In this work, a pilot plant with two rows of three electrodes in semipermeable electrolyte wells was used to study the electrokinetic treatment of a natural soil polluted with phenanthrene (PHE). The electrokinetic pilot plant was an open system, i.e., there was direct contact between the soil and air. To increase the solubility of phenanthrene, thereby enhancing its transport through the soil, an aqueous solution of the anionic surfactant dodecyl sulfate was used as a flushing fluid. The results show that at the pilot scale considered, gravity and evaporation fluxes are more relevant than electrokinetic fluxes. Contrary to observations at the laboratory scale, desorption of PHE promoted by electric heating appears to be a significant removal mechanism at the pilot scale. In addition, PHE is dragged by the electroosmotic flow in the cathodic wells and by electrophoresis after interaction of the surfactant with phenanthrene in the anodic wells. In spite of the long treatment time (corresponding to an energy consumption over 500kWhm(-3)), the average removal attained was only 25%.

Models of electrokinetic soil remediation systems have been developed significantly in recent decades. A wide range of physicochemical phenomena occurs in this type of process, which makes it difficult to capture all of the system's complexity in a model. Therefore, existing models do not attempt to simulate the behaviour of the entire geochemical system of natural soils and their porewaters but rather focus on the pollutant compounds of interest. This paper proposes a conceptual and numerical model that includes geochemical speciation other than the phenomena that have been described by other authors. In addition, a comparative modelling exercise is performed with a composition of natural porewater and a simplified equivalent composition. The results show that the buffering system of carbonates affects the temporal evolution and spatial distribution of the pH. Because the pH controls many of the phenomena that occur during this type of remediation, simulations using realistic geochemical systems are critical.

This study analyses the effect of the scale-up of electrokinetic remediation (EKR) processes in natural soils. A procedure is proposed to prepare soils based on a compacting process to obtaining soils with similar moisture content and density to those found in real soils in the field. The soil used here was from a region with a high agrarian activity (Mora, Spain). The scale-up study was performed in two installations at different scales: a mock-up pilot scale (0.175m(3)) and a prototype with a scale that was very similar to a real application (16m(3)). The electrode configuration selected consisted of rows of graphite electrodes facing each other located in electrolyte wells. The discharge of 20mg of 2,4-dichlorophenoxyacetic acid [2,4-D] per kg of dry soil was treated by applying an electric potential gradient of 1Vcm(-1). An increase in scale was observed to directly influence the amount of energy supplied to the soil being treated. As a result, electroosmotic and electromigration flows and electric heating are more intense than in smaller-scale tests (24%, 1% and 25%, respectively respect to the values in prototype). In addition, possible leaks were evaluated by conducting a watertightness test and quantifying evaporation losses.

In this work, the scale up of the flushing-fluid-assisted electrokinetic remediation of kaolin soil polluted with phenanthrene has been studied. Three different scales have been used: lab (25 cm 3), bench (28 x10 3 cm 3) and pilot scale (175x10 3 cm 3) plants. Results show that electrokinetic fluxes, removals of PHE and pollutant distribution in soil were very different in the three setups in spite of being the same soil, pollutant and operation conditions. Electroosmotic fluxes were much bigger in the case of the lab scale setup and very similar in the bench scale plant and in the pilot mock up, just as expected according to the PHE fluxes and to the distribution of PHE removal. Moreover, in the pilot scale plant used, hydraulic flux produced by gravity and evaporation flux by electric heating of the soil should be taken considered. This variety of results suggests a very complex process with many factors influencing on results. In the lab scale plant, the main mechanisms involved in the removal of PHE are dragging with electro-osmotic flow in the cathodic wells and electrophoresis after interaction of surfactant with phenanthrene in the anodic wells. Just on the contrary, desorption of PHE promoted by the electric heating seems to be a very significant removal mechanism in the bench scale plant and in the pilot mock-up.

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