**4. Conclusions**

236 Electrochemical Cells – New Advances in Fundamental Researches and Applications

In order to asses soil electroremediation efficiency in removal of phenanthrene, fluoranthene and pyrene, GC-MS was applied to the soxhlet extracted samples including both original and electroremediated soil. Concentration values were calculated from the area under the curve, and these were converted to percentage taking as reference concentration the one for each PAH registered in the extract from the original weathered soil. Results for the Ti cathode are shown in Figure 15 for the array I (physical barrier inclusion), and Figure 16 for

As it can be observed in Figure 15, (array with the physical barrier) there is a higher to lower trend from anode to cathode for the three PAHs which were analyzed, and removals are low; it seems that molecule size exerts an influence on their movement through the soil, since the 3 rings molecule (phenanthrene) has reached removals between 80 and 90%, while those with 4 rings (fluoranthene, pyrene) get similar removals between 60 and 85%. Otherwise, in Figure 16 it can be observed that allowing the electrode to make contact with soil enhances PAHs removal, getting similar residual concentrations for all, in this

Correlating these residual concentrations with pH observations (Figures 9 and 10) it seems that the fact of having a physical barrier between soil and electrode, which produces a more resistive system, does not allow for getting a high concentration gradient between electrodes, resulting in lower removals than those obtained when the electrode make contact with the soil; since the last arrangement produces a higher pH gradient between anode and

Phenanthrene Fluoranthene Pyrene

Fig. 15. Residual concentrations of representative PAHs in Array I physical barrier included, experimental conditions 0.1 M NaOH, current density 20 mA cm-2, experimental time 4 hours.

 IC 0.25 0.5 0.75

array II (soil contact).

experiment removals are above 90%.

0

20

40

% [C]/[C0

]

60

80

100

cathode, so far a higher driving force for PAHs transport.

Array I

For anode modification obtained results allows to claim that, effectively inclusion of anatase into the RVC matrix makes electrode reaction being more efficient. Also, by using the modified RVC-TiO2 electrode it is possible to increase the rate at which protons are generated and transported throughout the soil, and so far this influences pH at both electrode wells: anodic and cathodic. Also, it provides a higher electroosmotic flow, but this fast water transport does not allow for an adequate residence time, lowering phenanthrene removal. So far, the bare RVC electrodes provided a lower pH gradient between anodecathode, as well as a lower electroosmotic flow, both parameters are providing a better environment for phenanthrene removal, since with this option it was obtained up to 80% lowering in soil phenanthrene concentration.

For cathode modification obtained results have shown that cell resistance is lower when electrodes are in contact with soil sample, and this allowed for higher hydrocarbon mobility, so residual concentration profile exhibits an increasing trend from anode to cathode. Otherwise, physical barrier inclusion increased soil resistance and so far, hydrocarbon mobility is lowered, this fact resulted in a decreasing concentration trend from anode to cathode. From oil and grease extractions it was determined that CF provides higher hydrocarbon removal, although this option is not the best because transported hydrocarbons get adsorbed in the electrode, being difficult its recovery.

Even though Ti cathode provided lower hydrocarbon removal as it was estimated from Soxhlet extractions, when extracted samples were tested by GC-MS for quantification of three priority hydrocarbon pollutants, it happens that phenanthrene, fluoranthene and

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