Remediation of persistent organic pollutant-contaminated soil using biosurfactant-enhanced electrokinetics coupled with a zero-valent iron/activated carbon permeable reactive barrier

Enhanced nitrogen removal of micropolluted source waterbodies using an iron activated carbon system with siliceous materials: Insights into metabolic activity, biodiversity, interactions of core genus and co-existence

Aerobic denitrification technology can effectively abate the nitrogen pollution of water source reservoirs. In this study, 40% siliceous material was used as the carrier to replace the activated carbon in Fe/C material to enhance denitrification and purify water. The removal efficiency of new material for target pollutants were nitrate nitrogen (95.68%), total phosphorus (68.23%) and chemical oxygen demand (46.20%). Aerobic denitrification of water samples and anaerobic denitrification of sediments in three systems jointly assisted nitrogen removal. In a reactor with new material, diversity and richness of denitrifying bacterial communities were enhanced, and the symbiotic structure of aerobic denitrifying bacteria was more complex (Bacillus and Mycobacteria as the dominant bacteria); the microbial distribution better matched the Zif and Mandelbrot models. This system significantly increased the abundance of key enzymes in water samples. The new material effectively removed pollutants and represents a promising and innovative in-situ remediation method for reservoirs.

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.

MIL-101(Fe) based biomass as permeable reactive barrier applied to EK-PRB remediation of antimony contaminated soil

Numerous studies have demonstrated that electrokinetic-permeable reactive barrier (EK-PRB) can be used for the remediation of heavy metal contaminated soils, and their remediation efficiency is mainly determined by the filler material selected. By growing MIL-101(Fe) in situ on hollow loofah fiber (HLF), a novel material entitled HLF@MIL-101(Fe) was developed. The morphological characteristics and loading conditions were investigated, the adsorption characteristics were analyzed, and finally the synthesized composite material was applied to treat antimony-contaminated soil with EK-PRB as the reaction medium. The results show that MIL-101(Fe) is stably loaded on HLF. The adsorption capacity of Sb(III) can reach up to 82.31 mg g^-1, and the adsorption is in accordance with the quasi-secondary kinetic model, which indicates that chemisorption is dominant. The isothermal adsorption model indicates that the adsorption form of HLF@MIL-101(Fe) is mainly monolayer adsorption with more uniform adsorption binding energy. In the EK-PRB experiment, when ethylenediaminetetraacetic acid (EDTA) is used as the cathodic electrolyte, it can effectively enhance the electromigration and electroosmotic effects, and the overall remediation efficiency of the soil is increased by 38.12% compared with the citric acid (CA) group. These demonstrate the feasibility of HLF@MIL-101(Fe) in collaboration with EK-PRB in the treatment of antimony-contaminated soil.

Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences

This review aims to provide an overview of the sources and reactions of persistent organic pollutants (POPs) and surfactants in soil and sediments, the surfactant-enhanced solubilisation of POPs, and the unintended consequences of surfactant-induced remediation of soil and sediments contaminated with POPs. POPs include chemical compounds that are recalcitrant to natural degradation through photolytic, chemical, and biological processes in the environment. POPs are potentially toxic compounds mainly used in pesticides, solvents, pharmaceuticals, or industrial applications and pose a significant and persistent risk to the ecosystem and human health. Surfactants can serve as detergents, wetting and foaming compounds, emulsifiers, or dispersants, and have been used extensively to promote the solubilization of POPs and their subsequent removal from environmental matrices, including solid wastes, soil, and sediments. However, improper use of surfactants for remediation of POPs may lead to unintended consequences that include toxicity of surfactants to soil microorganisms and plants, and leaching of POPs, thereby resulting in groundwater contamination.

Possibility of New Active Substrates (ASs) to Be Used to Prevent the Migration of Heavy Metals to the Soil and Water Environments

This paper aims to propose an alternative to the known permeable reactive barriers (PRBs). PRB is one of the methods, which is a reactive barrier placed below the ground, to clean up contaminated groundwater. New polymer active substrates (ASs) were used to prevent soil contamination by toxic heavy metals. The active substrates consisted of a mixture of poly(vinyl chloride), Aliquat 336, and bis(2-ethylhexyl)adipate, which was applied to the skeleton material (fiberglass or textile). Aliquat 336 was used as a binding agent for metal ions (Cr(VI), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II)). In contrast with the PRBs, the ASs (from AS-1 to AS-5) were obtained in a simple way using the pouring method. The obtained ASs could be recycled and reused. The active substrates were used for the binding of various metal ions from aqueous solutions and the examined soil. It was found that the active substrate AS-1 decreased the concentrations of nickel, cadmium, and lead by more than 50% and that of chromium by more than 90% in the aqueous solution. High sorption efficiency for chromium and zinc metals (81% and 66%) with the use of AS-2 was also found, owing to which the migration of metals from soil to water can be limited. In the soil environment, active substrate AS-5 with the addition of a plasticizer showed the greatest effectiveness. This solution resulted in a reduction in each tested metal ion of at least 50%, and reductions in cadmium, lead, and copper of over 70%.

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.

Aqueous monomethylmercury degradation using nanoscale zero-valent iron through oxidative demethylation and reductive isolation

This paper proposes a Fenton-like reaction activated by nanoscale zero-valent iron (nZVI) for aqueous monomethylmercury (MMHg) decomposition. Reacting 10 μg L^-1 MMHg with 280 mg L^-1 nZVI removed 70% of the aqueous MMHg within 1 min, and its main product was aqueous Hg(II). Within 1 - 5 min, the aqueous Hg(II) decreased while the aqueous, solid, and gas-phase Hg(0) increased with 92% MMHg removal. Then, a secondary Hg(II) reduction to solid Hg(0) was prevalent within 30 - 60 min, with 98% MMHg removal. Diverse-shaped magnetite crystals were observed on the surface of nZVI in 2 h, suggesting that Fe(II) oxidation on magnetite can be a source of electrons for secondary Hg(II) reduction. When FeCl₂ and H₂O₂ were added to the MMHg solution without nZVI, 99% of the MMHg changed to Hg(II) within 1 min. The reactive oxygen species (ROS) produced by the Fenton-like reaction accounted for the rapid demethylation but not for the further reduction of Hg(II) to Hg(0). The results suggest a three-step pathway of MMHg decomposition by nZVI: (1) rapid MMHg demethylation by ROS; (2) rapid Hg(II) reduction by Fe(0); and (3) slow Hg(II) reduction by magnetite on the nZVI surface.

Removal of lindane using electrokinetic soil flushing coupled with air stripping

This paper evaluates the remediation of soil spiked with lindane using a combined treatment consisting of electrokinetic soil flushing (EKSF) with air stripping to elucidate the main processes occurring in the soil when electric fields of 0.75 V cm−1 and 1.50 V cm−1 are applied. The results demonstrate that lindane is efficiently transported to the anodic and cathodic wells using flushing fluids containing sodium dodecyl sulfate (SDS). Additionally, an important amount is volatilized and stripped with the injected air. In the cathodic well, lindane is rapidly transformed into other species because of the strongly alkaline media. These other species are also found in the portions of soil next to this well, confirming the efficient transport of chlorinated organics with SDS. After 14 days of operation, nearly 50% of the spiked lindane can be removed from the soil. Operation with large electric fields does not improve the performance of the treatment technology and results in lower current intensities and electro-osmotic fluxes and in higher evaporated water, despite the water content in the soil matrix, indicating the coexistence of multiple inputs in these processes.

Graphical abstract

Iron-Activated Carbon Systems to Enhance Aboriginal Aerobic Denitrifying Bacterial Consortium for Improved Treatment of Micro-Polluted Reservoir Water: Performances, Mechanisms, and Implications

Although many source waterbodies face nitrogen pollution problems, the lack of organic electron donors causes difficulties when aerobic denitrifying bacteria are used to treat micro-polluted water. Different forms of iron with granular activated carbon (AC) as carriers were used to stimulate aboriginal microorganisms for the purification of micro-polluted source water. Compared with the iron-absent AC system, targeted pollutants were significantly removed (75.76% for nitrate nitrogen, 95.90% for total phosphorus, and 80.59% for chemical oxygen demand) in the sponge-iron-modified AC system, which indicated that iron promoted the physical and chemical removal of pollutants. In addition, high-throughput sequencing showed that bacterial distribution and interaction were changed by ion dosage, which was beneficial for pollutant transformation and reduction. Microbial functions, such as pollutant removal and expression of functional enzymes that were responsible for the transformation of nitrate nitrogen to ammonia, were highly efficient in iron-applied systems. This study provides an innovative strategy to strengthen in situ remediation of micro-pollution in waterbodies.

Enhanced remediation of Cr(VI)-contaminated groundwater by coupling electrokinetics with ZVI/Fe3O4/AC-based permeable reactive barrier

Although widely used in permeation reaction barrier (PRB) for strengthening the removal of various heavy metals, zero-valent iron (ZVI) is limited by various inherent drawbacks, such as easy passivation and poor electron transfer. As a solution, a synergistic system with PRB and electrokinetics (PRB-EK) was established and applied for the efficient removal of Cr(VI)-contaminated groundwater. As the filling material of PRB, ZVI/Fe₃O₄/activated carbon (ZVI/Fe₃O₄/AC) composites were synthesized by ball milling and thermal treatment. A series of continuous flow column experiments and batch tests was conducted to evaluate the removal efficiency of Cr(VI). Results showed that the removal efficiency of Cr(VI) remained above 93% even when the bed volume (BV) reached 2000 under the operational parameters (iron/AC mass ratio, 2:1; current, 5 mA). The mechanism of Cr(VI) removal by the PRB-EK system was revealed through field emission scanning electron microscopy images, X-ray diffraction, X-ray photoelectron spectroscopy, Fe²⁺ concentration, and redox potential (E_h) values. The key in Cr(VI) reduction was the Fe²⁺/Fe³⁺ cycle driven by the surface microelectrolysis of the composites. The application of an externally supplied weak direct current maintained the redox process by enhancing the electron transfer capability of the system, thereby prolonging the column lifetime. Cr(VI) chemical speciation was determined through sequential extraction, verifying the stability and safety of the system. These findings provide a scientific basis for PRB design and the in-situ remediation of Cr(VI)-contaminated groundwater.

In-situ, Ex-situ, and nano-remediation strategies to treat polluted soil, water, and air - A review

Nanotechnology, as an emerging science, has taken over all fields of life including industries, health and medicine, environmental issues, agriculture, biotechnology etc. The use of nanostructure molecules has revolutionized all sectors. Environmental pollution is a great concern now a days, in all industrial and developing as well as some developed countries. A number of remedies are in practice to overcome this problem. The application of nanotechnology in the bioremediation of environmental pollutants is a step towards revolution. The use of various types of nanoparticles (TiO₂ based NPs, dendrimers, Fe based NPs, Silica and carbon nanomaterials, Graphene based NPs, nanotubes, polymers, micelles, nanomembranes etc.) is in practice to diminish environmental hazards. For this many In-situ (bioventing, bioslurping, biosparging, phytoremediation, permeable reactive barrier etc.) and Ex-situ (biopile, windrows, bioreactors, land farming etc.) methodologies are employed. Improved properties like nanoscale size, less time utilization, high adaptability for In-situ and Ex-situ use, undeniable degree of surface-region to-volume proportion for possible reactivity, and protection from ecological elements make nanoparticles ideal for natural applications. There are distinctive nanomaterials and nanotools accessible to treat the pollutants. Each of these methods and nanotools depends on the properties of foreign substances and the pollution site. The current designed review highlights the techniques used for bioremediation of environmental pollutants as well as use of various nanoparticles along with proposed In-situ and Ex-situ bioremediation techniques.

Can the green energies improve the sustainability of electrochemically-assisted soil remediation processes?

The green powering of electrochemically-assisted soil remediation processes had been strongly discouraged. Low remediation efficiencies have been reported as a consequence of the reversibility of the transport processes when no power is applied to the electrodes, due to the intermittent powering of renewable sources. However, it has been missed a deeper evaluation from the environmental point of view. This work goes further and seeks to quantify, using life cycle assessment tools, the environmental impacts related to the electro-kinetic treatments powered by different sources: grid (Spanish energy mix), photovoltaic and wind sources. The global warming potential and the ozone depletion showed higher environmental impacts in case of using green energies, associated with the manufacturing of the energy production devices. In contrast to that, results pointed out the lowest water consumption for the treatment powered with solar panels. The huge water requirements to produce energy, considering a Spanish energy mix, drop the sustainability of this powering strategy in terms of water footprint. Regarding toxicities, the pollutant toxicity was highly got rid of after 15 days of treatment, regardless the powering source used. Nevertheless, the manufacturing of energy and green energy production devices has a huge impact into the toxicity of the remediation treatments, increasing massively the total toxicity of the process, being this effect less prominent by the electro-kinetic treatment solar powered. In view of the overall environmental impact assessed, according to mid and endpoint impact categories, it can be claimed that, despite the high energy requirements and affectation to the global warming potential, the use of solar power is a more sustainable alternative to remediate polluted soils by electrochemical techniques.

Scale-up of electrokinetic permeable reactive barriers for the removal of organochlorine herbicide from spiked soils

This work aims to shed light on the scale-up a combined electrokinetic soil flushing process (EKSF) with permeable reactive barriers (PRB) for the treatment of soil spiked with clopyralid. To do this, remediation tests at lab (3.45 L), bench (175 L) and pilot (1400 L) scales have been carried out. The PRB selected was made of soil merged with particles of zero valent iron (ZVI) and granular activated carbon (GAC). Results show that PRB-EKSF involved electrokinetic transport and dehalogenation as the main mechanisms, while adsorption on GAC was not as relevant as initially expected. Clopyralid was not detected in the electrolyte wells and only in the pilot scale, significant amounts of clopyralid remained in the soil after 600 h of operation. Picolinic acid was the main dehalogenated product detected in the soil after treatment and mobilized by electro-osmosis, mostly to the cathodic well. The transport of volatile compounds into the atmosphere was promoted at pilot scale because of the larger soil surface exposed to the atmosphere and the electrical heating caused by ohmic losses and the larger interelectrode gap.

Synthesis of Rhamnolipid Derivatives Containing Ester Isosteres

Rhamnolipids are biosurfactants with many applications, arising from their inherent biological activity and their potential as bioremediation agents. Herein, we report the synthesis of four rhamnolipid derivatives in which the ester linkage connecting the two lipid chains in the natural compound is replaced with amide, ketone, ether, or hydrocarbon functional groups. Such compounds are anticipated to have enhanced hydrolytic stability and thus be useful probes of rhamnolipid-mediated biology and biotechnology.

Biosensor Design for Detection of Mercury in Contaminated Soil Using Rhamnolipid Biosurfactant and Luminescent Bacteria

In this study, a biosensor is designed to remove mercury as a toxic metal contaminant from the soil. The rhamnolipid biosurfactant was used to extract the mercury sorbed to soil to the aqueous phase. An immobilized bioluminescent bacterium (Escherichia coli MC106) with pmerRBPmerlux plasmid is assisted for mercury detection. A significant decrease in luminescence level was observed in a biosensor system containing contaminated soil sample extract. The concentrations of extracting mercury are well correlated with the mercury toxicity data obtained from experimental biosensor systems according to the RBL value. The optimum aeration rate of 20 ml/min was obtained for the biosensor systems. The advantage of such a biosensor is the in situ quantification of mercury as a heavy metal contaminant in soils. Therefore, this system could be proposed as a good biosensor-based alternative for future detection of heavy toxic metals in soils.

Chemical removal and selectivity reduction of nitrate from water by (nano) zero-valent iron/activated carbon micro-electrolysis

The processes of (n)ZVI/AC（（nano）zero valent iron/activated carbon）micro-electrolysis were applied for nitrate removal from groundwater, aiming to reduce nitrate to N₂, an environmentally friendly end product. (n)ZVI was utilized and combined with selected commercial AC to form the micro-electrolysis. Effect of different operational parameters, including reductant dosage, (n)ZVI/AC ratios, and reaction pH, on nitrate and TN removal were cleared. The results showed that nZVI presents higher reaction activities than ZVI in micro-electrolysis. With the increase of the (n)ZVI/AC mass ration from 1:2 to 2:1, the TN removal increased from 16.8% to 38.9%, then declined with the further increase of the ratio. The nitrate removal was negatively correlated with the initial pH of the solution. Compared to ZVI particles, even with a lower dosage, nZVI presented 100% nitrate removal at acidic and neutral pH conditions, and TN removal could maintain higher than 35% with pH lower than 9.0. A kinetic model was also established to explain the pathways of nitrate removal, and the results indicated that AC not only enriched nitrate as an adsorbent but also present highly potential in catalytic converting nitrate to N₂. The technique presented great potentials in removing nitrate from water and a promising application prospect.

MIL-100(Fe) and its derivatives: from synthesis to application for wastewater decontamination

MIL-100(Fe), an environmental-friendly and water-stable metal-organic framework (MOF), has caught increasing research and application attention in the recent decade. Thanks to its mesoporous structure and eximious surface area, MIL-100(Fe) has been utilized as precursors for synthesizing various porous materials under high thermolysis temperature, which makes the derivatives of MIL-100(Fe) pretty promising candidates for the decontamination of wastewater. Herein, this review systematically summarizes the versatile synthetic methods and conditions for optimizing the properties of MIL-100(Fe) and its derivatives. Then, diverse environmental applications (i.e., adsorption, photocatalysis, and Fenton-like reaction) of MIL-100(Fe) and its derivatives and the corresponding removal mechanisms are detailed in the discussion. Finally, existing knowledge gaps related to fabrications and applications are discussed to close and promote the future development of MIL-100(Fe) and its derivatives toward environmental applications. Graphical abstract.

Interactions between electrokinetics and rhizoremediation on the remediation of crude oil-contaminated soil

An electrokinetics (EK)-enhanced phytoremediation system with ryegrass was constructed to remediate crude oil-polluted soil. The four treatments employed in this study included (1) without EK or ryegrass (CK-NR), (2) EK only (EK-NR), (3) ryegrass only (CK-R), and (4) EK and ryegrass (EK-R). After 30d of ryegrass growth, EK at 1.0 V·cm^-1 with polarity reversal (PR-EK) was supplied for another 30 d. The electric current was recorded during remediation. The pH, electrical conductivity, total petroleum hydrocarbon content (TPH), 16S rDNA, functional genes of AlkB, Nah, and Phe, DGGE, and dehydrogenase activity in soil were measured. The physical-chemical indexes of the plant included the length, dry mass, and chlorophyll contents of the ryegrass. Results showed that EK-R removed 18.53 ± 0.53% of TPH, which was higher than that of other treatments (13.34-14.31%). Meanwhile, the values of 16S rDNA, AlkB, Nah, Phe, and dehydrogenase activity in the bulk soil of EK-R all increased. Further clustering analysis with numbers of genes and DGGE demonstrated that EK-R was similar to the ryegrass rhizosphere soils in both EK-R and CK-R, while the EK treatment of EK-NR was similar to that of CK-NR without EK and ryegrass. These results indicate that the PR-EK treatment used in this experiment successfully enlarged the existing scale of the rhizosphere microorganisms, improved microbial activity and enhanced degradation of TPH.

Evaluation of electrokinetics coupled with a reactive barrier of activated carbon loaded with a nanoscale zero-valent iron for selenite removal from contaminated soils

The range between dietary deficient and toxic levels for selenium is quite narrow. In this study, the synergistic effects of electrokinetics (EK) and a permeable reactive barrier (PRB) on the reductive sequestration of Se(IV) oxyanions from spiked soils were investigated in detail. Activated charcoal (AC)-supported Fe(II) and nanoscale zero-valent iron (nZVI) were prepared as the PRB media for use in an electrolyzer. In aqueous equilibrium adsorption tests, the AC-supported nZVI medium had a higher adsorption capacity than that of the other adsorbents. The Se(IV) removal isotherms were well-fitted using the Langmuir model. The Se(IV) removal rates were accurately predicted by both pseudo-first- and pseudo-second-order kinetic models. For the coupled systems, a moderate increase in the number of PRBs and decrease in the PRB thickness in the electrolyzer enhanced the removal and catalytic recovery of Se(IV) from the spiked soil samples. A Se(VI) removal efficiency of approximately 95% and Se(VI) reduction efficiency of 90% were achieved in the optimized electrochemical system. The Se(IV) species were reduced to Se° and FeSe by the AC-supported nZVI regardless of the pH distribution. The experimental results provide guidance for the multichannel recovery of Se from abandoned ore tailings or solid wastes.

Improvement of the electro-bioremediation process of a non-polar herbicide-polluted soil by means of surfactant addition

Oxyfluorfen is a non-polar herbicide that may cause severe soil pollution. The present work studies the possible improvement due to surfactant addition in the efficiency of electro-bioremediation of a clay soil polluted which such a non-polar, low-mobility pollutant. Two-week-long batch electro-bioremediation experiments were performed in a bench-scale device. Oxyfluorfen-polluted soil (20 mg kg^-1) was inoculated with an acclimated microbial culture, and several experiments were performed using different surfactant concentrations in the electrode wells (0.0, 2.5, 5.0, 10.0 and 20.0 g L^-1 of SDS, sodium dodecyl sulphate). Experiments were performed under 1.0 V cm^-1 and electrode polarity reversal. It was observed that the electro-osmotic flow (EOF) increased with SDS concentration and that SDS was successfully distributed across the soil, probably improving the oxyfluorfen mobility. Additionally, microbiological activity was fully maintained during the experiments. Electro-bioremediation without SDS removed 14% of the oxyfluorfen, while under 2.5 g L^-1 SDS, the efficiency increased to 22% because of an expected improvement in the contact between the different species in the soil. However, higher SDS concentrations (between 10.0 and 20.0 g L^-1) caused a decrease in the oxyfluorfen removal efficiency, as SDS is an easily biodegradable compound and was preferably used as substrate by the microbial culture instead of oxyfluorfen. Additionally, the use of high concentrations of SDS was clearly inefficient, as high amounts of the surfactant were lost through the EOF, and even low amounts of oxyfluorfen were removed to the electrode wells, which means that ex situ treatment of the polluted water would be needed.

Reversible electrokinetic adsorption barriers for the removal of organochlorine herbicide from spiked soils

This work aims to describe the removal of clopyralid from clay soils using electrokinetically assisted soil flushing (EKSF) coupled with a permeable reactive barrier (PRB), consisting of beds of Granulated Activated Carbon (GAC). To do this, two strategies have been evaluated on bench-scale electroremediation facilities (175 dm³): electrokinetic adsorption barrier (EKAB) and reversible electrokinetic adsorption barrier (REKAB). Likewise, to clarify the contribution of the different mechanisms to remediation process results are compared to those obtained in a reference test (without applying an electric field) and to results obtained in the EKSF of soils polluted with compounds with different polarity and vapour pressure. Results show that during EKAB and REKAB tests, clopyralid is removed from the soil by adsorption in PRB, electrokinetic transport and, very less decisively, by evaporation. The application of polarity reversion attains a higher retention of clopyralid in the activated carbon-PRB and a better regulation of pH because of the neutralization of H⁺ and OH^- generated in the electrolyte wells. After 30 days of operation, the removal of clopyralid by EKAB is 45% while it reaches 57% in the case of REKAB.