Conventional Electrokinetic Remediation Research Articles

New-style electrokinetic-adsorption remediation of cadmium-contaminated soil using double-group electrodes coupled with chitosan-activated carbon composite membranes

Global soil cadmium (Cd(II)) contamination threatens the soil environment, food safety, and human health. Conventional electrokinetic remediation (EKR) and enhancement methods usually operate in strong electric fields, leading to strong side reactions and uneven removal. In this work, to remove Cd(II) from soil effectively in a low-voltage electric field, a new-style electrokinetic-adsorption remediation using double-group electrodes coupled with chitosan-activated carbon composite membranes (DE-EKR-CAC) was developed. Chitosan-activated carbon (CAC) composite membranes were synthesized for easy recovery and reuse of adsorbents. The effects of pH, contact time, initial concentration, and foreign ions on the removal of Cd(II) by the CAC composite membranes were determined. The CAC composite membranes performed well except in a strongly acidic environment (pH = 2.0). The soil pH varied between 3.4 and 5.0 in DE-EKR-CAC, where the CAC composite membranes were applicable. High concentrations of Ca2+ interfered with the adsorption of Cd(II), which means that the selectivity of CAC composite membranes for Cd(II) is not high enough. The Langmuir (R2 = 0.999) and pseudo-second-order kinetic (R2 = 1.0) models revealed the monolayer coverage and chemisorption mechanism, and the maximum adsorption capacity was 40.81 mg/g. Furthermore, SEM, FTIR, and XPS analyses suggest that physical adsorption, complexation of oxygen-containing functional groups, chelation of amino groups, and ion exchange are potential mechanisms for the adsorption of Cd(II) on CAC. DE-EKR-CAC performed better than the group remediated with one set of electrodes, with higher removal efficiencies and more uniform removal. The lowest energy consumption was 3.33 kWh/m3, which is lower than other enhancement methods. Separation of CAC composite membranes from soil is easy, and reuse performance is good. DE-EKR-CAC provides a potential option for Cd(II) removal from soil because of its better performance using low-voltage direct current, low energy consumption, and ease of recycling the adsorbent.

Ecological assessment of different electrokinetic remediation strategies: a pilot scale study

The electrokinetic remediation method can function as a primary or secondary technology and can be applied in conjunction with other physical and biological methods, such as soil washing, phytoremediation, and bioremediation. Environmental impacts arising from the electrokinetic remediation process can be determined using life cycle assessment analysis (LCA) or other tools. This study compared the conventional electrokinetic remediation strategy with two hybrid strategies: electrokinetic-phytoremediation (EKR-Phyto) and electrokinetic-bioremediation (EKR-Bio). The environmental performance of the three strategies is then tested through LCA analysis. The database used was The Ecoinvent, and the freeware software used during the inventory stage was OpenLCA. The impact assessment stage was used in the Recipe I (2016) midpoints, Available Water Remaining (AWARE) midpoint, Intergovernmental Panel Climate Change (IPCC) midpoint (2003), UNEP Society of Environmental Toxicology (USEtox) midpoint, and cumulative energy demand midpoint. The significance of the analysis results was not obtained for the GWP parameter but for the freshwater eutrophication parameter. Among the three strategies, the EKR-Phyto strategy showed the highest significance in eutrophication but the lowest significance in land change. Substitution of chemical fertilizers into natural fertilizers in the EKR-Phyto strategy can be an opportunity for environmental sustainability. The highest impact for ecological analysis of the three strategies was EKR-Phyto in terms of GWP, the sum of primary energy, Acidification Potential (AP), and Photochemical Ozone Creation Potential (POCP).

Removal of Organic Pollutants Via Electrochemical Oxidation Near Anodes During Electrokinetic Remediation: Proof of Concept

This study designed a practical approach of separating electrodes chambers to prove the influence of electrochemical oxidation on pyrene removal during electrokinetic (EK) remediation. The anode and cathode electrodes were arranged in two independent soil chambers, and the soil chambers were connected by salt bridges. Salt bridges electrokinetic (SBEK) remediation avoided acid–base neutralization and facilitated the intensity of the current. The results showed that 99.5% of pyrene was removed within 7 days in anodic chamber. The removal rate of pyrene was ∼99.6–99.9% at SBEK1 anode and 29.5–36.2% at SBEK1 cathode after 42 days. The changes in current, pH, and redox potential values indicated that an efficient “oxidizer” was formed in the anode chamber. Compared with conventional EK remediation, SBEK can take place under a suitable oxidizing condition because of increasing current intensity and decreasing soil pH in the anode chamber. Furthermore, SBEK with electrode polarity reversal test had better decontamination efficiency of pyrene than fixed electrodes. Removal rate of pyrene increased to 62.9% after 14 days with polarity reversal; correspondingly, the energy consumption of SBEK test was ∼13 times higher than that of the conventional EK test. The novel application of separated electrodes chambers appears to be a viable strategy for removing organic pollutants.

Enhanced Electrokinetic Remediation of Cadmium (Cd)-Contaminated Soil with Interval Power Breaking

This study compared electrokinetic (EK) remediation with and without interval power breaking in the removal of total and plant available cadmium (Cd) in the soil. Two laboratory experiments, i.e. EK remediation with interval power breaking (24–12 h power-on-off cycles) and conventional EK remediation (continuous power supply), with the same accumulated time (192 h) of power supply, were conducted to remove soil Cd. After the EK remediation with interval power breaking, the total Cd removal efficiency in the soil rose to 38%, in comparison to 28% after the conventional EK remediation. As for the plant available Cd, the removal efficiency was enhanced from 52 to 63%. Additionally, the electric current during the EK remediation and electric conductivity after the EK remediation were higher in the soil treated by interval power breaking, which indicated an enhanced desorption and/or migration of charged species. It further meant that the higher removal efficiency of soil Cd by interval power breaking could be related to the enhanced desorption and/or migration of Cd species. This study indicated that both conventional EK remediation and EK remediation with interval power breaking were effective methods to remove soil Cd but EK remediation with interval power breaking was more efficient.

Influence of polarity exchange frequency on electrokinetic remediation of Cr-contaminated soil using DC and solar energy

Electrokinetic remediation (EKR) is a remediation method that can effectively remove heavy metals from soil. Traditional EKR uses an external power source to consume electrical energy, in the present study, through the experiment of different electrode exchange frequency to remediate Cr contaminated soil, the effect of polarity exchange electric remediation and the influencing factors of Cr(VI) to Cr(III) conversion are discussed. Five experiments were conducted using DC power supply with conventional EKR (T1), DC power supply with polarity exchange EKR (T2, T3) and solar energy with EKR (T4, T5). The results showed that the T1 experiment had the maximum removal rate of total Cr (42.03 %) and Cr(VI) (85.50 %) but had an adverse effect on soil pH. T2, which exchanged polarity every 24 h, and T3, which exchanged polarity after 84 h, had smaller adverse effects on soil pH, but the removal efficiency was reduced due to repeated migration. The reduction of Cr(VI) to Cr(III) occurred during the EKR processes, the content of Cr(III) increased greatly. Furthermore, few differences were observed between DC power and solar power on the EKR experiments. Therefore, the combination of electrokinetics and solar energy is a feasible method for Cr-contaminated soil.

Application of UV radiation for in-situ Cr(VI) reduction from contaminated soil with electrokinetic remediation

Restoring hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) from contaminated soil is a cost-effective alternative for attenuating Cr(VI) toxicity to the ecosystem. A new electrokinetic remediation (EKR) system with UV light was explored to overcome an energy barrier to catalyze Cr(VI) reduction from the surface soil near the anodic reservoir. Natural organic matters and minerals from the contaminated soil acted as electron donors and catalysts for Cr(VI) photo-reduction and no additional chemical reagent. There was almost no residual Cr(VI) in anolyte after UV/EKR compared with the conventional EKR. The reduction improved the efficiency of EKR in the soil near the anodic reservoir by dropped the Cr(VI) negative mass flux caused by electroosmosis advection and concentration diffusion. The pathways of Cr(VI) photo-reduction are possibly dominated by ligand-to-metal charge transfer, i.e., photocatalytic cyclic reduction by Fe(III)/Fe(II) complexes on the surface of the minerals and in soil pore fluid and the photo-induced decomposition of chromate ester. It is concluded that UV/EKR is a clean, efficient, and low-cost method for remediation of Cr(VI)-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.

Efficient removal of chromium from soil in a modified electrokinetic system using iron-treated activated carbon as third electrode

Abstract A modified electrokinetic remediation (EKR) system was designed to remediate Cr-contaminated soil by using iron-treated activated carbon (AC) as the third electrode. Controlled and orthogonal experiments were conducted with aim of evaluating effect of various factors on Cr removal in this modified system. The results revealed that remediation time was most influential on removal capacity of the three-dimensional (3D) electrode EKR system. The existence of particle electrodes buffered soil pH and the average removal efficiency of Cr(VI) was enhanced to 50.09% after 5 days compared with 42.49% by conventional EKR. Noticeably, the removal rate of Cr(VI) was enhanced to 86.46% after 10 days remediation at particle electrode of 2 mm. Besides, it was found that 3D electrode EKR system were effective to carbonates and exchangeable fraction of Cr by reducing/converting Cr(VI) to Cr(III) or more stable compounds. In addition to prevailing electromigration, the main removal mechanism in modified EKR system was adsorption/electrosorption of third electrode and substantial conduction of Cr(VI) in 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 polarity reversal on the enhanced electrokinetic remediation of 2,4-D-polluted soils: A numerical study

This article presents a numerical study of the transport phenomena involved in the electrokinetic remediation of soils polluted with polar pesticides. 2,4-Dichlorophenoxyacetic acid is used as a representative of this pesticide type. A one-dimensional configuration with two facing electrodes placed in electrolyte compartments and a cathodic overflow pollutant extraction system has been used for that purpose. The conventional electrokinetic remediation process is evaluated by keeping the electrode polarity constant, and to obtain acceptable yields, it is necessary to extend the treatment for more than 250 days. The application of periodic polarity reversals is proposed to improve these results. This strategy maximises the pesticide concentration in the cathodic compartment, thus maximising the pollutant extraction rate. The results show that by applying polarity reversals over 6-h periods, it is possible to accelerate the treatment, thus improving its overall efficiency up to 94.5% compared with the treatment using a constant electrode polarity.

Exchange electrode-electrokinetic remediation of Cr-contaminated soil using solar energy

Abstract The present work focused on analyzing the effects of solar energy on the electrokinetic remediation (EKR) of Cr-contaminated soil, compared to direct current (DC) power supply. Meanwhile, to control the remedied soil pH and focusing phenomena, the exchange electrode-EKR (EE-EKR) has also been employed. Four runs of tests were conducted using DC power supply with the conventional EKR (run A, run D), DC power supply with EE-EKR (run B) and solar energy with EE-EKR (run C) respectively. Important electrokinetic parameters such as electrical voltage and current, electroosmotic flow, soil pH, the remediation efficiency of total Cr, Cr(VI), Cr(III) and cost analysis were investigated to evaluate EE-EKR using solar energy. The results show that run B had the highest removal efficiency of total Cr (43.65%), Cr(VI) (91.88%), and Cr(III) (19.32%), and run C, run A, run D follow in turn. It was proved that EE-EKR could increase the removal efficiency of Cr, especially Cr(III) from contaminated soil, because it could reduce focusing phenomena and enhance electrical current. Meanwhile, the experimental results also indicated that the combination of electrokinetics and solar energy was feasible and effective to some extent for the remediation of Cr-contaminated soil.

Enhanced Electrokinetic Remediation of Copper-Contaminated Soils near a Mine Tailing Using the Approaching-Anode Technique

The soils contaminated by copper (Cu) near a mine tailing are remedied via an enhanced electrokinetical (EK) method utilizing approaching anodes (AAs). The variations in the removal efficiency and soil pH as a function of treatment time are determined. The maximum Cu removal efficiency is as high as 61.98% under a voltage gradient of 1 V/cm for 48 h; in contrast to 38.97% when the conventional electrokinetic remediation with one fixed anode (FA) is employed. Several anodes were inserted as AAs in the treated soil. They were switched in turn from the anode towards the cathode allowing for high H+ ions concentrations and high redox potentials to quickly migrate towards the cathode. As a result, the soil remediation is accelerated. The mechanism of Cu electromigration behavior in soils during an enhanced EK method is described as the elution in an electrokinetically-driven chromatogram.

Improvement in electrokinetic remediation of Pb-contaminated soil near lead acid battery factory

To improve the conventional electrokinetic remediation of Pb-contaminated soil, the Pb-contaminated soil near a lead acid battery factory in the Pearl River Delta region of China was electrokinetically remedied with polarity exchange technique. The variations in Pb removal efficiency and the soil pH value with the treatment time and the exchange polarity interval were determined. It is found that the removal efficiency of Pb reaches a maximum of 87.7% when the voltage gradient is 1 V/cm and the exchange polarity interval is 48 h. This value is far higher than that obtained with conventional electrokinetic remediation (61.8%). Additionally, the “focusing effect” which appears in the conventional electrokinetic remediation can be avoided, and thus additional chemicals are not needed for the polarity exchange technique. The mechanism of Pb electromigration behavior in soil during the treatment with the polarity exchange technique was described.

Electrokinetic Remediation of Fluorine‐Contaminated Soil Using Approaching Cathodes

The objective of this research was to analyze the effects of approaching cathodes (AC) on electrokinetic remediation of fluorine‐contaminated soil, compared to one fixed cathode. Important electrokinetic parameters such as soil pH, electrical current, the remediation efficiency of fluorine, and energy consumption were investigated to evaluate electrokinetic remediation with AC (AC‐electrokinetic remediation). It was proved that AC‐electrokinetic remediation could increase the removal efficiency of fluorine from contaminated soil, because it could increase soil pH and enhance electrical current. Experimental results showed that it could improve 5.2% of removal efficiency of fluorine, and save nearly 16% of energy and 20% of time than the conventional electrokinetic remediation. After electrokinetic remediation, the fractions of fluorine had been changed and fluorine in the soil was mainly found in residual fraction. Experimental results indicated that AC‐electrokinetic remediation was a considerable technology to eliminate fluorine in contaminated soils.

Electrokinetic remediation of chromium- and cadmium-contaminated soil from abandoned industrial site

This paper presents a systematic bench-scale study on removals of Chromium (Cr) and Cadmium (Cd) from abandoned industrial site in China with concentration of 510mg/kg for Cr and 200mg/kg for Cd. The polarity exchange and conventional electrokinetic remediation were conducted with treatment time of 192h to assess the removal efficiency and transient behavior of Cr and Cd. All the experiments were subjected to a voltage gradient of 1V/cm. Results showed that, polarity exchange electrokinetic remediation led to 88% of Cr and 94% of Cd removals when exchange polarity interval was 48h. Seventy percent of Cr and 82% of Cd were removed when exchange polarity interval was 96h. The removal efficiency was comparable with conventional electrokinetic remediation with removals of 57% of Cr and 49% of Cd. Soil pH was controlled between 5 and 7 by polarity exchange electrokinetic remediation. Additional chemicals and complex equipment were not required.

Behavior of zinc, nickel, copper and cadmium during the electrokinetic remediation of sediment from the Great Backa Canal (Serbia)

This paper describes a bench-scale study dealing with the removal of heavy metals by electrokinetic (EK) remediation from sediment of the Great Backa Canal (Vojvodina, Republic of Serbia), with an emphasis on the dependence of removal efficacies on the physicochemical states of the heavy metals and sediment chemistry. Sediment samples were spiked with the following heavy metals (mg kg− 1): Zn 4400, Ni 900, Cu 1140 and Cd 57. In addition to determining the pseudo-total metal content in the contaminated sediment before and after EK treatment, BCR sequential extraction was also performed to examine the distribution of the contaminants in the sediment. Conventional EK remediation (EXP I) was ineffective in removing the heavy metals investigated, so two enhanced processes were developed. In both these processes, the mass of treated sediment was reduced to avoid the presence of inactive electric field areas in the sediment and increase current density. The first enhanced experiment (EXP II) used acetic acid (HAc) solution (pH 2.9) as an anolyte. Combined with the smaller sediment mass, this resulted in an increase in overall removal efficacies (9% for Zn, 15% for Ni, 10% for Cu and 15% for Cd). The second enhanced experiment (EXP III), as well as using HAc solution as an anolyte, made use of a cation exchange membrane in the cathodic chamber to minimize pH changes in the region adjacent to the cathode, which negatively influenced the removal of some heavy metals. However, no improvement in removal efficacy was achieved in EXP III. Since the redox potential of the sediment drops during the EK process, metals removal is limited by the formation of their sulfides. In conclusion, the removal of heavy metals by EK remediation is governed by a complex interplay of the complexation, precipitation and reduction processes, and the difficulties encountered in their optimization can explain the unsatisfactory effectiveness achieved by the described remediation procedure. Improved understanding of the behavior of metal ions during EK treatment can be useful in predicting and enhancing the efficacy of the process.