Effect of electrokinetics on the bioaccessibility of polycyclic aromatic hydrocarbons in polluted soils

Bioaccessibility is one of the most relevant aspects to be considered in the restoration of soils using biological technologies. Polycyclic aromatic hydrocarbons (PAH) usually have residual fractions that are resistant to biodegradation at the end of the biological treatment. In some situations, these residual concentrations could still be above legal standards. Here, we propose that the available knowledge about electroremediation technologies could be applied to enhance bioremediation of soils polluted with PAH. The main objective of this study was to show that a previous electrokinetic treatment could reduce the PAH residual fractions when the soil is subsequently treated by means of a bioremediation process. The approach involved the electrokinetic treatment of PAH-polluted soils at a potential drop of 0.9 to 1.1 V/cm and the subsequent estimations of bioaccessibility of residual PAHs after slurry-phase biodegradation. Bioaccessibility of PAH in two creosote-polluted soils (clay and loamy sand, total PAH content averaging 300 mg/kg) previously treated with an electric field in the presence of nonionic surfactant Brij 35 was often higher than in untreated controls. For example, total PAH content remaining in clay soil after bioremediation was only 62.65 +/- 4.26 mg/kg, whereas a 7-d electrokinetic pretreatment had, under the same conditions, a residual concentration of 29.24 +/- 1.88 mg/kg after bioremediation. Control treatments without surfactant indicated that the electrokinetic treatment increased bioaccessibility of PAHs. A different manner of electric field implementation (continuous current vs. current reversals) did not induce changes in PAH bioaccessibility. We suggest that this hybrid technology may be useful in certain bioremediation scenarios, such as soils rich in clay and black carbon, which show limited success due to bioavailability restrictions, as well as in highly heterogeneous soils.