Reversible electrokinetic adsorption barriers for the removal of atrazine and oxyfluorfen from spiked soils

A comprehensive review of soil remediation contaminated by persistent organic pollutants using electrokinetic: Challenging enhancement techniques

The hydrophobic, hard-to-naturally-decompose compounds, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and pesticides, are categorized as persistent organic pollutants (POPs). POPs are toxic/hazardous and present serious risks to human health. Electrokinetic (EK) remediation is highly flexible and cost-effective, suitable for both in-situ and ex-situ applications. It effectively targets a wide range of contaminants, including metals and organic compounds, especially in low-permeability and low-hydraulic conductivity soils, where traditional methods are less effective. This technology is easy to install and can be combined with other strategies for enhanced remediation in complex soil environments. This paper underscores EK remediation as a promising method for addressing soil pollution caused by these organic pollutants, especially in low-permeability soil. The present review starts with the classification, toxicity effects, and source of POPs in the environment. Theoretical aspects and fundamentals of EK, including transport mechanisms and principles, are also reviewed. The theoretical underpinnings of effective factors are comprehensively explored, such as surface charge, zeta potential, pHpzc, and numerical modeling of transport fluxes. Moreover, a comprehensive examination is undertaken regarding the operation and design considerations of the EK process, encompassing factors like pH, electrode arrangement, electrolyte, and voltage. Subsequently, it is highlighted that EK has the potential to come in synergistically in contact with other remediation technologies to augment the POPs' degradation. Various enhancement techniques are also explored, including solvent extraction, chemical oxidation, bioremediation, and permeable reactive barriers to combine with EK. Each method is examined in terms of its advantages, limitations, recent developments, and ongoing research. Finally, the potential and challenges associated with enhanced EK methods combined with other techniques for the removal of POPs were reviewed.

Advances in understanding and mitigating Atrazine's environmental and health impact: A comprehensive review

Atrazine is a widely used herbicide in agriculture, and it has garnered significant attention because of its potential risks to the environment and human health. The extensive utilization of atrazine, alongside its persistence in water and soil, underscores the critical need to develop safe and efficient removal strategies. This comprehensive review aims to spotlight atrazine's potential impact on ecosystems and public health, particularly its enduring presence in soil, water, and plants. As a known toxic endocrine disruptor, atrazine poses environmental and health risks. The review navigates through innovative removal techniques across soil and water environments, elucidating microbial degradation, phytoremediation, and advanced methodologies such as electrokinetic-assisted phytoremediation (EKPR) and photocatalysis. The review notably emphasizes the complex process of atrazine degradation and ongoing scientific efforts to address this, recognizing its potential risks to both the environment and human health.

Environmental impact assessment of the electrokinetic adsorption barriers to remove different herbicides from agricultural soils

In this study, the sustainability of the electrokinetic remediation soil flushing (EKSFs) process integrated without and with adsorption barriers (EKABs) have been evaluated for the treatment of four soils contaminated with Atrazine, Oxyfluorfen, Chlorosulfuron and 2,4-D. To this purpose, the environmental effects of both procedures (EKSFs and EKABs) have been determined through a life cycle assessment (LCA). SimaPro 9.3.0.3 was used as software tool and Ecoinvent 3.3 as data base to carry out the inventory of the equipment of each remediation setup based on experimental measurements. The environmental burden was quantified using the AWARE, USEtox, IPPC, and ReCiPe methods into 3 Endpoint impact categories (and damage to human health, ecosystem and resources) and 7 Midpoints impact categories (water footprint, global warming potential, ozone depletion, human toxicity (cancer and human non-cancer), freshwater ecotoxicity and terrestrial ecotoxicity). In general terms, the energy applied to treatment (using the Spanish energy mix) was the parameter with the greatest influence on the carbon footprint, ozone layer depletion and water footprint accounting for around 70 % of the overall impact contribution. On the other hand, from the point of view of human toxicity and freshwater ecotoxicity of soil treatments with 32 mg kg-1 of the different pesticides, the EKSF treatment is recommended for soils with Chlorosulfuron. In this case, the carbon footprint and water footprint reached values around 0.36 kg of CO2 and 114 L of water per kg of dry soil, respectively. Finally, a sensitivity analysis was performed assuming different scenarios.

Cork barriers for the remediation of soils polluted with lindane

The in-situ removal of lindane from spiked soil was studied using cork barriers combined with electrokinetic and ohmic heating soil remediation processes. Both vertical and horizontal cork barriers have been evaluated to retain pollutants mobilized by electro-osmotic flow or volatilized by ohmic heating. Moreover, the addition of surfactant solutions in electrolyte wells has been evaluated to promote the dragging of lindane by electrokinetic fluxes. Results indicated that the drag of lindane by liquid flows is not as important as expected, opposite to what happened with the dragging by gaseous flows. The retention of gaseous lindane was also confirmed in adsorption tests carried out in a column packed with cork granules. The addition of surfactant had a very limited effect on the mobility of lindane, and dragging of this species to the electrode wells or to a permeable reactive barrier. On the contrary, the reactivity of lindane during the electrochemical treatments is relevant due to the electrokinetic basic front promoting the in-situ conversion of lindane into less chlorinated pollutants.

Iron slag permeable reactive barrier for PFOA removal by the electrokinetic process

The efficacy of the Standalone Electrokinetic (EK) process in soil PFAS removal is negligible, primarily due to the intersecting mechanisms of electromigration and electroosmosis transportation. Consequently, the redistribution of PFAS across the soil matrix occurs, hampering effective remediation efforts. Permeable reactive barrier (PRB) has been used to capture contaminants and extract them at the end of the EK process. This study conducted laboratory-scale tests to evaluate the feasibility of the iron slag PRB enhanced-EK process in conjunction with Sodium Cholate (NaC) biosurfactant as a cost-effective and sustainable method for removing PFOA from the soil. A 2 cm iron slag-based PRB with a pH of 9.5, obtained from the steel-making industry, was strategically embedded in the middle of the EK reactors to capture PFOA within the soil. The main component of the slag, iron oxide, exhibited significant adsorption capacity for PFOA contamination. The laboratory-scale tests were conducted over two weeks, revealing a PFOA removal rate of more than 79% in the slag/activated carbon PRB-EK test with NaC enhancement and 70% PFOA removal in the slag/activated carbon PRB-EK without NaC. By extending the duration of the slag/AC PRB-EK test with NaC enhancement to three weeks, the PFOA removal rate increased to 94.09%, with the slag/AC PRB capturing over 87% of the initial PFOA concentration of 10 mg/L. The specific energy required for soil decontamination by the EK process was determined to be 0.15 kWh/kg. The outcomes of this study confirm the feasibility of utilizing iron slag waste in the EK process to capture PFOA contaminants, offering a sustainable approach to soil decontamination. Combining iron slag PRB and NaC biosurfactant provides a cost-effective and environmentally friendly method for efficient PFOA removal from soil.

Application of a Zero-Valent Iron/Cork as Permeable Reactive Barrier for In Situ Remediation of Phenanthrene in Soil

This paper proposes an eco-efficient treatment technology for removing phenanthrene (PHE) from kaolinite soil, incorporating a permeable reactive barrier (PRB) in an electrokinetic (EK) remediation system, which was made by modifying the granulated cork (GC) with Fe@Fe2O3, identified as EK/Fe@Fe2O3/GC. The novel product Fe@Fe2O3/GC was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and element mapping. EK tests were conducted to investigate the performance of the EK/Fe@Fe2O3/GC for removal of PHE from soil. The results showed that PHE was driven by the electro-osmotic flow toward the cathode and reacted with the EK/Fe@Fe2O3/GC. Further, the removal efficiency of PHE in the soil was higher in the presence of H2O2 due to the additional reactions achieved. The results were discussed in light of the existing literature.

Enhancing soil vapor extraction with EKSF for the removal of HCHs

This paper evaluates the combination of electrokinetic soil flushing (EKSF) with soil vapor extraction (SVE) for the removal of four hexachlorocyclohexane (HCH) isomers contained in a real matrix. Results demonstrate that the combination of EKSF and SVE can be positive, but it is required the application of high electric fields (3 V cm^-1) in order to promote a higher temperature in the system, which improves the volatilization of the HCH contained in the system. Electrokinetic transport is also enhanced with the application of higher electric gradients, but these transport processes are slower than the volatilization processes, which are the primary in this system. Hence collection of species in the electrolyte wells is negligible as compared to the compound dragged with air by the SVE but the temperature increase demonstrates a good performance. Combination of EKSF with SVE can efficiently exhaust the four HCH isomers reaching a removal of more than 90% after 15 days of treatment (20% more than values attained by SVE) but it is required the application of high electric fields to promote a higher temperature in the system (to improve the volatilization) and EK transport (to improve the dragging). 1-D transport model can be easily used to estimate the average pore water velocity and the effective diffusion of each compound under the different experimental conditions tested.

Optimization, equilibrium, adsorption behaviour of Cu/Zn/Fe LDH and LDHBC composites towards atrazine reclamation in an aqueous environment

Cu-Zn-Fe Layered double hydroxides (LDH) and LDH dispersed on bamboo biochar (LDHBC) was used to study the adsorption of Atrazine by characterizing the adsorption kinetics, isotherms and response surface methodology (RSM) to reveal interactive effects of pH, adsorbent dosage and adsorbate initial concentration towards LDH optimum performance. The estimate of parameters determined for Langmuir isotherm quantities were in the range (21.84-37.91 mg/g) for LDH and (63.64-87.04 mg/g) for LDHBC. Regeneration and reusability after five cycles detected that the adsorption efficiencies of the adsorbents were reduced to 36% for LDH and 66% for LDHBC. Box Behnken design analysis could further reveal optimized conditions for higher Atrazine removal by LDH up to 74.8%. The adsorption mechanisms could be determined by π-π interactions occurring at the interfaces by hydrogen bonding and pore filling effects.

An overview of in-situ remediation for nitrate in groundwater

Faced with the increasing nitrate pollution in groundwater, in-situ remediation has been widely studied and applied on field-scale as an efficient, economical and less disturbing remediation technology. In this review, we discussed various in-situ remediation for nitrate in groundwater and elaborate on biostimulation, phytoremediation, electrokinetic remediation, permeable reactive barrier and combined remediation. This review described principles of each in-situ remediation, application, the latest progress, problems and challenges on field-scale. Factors affecting the efficiency of in-situ remediation for nitrate in groundwater are also summarized. Finally, this review presented the prospect of in-situ remediation for nitrate pollution in groundwater. The objective of this review is to examine the state of knowledge on in-situ remediation for nitrate in groundwater and critically evaluate factors which affect the up-scaling of laboratory and bench-scale research to field-scale application. This helps to better understand the control mechanisms of various in-situ remediation for nitrate pollution in groundwater and the design options available for application to the field-scale.

Bioremediation of polycyclic aromatic hydrocarbons contaminated soil under the superimposed electric field condition

An innovative superimposed electric field (SEF) was designed with the aim to achieve uniform removal of polycyclic aromatic hydrocarbons (PAHs) in soil. Also the influence of SEF on the bioremediation efficiency of PAHs was investigated in compared with the common electric field (CEF). Five experiments were conducted in this study, namely EK-CEF (applied CEF), EKB-CEF (CEF enhanced bioremediation), EK-SEF (applied SEF), EKB-SEF (SEF enhanced bioremediation), and Bio (bioremediation). The results indicated that electric field with periodically reversed polarity could effectively prevent the occurrence of large changes in soil pH, temperature, and electric current. The electric field intensity of SEF was concentrated in the range of 0.5-1.5 V/cm, and the difference between the maximum and minimum PAHs removal percentage in EK-SEF was just 5.4%, in comparison to 14.8% in EK-CEF. The bioremediation promoting effect did not show significant difference between SEF and CEF. Compared to Bio, the removal percentages of the 5-ring and 6-ring PAHs attributed to the degrading bacteria were much higher in EKB-SEF and EKB-CEF. Moreover, the microbial number increased with the distance away from electrodes, and the microbial community changed correspondingly. All these would be resulted in differences removal efficiencies among different PAHs components. Despite its intrinsic advantages, the influence of SEF on soil physicochemical and biological properties needs further study.

FeS2 assisted degradation of atrazine by bentonite-supported nZVI coupling with hydrogen peroxide process in water: Performance and mechanism

In this study, bentonite-supported nZVI (B-nZVI) was used as a catalyst to activate H₂O₂ for atrazine (ATZ) degradation in the presence of FeS₂. Results indicated that ATZ degradation by B-nZVI/H₂O₂ process was significantly enhanced when FeS₂ was introduced, and nearly 98% of ATZ was degraded by B-nZVI/FeS₂/H₂O₂ process within 60 min under the optimum conditions. ATZ degradation of B-nZVI/FeS₂/H₂O₂ process was much higher than the sum of B-nZVI and FeS₂/H₂O₂ processes. The presence of HCO₃^-, PO₄^3- and F^- exhibited significant negative effects on the ATZ degradation, whereas both Cu²⁺ and Ni²⁺ exhibited positive effects on that. Both citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) with lower concentration enhanced ATZ degradation rate, but significant suppression effects on that with higher concentration. The degradation of ATZ and 2,4-Dichlorophenol (2,4-DCP) could be simultaneously achieved in B-nZVI/FeS₂/H₂O₂ process under certain conditions. High soluble Fe²⁺ induced an excellent decomposition of H₂O₂ by B-nZVI and FeS₂. OH was dominant radical, and contributed to nearly 86% of the overall ATZ removal. A total of five intermediate products of ATZ were identified, and ATZ degradation was achieved via de-alkylation and hydroxylation processes. An enhanced reaction mechanism for ATZ degradation by B-nZVI/FeS₂/H₂O₂ process was proposed, and B-nZVI/FeS₂/H₂O₂ process exhibited an excellect catalytic performance within four successive runs.

Application of enhanced electrokinetic remediation by coupling surfactants for kerosene-contaminated soils: Effect of ionic and nonionic surfactants

Electrokinetic (EK) by coupling surfactants is an enhanced promising remediation technology to eliminate hydrophobic organic contaminants (HOC_s) from low-permeable soils. It is also applied to remediate kerosene-contaminated soils using anionic (SDS) and non-ionic (Tween 80) surfactants at different concentrations. There was negligible removal efficiency (40%) of kerosene during traditional EK without any enhancement technique. In the present study, the application of 0.005M and 0.01M SDS in EK-SDS-1 and EK-SDS-2 improved the removal efficiency to 50 and 55%, respectively towards the anode. Furthermore, the use of Tween 80 in EK-Tw80-1 and EK-Tw80-2 at 0.1 and 1% concentrations was able to raise kerosene removal gradually from 45% to 52% towards the cathode. These findings suggest that higher concentrations of SDS and Tween 80 contribute to the more effective elimination of kerosene. Thus, in EK-SDS-Tw80-V1.5 and EK-SDS-Tw80-V2, SDS and Tween 80 were used simultaneously at higher concentrations, which led to 63 and 67% kerosene removal, respectively. Considering the maximum removal in EK-SDS-Tw80-V2, the energy consumption in EK-SDS-Tw80-V2 was 178 KWh/m³ due to the higher voltage gradient; whereas without increased voltage in EK-SDS-Tw80-V1.5, this amount was decreased to 84 KWh/m³. It is to be mentioned that the electro-osmotic flow (EOF) played a significant role in minimizing kerosene concentration during the EK process, particularly when combined with surfactants.

Polyaniline-derived carbons: Remarkable adsorbents to remove atrazine and diuron herbicides from water

The contamination of water resources by hazardous organic compounds is becoming severe worldwide. In this study, the adsorptive removal of atrazine (ATZ) and diuron (DUR), two widely used herbicides, from water by polyaniline-derived carbons (PDCs) was investigated for the first time, under various conditions. A selected PDC, fabricated at optimum conditions, i.e., by pyrolysis at 800 °C (and labeled PDC(800)), showed remarkable adsorptivity for both herbicides, that is, 7.7 and 11.3 times the maximum adsorption capacity (Q₀) for ATZ and DUR, respectively, compared to activated carbon (AC). Or, the Q₀ values of PDC(800) for ATZ and DUR were 943 and 884 mg/g, respectively; however, the Q₀ values of AC were only 123 and 78.0 mg/g, respectively. Moreover, the optimum adsorbent PDC(800) had 4.5 and 3.1 times Q₀ that of the best adsorbent, that showed the highest performances, so far, for ATZ and DUR, respectively. Plausible adsorption mechanisms were suggested based on the porosity and the adsorption in a wide pH range. The new adsorbent was reusable via simple solvent washing. Based on its remarkable adsorption performance and facile reusability, PDC(800) can be considered a promising adsorbent to remove herbicides such as ATZ and DUR from contaminated water.

An approach to the photocatalytic mechanism in the TiO2-nanomaterials microorganism interface for the control of infectious processes

The approach of this timely review considers the current literature that is focused on the interface nanostructure/cell-wall microorganism to understand the annihilation mechanism. Morphological studies use optical and electronic microscopes to determine the physical damage on the cell-wall and the possible cell lysis that confirms the viability and microorganism death. The key parameters of the tailoring the surface of the photoactive nanostructures such as the metal functionalization with bacteriostatic properties, hydrophilicity, textural porosity, morphology and the formation of heterojunction systems, can achieve the effective eradication of the microorganisms under natural conditions, ranging from practical to applications in environment, agriculture, and so on. However, to our knowledge, a comprehensive review of the microorganism/nanomaterial interface approach has rarely been conducted. The final remarks point the ideal photocatalytic way for the effective prevention/eradication of microorganisms, considering the resistance that the microorganism could develop without the appropriate regulatory aspects for human and ecosystem safety.

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.

Assessment of hematological, hepato-renal, antioxidant, and hormonal responses of Clarias gariepinus exposed to sub-lethal concentrations of oxyfluorfen

Little is known about the effects of oxyfluorfen, a diphenyl ether herbicide, exposure on the African catfish (Clarias gariepinus) health. Consequently, the existing investigation was designed to highlight the impacts of oxyfluorfen exposure on C. gariepinus hematological indices, liver and kidney functions, reproductive hormones, and oxidative status. Furthermore, a consequent 10-day depuration period was adopted to evaluate the recovery of the disturbed indicators to normal values. In the first experiment, the 96-h lethal concentration 50 (LC₅₀) of oxyfluorfen for C. gariepinus was determined using probit analysis. Next, in a second experiment, 180 healthy fish (average initial body weight: 164.23 ± 0.24) were randomly assigned to 4 experimental groups exposed to 0, 1/10, 1/8, or 1/5 96-h LC₅₀ of oxyfluorfen. The hematological profile, hepatic enzymes, kidney damage byproducts, reproductive hormones, oxidative stress, and lipid peroxidation indicators together with acetylcholinesterase (AChE) content were assessed. A histopathological examination of the hepatic, renal, brain, and testicular tissues was accomplished. Moreover, the expression of the oxidative stress-related gene was carried out. The results showed that 96-h LC₅₀ of oxyfluorfen for C. gariepinus was 11.698 mg/L. Exposure to sublethal levels of oxyfluorfen induced macrocytic hypochromic anemia, leukopenia, lymphopenia, monocytopenia, and eosinopenia. Also, a concentration-dependent increase in alanine transaminase, alkaline phosphatase, aspartate transaminase, urea, creatinine, catalase, and malondialdehyde was detected following oxyfluorfen exposure together with upregulation of catalase gene. But, significant concentration-dependent reductions in AChE, glutathione transferase, reduced to oxidized glutathione ratio, estradiol, and testosterone activities were recorded. These biochemical alterations were accompanied by pathological perturbations in hepatic, renal, brain, and testicular tissues. Following 10 days of recovery, only the hematological impairments were abolished. Conclusively, the herbicides oxyfluorfen could induce multiple negative impacts on C. gariepinus with oxidative stress as a probable underlying mechanism. Additionally, a recovery period of 10 days was not enough to restore these impairments.

Development of a novel bio-organic fertilizer for the removal of atrazine in soil

The accumulation of atrazine in farmland is prone to cause phytotoxicity to kinds of sensitive crops, such as soybean. In addition, some kinds of agricultural solid wastes have long been considered as the important non-point pollution source. The aim of this experiment was to investigate the feasibility of removing atrazine from soil and alleviating the stress of atrazine on the growth of soybean by application a novel bio-organic fertilizer developed by agricultural solid wastes, such as cow manure organic fertilizer, biochar and poly-(γ-glutamic acid), as well as an atrazine-degrading strain Arthrobacter sp. DNS10. Sixteen potential bio-organic fertilizer formulations were designed by D-optimal mixture design of Design Expert software and atrazine-removal ability was selected to single out the optimal formulation. As a result, the optimal formulation of bio-organic fertilizer (named as DNBF10) was produced by the cow manure organic fertilizer 76.20%, biochar 4.46%, poly-(γ-glutamic acid) 8.63% (m/m) and the number of Arthrobacter sp. DNS10 with 0.91 × 10⁸ CFU/g. The atrazine removal percentage of DNBF10 for the atrazine in soil with the initial atrazine concentration 15.26 ± 0.49 mg/kg was 95.05% after 10 days' application with DNBF10 at the adding dosage of 5 mg/kg (relative to the dry weight of the soil). Furthermore, pot experiment results suggest that the growth of soybean seedlings in the soil (initial atrazine was 8.14 ± 0.16 mg/kg) that adding both of DNBF10 (25%) and chemical fertilizer (75%) were better than those of the treatment only adding chemical fertilizer (100%) under the same nutrient addition level. All the results indicate that the application of DNBF10 was a new alternative to reuse the typical agricultural solid wastes, as well as to reduce the harm caused by residual atrazine to soybean.

Techno-economic analysis of the scale-up process of electrochemically-assisted soil remediation

This work presents a techno-economic study of the scaling-up of the electrochemically-assisted soil remediation (EASR) process of polluted soil. Four scales have been selected for the study: laboratory, bench, pilot and prototype, with a capacity of treating a volume of soil of 1 × 10^-4, 2 × 10^-3, 0.11 and 21.76 m³, respectively. This study analyses the technical information produced by studies carried out at each scale, and informs about the fixed costs (construction of the electrokinetic remediation reactor, installation of auxiliary services and purchase of analytical equipment) and variable costs (start-up, operation and dismantling of the test) derived from running a test at each of the evaluated scales. The information discussed in based on the experience gained with many evaluations carried out over the last decade at these scales. This information can provide useful guidance for developing a scaling-up of the EASR for many researchers starting on the evaluation of this important environmental remediation technology.

Can electrochemistry enhance the removal of organic pollutants by phytoremediation?

An electrokinetic-assisted phytoremediation test using maize (Zea mays L.) was conducted in order to assess the role of the electric field on the enhancement of plant uptake and degradation of the moderate polar pesticide atrazine in spiked soils. Twelve different treatments, including two different initial atrazine soil doses (5 and 10 mg kg^-1) and two different values of the electric field applied (2 and 4 V cm^-1), together with the corresponding control treatments without plants and/or without electric current, were tested. The application of an electric field during a period of 4 h a day and with periodical polarity inversion (each 2 h) did not caused significant changes in soil pH; moreover, maize plants increased the buffering capacity of the soil. The application of an electric field of 2 V cm^-1 led to a slight decrease on maize biomass while the accumulation of atrazine and its main metabolites in plant tissues was significantly enhanced. On the overall, the yield of atrazine removal by electrokinetic-assisted phytoremediation with maize was increased up to 36.5% with respect to the phytoremediation process without electricity. On our knowledge, this work is the first one specifically focused on the removal of organic pollutants from soils by using the combination of phytoremediation and electrokinetic remediation.

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.

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.

Environmental Electrokinetics for a sustainable subsurface

Soil and groundwater are key components in the sustainable management of the subsurface environment. Source contamination is one of its main threats and is commonly addressed using established remediation techniques such as in-situ chemical oxidation (ISCO), in-situ chemical reduction (ISCR; most notably using zero-valent iron [ZVI]), enhanced in-situ bioremediation (EISB), phytoremediation, soil-washing, pump-and-treat, soil vapour extraction (SVE), thermal treatment, and excavation and disposal. Decades of field applications have shown that these techniques can successfully treat or control contaminants in higher permeability subsurface materials such as sands, but achieve only limited success at sites where low permeability soils, such as silts and clays, prevail. Electrokinetics (EK), a soil remediation technique mostly recognized in in-situ treatment of low permeability soils, has, for the last decade, been combined with more conventional techniques and can significantly enhance the performance of several of these remediation technologies, including ISCO, ISCR, EISB and phytoremediation. Herein, we discuss the use of emerging EK techniques in tandem with conventional remediation techniques, to achieve improved remediation performance. Furthermore, we highlight new EK applications that may come to play a role in the sustainable treatment of the contaminated subsurface.