Electrokinetic Remediation Technology Research Articles

Surfactant-enhanced electrokinetic remediation of polycyclic aromatic hydrocarbons in heterogeneous subsurface environments

Polycyclic aromatic hydrocarbon (PAH) contamination exists at numerous sites and poses a substantial risk to public health and the environment. Electrokinetic remediation technology has the potential to treat PAH-contaminated soils, but the effect of soil heterogeneities such as layers, lenses, and mixtures of different soils on the electrokinetic process has not been adequately studied. This study evaluates surfactant-enhanced electrokinetic remediation under heterogeneous soil conditions. A series of bench-scale experiments was conducted using two soils (sand and kaolin) spiked with a representative PAH compound (phenanthrene) in a two-dimensional electrokinetic test apparatus under various layered, lens, or mixed soil configurations. In addition, the homogeneous sand and kaolin soils were each tested alone for comparison purposes. All the experiments employed the same nonionic surfactant (5% Igepal CA-720) flushing solution and a low (0.05) hydraulic gradient. The results showed that the surfactant flushing under the low hydraulic gradient alone was sufficient for complete removal of the contaminant from the homogeneous sand profile, whereas the electroosmotic flow generated by the application of a DC 2.0 V/cm electric potential in a periodic mode considerably enhanced the removal efficiency for the homogeneous and heterogeneous soil profiles containing kaolin. The voltage gradient varied spatially and temporally through the soil profiles and affected the electroosmotic flow and contaminant removal. Key words: clays, electrokinetic remediation, electroosmosis, flushing, heterogeneity, polycyclic aromatic hydrocarbons (PAHs), phenanthrene, soils, sorption, solubilization, surfactants.

Washing enhanced electrokinetic remediation for removal cadmium from real contaminated soil

The main objective of this study is to evaluate the combination of electrokinetic remediation and soil washing technology in order to remove cadmium from contaminated soil. This paper presents the results of an experimental research undertaken to evaluate different washing and purging solutions to enhance the removal of cadmium from a real contaminated soil during electrokinetic remediation. Two different experimental modules were applied in the laboratory. Soil was saturated with tap water, while acetic and hydrochloric acids, as well as ethylenediaminetetraacetic acid (EDTA) were used as purging solutions in the first module. Results show that there was a decrease of cadmium concentration near anode, but a significant increase in the middle of the cell, due to the increasing pH. Citric, nitric and acetic acids were used for soil washing and purging solutions in the second module. In this case, an 85% reduction of cadmium concentration was achieved. Therefore, results indicate that soil pH and washing solutions are the most important factors in governing the dissolution and/or desorption of Cd in a soil system under electrical fields.

Enhanced electrokinetic extraction of heavy metals from soils assisted by ion exchange membranes

The potential of electrokinetic remediation technology has been successfully demonstrated for the remediation of heavy metal contaminated fine-grained soils through laboratory scale and field application studies. Various enhancement techniques have been proposed and used in order to further improve the remediation process. However, it has been reported that such enhancement schemes can create other obstacles, such as the introduction of non-target ions into the system and thereby decrease the efficiency of the remediation process. Electrokinetic soil remediation technology enhanced by an ion exchange membrane (IEM), IEM-enhanced EK processing, was experimentally evaluated for the purpose of overcoming these obstacles. In particular, this study focused on observations of a fouling problem and its settlement using an auxiliary solution cell (ASC). In addition, the efficacies of two different types of electrode configurations, rectangular and cylindrical, were investigated. The experimental results indicate that the effectiveness of the technology was increased by an enhancement scheme using an IEM. This may be explained by the prevention of metal precipitation in the region near the cathode originating from hydroxide ions generated by the electrolysis of water in the cathode. The experimental results also imply that placement of the ASC can nullify the fouling problem within the cation exchange membranes used in IEM-enhanced EK processing, and thus improve the overall effectiveness of the process. The experimental results indicate that the cylindrical electrode configuration can be implemented in practical situations to improve the treatability of cathode effluent containing a high level of contaminants after processing.

Removal of Nickel and Phenanthrene from Kaolin Soil Using Different Extractants

Numerous sites exist where low permeability clayey soils have been contaminated with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals. To remediate these sites, innovative treatment methods are urgently required. Electrokinetically enhanced in situ flushing offers great potential to remediate low permeability soils, but this method is highly dependent on the type of extracting solution used. This study investigated the feasibility of using different extracting solutions at various concentrations to remove PAHs as well as heavy metals from low permeability clayey soils. The most efficient extracting solutions could be used as purging/extracting solutions in electrokinetic remediation and other technologies such as soil washing. For the present study, kaolin was selected as a model clayey soil, and it was spiked with phenanthrene as well as nickel at concentrations of 500 mg/kg each to simulate typical field contamination. Several batch tests were conducted using a known amount of the spiked ka...

Ultrasonically enhanced electrokinetic remediation for removal of Pb and phenanthrene in contaminated soils

Electrokinetic and ultrasonic remediation technologies were studied for the removal of heavy metal and polycyclic aromatic hydrocarbon (PAH) in contaminated soils. The study emphasized the coupled effects of electrokinetic and ultrasonic techniques on migration as well as clean-up of contaminants in soils. The laboratory soil flushing tests combined electrokinetic and ultrasonic technique were conducted using specially designed and fabricated devices to determine the effect of both techniques. The electrokinetic technique was applied to remove mainly the heavy metal and the ultrasonic technique was applied to remove mainly organic substance in contaminated soil. A series of laboratory experiments involving electrokinetic and electrokinetic and ultrasonic flushing tests were carried out. Natural clay was used as a test specimen and Pb and phenanthrene were used as contaminants. An increase in out flow, permeability and contaminant removal rate was observed in electrokinetic and ultrasonic tests. Some practical implications of these results are discussed in terms of technical feasibility of in situ implementation of electrokinetic ultrasonic remediation technique.

Effect of clay mineralogy on the feasibility of electrokinetic soil decontamination technology

To evaluate the effect of clay mineralogy on the feasibility of electrokinetic soil remediation technology, we contaminated six soils with Cu(II), Zn(II) and Pb(II) and performed electroremediation for 570 h. Cation exchange resin saturated with H + was placed between soil and cathode to prevent soil alkalinization and trap the migrated heavy metal cations. After the treatment, the heavy metal cations were sequentially extracted with water, 1 M MgCl 2 and hot 6 M HCl. In soils dominated by crystalline clay minerals, Cu(II) and Zn(II) significantly migrated from anode end and accumulated at the cathode end forming sparingly soluble hydroxides. Removal rates of Cu(II) and Zn(II) were highest in a soil dominated with kaolinite and crystalline hematite. In humic–allophanic and allophanic soils, the high pH-buffering capacity of allophane kept the soil pH above 5, even at the anode end, and Cu(II) and Zn(II) did not migrate significantly. In all soils, the migration of Pb(II) was infinitesimal due to the formation of insoluble PbSO 4 and very strong surface complexation at the mineral surfaces. These results show that the reactivity of component clay minerals to H + and heavy metal cations has a crucial effect on the efficiency of the electrokinetic remediation technology and it is not effective for remediation of allophanic soils. The results also indicate that allophanic soils may be useful as a barrier material in landfill sites.

Electrokinetic soil remediation — critical overview

In recent years, there has been increasing interest in finding new and innovative solutions for the efficient removal of contaminants from soils to solve groundwater, as well as soil, pollution. The objective of this review is to examine several alternative soil-remediating technologies, with respect to heavy metal remediation, pointing out their strengths and drawbacks and placing an emphasis on electrokinetic soil remediation technology. In addition, the review presents detailed theoretical aspects, design and operational considerations of electrokinetic soil-remediation variables, which are most important in efficient process application, as well as the advantages over other technologies and obstacles to overcome. The review discusses possibilities of removing selected heavy metal contaminants from clay and sandy soils, both saturated and unsaturated. It also gives selected efficiency rates for heavy metal removal, the dependence of these rates on soil variables, and operational conditions, as well as a cost–benefit analysis. Finally, several emerging in situ electrokinetic soil remediation technologies, such as Lasagna™, Elektro-Klean™, electrobioremediation, etc., are reviewed, and their advantages, disadvantages and possibilities in full-scale commercial applications are examined.

Theoretical evaluation of a technique for electrokinetic decontamination of soils

An electrokinetic decontamination process has been modeled to investigate the feasibility of using electrokinetic soil remediation technology to remove 137Cs and 90Sr from the soil. 100 V DC current is applied to a 3-meter-long soil column by electrodes connected to the soil. The prediction results have shown that the efficiency of the electrokinetic treatment depends on the sorption and diffusion parameters. High sorption and slow diffusion will demand long treatment time. If the soil to be treated has similar sorption and diffusion properties as bentonite, and when the soil is flushed with saline water that leads to less sorption, both 137Cs and 90Sr may be cleaned by the electrokinetic process within a few months.