Solubilization of residual dodecane by surfactants in porous media: The relation between surfactant partition and solubilization

One-dimensional flow column experiments are conducted to specifically compare the transport behavior of three surfactants (sodium dodecyl benzene sulfonate (SDBS), Triton X-100, rhamnolipid) and a solvent n-propanol and their solubilization on dodecane in porous media. Compared to pentafluorobenzoic acid (PFBA), the low adsorption or partition loss of n-propanol incurred no retardation, shouldering or retention in breakthrough curves. While for surfactants, all the breakthrough curves exhibited retardation, shouldering or retention to different degrees in the presence of dodecane phase. Compared to the anionic SDBS with no significant bulk partition to non-aqueous phase liquid (NAPL), the non-ionic Triton X-100 with partition induced significant retardation and shouldering in breakthrough curves. The retention loss of solubilized aggregates resulted in obvious retention of rhamnolipid at different pore-water velocities. The increase of pore-water velocity could promote the transport of surfactants and the dodecane-surfactant aggregates. The elution of dodecane in the presence of surfactants showed a significant relation to the partition behaviors of surfactants and a characteristic of the rate-limited solubilization. In contrast, the n-propanol, which is basically a non-reactive solvent, exhibited the rapid equilibrium dissolution of dodecane. The results indicated that in remediation of field sites contaminated by hydrophobic organic contaminants (HOCs), the surfactants should be rationally selected, and a favorable pore-water velocity should be used to obtain a high remediation efficiency and to reduce the retention loss of surfactants as well.