Solubilization of DNAPLs by mixed surfactant: synergism and solubilization capacity

Efforts to remove the dense nonaqueous phase liquids (DNAPLs) in subsurface by mobilizing them face with risks of driving the contaminants deeper into aquifer zones. In this paper, a synergistical solubilization of DNAPLs by mixed nonionic and anionic surfactant, Triton X-100 (TX100) and sodium dodecylbenzene sulfonate (SDBS) in DNAPL/water systems was presented. Given 1:40 phase ratio of DNAPL:water (v/v), mixed TX100-SDBS exhibited significantly synergistical solubilization for the DNAPLs, trichloroethene (TCE), chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB), respectively, when the total surfactant concentration was up to 6000mg/L, i.e. the condition when solubilization by the mixture was better than those attainable with individual components by themselves. The synergistical extents depended on the initial ratios of TX100 to SDBS, the initial surfactant concentrations and the properties of DNAPLs. Given the total surfactant concentration, synergistical extents increased with the fraction of SDBS in mixed surfactant. On the contrary, did with the total surfactant concentration. The solubilization capacity by 3:1, 1:1 and 1:3 of mass ratio of TX100-SDBS were determined and compared with those by single ones. In the view of the mass solubilization ratio (SR), the mixed TX100-SDBS could solubilize more DNAPLs than single SDBS at given surfactant concentration. Reduction in partition of TX100 and synergistic solubilization were responsible for the significant solubilization extent of mixed system. The work presented here demonstrates that mixed nonionic-anionic surfactants would be preferred over the corresponding single surfactants for solubilization remediation of DNAPLs, which could decrease risks of driving the contaminants deeper into aquifers.