Electrokinetically enhanced in-situ
flushing using
surfactants has the potential to remove
polycyclic aromatic hydrocarbons (PAHs) from low permeability
clay soils; however, previous research has shown that the applied electric potential produces complex physical, chemical, and electrochemical changes within
clay soils that affect mass transfer and overall efficiency. This article presents the results of a laboratory investigation conducted to determine the contaminant mass removal by using a periodic voltage application. The periodic voltage effects were evaluated by performing four different bench-scale electrokinetic tests with the voltage gradient applied continuously or periodically, under relatively low voltage (1.0 VDC/cm) and high
anode buffering (0.1 M NaOH) as well as high voltage (2.0 VDC/cm) and low
anode buffering (0.01 M NaOH) conditions. For all the tests,
kaolin soil was used as a representative
clay soil and it was spiked with
phenanthrene, a representative PAH, with a target concentration of 500 mg/kg. A nonionic
polyoxyethylene surfactant,
Igepal CA 720, was used as the
flushing solution in all the tests. The voltage was applied according to a cycle of five days of continuous application followed by two days of "down time," when the voltage was not applied. The results of these experiments show that considerable contaminant removal can be achieved by employing a high, 2.0 VDC/cm, voltage gradient along with a periodic mode of voltage application. The increased removal was attributed to increased
phenanthrene solubilization and mass transfer due to the reduced flow of the bulk
solution during the down time as well as to the pulsed electroosmotic flow that improved
flushing action.