Removal of 2, 4, 6-Trichlorophenol from Spiked Clay Soils by

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Removal of 2,4,6-Trichlorophenol from Spiked Clay Soils by Electrokinetic Soil Flushing Assisted with Granular Activated Carbon Permeable Reactive Barrier Clara Ruiz,† Esperanza Mena,‡ Pablo Cañizares,† José Villaseñor,‡ and Manuel A. Rodrigo†,* †

Chemical Engineering Department, Faculty of Chemical Sciences and Technology, University of Castilla La Mancha, 13071, Ciudad Real, Spain ‡ Chemical Engineering Department, Research Institute for Chemical and Environmental Technology (ITQUIMA), University of Castilla La Mancha, 13071, Ciudad Real, Spain ABSTRACT: A study was performed on the removal of 2,4,6-trichlorophenol (TCP) from synthetic polluted soils using electrokinetic soil flushing (EKSF) assisted by a granular activated carbon-permeable reactive barrier (GAC-PRB). The polluted soils consist of spiked kaolin and were obtained by directly mixing kaolin with a 200 mg dm−3 TCP solution. Remediation tests were conducted at the bench-scale. The obtained results demonstrated that EKSF assisted with GAC-PRB is a very efficient technology for the removal of TCP from soils. For a given remediation period, the applied electric field is a very important parameter that influences the removal efficiency. Under optimized conditions, the one week-long remediation test obtained removals greater than 80% with energy consumptions below 200 kWh m−3. The effects of the electric field on the temperature and TCP profiles were also assessed and explained in terms of ohmic drops and electrokinetic processes.

1. INTRODUCTION Chlorophenols (CPs) are aromatic chlorinated compounds in which a phenol molecule includes one to five chlorine atoms, leading to 15 different congener compounds. CPs are usually used as pesticides, herbicides, disinfectants, and as preservative agents for woods, paints, vegetable fibres, and leather.1−3 Unfortunately, these compounds are known to cause environmental pollution in superficial waters and aquifers, and CPs that do not degrade in water can be incorporated into soils and sediments. They are considered hazardous wastes and priority toxic pollutants as listed by the USEPA4,5 because the majority of CPs are toxic and not biodegradable. Particularly, 2,4,6trichlorophenol and 2,4-dichlorophenol are listed in the Drinking Water Contaminant Candidate List.6 The toxic effect of CPs depends on the degree of chlorination and the position of the chlorine atoms, and their persistence in soils depends on their adsorption and desorption characteristics.1 Different technologies for polluted soil remediation are available and are based on thermal, chemical, physicochemical, or biological fundamentals. To the author’s knowledge, there is not enough research experience in treatment of CPs polluted soils, but there are several works about treatment of CPs polluted groundwater. The main technologies used are advanced oxidation processes,7 dechlorination by Fenton reaction,8 biological treatment9 (which offers successful results although inhibition phenomena can be present under high CPs concentrations), and reduction by zerovalent metals or adsorption by organic materials.10 All of these technologies can be classified into two main groups: in-situ and ex-situ treatments. In-situ technologies do not need to remove the polluted soil from its original site, which is an important advantage as all mass and energy transport processes required to clean the soil are disadvantages. This limitation is especially important in fine-grained soils, such as clay. © 2013 American Chemical Society

Electrokinetic (EK) soil remediation is a recently developed technology that is especially recommended for the cleaning of low permeability soils with very low hydraulic and pneumatic conductivity values (i.e., sites where hydrodynamic transport would not be suitable). EK remediation is based on the application of two electrodes and a direct electric current across the soil, which produces several transport mechanisms:11 electromigration (transport of ions and ionic complexes to the opposite electrodes), electrophoresis (transport of charged particles to the opposite electrodes, including pollutants bound to mobile particulate matter), and electro-osmosis (movement of groundwater to the cathode, caused by superficially charged phenomena). Additionally, different electrochemical reactions, such as electrolysis and electrodeposition, and contaminant migration in soil is simultaneously controlled by sorption, desorption, precipitation, and dissolution mechanisms.12 EK remediation has been reported to be successful and cost-effective for treating both organic and inorganic contaminants, including chlorophenols, from lowpermeability soils.1 However, EK remediation can include some limitations related to the mobility and solubility of contaminants, control of pH, removal of the accumulated contaminants in the electrode wells, etc. In many cases, using EK remediation alone would not reach the required remediation level. Therefore, the technology could be enhanced by coupling with other technologies as part of a global remediation train of processes, which could offer better results than the sum of technologies applied individually.13 Received: Revised: Accepted: Published: 840

August 27, 2013 November 28, 2013 December 10, 2013 December 10, 2013 dx.doi.org/10.1021/ie4028022 | Ind. Eng. Chem. Res. 2014, 53, 840−846

Industrial & Engineering Chemistry Research

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One type of system coupled to EK remediation is permeable reactive barriers (PRBs). A PRB is an engineered zone of reactive material placed in an aquifer that helps intercept the pollution plume carried within the aquifer by retaining or degrading the pollutants. The barrier has to be at least as permeable as the surrounding aquifer material. It is typically a semicontinuous operation-mode process that requires the periodic replacement of the PRB material.14 The subsurface pollution plume flows through the PRB under natural hydraulic gradients or using pump-and-treat methods. When a PRB is coupled with electrokinetic remediation, the flow of pollutants through the barrier is not driven by the advective transport of the hydraulic gradient of groundwater; rather, it is driven by the electro-osmotic flow of soil pore fluid, electromigration, or electrophoresis, especially in low permeability soil. Different materials have been used to construct barriers based on several different mechanisms (reduction using elemental metals, adsorption with porous high-surface materials, ion exchange with resin-based materials, biological degradation, etc.) to remove halogenated organics and heavy metals flowing through the PRB. The most extensively used material is granular zerovalent iron (ZVI), which is used as a reducing agent.15−17,3 However, other materials have also been used. Weng,18 and recently Yeung and Gu,13 reported extensive reviews about the current research that couples EK and PRB to remediate soils, including different pollutants and PRB materials. For instance, heavy metals such as As, Cr, Cd, and Ni have been removed from soils by coupling EK/PRB using ZVI,15,16 atomising slag,19 carbonized food waste,20 calcined hydrotalcite,21 and activated carbon.22 Suzuki et al.23 removed nitrates using ZVI-PRB. Regarding the case of organic chlorinated compounds, Gomes et al.10 reported a review in the case of the EK/PRB technology for the removal of organochlorine from the soil. For instance, pentachlorophenol removal has been studied by Li et al.24 using EK and Pd/Fe PRB; 2,4-dichlorophenol removal has been studied by Yang et al.25 using EK and a combined PRB for adsorption (activated carbon) and reduction (ZVI); and 2,6dichlorophenol removal has been studied by Polcaro et al.26 using an EK and the simultaneous adsorption in a kaolinite− humic acid soil. To date, no studies concerning trichlorophenol (TCP) removal in soils by EK/PRB coupling have been reported. Choi et al.3 studied the hydrodechlorination of 2,4,6,-TCP in water by ZVI barriers but without using EK. Taking this into account, the authors of the present work considered that it was interesting to study the feasibility of coupling EK and PRB to remove 2,4,6-TCP from low permeability soils. In this context, this work aims to describe the removal of 2,4,6-TCP from clay soils using electrokinetically assisted soil flushing coupled with permeable reactive barriers consisting of beds of granular activated carbon and to assess the influence of the electric field on the efficiency of this technology.

Table 1. Properties of Soil Used in This Study mineralogy (%) kaolinite Fe2O3 TiO2 CaO K2O SiO2 Al2O3 others

100.00 0.58 0.27 0.10 0.75 52.35 34.50 11.42

particle size distribution (%) gravel sand silt clay specific gravity hydraulic conductivity organic content pH

0 4 18 78 2.6% 1 × 10−8 cm/s 0% 4.9

a 200 mg dm−3 TCP solution (750 cm3) with kaolinite (2000 g). The spiked clay was then placed in the experimental setup. A mixture of 2.5 g of granular activated carbon (GAC) and 500 g of spiked kaolinite was used as the PRB material. Granular activated carbon F400 manufactured by Calgon Carbon Corporation (Pittsburgh, EEUU) and supplied by Chemviron Carbon (Belgium) was used as the adsorbent in this study. The activated carbon F400 is made from bituminous coal and activated by steam. The original carbon was used as received. The surface area was determined using nitrogen as the sorbate at 77 K in a static volumetric apparatus (Micromeritics ASAP 2010 sorptometer). Specific total surface areas were calculated using the BET equation. Carbon composition was also analyzed with a fluorescence detector attached to a Phillips XL30CPDX41 scanning electron microscope (SEM). FT-IR analyses were conducted using a Perking Elmer FT-IR 16 PC. The primary characteristics of the GAC are shown in Table 2. Table 2. Activated Carbon Characterization ratios (%) O/C

Al/C

Si/C

BET surface area (m2/g)

3.60

0. 98

1.00

1026.5

Although different materials can be used for adsorption, the authors considered that activated carbon is the most common adsorption material, and it is the first material that should be tested. Tap water was used as the electrolyte and processing fluid in the electrokinetic experiments. 2.2. EK Testing Setup. The bench-scale EK-PRB experiments were performed using the setup shown in Figure 1. The setup consisted of a horizontal methacrylate column with different compartments. It included two electrolyte compartments and reservoirs, using a graphite anode and a titanium cathode (10 × 10 cm2 each) at the left and right compartment ends (the volume of the electrolyte compartments was 10 × 10 × 5 cm3; the volume of the electrolyte reservoirs was 10 × 10 × 10 cm3), and a central methacrylate horizontal soil column (10 × 10 × 25 cm3) in which the polluted soil was located, except one section, which was used as the PRB compartment, was closed to the anode compartment (10 × 10 × 5 cm3). The setup also contained a direct current power supply and one multimeter. The central soil column contained five vertical holes as sampling points, including one in the PRB compartment. 2.3. Experimental Procedure of Equilibrium Adsorption Tests. To further understand the removal behavior of TCP by GAC, aqueous equilibrium adsorption isotherms (25 °C) were recorded with several batch tests using agitated vessels with 1.5 L solutions of 200 mg L−1 of TCP and

2. MATERIALS AND METHODS 2.1. Materials. Kaolinite was selected as a model for low permeability soil. This soil is characterized by its inertness, low hydraulic conductivity, lack of organic content, and low cation exchange capacity. The properties of this particular synthetic soil used in this study are provided in Table 1. The chemical selected as a pollutant was 2,4,6-trichlorophenol (TCP). It was of analytical grade and purchased from Sigma Chemical Co. The polluted soil sample was produced by mixing 841

dx.doi.org/10.1021/ie4028022 | Ind. Eng. Chem. Res. 2014, 53, 840−846


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Figure 2. Effect of the electric field on the pH changes monitored in the anode and cathode compartments during the EKSF tests. Full points, anode compartment. Empty points, cathode compartment (square, 0.25 V/cm; upright triangle, 0.75 V/cm; diamond, 1.25 V/cm; star, 2.00 V/cm; right pointing triangle, 4.00 V/cm).

of the electrodic oxidation and reduction of water, which develops according to well-known eqs 2 and 3. 1 H 2O + e− → H 2 + OH− (2) 2

Figure 1. Picture and layout of the bench scale EKSF assisted with GAC-PRB testing setup.

increasing amounts (0.25 to 1.50 g) of GAC until equilibrium was reached, while measuring the dissolved TCP concentration in water. 2.4. Experimental Procedure of EKSF Assisted with GAC-PRB. The TCP-polluted soil was moistened with the flushing liquid prior to insertion into the electrokinetic cell. The initial target moisture level for the kaolin was 27.3%. The anode and cathode compartments were filled with the same electrolyte-flushing liquid. Every experiment was initiated by applying a direct electric current. Five batch experiments, each 7 days in duration, were performed, using the applied voltage as the sole variable under study (5, 15, 25, 40, and 80 V). The electro-osmotic flux, TCP concentration, and temperature across the soil column, and the electrolyte pH and conductivity in the anode and cathode compartments were measured periodically during the experiments. 2.5. Sampling and Analysis. Liquid samples were periodically taken from the adsorption tests and the EK experiments through the sampling points. The TCP concentration was measured by HPLC using a C18−110 column of an Agilent 1100 analyzer (Agilent Technologies, Palo Alto, CA, USA). The pH was measured with a pH-meter GLP-22 (Crison). Electrical conductivity was measured with a GLP-31 conductometer (Crison). The TCP removal efficiency was calculated as follows: TCPremoval (%) =

(TCP0 − TCP) t 100 TCP0

1 O2 + 2H+ + 2e− (3) 2 These pH changes in the anodic and cathodic wells produce an acidic and basic front in the soil that may influence the mobility of the pollutants and water.27−30 These fronts are also known to seriously influence the various precipitation, dissolution, and ion exchange equilibria that may occur in the soil. In the case of TCP, the acid−base properties (eq 4) of the phenolate group of the molecule with a pKa of 6.15 has to be taken into account.31 H 2O →

C6H 2Cl3 − OH → C6H 2Cl3 − O− + H+

(4)

According to the measured pKa and pH, in the proximity of the anode, this phenolate group would be protonated and migration would be less favored than if in the proximity of the cathode, in which the negative charge of the phenolate would increase the mobility. This is not the only mechanism for the transport of TCP due to the dragging with the electro-osmotic flow and because diffusion explains the TCP transport. In the case of migration, the most important changes should occur in the direction cathode-to-anode because of the negative charge of phenolates. In the case of the dragging with electro-osmotic flow, the most important direction expected for the TCP transport is from anode-to-cathode. Another interesting parameter to be monitored in an electrochemically assisted soil remediation process is temperature. Figure 3 shows the temperature profile at the end of three of the tests (each corresponding to different electric fields within the assessed range). As can be observed, the application of an increased electric field produces a more significant increase in temperature with a clear profile, which can be explained by the electric heating associated to the ohmic loses in this type of process. The higher increase observed in the center of the experimental setup can be explained by the cooling effect of the flushing fluid added in the wells and also by the higher resistance (lower ionic conductivity) of the electrolyte, which makes the effect of the electric heating

(1)

where TCP0 is the TCP concentration at the beginning, and TCPt is the TCP concentration at the end of the experiments.

3. RESULTS AND DISCUSSION 3.1. pH and Temperature Evolution. In Figure 2, the changes in the pH of the anode and cathode wells during the different tests performed in this work are shown. Except for the experiment conducted at the lowest electric field, the pH changes followed the same trend for the entire applied electric field range: the analyte pH decreased to a constant value, approximately 2−3, while the catholyte pH increased to approximately 11−12.24,8,9 This result is a direct consequence 842



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Figure 4. Effect of the electric field on the electro-osmotic fluxes resulting in each EKSF experiment.

be possible that the relatively high pH values in the anode (not so acidic than the other tests) favored the electro-osmotic flux. veo = −

Dεoζ Ex η

(6)

3.3. TCP Removal. Figure 5 shows the TCP concentrations measured at the end of the electrochemical soil remediation Figure 3. Temperature profiles caused by ohmic drops during EKSF tests. (a) Effect of the electric field on the profiles (●, 0.25 V/cm; □, 2.00 V/cm; ▲, 4.00 V/cm). (b) Time course of the temperature profiles for an electric field of 4.00 V/cm (■, 0.0 h; ▲, 2.5 h; ●, 8.0 h; ◇, 1.0 d; △, 7.0 d).

more intense (eq 5). The greater the electric field is , the higher is the intensity and the greater are the ohmic losses. Temperature profiles have a great influence on many of the processes occurring in the soil remediation electrochemical cell affecting fluid viscosity, evaporation, and many other processes. This influence is usually direct and occasionally indirect, but it is clear that its effect should be promoted for greater electric fields. (5) W = IR Figure 3b shows the temperature dynamics in one of the tests carried out. It can be observed that heating was progressive and did not stabilize during the duration of the experiment. This change may have a significant importance in the treatment of volatile pollutants. However, according to the EPA,32 TCP should not be included in this category of pollutants because of its low Henry’s constant (4.0 × 10−6 atm m3 mol−1) 3.2. Electro-osmotic Flux. Figure 4 shows the changes in the electro-osmotic flux (quantified as the amount of water that was collected in the cathodic wells). While a linear trend was expected according to the Helmholz−Smoluchowski equation (shown in eq 6, where D stands for dielectric constant, εo for vacuum permittivity, ζ for the zeta potential, η for the fluid viscosity, and Ex for the potential gradient), a sigmoid curve was obtained. At this point, the low value obtained at the highest electric field could be explained by different causes: the increased water evaporation caused by the more important temperature profile, and also, more H+ are produced in the anode, migrating faster into the soil and acidifying the soil and depressing the electro-osmotic flux. On the other hand, to the authors’ knowledge, it is difficult to explain the high value obtained for the lowest electric field applied because the clay soil did not promote any type of hydraulic flux.33−35,12 It could

Figure 5. Concentration profile of TCP in the soil after a 1 week remediation test with an electric field applied of 2.00 V/cm: Average values (a) and dispersions (b) measured in each portion of the five monitoring sections used (monitoring portion in each section: ■, upper right; △, upper left; ▲, bottom right; □, bottom left).

treatment for each sample point for an experiment carried out at 2.00 V/cm (40 V), compared with the initially measured concentration. The data are presented against the position (on the anode−cathode axis) at which the samples were collected. In each position, four samples were collected to check for axial dispersion. In part b of Figure 5, the axial dispersion of data and 843



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are previously published efficiency data regarding removal of others CPs in soil. The results have been summarized in Table 3. One important point is the removal observed at position 5 where the barrier is placed. The higher the electric field is, the higher is the amount of TCP contained in the soil. This can be a consequence of the acidification of this zone caused by its proximity to the anode well (due to the lower mobility of the protonated phenolate) and because of the more efficient transport of TCP from the rest of the soil to the barrier. For every test conducted in this work, the treatment time was the same but the electric field was changed. In other words, in every test, a different charge and power were applied. This is very important in terms of the applicability of this technology because the cost associated with the treatment can vary significantly. In Figure 7, the total removal after the tests is

the range of this dispersion (i.e., the difference between the maximum and the minimum value measured at each distance from the electrodes) are also presented. It can be seen that the pollutant is efficiently removed from the soil and that a profile of TCP is clearly generated during the treatment. TCP amounts measured in each section are similar (low axial dispersion). Sampling point 2 had the highest dispersion and the lowest removal of TCP. This sampling point is far from the GAC permeable reactive barrier but is close to the cathode. This may explain the lower efficiency because it does not take advantage of both the dragging effect promoted in zone 1 and the migration-adsorption promoted in zone 5. The effect of the electric field on the removal of TCP can be observed in Figure 6. It can be seen that the greater is the

Figure 6. Effect of electric field on the removal of TCP by EKSF after a 1 week remediation test. (a) Concentration of TCP in each section after the remediation process; (b) maximum dispersion measured in each section (×, initial value in all tests; ■, 0.25 V/cm; ●, 0.75 V/cm; △, 1.25 V/cm; ▲, 2.00 V/cm; ◇, 4.00 V/cm). Figure 7. Removal efficiency of TCP by EKSF after a 1 week-long remediation test. (a) Effect of electric field; (b) effect of energy applied in each test.

electric field, the greater is the removal of TCP. Additionally, the position with the lowest removal appears to depend on the applied electric field. This is especially important for the greater electric fields, in which position 2 appears to display the poorest results. However, this is also the position with the higher dispersion, suggesting that many processes can influence the results. As indicated in the Introduction section, to date no similar studies about TCP removal were found. However, there

plotted against the electric field and against the energy consumption. As shown, the application of large electric fields is not worthwhile for this technology and only contributes to higher energy consumption. Only with energy consumption

Table 3. CPs Removal Results in Different EK/PRB Studies pollutant

soil

duration (d)

technology

voltage gradient (V cm−1)

removal best results (%)

ref

pentachlorophenol

spiked kaolin

EK/ZVI reduction

18

1.0

45−55

pentachlorophenol 2,4- dichlorophenol and Cd pentachlorophenol 2,4,6- trichlorophenol

spiked soil spiked sandy loam spiked soil kaolinite

EK/biobarrier EK/activated bamboo charcoal (adsorption) EK/Pd−Fe reduction EK/GAC adsorption

36−95 10.5

1.0 1.0

85 55

Reddy and Carry36 Harbottle et al.37 Ma et al.38

5−15 7

2.0 0.25−4.0

49 80

Li et al.24 this work

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below 200 kWh m−3 is it possible to obtain an efficient removal of TCP using this technology. A final important point is the adsorption capacity used of the GAC bed placed in the soil as a permeable reactive barrier. Figure 8 shows the amount of TCP in solution contained in the

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position of the GAC-PRB, almost no TCP was found in the electrolyte wells. Soil temperature profiles with time are very important and should be accounted for in the treatment of volatile pollutants. The granular activated carbon-permeable reactive barrier is very effective in the removal of TCP. During the experiment, only 10−25% adsorption capacity was used. The main path of change is a shift in the direction from anode-to-cathode. Dispersion in the axial direction is very small. The more significant dispersion is in the soil section at a greater distance from the PRB, but not in direct contact with the catholyte well.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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Figure 8. Characterization of TCP at the end of the EKSF tests: ■, TCP monitored in solution contained in the soil; □, TCP adsorbed according to the mass balance; ■, TCP adsorbed according to an experimental isotherm made off line with a pure solution of TCP; ∗, TCP desorbed from GAC bed after a treatment with methanol of the GAC contained in the barrier.

ACKNOWLEDGMENTS Financial support of the Spanish Government (Ministerio de Economiá e Innovación) through projects CTM2010-18833 and INNOCAMPUS is gratefully acknowledged.

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soil and the amount of TCP adsorbed according to the mass balance and according to an experimental isotherm from a separate experiment with TCP and the same activated carbon. The adsorption tests showed that the equilibrium between GAC and TCP under batch conditions was quickly reached, in less than two hours. According to that, the treatment time of the scale tests should have been enough in order to use all the capacity of the barrier. However, as observed, only 10−25% of the adsorption capacity is used in the results of the mass balance and of the isotherm (it should be noted that the isotherm was calculated at a constant temperature of 25 °C, while the temperature of the adsorption in the soil changes significantly as a consequence of the electric heating). In addition to the temperature influence, the heterogeneous structure of the soil could make the interaction between TCP and GAC particles difficult, and consequently it could be possible that the equilibrium in the barrier was not reached when the test concluded. Figure 8 also shows the amount of TCP desorbed after a treatment with methanol of the activated carbon contained in the barrier. Desorption efficiency is not an indication that other mechanisms (such as volatilization) do not influence the process. It is important to note that this irreversible adsorption process prevents the total recovery of TCP and that the degrees of recovery (i.e., in the 60−80% range) are sufficient to support this assumption.

REFERENCES

(1) Lu, X.; Yuang, S. Electrokinetic removal of chlorinated organic compounds. In Electrochemical Remediation Technologies for Polluted Soils, Sediments and Groundwater; Reddy, K. R.; Cameselle, C., Eds.; John Wiley & Sons Inc.: Hoboken, NJ, 2009; 223−227. (2) Choi, J. H.; Kim, Y. H.; Choi, S. J. Reductive dechlorination and biodegradation of 2,4,6-trichlorophenol using sequential permeable reactive barriers: Laboratory studies. Chemosphere 2007, 67, 1551− 1557. (3) Choi, J. H.; Choi, S. J.; Kim, Y. H. Hydrodechlorination of 2,4,6trichlorophenol for a permeable reactive barrier using zero-valent iron and catalyzed iron. Korean J. Chem. Eng. 2008, 25, 493−500. (4) Cong, Y. Q.; Ye, Q.; Wu, Z. C. Electrokinetic behaviour of chlorinated phenols in soil and their electrochemical degradation. Process Saf. Environ. Prot. 2005, 83, 178−183. (5) Puyol, D.; Mohedano, A. F.; Sanz, J. L.; Rodriguez, J. J. Comparison of UASB and EGSB performance on the anaerobic biodegradation of 2,4-dichlorophenol. Chemosphere 2009, 76, 1192− 1198. (6) EPA, U. http://www.epa.gov/safewater (accessed 2013). (7) Gimeno, O.; Carbajo, M.; Beltrán, F. J.; Rivas, F. J. Phenol and substituted phenols AOPs remediation. J. Hazard. Mater. 2005, 119, 99−108. (8) Ahuja, D. K.; Bachas, L. G.; Bhattacharyya, D. Modified Fenton reaction for trichlorophenol dechlorination by enzymatically generated H2O2 and gluconic acid chelate. Chemosphere 2007, 66, 2193−2200. (9) Wang, C. C.; Lee, C. M.; Lu, C. H.; Chuang, M. S.; Huang, C. Z. Biodegradation of 2,4,6-trichlorophenol in the presence of primary substrate by immobilized pure culture bacteria. Chemosphere 2000, 41, 1873−1879. (10) Gomes, H. I.; Dias-Ferreira, C.; Ribeiro, A. B. Electrokinetic remediation of organochlorines in soil: Enhancement techniques and integration with other remediation technologies. Chemosphere 2012, 87, 1077−1090. (11) Virkutyte, J.; Sillanpaa, M.; Latostenmaa, P. Electrokinetic soil remediationCritical overview. Sci. Total Environ. 2002, 289, 97−121. (12) Yeung, A. T. Contaminant extractability by electrokinetics. Environ. Eng. Sci. 2006, 23, 202−224. (13) Yeung, A. T.; Gu, Y. Y. A review on techniques to enhance electrochemical remediation of contaminated soils. J. Hazard. Mater. 2011, 195, 11−29.

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CONCLUSIONS From this work, the following conclusions can be drawn: Removal of TCP by electrokinetic soil flushing assisted with GAC PRB is a very efficient process. More than 80% of the TCP contained in the soil can be removed in less than 1 week of operation with an energy consumption below 200 kWh m−3. The two main mechanisms to explain the transport of TCP are the dragging by electro-osmotic flow in cathodic wells and the electromigration to anodic wells. Because of the significant importance of migration and to the 845



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