Electrokinetic-Fenton technology for the remediation of hydrocarbons historically polluted sites

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Comparison of 2- and 3-compartment electrodialytic remediation cells for oil polluted soil from northwest Russia

Electrodialytic remediation is a method based on electrokinetics, in which an electric field of low intensity increases the availability of pollutants in solid waste materials. The electric field induces processes that mobilise and transport inorganic and organic pollutants. The transport of ions in the electrodialytic cell is controlled by employing ion-exchange membranes, allowing separation of the electrodes from the solids. In this study, using a two cell design, electrodialytic experiments were conducted to compare remediation of a heavily oil-polluted soil from Arkhangelsk, Russia. The 2-compartment cell has not previously been employed for electrodialytic removal of organic pollutants and was tested along with the traditional 3-compartment design. The influence of experimental variables (current density, remediation time, stirring and light) and settings on the two cell designs was investigated. The highest removal (77%) of total hydrocarbons (THC) was observed in the 3-compartment cell at high current density (0.68 mA/cm²), longer remediation time (28 days), stirring and exposure to daylight. High current density and stirring increased the removal efficiencies in both cell designs. Within the studied experimental domain, the removal efficiencies in the 3-compartment cell (10-77%) were, however, higher than those observed in the 2-compartment cell (0-38%).

Phenanthrene removal from the contaminated soil using the electrokinetic-Fenton method and persulfate as an oxidizing agent

Remediation of soils contaminated with hydrocarbon materials is of particular importance due to their association with food chain. One of the remediation methods, which has been taken into account in recent years by researchers, is the electrokinetic technique. In this study, the electrokinetic method was used in combination with the Fenton technique to remove phenanthrene from clay soil. Oxidizing agent and catalyst used in the Fenton technique greatly influenced the efficiency of the remediation process. To investigate the effect of these two factors on the remediation process, it was made use of three different types of electrodes as catalyst, including graphite, iron, and copper, as well as hydrogen peroxide and sodium persulfate with different concentrations as oxidizing agent. During the 9 experiments designed, factors affecting removal efficiency, such as remediation time, electric current intensity, electroosmotic flow rate, and pH of the cathode and anode reservoirs were also investigated. Overall, the use of the electrokinetic-Fenton method with 15% hydrogen peroxide and copper electrode exhibited a 100% increase in the process efficiency over the same time period required to perform the conventional electrokinetic method and removed 93% of the soil phenanthrene, these findings indicated that combining the Fenton technique with the electrokinetic method enhanced the efficiency of this method in removing organic pollutants from the soil. Also, the use of sodium persulfate as an oxidizing agent in the electrokinetic method increased the removal efficiency by more than 95% over the half time period required to perform the conventional electrokinetic method.

Potential impact of active substances in non-thermal discharge plasma process on microbial community structures and enzymatic activities in uncontaminated soil

Soil microbial community structures and enzymatic activity are important indicators for judging biochemical process intensity and soil quality. Non-thermal discharge plasma (NDP), an advanced oxidation technique, has received great attention in soil remediation. Potential impact of NDP treatment on microbial community structures and enzymatic activities in uncontaminated soil samples was evaluated in this study. The NDP treatment significantly altered soil microbial community structures and enzymatic activity. The exposure of soil samples to NDP decreased the enzymatic activities including glutamic acid enzyme, arylsulphatase, leucine enzyme, acetyl glucosaccharase, glucosaccharase, cellulose, phosphatase, and ligninase. The contents of some soil microbes including Gram-negative bacteria, Fungi, Anaerobes, AM Fungi, Eukaryotes, and Actinomycetes also decreased after NDP treatment, as well as the diversity index and equitability index of the soil microbes. In addition, the total phospholipid fatty acid (PLFA), Fungi PLFA, bacteria PLFA, and Actinomycetes PLFA of the soil microbes were also reduced after treatment. Principal component analysis confirmed these changes. Actinomycetes and Fungi were the most sensitive microbes to the NDP, and Phosphatase activity and Cellulose activity were relatively insensitive to the NDP. The potential impacts could be attributed to chemically active substances and ultraviolet irradiation.

Low permeability zone remediation of trichloroethene via coupling electrokinetic migration with in situ electrochemical hydrodechlorination

To address the challenge of trichloroethene (TCE) remediation in low permeability zone, an inexpensive Cu-Ni bimetallic cathode was proposed in electrokinetic (EK) remediation system to couple electrokinetic migration with in situ electrochemical hydrodechlorination. Aqueous phase TCE was originally added into the anolyte so that breakthrough curves through the low permeability porous soil compartment could be obtained to better understand TCE migration driven by electroosmosis flow using different cathodes. The Cu-Ni cathode resulted in more TCE migration of 7.64 mg compared to that of 5.99 mg with Ni and 4.22 mg with mixed metal oxide (MMO) cathode, suggesting that the Cu-Ni cathode was capable of driving more TCE flux out of the contaminated soil. With the Cu-Ni cathode, 98.4% of TCE flux that reached the cathode was electrochemically reduced on the cathode, which was much higher than that with MMO cathode (77.9%) or Ni cathode (59.6%). TCE mass that was transported by electroosmosis flow increased from 2.04 to 6.68 mg when the voltage gradient increased from 1 to 4 V cm^-1, with the normalized energy consumption increasing from 0.06 to 0.16 kWh kg^-1 per unit water movement, and from 0.54 to 2.55 kWh g^-1 per unit TCE transport. For TCE that did reach the cathode compartment, > 98% degradation maintained at the Cu-Ni cathode with various voltage gradients. The coupled electrokinetic and electrochemical hydrodechlorination technology appears to be a promising strategy for the remediation of low permeability porous media.

Electrokinetic-Fenton for the remediation low hydraulic conductivity soil contaminated with petroleum

The use of electrokinetic Fenton (EK Fenton) process, as promising soil remediation approach, was investigated by using an iron electrode with different supporting electrolytes (tap water, H₂O₂, and citric acid) to depollute soil spiked with petroleum where kaolin was selected as low hydraulic conductivity. The results clearly confirm that, the combination of electrokinetic remediation (EK) and Fenton technologies, is an efficient oxidizing approach for removing hydrocarbons from this kind of soil. In fact, the electrokinetic Fenton reactions and the control of the soil pH conditions by adding citric acid enhanced the oxidation process because the addition of the H₂O₂ with iron electrode resulted in higher removal efficiencies (89%) for total petroleum hydrocarbons (TPHs). These figures allowed to confirm that EK Fenton process with pH control contributed for the transport of H₂O₂ and Fe²⁺ ions in the soil by electromigration and eletro-osmotic phenomena. Conversely, no control of pH conditions when only EK was applied, achieved lower hydrocarbons removal (27%) after 15 d of treatment due to the precipitation of iron ions. Finally, the efficiency of the EK Fenton remediation prevented the generation of secondary effluent with higher organic content, avoiding its treatment by other advanced oxidation process.

AOPs-based remediation of petroleum hydrocarbons-contaminated soils: Efficiency, influencing factors and environmental impacts

Petroleum hydrocarbons are a class of anthropogenic compounds including alkanes, aromatic hydrocarbons, resins, asphaltenes and other organic matters, and soil pollution caused by petroleum hydrocarbons has drawn increasing interest in recent years. Multiple advanced oxidation processes (AOPs) are emerging to remediate petroleum hydrocarbons-contaminated soils, while very few studies have focused on the features of AOPs applied in soils. This review aims to provide an updated overview of the state of the science about the efficiency, influencing factors and environmental implications of AOPs. The key findings from this review include: 1) cyclodextrin and its derivatives can be used to synthesize targeting reagents; 2) soil organic matter (SOM), glucose and cement can activate persulfate; 3) SOM affects redox circumstance in soil and could be further developed for enhancing the catalysis effect of transition metals; 4) non-thermal plasma and wet oxidation are promising methods of AOPs to remove petroleum hydrocarbons from soil; 5) the occurrence, fate, and transformation of intermediates during the degradation of petroleum hydrocarbons in soil should be considered more. Overall, this review reveals an urgent need to develop the cost-effective remedial strategies for petroleum hydrocarbons contaminated soils, and to advance our knowledge on the generation, transport and propagation of radicals in soils.

Combining potassium chloride leaching with vertical electrokinetics to remediate cadmium-contaminated soils

This study evaluated the feasibility of combining potassium chloride (KCl) leaching and electrokinetic (EK) treatment for the remediation of cadmium (Cd) and other metals from contaminated soils. KCl leaching was compared at three concentrations (0.2%, 0.5%, and 1% KCl). EK treatment was conducted separately to migrate the metals in the topsoil to the subsoil. The combined approach using KCl leaching before or after EK treatment was compared. For the single vertical EK treatment, the removal of Cd, lead (Pb), copper (Cu) and zinc (Zn) from the topsoil (0-20 cm) was 9.38%, 4.80%, 0.95%, and 10.81%, respectively. KCl leaching at 1% KCl removed 84.06% Cd, 9.95% Pb, 4.34% Cu, and 19.93% Zn from the topsoil, with higher removal efficiency than that of the 0.2% and 0.5% KCl leaching treatments. By combining the KCl leaching and EK treatment, the removal efficiency of heavy metals improved, in particular for the 1% KCl + EK treatment, where the removal rate of Cd, Pb, Cu, and Zn from the upper surface soil reached 97.79%, 17.69%, 14.37%, and 41.96%, respectively. Correspondingly, the soil Cd content decreased from 4 to 0.21 mg/kg, and was below the Chinese standard limit of 0.3 mg/kg soil. These results indicate that 1% KCl + EK treatment is a good combination technique to mitigate Cd pollution from contaminated soils used for growing rice and leafy vegetables.

Remediation of soil co-contaminated with decabromodiphenyl ether (BDE-209) and copper by enhanced electrokinetics-persulfate process

This work investigated the influences of citric acid and methyl-β-cyclodextrin (MCD) as enhancing agents during the electrokinetics (EK)-persulfate process on the remediation of soil artificially contaminated with decabromodiphenyl ether (BDE-209) and copper (Cu) with an initial concentration of 50 and 1000 mg/kg, respectively. The results clearly demonstrate the efficiency of the process while at the same time, the distribution of the residual contaminants in soil and the EK parameters were greatly influenced by the presence of persulfate, MCD and citric acid. The results show that there was significant removal of BDE-209 and Cu from the soil. MCD-assisted process gave the highest BDE-209 removal (88.6%) and the third largest Cu removal (54.3%) from the soil. Comparatively, the highest Cu removal (92.5%) and the second largest BDE-209 removal (85.6%) were achieved by the joint application of MCD and citric acid in anolyte during the EK-persulfate treatment. MCD and citric acid could increase soil electrical current and electroosmotic flow during EK. The alkalization of soil near cathode was alleviated by the acidic byproducts of persulfate decomposition which could be transported to the soil by electroosmosis and electromigration. This integration process may provide a green efficient technology for remediating co-contaminated soil.

Electrochemical degradation of ibuprofen-contaminated soils over Fe/Al oxidation electrodes

Ibuprofen (IBP) is one of the most known non-steroidal anti-inflammatory drugs. Due to the high consumption and the several ways of discharge, both the aquifer and soil matrix were contaminated by IBP. This study examined the degradation of the IBP in a soil matrix over Fe/Al oxidation electrodes in an electrokinetic system with processing fluids of sodium dodecylsulfate (SDS). The preparation of the Fe/Al oxidation electrode was carried out at a calcination temperature of 500, 550, and 600 °C, which accounted for Fe³⁺ coating rate of 3.89 ± 0.03%, 4.62 ± 0.04%, and 4.72 ± 0.04%, respectively. Results indicated the generation of hydroxyl radical was proportional to the coating rate of Fe³⁺ on the electrode. A 200 mg kg^-1 of IBP-spiked soil sample was conducted in an electrokinetic system under a potential gradient of 2 V cm^-1. The experimental parameters included electrode area of 11-33 cm² and treatment time of 5-9 days. The remediation efficiency of IBP in the EK systems coupled with Fe/Al oxidation electrode was 70.1-94.6%, which was highly dependent on H₂O₂ addition, electrode area, and treatment time. Both addition of H₂O₂ and prolonging treatment time significantly enhanced the degradation of IBP. Whereas increasing electrode area was only favorable for removal mechanism of IBP. Five reaction mechanisms were clearly provided in this study. The aluminum plays an electron donner to trigger Fenton-like reaction continuously to produce hydroxyl radicals. This study confirmed that the electrokinetic process coupled with Fe/Al oxidation electrodes is a viable technique for the remediation of IBP-contaminated soil. Make good use of redox characteristic of aluminum to trigger the Fenton-like reaction in Fe²⁺-rich environment is a great success in this study. The use of Fe/Al electrodes effectively expands the application of electrochemical degradation in soil remediation.

Current advances and trends in electro-Fenton process using heterogeneous catalysts - A review

Over the last decades, advanced oxidation processes have often been used alone, or combined with other techniques, for remediation of ground and surface water pollutants. The application of heterogeneous catalysis to electrochemical advanced oxidation processes is especially useful due to its efficiency and environmental safety. Among those processes, electro-Fenton stands out as the one in which heterogeneous catalysis has been broadly applied. Thus, this review has introduced an up-to-date collation of the current knowledge of the heterogeneous electro-Fenton process, highlighting recent advances in the use of different catalysts such as iron minerals (pyrite, magnetite or goethite), prepared catalysts by the load of metals in inorganic and organic materials, nanoparticles, and the inclusion of catalysts on the cathode. The effects of physical-chemical parameters as well as the mechanisms involved are critically assessed. Finally, although the utilization of this process to remediation of wastewater overwhelmingly outnumber other utilities, several applications have been described in the context of regeneration of adsorbent or the remediation of soils as clear examples of the feasibility of the electro-Fenton process to solve different environmental problems.

Kaolinite adsorption-regeneration system for dyestuff treatment by Fenton based processes

The regeneration and reuse of adsorbents is a subject of interest nowadays in order to reduce the pollution and the wastes generated in the adsorption wastewater treatment. In this work, the regeneration of the spent kaolinite by different advanced oxidation processes (Fenton, electro-Fenton and electrokinetic-Fenton) was evaluated. Initially, it was confirmed the ability of a low cost clayey material, kaolinite, for the adsorption of model dye such as Rhodamine B showing Freundlich isotherm fitting. Then, the regeneration and consequent degradation of the pollutant in the adsorbent by Fenton based processes was carried out. The role of different parameters affecting the regeneration process (H₂O₂:Fe²⁺ ratio, liquid:solid ratio) were evaluated. Working at 100:1 H₂O₂:Fe²⁺ ratio and 30min near complete dye removal (around 97%) from kaolinite was obtained by Fenton treatment. After that, a two-stage treatment for adsorption-regeneration was evaluated during five treatment cycles demonstrating its viability for regeneration of the adsorbent through dye degradation. Based on the successful application of Fenton technique, the improvement of the treatment by electro-Fenton and electrokinetic-Fenton were studied for different solid:liquid ratios achieving satisfactory regeneration values.

Electrokinetic-Fenton remediation of organochlorine pesticides from historically polluted soil

Soil contamination by persistent organic pollutants (POPs) poses a great threat to historically polluted soil worldwide. In this study, soils were characterized, and organochlorine pesticides contained in the soils were identified and quantified. Individual electrokinetic (IE), EK-Fenton-coupled technologies (EF), and enhanced EK-Fenton treatment (E-1, E-2, and E-3) were applied to remediate soils contaminated with hexachloro-cyclohexane soprocide (HCH) and dichloro-diphenyl-trichloroethane (DDT). Variation of pH, electrical conductivity, and electroosmotic flow was evaluated during the EK-Fenton process. The IE treatment showed low removal efficiency for HCHs (30.5%) and DDTs (25.9%). In the EF treatment, the highest removal level (60.9%) was obtained for α-HCH, whereas P,P-DDT was the lowest (40.0%). Low solubility of pollutants impeded the HCH and DDT removal. After enhanced EK-Fenton treatment, final removal of pollutants decreased as follows: β-HCH (82.6%) > γ-HCH (81.6%) > α-HCH (81.2%) > δ-HCH (80.0%) > P,P-DDD (73.8%) > P,P-DDE (73.1%) > P,P-DDT (72.6%) > O,P-DDT (71.5%). The results demonstrate that EK-Fenton is a promising technology for POP removal in historically polluted soil.

Decontamination of Petroleum-Contaminated Soils Using The Electrochemical Technique: Remediation Degree and Energy Consumption

Currently, there are different remediation technologies for contaminated soils, but the selection of the best technology must be not only the treatment efficiency but also the energy consumption (costs) during its application. This paper is focused on assessing energy consumption related to the electrochemical treatment of polluted soil with petroleum hydrocarbons. In the framework of a research project, two types of experiments were conducted using soil that was artificially contaminated with diesel fuel at the same level of contamination. The experimental conditions considered for each experiment were: different amounts of contaminated soils (6 kg and 18 kg, respectively), the same current intensity level (0.25A and 0.5A), three different contamination degrees (1%, 2.5% and 5%) and the same time for application of the electrochemical treatment. The remediation degree concerning the removal of petroleum hydrocarbons from soil increased over time by approximately 20% over 7 days. With regard to energy consumption, the results revealed that with an increase in the quantity of treated soil of approximately three times, the specific energy consumption decreased from 2.94 kWh/kg treated soil to 1.64 kWh/kg treated soil.

Minimizing the Health Risks from Hydrocarbon Contaminated Soils by Using Electric Field-Based Treatment for Soil Remediation

The present work addresses the assessment of human health risk from soil contaminated with total petroleum hydrocarbons (TPHs) due to crude oil pollution, with a particular focus on the polycyclic aromatic hydrocarbon (PAH) group of carcinogenic and toxic substances. Given that the measured risk for human health exceeded the accepted level, the study considered an electrochemical remediation method. The laboratory-scale experiments were conducted by using an electric field-based treatment as a possible solution for the remediation of contaminated soil. After 20 days of treatment, while the voltage applied was 15 V (specific voltage of 1 V/cm), the hydrocarbon content was significantly reduced. The parameters measured to determine the overall remediation efficiency were pH, redox potential, ionic strength, soil characteristics, voltage gradient, and zeta potential. The remediation degree observed during the experiments was around 50% for TPHs and 46% for PAHs. The applied remediation method resulted in significant removal efficiency of the tested contaminants from the soil. Consequently, the human health risk assessment for the new degree of contaminants in the soil was achieved. This data demonstrated to what extent the application of the remediation applied technology ensured an acceptable risk under the same exposure conditions for the industrial workers.

Evaluation methods for assessing effectiveness of in situ remediation of soil and sediment contaminated with organic pollutants and heavy metals

Soil and sediment contamination has become a critical issue worldwide due to its great harm to the ecological environment and public health. In recent years, many remediation technologies including physical, chemical, biological, and combined methods have been proposed and adopted for the purpose of solving the problems of soil and sediment contamination. However, current research on evaluation methods for assessing these remediation technologies is scattered and lacks valid and integrated evaluation methods for assessing the remediation effectiveness. This paper provides a comprehensive review with an environmental perspective on the evaluation methods for assessing the effectiveness of in situ remediation of soil and sediment contaminated with organic pollutants and heavy metals. The review systematically summarizes recent exploration and attempts of the remediation effectiveness assessment based on the content of pollutants, soil and sediment characteristics, and ecological risks. Moreover, limitations and future research needs of the practical assessment are discussed. These limitations are not conducive to the implementation of the abatement and control programs for soil and sediment contamination. Therefore, more attention should be paid to the evaluation methods for assessing the remediation effectiveness while developing new in situ remediation technologies in future research.