Removal of hydrocarbon from soils possessing macro-heterogeneities using electrokinetics and surfactants

Abstract

The removal of n-hexadecane from soil in two-dimensional (vertical) setups was investigated using electrokinetics (EK), hydraulic gradient (HG), and anionic surfactant SDS (Sodium Dodecyl Sulfate) and nonionic surfactant Tween 80. The investigation relied on creating a two-dimensional block containing 3 × 3 cells each 3 cm in dimension. The soils in the blocks were created by mixing loamy sand soil (LSS) with kaolinite (clay) at three proportions: 100% LSS + 0% clay, 95% LSS + 5% clay and 90% LSS + 10% clay. This approach is very different from existing approaches where heterogeneity is layered. The surfactant concentration exhibited a large variability in space, including in the sand around the soil which highlights the limitations of one-dimensional investigations. In general, HG delivered surfactant more uniformly in the sand, but not in the soil. The performance of Tween 80 with EK was slightly higher than that of SDS, as the removal was 64% to 51%, respectively; and was better than SDS when HG was used, 65% to 46%. Another set of experiments was conducted using one cell made of 20% LSS + 80% clay with Tween 80. The EK provided a much higher removal efficiency (77%) than HG (43%), which indicates that EK performs better than HG for clayey soils. Overall, the study indicates that for both anionic and nonionic surfactant, the removal of n-hexadecane using EK was comparable to or better than HG, and that EK is capable of delivering the surfactants in two-dimensional systems.