**5. Conclusion**

42 New Technologies in the Oil and Gas Industry

electroosmotic flow in the soil.

electrobioremediation resulting in an reduction of PAH.

In similar conditions with saturated soil this effect was not observed [18, 28, 45]. The lack of moisture change in experiment I is thought to be because the acidic pH increased the soil zeta potential, rapidly causing electroosmotic flow into the acidified region to reduce or even reverse [46]. By removing electrode fluid moisture content change was avoided but pH control had to be implemented using a regularly reversed current [47] and it may be that part of hydrocarbon fraction is eliminated in the fluids producing other contaminated residue. Changes in the concentration of pH and moisture in the soil may have mobilized pollutant fractions present in the soil in the porosity, which are often not accessible to soil microorganisms [48]. Thus, the occurrence of electroosmosis inside soil aggregates may have caused the mobilization of slowly desorbing hydrocarbons into the fast-desorbing pool, which possesses a higher bioavailability to microorganisms [49, 50]. Bioremediation in Patagonian soil with the addition of nutrients is possible; however, the remediation of PAH is problematic [29] because of their low bioavailability, which can be improved by

Maintenance of soil moisture levels proved essential, because if it decreases much it will generate problems at a metabolic level in soil bacteria. It is also necessary to apply a voltage greater than the potential in the electrodes to keep the voltage value of 0.5 V.cm-1 thus increasing the cost of treatment energy. By working with saturated soils, the electrolyte circulation volumes, generated by electroosmosis, are contaminated is a contaminated liquid residue. One of the benefits of our system is that unsaturated soil was not observed as a leachate product of the current application. The decrease in moisture of the tanks could also be due to factors, such as the heating system or for undesirable exothermic chemical reactions [5]. Soil temperature in electrokinetics cell remained at 24 ± 3 °C throughout the 150 days of runtime. A temperature range of 24 ± 3 °C can be considered an acceptable temperature for the biodegradation of hydrocarbons by native soil microbes. These results are in accordance with results from previous studies in which an applied voltage density of 0.3 V/cm was used for this purpose [16]. This indicates that the reduction of moisture in the anode is mainly due to the presence of

Whilst the migration of bacteria towards the anode was expected (negative surface charge being responsible for this migration), bacteria were also found to migrate towards the cathode, which may be considered surprising at first glance. This bidirectional migration of bacteria may well have resulted from the competition between two phenomena: electrophoresis and electroosmosis [51, 52]. However, other phenomena may have contributed to the migration of bacteria to the cathode. The migration of ions and water in soil toward the cathode under the influence of the electric field is one such reason. This process could create favorable conditions for bacterial growth in the area near the cathode., although the net negative charge at their surface should make them move toward the anode. Kim et al. [53], concluded "Especially the number of culturable bacteria decreased significantly and only *Bacillus* and strains in *Bacillales* were found as culturable bacteria. It is thought that the main causes of changes in microbial activities were soil pH and direct These results indicate that biodegradation and electroosmosis can be successfully integrated to enhance PAH removal from soil, improved mobilisation of the less bioaccessible fraction of PAH with an electrokinetic pretreatment to reach lower residual levels through bioremediation. This process has the potential to provide an effective technology for the treatment of problematic soil. Whereas normal soil can be treated by 'classical' bioremedation. The optimization of these processes for a cost-effective application of the technology in situ to meet remediation will be the subject of future investigations.

Given the costs of this technology, we recommend this technique to Patagonian and other problematic soils which, after previous degradation, do not reach the levels prescribed by regulation. Optimization of this process for the removal of polyaromatic hydrocarbon from contaminated sites is the subject for future studies.
