Electrokinetic Treatment Research Articles

Hybrid Technologies for the Remediation of Diesel Fuel Polluted Soil

AbstractDiesel fuel may be released into soil due to anthropogenic activities, such as accidental spills or leaks in underground storage tanks or pipelines. Since diesel fuel is mainly composed of hydrophobic organic compounds, it has low water solubility. Therefore, treating contaminated areas with conventional techniques is difficult. In this study, electrokinetic treatment of soil contaminated with diesel fuel was carried out. Two different hybrid approaches to pollutant removal were tested. A surfactant was used as a processing fluid during electrokinetic treatment to increase desorption and the solubility of diesel fuel. Additionally, a hybrid technology combining a Fenton reaction and electrokinetic remediation (EK‐Fenton) was tested in an attempt to generate favorable in situ degradation of pollutants. The efficiency of each treatment was determined based on diesel fuel removal. After 30 days of treatment, the highest removal of diesel fuel was found to be achieved with the EK‐Fenton process.

Electrophoresis of a Charged Colloidal Particle in Porous Media: Boundary Effect of a Solid Plane

Electrokinetic treatments such as the electrophoretic technique have been applied successfully to various soil remediation and contaminant removal situations. To understand further the fundamental features involved, the electrophoretic motion of a charged particle in porous media is investigated theoretically in this study, focusing on the boundary effect of a nearby solid plane toward which the particle moves perpendicularly. The porous medium is modeled as a Brinkman fluid with a characteristic screening length (λ(-1)) that can be obtained directly from the experimental data. General electrokinetic equations are used to describe the system and are solved with a pseudospectral method based on Chebyshev polynomials. We found that the particle motion is deterred by the boundary effect in general. The closer the particle is to the boundary, the more severe this effect is. Up to a 90% reduction in particle mobility is observed in some situations. This indicates that a drastic overestimation (10-fold!) of the overall transport rate of particles may occur for large-scale in situ operations in porous media, such as soil remediation utilizing large planar electrodes, should a portable analytical formula valid for bulk systems only be used. Correction factors for various situations in porous media are presented as convenient charts with which to aid engineers and researchers in the field of environmental engineering, for instance, as a realistic estimation of the actual transport rate obtainable. In addition, the results of present study can be applied to biomedical engineering and drug delivery as well because polymer gels and skin barriers both have a porous essence.

Pilot-scale ex situ electrokinetic restoration of saline greenhouse soil

This study was conducted to investigate the feasibility of using an ex situ electrokinetic system for the restoration of saline greenhouse soil. An experiment was conducted in a pilot-scale reactor (1 × 1 × 0.25 m) during 14 days. Chloride accumulated in the top layer through pore-water evaporation. There was no removal of the nitrate in the top layer because of the continuous upward transport of nitrate accompanying the evaporation of soil moisture. However, the removal of sulfate was uniform across all the layers. In the case of cations, a significant amount (64.4%) of potassium was removed, and there was no removal of the magnesium in the top layer. The electrokinetic treatment changed the speciation of calcium in the soil, resulting in an increase in the amount of exchangeable calcium. Furthermore, nitrate was transported toward the anode and reduced to nitrogen gas as the result of an electrochemical reaction at the surface of the anode. Sulfate formed a very stable and insoluble precipitate with calcium—calcium sulfate (gypsum). Ex situ electrokinetic system removed salts from nitrate and sulfate-accumulated saline soil. However, the overall removal efficiency was not high enough because of relatively short operation time.

금속오염(金屬汚染) 토양세척(土壤洗滌) 폐수(廢水)의 화학적(化學的) 처리(處理)와 재순환(再循環) 기술(技術)

본 고는 토양세척-폐수처리-처리수재활용의 친환경공정순환시스템에 대한 이론적인 조사와 국내외 실제적용사례를 조사하였다. 광산폐기물에 함유된 이동성과 용해성이 큰 비소 및 독성 중금속들은 주변 토양 및 지하수를 오염시킬 수 있기 때문에 오염토양은 적절하게 처리되어야 한다. 국내외에서 비소와 중금속 오염토양에 시도되었거나 성공한 기술은 반응벽체(reactive barriers) 및 복토(encapsulation), 고형화(solidification)/안정화(stabilization), 토양세척(soil washing), 식물정화기법(phytoremediation) 등이 있는데, 이 중 본고는 용액을 사용하여 토양으로부터 오염물질들을 제거하는 물리화학적인 기술인 토양세척에 대해 다루었다. 토양세척의 한가지 큰 문제점은 처리 후에 폐수가 대량으로 발생한다는 것이고, 이 폐수에는 세척용액의 리간드와 결합한 오염물질들이 함유되어 있기 때문에 추가적인 처리공정이 필요하다. 그 처리기술에는 오염물질과 세척용액의 특성에 따라 다양한 물리, 화학, 생물학적 처리가 있는데, 그 중에서 화학적 처리기술인 침전/공동침전법, 멤브레인막여과법, 흡착처리법, 이온교환처리법, 동전기처리법에 대해서 본문에 자세히 언급하였다. 마지막으로 각각의 처리법에 따라 실제 토양세척폐수처리 및 재활용에 관한 최근 국내외 연구사례 대해 소개하였고, 이러한 기술들을 바탕으로 토양세척폐수발생문제를 해결하고 수자원절감을 통한 공정의 전반적인 비용효과를 높일 수 있을 것이다. This review investigated theoretical principals and practical application examples on recirculation system of soil washing-wastewater treatment-treated water recycling. As for technologies which have attempted to remediating metals-contaminated soil in and around country, there are reactive barriers, encapsulation, solidification/stabilization, soil washing, and phytoremediation. Among those, in particular, this review covers soil washing technology which physicochemically removes contaminants from soils. The major drawbacks of this technology are to generate a large amount of wastewater which contains contaminants complexed with ligands of washing solution and needs additional treatment process. To solve these problems, many chemical treatment methods have been developed as follows: precipitation/coprecipitation, membrane filtration, adsorption treatment, ion exchange, and electrokinetic treatment. In the last part of the review, recent research and field application cases on soil washing wastewater treatment and recycling were introduced. Based on these integrated technologies, it could be achieved to solve the problem of soil washing wastewater and to enhance cost effective process by reducing total water resources use in soil washing process.

Electrokinetic remediation of β-cyclodextrin dissolved petroleum hydrocarbon-contaminated soil using multiple electrodes

Electrokinetic (EK) migration of β-cyclodextrin (β-CD), which is inclusive of total petroleum hydrocarbon (TPH), is an economically beneficial and environmentally friendly remediation process for oil-contaminated soils. This study investigated the removal of TPHs from soil samples collected at a field site via EK remediation using multiple electrodes at 200 V/m. The TPH contents declined after the 10-day EK remediation, with removal rate decreased with increasing chain length of hydrocarbons. During EK treatment, pH decreased at the anode and increased at the cathode. The microbial strains in the original soil sample were partly flushed out. The power consumption to remove one gram of TPH from the studied soil was estimated 0.37 kWh. The EK remediation presents a cost effective remediation technology for the present field sample.

Effect in the Physical and Chemical Properties of Gleysol Soil after an Electro-kinetic Treatment in Presence of Surfactant Triton X - 114 to Remove Hydrocarbon

Effect in the Physical and Chemical Properties of Gleysol Soil after an Electro-kinetic Treatment in Presence of Surfactant Triton X - 114 to Remove Hydrocarbon

Electrokinetic transport of aerobic microorganisms under low-strength electric fields

To investigate the feasibility of utilizing low strength electric fields to transport commonly available mixed cultures such as those from an activated sludge process, bench scale batch reactor studies were conducted in sand and sandy loam soils. A readily biodegradable substrate, dextrose, was used to test the activity of the transported microorganisms. Electric field strengths of 7V, 10.5V, and 14V were used. Results from this investigation showed that an electric field strength of 0.46 Volts per cm was sufficient to transport activated sludge microorganisms across a sandy loam soil across a distance of about 8 cm in 72 h. More importantly, the electrokinetically transported microbial culture remained active and viable after the transport process and was biodegrade 44% of the dextrose in the soil medium. Electrokinetic treatment without microorganisms resulted in removal of 37% and the absence of any treatment yielded a removal of about 15%.

Laboratory Model Test on Improving the Properties of Soft Clay by Electrokinetics

This experimental study was carried out in two test series to investigate the feasibility of decreasing the water content and increasing the shear strength and axial load capacity of laboratory-prepared soft clay by electrokinetic treatment. The focus of the investigations is the influence of pore fluid chemistry (fresh or highly saline water) on the gained improvement and on the energy consumption. The results showed that electrokinetics was effective in improving the properties of the soft clay with fresh and saline water. The degree of improvement, however, was superior in tests with freshwaters along with a lower energy consumption. The minimum water content and the maximum shear strength after the treatment were reported near the anode (28% ± 3.6 and 99.3 kPa ± 15.4 compared to 49.7% ± 3.1 and 12.1 kPa ± 1.7 in the control). The maximum axial load capacity of the foundation model after the treatment was 416 N compared to 28 N in the control. The energy consumption varied between 69.1 and 1994.6 Whr.

Electro-Osmotic Consolidation Experiments on an Organic Soil

A series of electro-osmotic consolidation experiments were carried out on an organic soil from the central Sarawak region of Malaysia. Commercially available EVD was used to induce electro-osmosis and drainage of pore water. The influence of the method of drainage and pumping interval of drained water on electro-osmotic consolidation was investigated. The combination of electro-osmotic consolidation and chemical stabilization techniques was investigated by installing lime or cement columns near the anode end of the test bed. The binder factor in the lime and cement columns was varied. The paper presents the experimental set-up, test procedures, experimental program, results and conclusions of the study. Electro-osmosis, using EVDs, was effective in the electrokinetic treatment of the organic soil. The two types of drainage, namely drainage at bottom and drainage tubes, were effective. Electro-osmotic consolidation improved with decrease in pumping interval. The lime and cement columns, used in combination with electro-osmosis, increased the undrained strength further.

THE STRUCTURAL CONTROL OF NUTRIENT SOLUTION FOR STABLE PRODUCTION OF HIGH-QUALITY VEGETABLES IN GREENHOUSES

With the increase in consumption of natural resources and energy, global environmental problems have appeared. On one hand, by eco-systemic agriculture, environmental preservation, and energy saving measures, the establishment of innovative techniques for year-round stable production of high-quality vegetables in green houses has been expected. On the other hand, the deterioration of water in the environment leads to an increase in health hazards because of active oxygen in living organisms, and raising the quality of water is an important issue to be addressed. In this study, efficient approaches to managing nutrient solution were developed. The upper and lower sides of a fluidized layer are sectioned with stainless steel nets. Sintered silicate mineral ceramics were inserted into the section. The flow of nutrient solution can be directed using a pump from the lower to the upper side so that the ceramic particles are fluidized. The nutrient solution allowed to flow through the fluidized layer would be fed back into a nutrient solution tank, and a structured nutrient solution with antioxidation property is induced by electrokinetic treatment. The nutrient solution was found to become positively charged by the formation of an electric double-layer interface between the ceramic surface and the nutrient solution. The structured nutrient solution was studied under thermally stimulated depolarized current (J), temperature profiles (TSDC analysis), and viscosity. Effects of surface activity were seen in the structured nutrient solution at similar temperature conditions. Effects of structured nutrient solution on plant growth were examined in Komatsuna (Brassica rapa L. nothovar) plants growing under NFT system. The structured nutrient solution was efficiently absorbed on contact with roots and the root mass significantly increased. Komatsuna plants grew fast and a larger root mass contributed to an increase of total free amino acid in leaves.

THE INFLUENCE OF ELECTRO KINETIC NUTRIENT TREATMENT SYSTEM USING BAKUHAN-SEKI ON VEGETATIVE GROWTH OF TOMATO

To produce a quality tomato (Lycopersicon esculentum), it is necessary to have a quality environment. Greenhouses are widely employed to create a favourable environment for growing tomatoes, both with soil and soilless cultivation techniques. It is natural to endeavour a properly planned layout to make the best possible use of the available natural resources, but at the same time ensuring the environment for the growing plants is conducive to high yield and quality. In this study an innovative nutrient treatment system in which Bakuhan-seki, a silicate mineral fluidized in nutrient solution was attempted. The nutrient solution was pumped from the nutrient tank through the lower to the upper side of the fluidization layer, in order to return to the tank again. This activates nutrient through the electro chemical energy of the minerals fluidized in a circling current. In the activation of nutrient solution, negative charges on the surface of Bakuhan-seki caused pH-buffer and ion exchange actions. The benefits of activated water have been demonstrated by extensive experimental works. Moreover when nutrient solution passed on the surface of silica, an electric double layer was formed between interfaces of silica and water giving negative and positive charges. Plants can absorb nutrient easily, promoting their growth and increasing their yield. For a detailed description of this relationship, the effects of fluidized nutrient solution on hydroponically grown tomatoes were investigated. The germination rate was tendentiously enhanced, and the early growth of seedlings was significantly improved by using treated nutrient solution. Additionally, the fluidization of nutrient solution caused an increase in shoot and root length, stem diameter, shoot and root weight and SPAD value of tomato plants. As all desirable characteristics in the produced plants increased when exposed to electro kinetic treatment, the treatment itself constitutes an alternative method to improve vegetative growth of tomato plants.

Enhanced nano-Fe 3O 4/S 2O 82− oxidation of trichloroethylene in a clayey soil by electrokinetics

The effectiveness of electrokinetically enhanced persulfate oxidation for destruction of trichloroethylene (TCE) in a spiked sandy clay soil was evaluated in this work. In addition, the effect of nanoscale Fe 3O 4 on activating persulfate oxidation was also evaluated. The TCE-spiked soil was compacted in the soil column of the electrokinetic (EK) treatment system, and both the anode and cathode reservoirs were filled with simulated groundwater. The electrode material for both the anode and cathode was graphite. An electrical potential gradient of 1 V cm −1 was applied to the EK treatment system by a DC power supply for a period of 7–14 d. Sodium persulfate (Na 2S 2O 8) was injected daily at a dose of 1.0–10.0 g L −1 into the anode or cathode reservoir, starting from the very beginning of the treatment. To evaluate the performance of persulfate alone in chemical oxidation of TCE in the EK treatment system, EK-alone test was also carried out for comparison. Experimental results have shown that the EK process greatly enhances the transport of injected persulfate from the anode reservoir to the cathode reservoir via the soil compartment by means of electroosmotic flow, aiding in situ chemical oxidation of TCE. In addition, nanoscale Fe 3O 4 was found to play a significant role in activating persulfate oxidation. Such a coupled process was found to be capable of effective destruction of TCE in the soil compartment and electrode compartments. Under optimal conditions, the residual TCE concentration in the soil compartment was found to be lower than Taiwan EPA's regulatory threshold (i.e., 60 mg kg −1). The residual TCE concentrations in both electrode reservoirs (i.e., not detectable and 0.01–1.74 mg L −1 for the anode and cathode reservoirs, respectively) also met the local regulatory standards for Type II groundwater quality (i.e., <0.05 mg L −1).

Electrokinetic decontamination of heavy metals in construction materials: contribution of the different parameters to the global efficiency

To discriminate between the relative weights of each factor involved in the global process of an electrokinetic treatment for remediation, mortar and brick contaminated with Cs, Sr, Co, Cd and Cu were submitted to electrokinetic treatments with different enhancing electrolytes (distilled water, Na2-EDTA, oxalic acid and citric acid), and the efficiency was analysed in function of the parameters involved in the process. The data obtained in this research, a matrix including 40 cases, have been correlated for the decontamination percentage in function of the key variables of the treatment, and the best correlation found, able to explain a variance of the 78.5% of the data, was a non linear exponential grow regression. An order in the weight of the contributions has been established that, from bigger to smaller contribution, is: constants of chelation equilibriums > precipitation as hydroxide constants > zeta potential > conductivity of the catholyte > pH catholyte > diffusion coefficient > pH of the material.

Removal of organic contaminants from soils by an electrokinetic process: The case of molinate and bentazone. Experimental and modeling

The herbicides molinate and bentazone are used in paddy rice fields. Their behaviour in soils when submitted to an electric field was studied and the applicability of the electrokinetic (EK) process in soil remediation was evaluated. Three soils were used and nine EK experiments were carried out at a laboratory scale. A one-dimensional model is developed for simulating the EK treatment of soils containing the herbicides. The model reproduces satisfactorily the experimental data of cumulative volumes removed towards the anode and the cathode compartments, as well as the difference between catholyte and anolyte cumulative volumes, showing that the electroosmotic flow (EOF) is very sensible to soil pH. The experimental results show that the EK process is able to mobilize molinate and bentazone from soils, and remove them from soil solution. Molinate seems to be mobilized preferentially to the cathode compartment. The model also satisfactorily reproduces the experimental data. The highest quantities of molinate move towards the catholyte, particularly when the EOF is kept constant, allowing molinate to be constantly swept towards it. Bentazone also shows a high decay from soil, being mobilized towards both electrode compartments. The results point towards a relationship between the differential pH in the catholyte and anolyte, and the bentazone decay. The model shows that bentazone is mobilized towards the anolyte in higher current intensity conditions, because there is a predominant electromigration (EM) movement of enolate towards the anode compartment, against the electroosmotic transport of bentazone towards cathode, whereas in lower intensity conditions the opposite occurs. This happens because the EOF grows less than EM, when current intensity is duplicated.

Pilot-scale study on in situ electrokinetic removal of nitrate from greenhouse soil

In greenhouses, excessive nutrients generally accumulate in the soil, which may induce adverse effects on crop yield and quality. In situ electrokinetic (EK) tests were conducted on a pilot-scale to remove nitrate from greenhouse soil for 64 days using a specially designed electrode module. When a pair of electrodes was installed horizontally in the furrows (EK pilot test I), a significant amount of nitrate was removed by electromigration towards the anode although the electroosmotic flow was not obtained. In the other test (EK pilot test II), where two anodes and one cathode were placed in the furrows and under the ridge, respectively, the efficiency of nitrate removal was comparable with that in the EK pilot test I. However, the removal pattern was asymmetric with respect to the cathode because soil heterogeneity affected the main transport mechanism, electromigration or electroosmosis, depending on location. After the EK treatment the overall efficiency of the nitrate removal was >90% in both tests. The main cation, K + was also removed, and thereby the electrical conductivity of the soil was reduced up to 87%. The energy consumed for the EK pilot test I operation was much lower than that used in the EK pilot test II. During the EK tests, indigenous nitrate reducing bacteria were introduced to enhance nitrate biodegradability but the effect of bio-augmentation was insignificant. From the results it can be concluded the EK technology is feasible to remove salts from greenhouse soils and the EK pilot system I is more applicable to greenhouse soil remediation. However, there is still a room for improvement to achieve a successful field application.

Electrokinetic treatment on a tropical residual soil

The results of shear box and consolidation tests on electrokinetically-treated tropical residual soil are presented. Injections of selected chemicals (calcium chloride, aluminium chloride and phosphoric acid) into the soil samples at the anodes or cathodes were carried out in cylindrical electrokinetic cells via applications of 30 V DC electrical potential for 168 h. Four different open-anode and open-cathode electrokinetic systems utilising different anolytes and catholytes were employed to treat the soil samples. The shear resistances of the treated soil utilising distilled water as the anolyte and 1·0 mol/l phosphoric acid as the catholyte was enhanced, whereas the treated soil near the cathode showed significant reduction in compressibility. Soil treated utilising the other chemicals showed no significant changes.

Recovery from Sulfate Attack in Concrete via Electrokinetic Nanoparticle Treatment

Microstructural damage induced by sulfate attack in concrete is a cause of primary concern in building foundations and other structures. Most research focuses on prevention. In contrast, the concept of damage recovery has not received significant attention. Studies were conducted using alumina-coated-silica nanoparticles to facilitate an electrochemical recovery of strength. Treatments were applied to extract sulfates while the nanoparticles were being injected. Initial sodium sulfate exposure on cylindrical concrete specimens was conducted for a period of 30 days. This exposure induced body cracking and microstructural damage. The specimens were subjected to electrokinetic treatment using a constant current density of 1 A/m2 for 7 days. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis revealed significant sulfate content in the sulfate-exposed specimens that was not detected in the treated cases. Raman spectroscopy also indicated a higher C-S-H among the treated specimens, ...

Effect of Electrokinetics on the Bioaccessibility of Polycyclic Aromatic Hydrocarbons in Polluted Soils

Bioaccessibility is one of the most relevant aspects to be considered in the restoration of soils using biological technologies. Polycyclic aromatic hydrocarbons (PAH) usually have residual fractions that are resistant to biodegradation at the end of the biological treatment. In some situations, these residual concentrations could still be above legal standards. Here, we propose that the available knowledge about electroremediation technologies could be applied to enhance bioremediation of soils polluted with PAH. The main objective of this study was to show that a previous electrokinetic treatment could reduce the PAH residual fractions when the soil is subsequently treated by means of a bioremediation process. The approach involved the electrokinetic treatment of PAH-polluted soils at a potential drop of 0.9 to 1.1 V/cm and the subsequent estimations of bioaccessibility of residual PAHs after slurry-phase biodegradation. Bioaccessibility of PAH in two creosote-polluted soils (clay and loamy sand, total PAH content averaging 300 mg/kg) previously treated with an electric field in the presence of nonionic surfactant Brij 35 was often higher than in untreated controls. For example, total PAH content remaining in clay soil after bioremediation was only 62.65 +/- 4.26 mg/kg, whereas a 7-d electrokinetic pretreatment had, under the same conditions, a residual concentration of 29.24 +/- 1.88 mg/kg after bioremediation. Control treatments without surfactant indicated that the electrokinetic treatment increased bioaccessibility of PAHs. A different manner of electric field implementation (continuous current vs. current reversals) did not induce changes in PAH bioaccessibility. We suggest that this hybrid technology may be useful in certain bioremediation scenarios, such as soils rich in clay and black carbon, which show limited success due to bioavailability restrictions, as well as in highly heterogeneous soils.

Application of sequential extraction analysis to electrokinetic remediation of cadmium, nickel and zinc from contaminated soils

An enhanced electrokinetic process for the removal of cadmium (Cd), nickel (Ni) and zinc (Zn) from contaminated soils was performed. The efficiency of the chelate agents nitrilotriacetic acid (NTA), diethylenetriaminepentaacetic acid (DTPA) and diaminocycloexanetetraacetic acid (DCyTA) was examined under constant potential gradient (1.23V/cm). The results showed that chelates were effective in desorbing metals at a high pH, with metal–chelate anion complexes migrating towards the anode. At low pH, metals existing as dissolved cations migrated towards the cathode. In such conflicting directions, the metals accumulated in the middle of the cell. Speciation of the metals during the electrokinetic experiments was performed to provide an understanding of the distribution of the Cd, Ni and Zn. The results of sequential extraction analysis revealed that the forms of the metals could be altered from one fraction to another due to the variation of physico-chemical conditions throughout the cell, such as pH, redox potential and the chemistry of the electrolyte solution during the electrokinetic treatment. It was found that binding forms of metals were changed from the difficult type to easier extraction type.

Enhanced electrokinetic treatment of marine sediments contaminated by heavy metals and PAHs

Dredged sediments contaminated by heavy metals and PAHs were subjected to both unenhanced and enhanced electrokinetic remediation under different operating conditions, obtained by varying the applied voltage and the type of conditioning agent used at the electrode compartments in individual experiments. While metals were not appreciably mobilized as a result of the unenhanced process, metal removal was found to be significantly improved when both the anodic and cathodic reservoirs were conditioned with the chelating agent EDTA, with removal yields ranging from 28% to 84% depending on the contaminant concerned. As for the effect on organic contaminants, under the conditions tested the electrokinetic treatment displayed a poor removal capacity towards PAHs, even when a surfactant (Tween 80) was used to promote contaminant mobilization, indicating the need for further investigation on this issue. Further research on organics removal from this type of materials through electrokinetic remediation is thus required. Furthermore, a number of technical and environmental issues will also require a careful evaluation with a view to full-scale implementation of electrokinetic sediment remediation. These include controlling side effects during the treatment (such as anodic precipitation, oxidation of the conditioning agent, and evolution of toxic gases), as well as evaluating the potential ecotoxicological effects of the chemical agents used.