by the nonionic Polyoxyethylene 10 Lauryl ether (Pol 10) surfactant. The applications for the results obtained from the batch experiments were extended to soil washing and soil column flooding experiments. The thermodynamic activities of the TPH and PAHs were used to analyze the data obtained from the aqueous experiments. They were found to be close to unity for all aqueous experiments, indicating that micelles were efficient in solubilizing TPH and PAHs. The activity coefficients increased for individual components when measured in a multicomponent system compared to the values for pure compounds. The amount of oil and PAHs solubilized in surfactant micelle pseudo-phase decreased in a multicomponent system compared with the individual system. Slightly higher solubilization of oil and PAHs occurred in soil washing experiments than in aqueous experiments. In the column study, about 60% of oil and 80% of PAHs were solubilized using 92 pore volumes of surfactant solutions. Only trace amounts of both oil and PAHs could be extracted from the soil following treatment; the balance of the contaminants was probably removed by mobilization. The overall study agreed that the nonionic Pol 10 surfactant was a good solubilizer for the mixture of oil and PAHs. In general, the solubilization efficiency was observed to increase above the critical micelle concentration (CMC). This was confirmed by the surfactant loss measurements done for post-experiment samples.