Electrokinetic Soil Remediation Research Articles

Assessing the Effect of Weak and Strong Acids as Electrolytes in the Removal of Cesium by Soil Electrokinetic Remediation

The removal of cesium from artificially contaminated soil using electrokinetic remediation with nitric and acetic acid as electrolytes had been evaluated. In this study, uncontaminated soil was taken from four different sampling points (i.e., A, B, C, and D) in Kotagede, Yogyakarta, Indonesia. All samples were prepared as cesium contaminated soil (100 mg CsCl/kg soil), which have similar physicochemical characteristics with Fukushima soil, Japan. The electrokinetic remediation (EKR) was conducted using a graphite electrode in a constant voltage of 1.0 Vcm–1 for 7 days without electrolyte pH control, with 1.0 M nitric and acetic acid as electrolytes. The current profile during the EKR was recorded by a data logger for every 10 min. The remaining cesium in the soil was measured by a flame atomic absorption spectrophotometer at a wavelength of 852.1 nm. The results showed that the type of acid used in the experiments affected the removal of cesium. The highest cesium removal was achieved when nitric acid was used in the experiment and then followed by acetic acid. For all acids, the removal ability of cesium from soil was in the following order: soil C > soil A > soil D > soil B.

Application of Biosurfactants and Pulsating Electrode Configurations as Potential Enhancers for Electrokinetic Remediation of Petrochemical Contaminated Soil

The remediation of soil contaminated with petrochemicals using conventional methods is very difficult because of the complex emulsions formed by solids, oil, and water. Electrokinetic remediation has of recent shown promising potential in the removal of organics from contaminated media as calls for further improvement of the technology are still made. This work investigated the performance of electrokinetic remediation of soil contaminated with petrochemicals by applying fixed electrode configurations and continuous approaching electrode configurations. This was done in combination with bioremediation by inoculating hydrocarbon degrading bacteria and biosurfactants with the aim of obtaining an improved method of remediation. The results obtained show that the biosurfactant produced by the hydrocarbon degrading bacteria Pseudomonas aeruginosa was able to enhance oil extraction to 74.72 ± 2.87%, 57.375 ± 3.75%, and 46.2 ± 4.39% for 185 mm fixed electrodes, 335-260-185 mm continuous approaching electrodes, and 335 mm fixed electrode configurations, respectively. By maintaining high current flow, the 335-260-185 mm continuous approaching electrodes configuration enhanced electroosmotic flow (EOF) on every event of electrodes movement. The fixed electrode configuration of 185 mm provided amiable pH conditions for bacterial growth by allowing quick neutrality of the pH due to high EOF as compared to the 335 mm fixed electrodes configuration. After 240 h, the carbon content in the soil was reduced from 0.428 ± 0.11 mg of carbon/mg of the soil to 0.103 ± 0.005, 0.11355 ± 0.0006, and 0.1309 ± 0.004 for 185 mm, 335-260-185 mm, and 335 mm, respectively. The application of biosurfactants and continuous approaching electrodes reduced the energy expenditure of electrokinetic remediation by enhancing the decontamination process with respect to time.

Cadmium adsorption behavior of porous and reduced graphene oxide and its potential for promoting cadmium migration during soil electrokinetic remediation

In this study, a porous reduced graphene oxide (PRGO) carbon nanomaterial was successfully obtained by activation of natural graphite with KOH at high temperature and was applied as an auxiliary electrode in soil electrokinetic remediation to investigate the promoting effect on Cd migration. We found that PRGO contained a large amount of oxygen-containing groups (hydroxyl and carboxyl groups) and exhibited high Cd2+ adsorption efficiency at pH values above 4, achieving a maximum adsorption capacity of 434.78 mg/g for Cd. In addition, PRGO could selectively adsorb Cd, Pb, Cu, and Zn but not K, Na, or Mg from soil solution. The electrokinetic remediation experiment showed that the PRGO auxiliary electrode promoted the migration of Cd and effectively controlled the increase in soil pH near the cathode, possibly due to ion exchange between the surface functional groups on the auxiliary electrode and Cd2+. In addition, the location of the PRGO auxiliary electrode strongly influenced the migration of Cd. For instance, the soil Cd concentration of treatment H-5 was 57.86% lower than that of H-0 at a distance of 5–10 cm from the electrode; however, the soil Cd concentration measured at 0–5 cm for treatment H-5 was 34.84% higher than that of treatment H-0. Our study demonstrated that PRGO could be applied as an auxiliary electrode to promote Cd migration during electrokinetic remediation of Cd-contaminated soil.

Strategies for powering electrokinetic soil remediation: A way to optimize performance of the environmental technology

The electro-kinetic remediation of soils using different powering strategies has been studied, in order to clarify which is the best strategy to couple solar powering with this remediation technology, in a context of developing more sustainable electrochemical remediation technologies. Direct powering from photovoltaic panels (Case a), application of constant electric fields with the same average value of Case a (Case b) and application of constant specific power with the same average value of Case a (Case c) have been compared. Results show an outstanding influence of the powering strategy on the removal efficiency of clopyralid (model of herbicide used in this work). The direct use of solar power profiles obtained the lowest removal efficiencies, which contrasts with the higher expected sustainability of this powering strategy. Reversion of pollutant transport overnight and extreme electric field values at noon help to explain the lower efficiency of this strategy. Evaporation mechanisms are promoted by operating at extreme large electric fields. In addition, harsher conditions lead to a higher negative soil affectation in terms of regions affected by extreme pHs, water contents and/or conductivities and to lower specific pollutant removals. Therefore, maximum efficiencies were found for Case b (constant electric potential gradient) with a total removal over 110 g kWh−1 and only a slight affectation into the final soil properties.

Remediation of Copper Contaminated Soils Using Water Containing Hydrogen Nanobubbles

This basic research study was undertaken to use ecofriendly nanobubbles that can improve the electrokinetic remediation of copper-contaminated soil, as well as to determine that remediation efficiency. The nanobubbles were generated by using pressurized hydrogen gas, and the quantity of hydrogen gas bubble that remained over 14 days was measured. The generated nanobubbles were used as an enhancer to remove a heavy metal on contaminated soil, and their applicability was confirmed. A batch test was used to compare the remediation effects of nanobubbles and distilled water on copper-contaminated soil. The results proved that the nanobubbles are a proper desorption agent for copper-contaminated sand and clay specimens. The solid–liquid ratio and the contact time for desorption of the sand and clay were then respectively determined. A large amount of effluent was obtained from electrokinetic remediation of the sand sample after applying the nanobubbles as an enhancer. The remediation efficiency demonstrated with sand proved to be higher than that for clay. This greater efficiency was attributed to a wider specific surface area, demonstrating the potential use of the nanobubbles as an enhancer for soil contaminated by copper with a large amount of effluent outflow. It was also assumed to be affected by the moving capability of the nanobubbles in the soil layer. Thus, the nanobubbled water can be used to improve the removal of heavy metals from contaminated soils. An ecofriendly enhancer for electrokinetic remediation with a relatively large void ratio and fast flowrate was confirmed by the nanobubbles.

Response Surface Method Analysis on Electro-Enhanced Technique for Remediation of Cadmium Contaminated Soil

In view of the problems of long remediation time, high energy consumption and low remediation efficiency in electrokinetic remediation of heavy metal contaminated soil, Cd was used to simulate heavy metals in contaminated soil, and response surface method (RSM) was used to optimize the factors influencing electrokinetic remediation. Central Composite (CCD) experimental design method was taken to study the effects of electric field strength, remediation time and water content on removal rate of Cd in soil. Also, polynomial regression mathematical model and optimal reaction conditions were provided for Cd pollution in electrokinetic soil remediation. The simulated equation F was 15.67, the correlation coefficient was 0.9338, and the adjustment correlation coefficient was 0.9042, indicating good regression and strong significance of the equation. The model results showed that, for the optimal experimental conditions, electric field strength was 2.25V·cm-1, the remediation time was 120.79h, and the water content was 17.06%. On the basis of such reaction condition, intermittent current flow method was adopted d to further enhance the electrokinetic remediation effect. The cadmium removal rate in the soil was increased by 3.17%, 2.86% and 2.43%, respectively, and the electric energy consumption was decreased by 10.54%, 11.28% and 9.97%, respectively, suggesting that the method could effectively improve the removal rate of Cd and reduce energy consumption.

Time-lapse monitoring of an electrokinetic soil remediation process through frequency-domain electrical measurements

The electrokinetic (EK) method is an emerging technique for soil remediation, even though a monitoring system of the contaminant removal through geophysical methods has not been developed yet. In this paper, frequency-domain time-lapse measurements are used on heavy-metal contaminated sediments for monitoring an EK remediation process in a small-scale measuring cell. Our goal is to monitor the development of the electrokinetic process within the sediment and to evaluate the total time needed for the treatment. In fact, frequency-domain electrical monitoring provides complex resistivity spectra at different time steps that can be correlated to changes in the physical properties of the sediments. We perform laboratory spectral induced polarization (SIP) measurements on different samples before, during and after the EK treatment, using different electrolyte solutions (acids and tap water), commonly employed in EK remediation. Direct-current measurements (resistivity and chargeability) were also acquired on one sample for testing the reliability of the system by a comparison with a widespread commercial instrumentation for field measurements.Results indicate that resistivity is a diagnostic parameter as long as it is linked to changes in water saturation, pH and ionic concentration and not to the percentage of metal extraction. The resistivity exhibited well-defined signatures as a function of time that changes depending on the conditioning agent and the grain size distribution. These peculiarities were used to understand the physical processes occurring within the cell and consequently to assess the effectiveness of the electrokinetic treatment.Conversely, the polarization effect was negligible using acids as conditioning agents at the electrolyte chambers. Therefore, the SIP method is not effective under these conditions, being the polarization effect significant only when tap water was used at both ends of the measuring cell. In this case, we were able to correlate changes in water saturation with the time-shift observed on relaxation time distributions (RTDs) after inversion of SIP data and to observe, using normalized chargeability, that polarization is stronger at high pH values.On these basis, resistivity is suitable to monitor the development of the remediation, to optimise the energy levels required for treatment and to assess the end time of the EK process (time when metal mobilization ends). In fact, the end time of treatment can be associated with the time at which resistivity becomes stable. This time is highly dependent on the particular working conditions and sediment grain size as demonstrated by our experiments.

The mechanism of acid-washed zero-valent iron/activated carbon as permeable reactive barrier enhanced electrokinetic remediation of uranium-contaminated soil

Zero-valent iron/activated carbon (ZVI/AC) particles can promote the reduction of U(VI) by micro-electrolysis. Therefore, they can be used to develop materials for permeable reactive barrier (PRB). In this study, citric acid (CA) mixed with ferric chloride (FeCl3) was selected as composite electrolyte, and we investigated the feasibility of electrokinetic (EK) coupled with Fe/C-PRB on the remediation of red soil artificially contaminated with U(VI). Seven EK experiments were conducted to study the effect of the type, location, and amount of PRB media on the removal of U(VI) in soil by the EK-PRB system. The results showed that the ZVI/AC mixture is superior to the single ZVI or AC as the PRB medium. For the EK-PRB system, a moderate increase in the number of PRBs and decrease in the thickness of the PRB in soil chamber can enhanced the removal of U(VI) from the contaminated soil. Under optimized conditions, after the 120 h remediation experiment obtained the maximum removal efficiency (80.58 ± 0.99%) of U(VI). Scanning electron microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to study the surface properties of the ZVI/AC mixture before and after the reaction. The results demonstrated that the soluble U(VI) was reduced to the insoluble U(IV) in the ZVI/AC mixture, or adsorption of activated carbon or iron corrosion products regardless of the pH distribution. This work provides a green efficient technology for the recovery of U(VI) from contaminated soil, waste slag or solid waste.

M4EKR, Multiphysics for ElectroKinetic Remediation of Polluted Soils

Electrokinetic soil remediation (EKR) is one of the most promising techniques for decontamination of low permeability soils, in which the most classical techniques have been found to be less efficient. However, its practical application on a real scale has been rather limited since the phenomena involved in these processes are very complex. For this reason, it is essential to use numerical models that allow us to know the main trends in the behaviour of soils and natural waters subjected to EKR processes. This study presents the numerical model M4EKR (Multiphysics for ElectroKinetic Remediation). The M4EKR module is a reactive transport model for partially saturated soils that allows reproducing the transport of species due to electroosmosis, electromigration, diffusion and advective flow. The model was completely implemented in COMSOL Multiphysics, a partial differential equation solver. The system of differential and algebraic equations to solve the chemical and transport problem was fully defined by the authors, and they were solved by the M4EKR module in COMSOL (monolithic approach). The scope of the model is illustrated by simulating an EKR process of a natural soil and porewater contaminated with a polar pesticide: 2,4-Dichlorophenoxyacetic acid. For simplicity, the M4EKR version used in this study does not include gas transport, it does not consider the deformability of the soil and it is assumed the processes occur under isothermal conditions.

Mechanisms of electrokinetic technology to remediate different soils contaminated by cadmium

Five typical soils were selected as Cd-contaminated media in an electrokinetic remediation experiment, to reveal comprehensive relationships between soil physicochemical properties and electrokinetic remediation. Results showed that after 20 days of remediation, removal efficiencies of Cd from red soil, black soil, yellow brown soil, fluvo-aquic soil, and paddy soil were 80.8%, 79.3%, 78.2%, 62.7%, and 74.1%, respectively. Levels of soil pH, conductivity, cation exchange capacity in fluvo-aquic soil and paddy soil treatments were generally higher than the other three types of soils, which indicated some connections between Cd removal efficiencies and the above soil characteristics. Pearson correlation analysis showed that soil H+ concentration was significantly correlated with Cd concentration and soil cation exchange capacity, and the correlation coefficients were -0.462 and -0.457, respectively. It is confirmed that H+ concentration is one of the important factors affecting the electrokinetic remediation of soil polluted by Cd.

Electrokinetic remediation of uranium(VI)-contaminated red soil using composite electrolyte of citric acid and ferric chloride.

In the process of electrokinetic (EK) remediation of uranium-contaminated soil, the existence form of uranium in soil pore fluid will affect on its migration behavior. In this paper, a novel type of electrolyte (citric acid + ferric chloride, CA+ FeCl3) has been investigated for the EK remediation of uranium-contaminated red soil. The effects of different electrolyte and the concentrations of FeCl3 on migration behavior of U(VI) and environmental risks were investigated after EK remediation. The result showed that the optimum concentration was 0.1mol/L CA mixed with 0.03mol/L FeCl3 in this study. At this time, the removal efficiency of uranium was about 61.55 ± 0.41%, and the cumulative energy consumption was 0.2559kWh. Compared with deionized water and single CA, combined CA with FeCl3 has the advantages of high removal efficiency, low leaching toxicity, and less damage to the soil after the electrokinetic remediation treatment.

Reducing Agents Enhanced Electrokinetic Soil Remediation (EKSR) for Heavy Metal Contaminated Soil

Reducing agents-Enhanced electrokinetic Soil Remediation (EKSR) was performed for the removal of chromium (Cr), cobalt (Co) and nickel (Ni) from contaminated soil. The reducing agents oxalic acid and ascorbic acid were investigated under constant voltage gradient (2.0 V/cm), current changes, pH, redox potential, concentration changes and removal performance of Heavy Metals (HMs). The results indicated that the reducing agents were effective in the desorption of metals at the cathode with catholyte conditioning pH. The removal performance of heavy metals in reducing agents-enhanced EKSR was about 2-2.5 times more than in unenhanced treatment. The amount of HMs migrated to the catholyte was more than in the anolyte, which might be evidenced that the negatively charged metal-oxalate/ascorbate complexes migrated via electroosmosis. However, positively charged HM-oxalate/ascorbate complexes and free HM cations moved to the catholyte by electromigration action. Furthermore, the mass balance and cost analysis were performed for all EKSR experiments after 20 days of operation. The energy consumption per cubic meter of treated soil was 1104-18496 kWh/m3 and the total cost was about US$ 110.4-2095, including the cost of the enhancing agents. The study demonstrated that reducing agents-enhanced EKSR is cost-effective and efficient in the removal of HMs from contaminated soil.

Enhanced electrokinetic remediation and simulation of cadmium-contaminated soil by superimposed electric field

The ‘focusing’ effect has become a limiting factor for the removal of heavy metals from soils by electrokinetic (EK) remediation. A superimposed electric field EK (SE-EK) method is proposed to address this problem. Two sets of fixed electrodes placed at different positions were switched to move the ‘focusing’ region of Cd to the cathode by controlling the location of the pH jumping front. Moreover, a model was established to simulate and optimize the process of Cd transport in soil under the superimposed electric field. Results showed that, after 35 d of SE-EK remediation, Cd was mainly accumulated in the soil section near the cathode (S5), where the acid and alkaline fronts converged. The removal rate of Cd in the soil sections from S1 to S4 reached 87.60%, which was 6.13 times that in conventional EK remediation. Meanwhile, the energy utilization efficiency in SE-EK was 6.38 times that in conventional EK. The pH changes and Cd distribution during the SE-EK experiment were simulated well, with good agreement between the modeled and experimental data. The removal of Cd in SE-EK remediation could therefore be optimized through simulating the distribution of Cd in five situations with differences in switching time and electrode position. This research provides valuable technical support for effective EK remediation of heavy metal contaminated soil.

Application of a multi-electrode system with polyaniline auxiliary electrodes for electrokinetic remediation of chromium-contaminated soil

In this study, a polyaniline (PANI) composite supported by nonwoven fabric was synthesized and applied as an auxiliary electrode in conventional electrokinetic remediation for the first time to investigate the effectiveness of the multi-electrode system in remediating Cr-contaminated soil. Firstly, PANI was successfully combined with nonwoven fabric and has a good adsorption performance for chromium (VI) in aqueous solution, which is highly dependent on the pH of the solution. Then a series of electrokinetic experiments with four different auxiliary electrode configurations were conducted to evaluate Cr (VI) removal and its migration behavior. The results show that the Cr (VI) removal can be up to 20% higher than that of the conventional electrokinetic remediation with the existence of auxiliary electrode. And the mechanism about it was the combined effect of electromigration and the adsorption of PANI. The role of PANI auxiliary electrode was more than an adsorbent, but also an accelerator for Cr (VI) migration to the anode, which means it can intercept and adsorb the heavy metal ions passed through during strengthening the electrolysis process. The acidic environment of anode is more favorable for PANI auxiliary electrode’s adsorption, but the most effective and economical arrangement about it was on the cathode side with less energy consumption of 115 kW·h/g. Because the effect of the particle acceleration of the PANI auxiliary electrode was greater than that of the adsorption. This multi-electrode system should also be applicable for the removal of anionic chemicals from contaminated soils.

Effect of chemical additives on electrokinetic remediation of Cr-contaminated soil coupled with a permeable reactive barrier.

Chromium (Cr) contamination in soil, especially Cr(VI), is a serious threat to the environment and human health. The electrokinetic remediation (EKR) is a promising technology to remediate the Cr(VI). Therefore, in this study, EKR coupled with a permeable reactive barrier (PRB) was used to treat the Cr(VI)-contaminated soil. The CTMAB-Z, a modified zeolite (prepared with cetyltrimethyl ammonium bromide) alone and a mixture of CTMAB-Z and Fe(0) were used as PRB-1 and PRB-2 reactive media, respectively. The effect of chemical enhancers/additives, i.e. DL-tartaric acid and Tween 80 on EKR of Cr(VI) was also analysed in the contrasting experiments. While the effects of repair time, voltage gradient and DL-tartaric acid concentration on Cr(VI) remediation were investigated by using the multifactor orthogonal experiment which was based on contrasting experiments. The contrasting experiment results showed that the highest Cr(VI) removal rate (66.27%) and leaching efficiency (71.29%) were observed in the experimental group which had DL-tartaric acid and PRB-2. Furthermore, the multifactor orthogonal experiment results had depicted that the highest Cr(VI) removal rate (80.92%) and leaching efficiency (85.25%) were achieved after treating the samples at a voltage gradient of 2.5 V cm−1 for 8 days in the presence of 0.15 M concentration of DL-tartaric acid. This study demonstrated that Cr(VI) remediation through EKR process could be significantly enhanced by the use of PRB and additives.

Electrokinetic remediation of antibiotic-polluted soil with different concentrations of tetracyclines.

This study investigated the efficacy of electrokinetic remediation of soils polluted with different concentrations of tetracyclines (TCs). Three widely used TCs (oxytetracycline, chlortetracycline, and tetracycline) were selected, and concentrations of 0, 5, 10, 20, and 50mg/kg (C0, C5, C10, C20, C50) were selected for comparison. Antibiotic-polluted soils with no electric field served as controls. The average removal rates of TCs in different treatments ranged from 25 to 48% after 7-day remediation. The contributing ratios of electrokinetics to TCs removal varied from 22 to 84%. The concentrations of NH4+ increased in soils and electrolytes, which indicated the decomposition of TCs in the electric field. The highest removal amount of TCs was obtained in the C50 treatment, due to efficient reactions of TCs with oxidative radicals generated during the electrolysis. The fluctuant range of pH in the electrolytes was decreased with increasing concentration of TCs, while the soil pH was increased. The removal rate of antibiotic-resistant bacteria (ARB) in the C5 treatment was significantly higher than that in other treatments. The abundance of antibiotic resistance genes (ARGs) increased with the concentrations of TCs in soils. It might result from the induction of increasing selective pressure of antibiotics. Significant removal of ARGs occurred in the C50 treatment (38-60%). In terms of controlling ARB and ARGs, which were more resistant, the electrokinetic technology showed advantageous effects. Above all, electrokinetic technology provides an effective remediation method, especially for TC-polluted soil with a concentration of 20-50mg/kg.

Mitigation of Contamination Levels and Ecological Risk of Toxic Metal Contaminated Soil using CA-EKSR Process

Many studies have focussed on decontamination of the soil by incorporating electrokinetic technologies. However, these not considered to determine the contamination and decontamination levels before and after treatment. We addressed this problem and determined the decontamination levels of toxic metals(TMs) after treatment. In this study, TMs contaminated granite mining soil was treated with the chelating agents and electrokinetic soil remediation (CA-EKSR) process. After 20 days of treatment, we determined the decontamination levels and ecological risk indices of TMs through pollution index (PI), Geoaccumulation index (Igeo) and potential ecological risk indes (RI). The removal performance of TMs was found in CA-EKSR (cirtric acid and EDTA as chelating agents) treatment about 5-6 times ore than when conventional treatment. The overall ecological risk index (RI) was reduced from 224 to 35.6, after treatment with chelating agent, which indicated that the soil has low environmental risk. It is observed that the CA-EKSR treatment was an effective in the remediation and mitigation of TMs from contaminated mining waste. The study is useful for the researchers to investigate the soil quality, contamination levels and ecological risk indices particularly in the soil decontamination studies

Calcite buffer effects in electrokinetic remediation of clopyralid-polluted soils

This work presents a study of the dissolution-precipitation processes of calcite in soil undergoing electrokinetic remediation processes. For this purpose, a numerical inspection of one of these processes in a calcareous soil (10% calcite content) contaminated with an of the organochlorine acid herbicide (3,6-dichloro-2-pyridinecarboxylic acid) was carried out. The numerical tool used to perform this analysis was the Multiphysics for EKR (M4EKR), a module programmed by the authors in the COMSOL Multiphysics platform. A detailed analysis of the pH, the distribution of species that have a significant influence on soil buffering capacity (carbonates and calcite), as well as the pollutant, has been performed. In this way, the kinetics of the calcite dissolution-precipitation processes have been analysed in order to determine the pH of the water in the pores and, therefore, how it directly affects the effectiveness of the treatment. Additionally, a sensitivity analysis of the selected EKR process has been carried out at different values of the rate of calcite dissolution due to the uncertainty associated with the reactive surface area parameter.

Application of iron-loaded activated carbon electrodes for electrokinetic remediation of chromium-contaminated soil in a three-dimensional electrode system

Hexavalent chromium from industrial residues is highly mobile in soil and can lead to the contamination of groundwater through runoff and leaching after rainfall. This paper focuses on the three-dimensional (3D) electrokinetic remediation (EKR) of chromium-contaminated soil from an industrial site. Activated carbon particles coupled with Fe ions (AC-Fe) were used as the third electrode. The optimum dose ratio of the electrode particles and remediation time were selected on the basis of single-factor experiments. X-ray photoelectron spectroscopy (XPS) analysis was carried out to explore the reduction of Cr(VI) on the surface of the electrode particles (AC-Fe). The results showed that AC-Fe had a positive effect on Cr(VI) reduction with a removal rate of 80.2%, which was achieved after 10 d by using a 5% dose of electrode particles. Finally, it was concluded that the removal mechanism combined the processes of electromigration, electrosorption/adsorption and reduction of Cr(VI) in the 3D EKR system.

Enhanced electrokinetic remediation of polluted soils by anolyte pH conditioning

In the treatment of a polluted soil, the pH has a strong impact on the development of different physicochemical processes as precipitation/dissolution, adsorption/desorption or ionic exchange. In addition, the pH determines the chemical speciation of the compounds present in the system and, consequently, it conditions the transport processes by which those compounds will move. This question has aroused great interest in the development of pH control technologies coupled to soil remediation processes. In electrokinetic remediation processes, pH has usually been controlled by catholyte pH conditioning with acid solutions, applied to cases of heavy metals pollution. However, this method is not effective with pollutants that can be dissociated in anionic species. In this context, this paper presents a study of the electrokinetic remediation of soils polluted with 2,4-Dichlorophenoxyacetic acid, a common polar pesticide, enhanced with an anolyte pH conditioning strategy. A numerical study is proposed to evaluate the effectiveness of the strategy. Several numerical tests have been carried out for NaOH solutions with different concentrations as pH conditioning fluid. The results show that the anolyte pH conditioning strategy makes it possible to control the pH of the soil and, consequently, the chemical speciation of pollutant species. Thus, it is possible to achieve an important flux of pesticide into the anolyte compartment (electro-migration of anionic species and diffusive transport of acid species). This way, it possible to maximise the pesticide accumulation in this compartment, allowing a much more effective removal of pollutants from the soil than without the anolyte pH conditioning strategy.