Enhancement of tetrachloroethylene removal efficiency by using extended surfactants

Abstract

This research aims to introduce seven extended anionic surfactants, Alfoterra series, to enhance the tetrachloroethylene (PCE) removal from contaminated sand, and to investigate the optimum condition of different extended surfactants and electrolyte concentrations that yields the highest PCE removal. Alfoterra surfactants varying alkyl chain length and number of propylene oxide (PO) group in their molecules were used and mixed with sodium dihexyl sulfosuccinate (AMA), anionic surfactant, to form microemulsion solutions with PCE. This study hypothesized that the optimum condition to maximize the solubilization of PCE in micelles occurs at the supersolubilization region in the type I microemulsion. The supersolubilization condition for microemulsion of each Alfoterra mixed with AMA was obtained by measuring interfacial tension incorporated with an observation of an aqueous phase appearance. The critical micelle concentrations (CMC) of mixed Alfoterra surfactants with AMA were determined and found that the longer the Alfoterra chain length or the higher the number of PO group, the lower the CMC. The solubilization study of the seven systems of Alfoterra mixed with AMA was carried out in batch experiments. The results showed that the longer the chain length or the higher the number of PO groups in Alfoterra gives the higher micelle-water partitioning coefficient (Km) indicating that the PCE solubilization is higher. However, the effects of both factors are not linearly correlated, especially for the very long alkyl chain length, the PCE solubilization is remarkably reduced. From the solubilization study result, the three surfactant systems were selected for column study based on the solubilization capacity for PCE as low, medium, and high namely; C[subscript 12,13]H[subscript 25,27]-(PO)[subscript 4]–SO[subscript 4]Na+AMA, C[subscript 14,15]H[subscript 29,31]-(PO)[subscript 4]–SO4Na+AMA and C[subscript 14,15]H[subscript 29,31]-(PO)[subscript 8]–SO[subscript 4]Na+AMA, respectively. The total removal of PCE in the column using three surfactant systems was illustrated and the removal mechanism was distinguished as mobilization and solubilization. The results revealed that PCE can be removed from contaminated sand in the range of 59-83%. As expected, the system of C[subscript 14,15]H[subscript 29,31]-(PO)[subscript 8]–SO[subscript 4]Na+AMA, which yields the highest solubilization in batch experiments, gives the highest PCE removal by solubilization mechanism.