Tetrachloroethylene removal from wastewater using a phase separation of cationic and anionic surfactant mixtures : efficiency enhancement by lipophilic linkers and nonionic surfactants addition

Abstract

Tetrachloroethylene (PCE) is a volatile chlorinated hydrocarbon commonly used as a solvent in metal degreasing and dry cleaning industries. A high concentration of PCE can be evidently found in the surface water and groundwater. This research aimed to investigate a novel separation technique called aqueous surfactant two-phase system (ASTP) using mixtures of cationic and anionic surfactants to preconcentrate and extract PCE from wastewater. The ASTP system has a unique characteristic where an aqueous surfactant solution can separate into two micellar phases. One is the surfactant-rich phase containing most of surfactant aggregates and solubilized pollutants; and the other is the surfactant-dilute phase which contains only small amount of surfactants and pollutants as treated water. The preliminary study on surfactant system selection reveals that the suitable cationic and anionic surfactants composition forming a stable ASTP system is DTAB:DOWFAX 8390 at molar ratio of 2:1. The total surfactant concentration was investigated in the range of 30 to 110 mM and found that the total surfactant concentration of 70 mM is the most suitable working condition in which the fraction of PCE removal is 91.4% or only 8.6 ppm of PCE remains in the surfactant-dilute phase from the original PCE concentration of 100 ppm. Moreover, an addition of lipophilic linkers (long straight chain alcohols; n-octanol, n-dodecanol, and n-hexadecanol) and nonionic surfactants (POE surfactants; TX-114 and TX-100) was found to enhance the PCE solubilization of this ASTP system. An addition of small amount of nonionic surfactant (2 mM) can greatly increase the fraction of PCE removal to about 96 % or only 4 ppm of PCE is left in the surfactant-dilute phase. Among three alcohols studied here, n-dodecanol shows the greatest ability to enhance the PCE solubilization, in which up to 98% of PCE is extracted within single stage with an addition of 0.1 mM dodecanol only. However, the concentrations of nonionic surfactants and alcohols added do not have significant effect onto the PCE removal efficiency.