Anionic surfactant transport characteristics in unsaturated soil

Surfactants have potential use with respect to in situ removal of organic contaminants from soil, The efficiency and effectiveness of using surfactants for this purpose may depend on their mobility under unsaturated flow conditions. For this reason, transient horizontal unsaturated column tests were used to study anionic surfactant transport characteristics in a loamy soil. Two commercial anionic surfactants, an alkyl ether sulfate (AES) and a linear alkylbenzene sulfonate (LAS), were tested, For each surfactant, the concentration and moisture content profiles plotted versus the Boltzmann transform (column distance/(test time)(0.5)) exhibited similarity between experiments having the same boundary conditions but different time durations, Concentration profile similarity is an indication that soil/surfactant interactions were reversible and equilibrium conditions quickly achieved for AES and LAS during testing. Penetration of the AES and LAS concentration fronts were, respectively, one-half and one-fifth the advance of the wetting front, indicating a high degree of sorption. Where present at substantial concentrations, both surfactants reduced soil moisture diffusivity values significantly.