Nonionic surfactant-enhanced solubilization and recovery of organic contaminants from within cationic surfactant-enhanced sorbent zones .1. Experiments

Recent studies have shown that cationic surfactants can be used to increase the organic carbon content of aquifer materials, creating enhanced sorbent zones for hydrophobic organic contaminants (HOCs) migrating in groundwater. The coupling of nonionic surfactant-enhanced solubilization of HOCs to the cationic surfactant-enhanced sorption zone concept is examined as a possible groundwater remediation scheme. The partitioning behavior of 1,2,4-trichlorobenzene (TCB) and lgepal CO 730 (CO 730, a nonionic surfactant), both singly and jointly, were determined in batch hexadecyltrimethylammonium (HDTMA, a cationic surfactant) chloride-modified aquifer material/water systems. The apparent CO 730 critical micelle concentration (cmc) was found to decrease by a factor of 17 due to nonideal mixed micelle formation in the presence of low aqueous phase HDTMA concentrations that resulted from exposure to HDTMA-modified aquifer material. A greater portion of CO 730 will be present in the micellar psuedophase (the HOC solubilizing phase) as a result of the lowered cmc. The TCB partitioning behavior in the HDTMA-modified aquifer material/water systems was found to be dependent upon the aquifer material organic carbon content, the apparent CO 730 cmc, and the partitioning of TCB between the micellar pseudophase and the bulk aqueous phase containing surfactant monomers. The batch experiments indicate that the micellar pseudophase would be a more favorable partitioning medium for TCB relative to the solid phase organic carbon within an enhanced sorbent zone. One-dimensional column experiments were performed using HDTMA-treated and untreated aquifer materials to determine the transport behavior of CO 730 and to assess the feasibility of using CO 730 to solubilize and recover TCB bound within a cationic surfactant-enhanced sorbent zone. Complete removal (> 99%) of the bound TCB was achieved using a 12-column pore volume Rush of 50 g/L CO 730. The column experiments demonstrated that a nonionic surfactant can effectively remove an HOC from a cationic surfactant-enhanced sorbent zone.