Surfactant-Enhanced Electroosmotic Flushing in a Trichlorobenzene Contaminated Clayey Soil.

Remediation of the sites contaminated with organic contaminants, such as chlorobenzenes, remains a challenging issue. Electroosmotic flushing can be a promising approach which is based on mechanism of electrokinetic remediation for removal of organic contaminants from fluids in low-permeability soil. To select an optimum surfactant that can effectively enhance electroosmotic flushing, three common surfactants, Triton X-100 (EK2), Tween 80 (EK3), and a mixture of sodium dodecyl sulfate and Triton X-100 (EK4) buffered with Na2 HPO4 /NaH2 PO4 solution, were tested. The efficiency of each kind of surfactant was evaluated using a three-dimensional box filled with a clayey soil spiked with 1,2,4-trichlorobenzene, and compared with a test (EK1) without surfactant. The results demonstrated that the buffer solutions efficiently neutralized H+ and OH- produced by electrolysis. EK3 with Tween 80 added in the flushing solution reached the highest electroosmotic permeability of 10-4  cm2 /v/s and achieved a notably high cumulative electroosmotic flow (EOF) of 5067 mL within 6 d, which was 6.3, 3.4, and 4.2 times higher than that in EK1, EK2, and EK4, respectively. There were 420 mL more cumulative EOF obtained after 50 h of electrical application in EK4 than in EK2. The introduction of nonreactive ions can increase the current, thereby benefiting the EOF. Both the higher pH caused by the buffer and the application of nonionic surfactants can make the zeta potential more negative, thereby increasing the EOF. Tween 80 can be recommended as the best flushing solution for removing organic contaminants from sites when electrokinetic remediation is applied.