**2.1 Anode modification**

For this set of experiments soil was collected at 50 cm depth in an undisturbed site of Guanajuato, México. Applying the ASTM D4318-10 methodology soil was characterized for liquid (LL) and plastic (PL) limits, the water content difference between LL and PL provides the plasticity index (PI), which is an indicator of soil response, because greater PI values correspond to a soil which is more plastic and compressible and so far it exhibits greater volume changes using LL and PI values on the plasticity chart (Helwany, 2007), can be obtained a fast classification of soil type, providing an insight on the possible soil response, before any electrical perturbation is applied. Also, textural classification was done following the USCS-P13-B-2 procedure. This soil was artificially polluted by mixing it with a phenanthrene solution, let stand overnight, and room temperature dried. Later on, it was characterized for sorbed phenanthrene, which resulted in 12 mg Kg-1. For experiments polluted soil was rewetted with deionized water.

This set of experiments considered electrodes made from 100 ppi (pores per inch) reticulated vitreous carbon (RVC), impregnated with TiO2 by a sol-gel method. Impregnating solution was prepared dissolving metallic Ti in concentrated HCl; later on it was precipitated with NH4OH, obtained product was filtered and washed before dispersing it into a 10% ethanol solution; in this solution RVC pieces were immersed for 24 hours; after that, they were dried and subjected to a 3 hours calcination, this procedure pursues formation of the anatase phase in the deposit; confirmation of anatase presence was done by Raman spectroscopy and some micrographs were obtained with a Leica S8APO stereomicroscope. The electrochemical cell was a rectangular one (14 cm length, 10 cm width, 9 cm high).

Electrokinetic experiments were run for 24 hours, a 25 mA cm-2 electrical current density was imposed with an electrophoresis power supply FR500-125 BIOELEC. Electrode arrangement considered keeping constant a bare RVC cathode, and switching the anode from bare RVC to RVC-TiO2, recorded parameters correspond to: pH and electric conductivity measured with a Multipurpose Lab Interphase Vernier Software; electroosmotic flow was registered with an illuminated multitester MUL-270 Steren.

In order to quantify residual phenanthrene concentrations, at the end of each experiment, soil sample was cut in slices, room temperature dried, and phenanthrene was Soxhlet extracted with ethylic ether. After that, the solvent was evaporated and phenanthrene was solubilized in 5 mL of HPLC grade acetonitrile, this sample was centrifuged and injected into an inverse phase Hypersil chromatographic column C-18 ODS (100 mmx4.6 mm, and 3 mm particle size); detection was done using a mobile phase made of a mixture CH3CN/H2O/CH3OH in proportions 30:15:55 % v/v; using a flow rate of 0.4 mL min-1 and 254 nm detection wavelength.
