Iron slag/activated carbon-electrokinetic system with anolyte recycling for single and mixture heavy metals remediation

The electrokinetic process has been proposed for in-situ soil remediation to minimize excavation work and exposure to hazardous materials. The precipitation of heavy metals in alkaline pH near the cathode is still challenging. Reactive filter media and enhancement agents have been used in electrokinetics to enhance the removal of heavy metals. This study investigated coupling industrial iron slag waste and iron slag-activated carbon reactive filter media with electrokinetic for a single and mixture of heavy metals treatment. Instead of using acid enhancement agents, the anolyte solution was recycled to neutralize the alkaline front at the cathode, reducing the operation cost and chemical use. Experiments were conducted for 2 and 3 weeks at 20 mA electric current. Copper removal increased from 3.11 % to 23 % when iron slag reactive filter media was coupled with electrokinetic. Copper removal increased to 70.14 % in the electrokinetic experiment with iron slag-activated carbon reactive filter media. The copper removal increased to 89.21 % when the anolyte solution was recycled to the cathode compartment. Copper removal reached 93.45 % when the reactive filter media-electrokinetic process with anolyte recirculation was extended to 3 weeks. The reactive filter media- an electrokinetic process with anolyte recycling was evaluated for removing copper, nickel, and zinc mixture, and results revealed 81.1 % copper removal, 89.04 % nickel removal, and 92.31 % zinc removal in a 3-week experiment. The greater nickel and zinc removal is attributed to their higher solubility than copper. The results demonstrated the cost-effectiveness and efficiency of the electrokinetic with iron slag-activated carbon reactive filter media with anolyte recirculation for soil remediation from heavy metals.

Electrokinetic bioremediation of trichloroethylene and Cr/As co-contaminated soils with elevated sulfate

Co-contaminants and complex subsurface conditions pose great challenges to site remediation. This study demonstrates the potential of electrokinetic bioremediation (EK-BIO) in treating co-contaminants of chlorinated solvents and heavy metals in low-permeability soils with elevated sulfate. EK-BIO columns were filled with field soils, and were fed by the electrolyte containing 20 mg/L trichloroethylene (TCE), 250 μM Cr(VI), 25 μM As(III), 10 mM lactate, and 10 mM sulfate. A dechlorinating consortium containing Dehalococcoides (Dhc) was injected several times during a 199-d treatment at ∼1 V/cm. Sulfate reduction, Cr/As immobilization, and complete TCE biodechlorination were observed sequentially. EK-BIO facilitated the delivery of lactate, Cr(VI)/As(III), and sulfate to the soils, creating favorable reductive conditions for contaminant removal. Supplementary batch experiments and metagenomic/transcriptomic analysis suggested that sulfate promoted the reductive immobilization of Cr(VI) by generating sulfide species, which subsequently enhanced TCE biodechlorination by alleviating Cr(VI) toxicity. The dechlorinating community displayed a high As(III) tolerance. Metagenomic binning analysis revealed the dechlorinating activity of Dhc and the potential synergistic effects from other bacteria in mitigating heavy metal toxicity. This study justified the feasibility of EK-BIO for co-contaminant treatment and provided mechanistic insights into EK-BIO treatment.

Can rare earth elements be recovered from abandoned mine tailings by means of electrokinetic-assisted phytoextraction?

Given the high impact of traditional mining, the recovery of rare earth elements (REEs) from hazardous waste materials could become an option for the future in accordance with the principles of the circular economy. In this work, the technical feasibility of REEs recovery from metal mine tailings has been explored using electrokinetic-assisted phytoremediation with ryegrass (Lolium perenne L.). Phytoextraction combined with both AC current and DC current with reversal polarity was applied (1 V cm-1, 8 h day-1) to real mine tailings containing a total concentration of REEs (Sc, Y, La, Ce, Pr, and Nd) of around 146 mg kg-1. Changes in REEs geochemical fractionation and their concentrations in the soil pore water showed the mobilization of REEs caused by plants and electric current; REE availability was increased to a higher extent for combined electrokinetic-assisted phytoextraction treatments showing the relevant role of plants in the process. Our results demonstrated the initial hypothesis that it is feasible to recover REEs from real metal mining waste by phytoextraction and that the performance of this technology can be significantly improved by applying electric current, especially of the AC type, which increased REE accumulation in ryegrass in the range 57-68% as compared to that of the treatment without electric field application.

Improving device design in insulator-based electrokinetic tertiary separations

This study presents a methodology for designing effective insulator-based electrokinetic (iEK) systems for separating tertiary microparticle samples, which can be extended to more complex samples. First, 144 distinct iEK microchannel designs were built considering different shapes and arrangements of the insulating posts. Second, a mathematical model was developed with COMSOL software to predict the retention time of each particle type in the microchannel, this allowed identifying the best channel designs for two distinct types of separations: charge-based and sized-based. Third, the experimental charge-based and size-based separations of the tertiary microparticle mixtures were performed employing the improved designs identified with COMSOL modeling. The experimental results demonstrated successful separation in terms of separation resolution and good agreement with COMSOL predictions. The findings from this study show that the proposed method for device design, which combines mathematical modeling with varying post shape and post arrangement is an effective approach for identifying iEK systems capable of separating complex microparticle samples.

Removal of heavy metals from dredging marine sediments via electrokinetic hexagonal system: A pilot study in Italy

Among the several treatment options, electrokinetic (EK) remediation is recognized as an effective technique for the removal of heavy metals from low-permeability porous matrices. However, most of the EK decontamination research reported was performed on linear configuration systems at a laboratory scale. In this study, a series of experiments were performed on a pilot-scale system where the electrodes were arranged in a hexagonal configuration, to assess the improvement of the EK process in the removal of inorganic contaminants from sediments dredged in the harbor of Piombino, Italy. HNO3 was used as acid conditioning and both pH effect and treatment duration time were investigated. Sediment characterization and metal fractionation were also presented, in order to understand how the bioavailability of metals affects the process efficiency. The increase in pH due to the buffering capacity of the sediment in the sections close to the cathode favored the precipitation and accumulation of metals. However, the results highlighted that longer treatment times, combined with an efficient pH reduction, can improve treatment performance, resulting in high removal efficiencies for all the target metals considered (a percentage removal greater than 50% was reached for Cd, Ni, Pb, Cu and Zn). Compared to different EK configuration systems, the hexagonal configuration arrangement applied in our study provides better results for the remediation of dredged marine sediment.

Development of an environmentally sustainable technique to minimize the sludge production in the textile effluent sector through an electrokinetic (EK) coupled with electrooxidation (EO) approach

This study presents an environmentally sustainable method for minimizing sludge production in the textile effluent sector through the combined application of electrokinetic (EK) and electrooxidation (EO) processes. AAS and XRF analyses reveal that utilizing acidic electrolytes in the EK method successfully eliminates heavy metals (Cu, Mn, Zn, and Cr) from sludge, demonstrating superior efficiency compared to alkaline conditions. In addition, the total removal efficiency of COD contents was calculated following the order of EK-3 (60%), EK-1 (51%) and EK-2 (34%). Notably, EK-3, leveraging pH gradient fluctuations induced by anolyte in the catholyte reservoir, outperforms other EK systems in removing COD from sludge. The EK process is complemented by the EO process, leading to further degradation of dye and other organic components through the electrochemical generation of hypochlorite (940 ppm). At an alkaline pH of 10.0, the color and COD removal were effectively achieved at 98 and 70% in EO treatment, compared to other mediums. In addition, GC-MS identified N-derivative residues at the end of the EO. This study demonstrates an integrated approach that effectively eliminates heavy metals and COD from textile sludge, combining EK with EO techniques.

Electrochemical remediation of synthetic and real marine sediments contaminated by PAHs, Hg and As under low electric field values

To date, remediation, protection, and restoration of contaminated sites is a global concern. The current technologies to restore sediments characterized by heterogeneous characteristics, several pollutants, fine grains, and low hydraulic permeability are poorly effective; hence their remediation is still challenging. A promising approach for the sediment's remediation could be the electrochemical route since it is a not-expensive, effective and noninvasive in situ technology. Electrochemical remediation (ER) is commonly studied under relatively high electric fields (E ≥ 1 V cm-1) and using costly processing fluids in a three compartments cell aiming to desorb and transport the contaminants into the processing fluids (secondary dangerous effluent). In this work, contaminated marine sediments were electrochemically treated focusing on the insertion of electrodes directly in the sediments and adopting, for the first time for real sediments, low E values (≤ 0.25 V cm-1) for 4-days period. It was observed that PAHs can be simultaneously transported and degraded in situ preventing the production of a secondary dangerous effluent and reducing the energy consumption. Firstly, clay marine sediments dragged from Capo Granitola Coast (Trapani, Italy) spiked with five PAHs congeners (5PAHs), Hg and As were used as a simplified model matrix and treated to simulate a real case study. A total PAHs removal efficiency of 57% was reached after 96 h of treatment under 0.05 V cm-1. Then, real polluted marine sediments from Augusta Bay (Syracuse) and Bagnoli-Coroglio Bay (Naples) in the southern Italy were treated as real contaminated sediments to be restored, to validate the proposed approach for real cases. A quite good removal efficiency of PAHs was reached after 96 h of electrochemical treatment coupled with a low energetic consumption due to the rather E values adopted. In addition, it was observed that this approach, under the adopted conditions, is unsuitable for the remediation of Hg and As.

Effect of electrokinetic process on in situ stabilization and detoxification of arsenic-contaminated soil with high content of calcium

Owing to the high risk of human exposure to arsenic-contaminated soil, reducing its toxicity is essential. This study used the electrokinetic (EK) process with iron-rich electrodes to synchronously achieve the accumulate, stabilize and detoxify soil arsenic. Changes in arsenic valence, leaching toxicity, and microbial communities related to toxicity were comprehensively considered. The results demonstrated that arsenic was mainly transported toward the anode and accumulated by electromigration owing to the negatively charged arsenic anions under EK conditions. The cathode approaching effectively promote arsenic movement to the anode; the largest As(T) transportation rate of 30.61% was achieved near the cathode (S4). The transportation ratio of As(III) was 1.84 times more than that of As(V). The As(III) content and leaching toxicity of soil arsenic in all treatments decreased after applying the EK process. In particular, the anode approaching effectively elevated the average ratios of soil As(III) oxidation and stabilization to 37.88% and 61.73%, respectively. Correspondingly, the total phospholipid fatty acid content increased substantially after EK treatment and showed a pollution stress elimination effect. The electrokinetic effect can essentially cause highly active and easily migrated arsenic to accumulate near the anode and middle sections. The electric field mediated iron mineralization and stabilized arsenic by oxidizing As(III) and reacting with newly formed iron-rich phases (S). Meanwhile, the electric field regulated the form of soil calcium from CaCO3 to CaSO4 and caused calcium-bound arsenic to change to a more stable form. According to these results, in situ stabilization and detoxification of arsenic-contaminated soil can be realized by the EK process, avoiding stabilizer addition and excavation.

Innovative method for the brine treatment by electrokinetic principles integrated with solar photovoltaic plants

With the growing world population and industrial production, the demand for water has been continuously increasing. By 2030, it was estimated that 60.0 % of the world population will not have access to freshwater, which is about 2.50 % of the total global water. For this, a total of over 17,000 operational desalination plants have been constructed worldwide. However, the key barriers to expansion of the desalination treatments are the brine production and energy consumption. In fact, the brine production is 50.0 % higher than the freshwater, and its treatments could account for 5.0-33.0 % of total desalination cost. Here, a new theoretical approach for brine treatments integrated to solar photovoltaic plants (PVs) to supply renewable energy to the whole system has been proposed. This approach consists in combining electrokinetic and electrochemical phenomena to dilute the brine, by using an alkaline clay with high buffering power. This method substantially desalinates the brine to produce new treated seawater, using clean energy, optimizing energetic and management costs. Some hypotheses and secondary effects should validate the model, e.g., relatively high Ca2+ promotes the electro-migration; the Cl2 production reduces the Cl- concentrations; and the production of H2 can be used to store energy. A practical example for PVPs design is shown.

Coupling electrokinetic remediation with flushing using green tea synthesized nano zero-valent iron/nickel to remediate Cr (VI)

This study focuses on a flushing-electrokinetic remediation technology of hexavalent chromium from the chromium slag dump site. A suspension of nanoscale zero-valent iron/nickel fabricated from green tea (GT-nZVI/Ni), was employed as an eluent to degrade Cr (VI) and enhance the remediation effectiveness of a single EK. The removal efficiency of Cr (VI) was compared under different voltages, electrode spacings and pH values of the anolyte. The results demonstrated that the combined flushing and EK achieved a removal rate of Cr (VI) in the soil throughout all the experiments ranging from 83.08 to 96.97% after 120 h. The optimal result was obtained when the voltage was 28 V, the pH value of anolyte was 3 and the electrode spacing was 15 cm. The removal of Cr (VI) reached 91.49% and the energy consumption was 0.32606 kW·h·g-1. The underlying mechanisms responsible for the removal of Cr (VI) by GT-nZVI/Ni flushing-EK primarily involved electromigration, reduction and adsorption co-precipitation processes. The fractionation analysis of Cr (VI) concentration in the soil after remediation showed that the presence of GT-nZVI/Ni facilitated the conversion of Cr (VI) into oxidizable and residual states with low mobility and toxicity. The results of toxicity characteristic leaching procedure (TCLP) indicated that the leaching concentration of Cr (VI) was below 1 mg·L-1, complying with the standards set by the Environmental Protection Agency. Additionally, the phytotoxicity testing revealed that the germination index (GI) of the remediated soil reached 54.75%, indicating no potential harm to plants.

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.

Protein corona formation on lipidic nanocapsules: Influence of the interfacial PEG repartition

The parameters currently used for characterization of nanoparticles, such as size and zeta potential, were not able to reflect the performance of a nanocarrier in the biological environment. Therefore, more thorough in vitro characterization is required to predict their behavior in vivo, where nanoparticles acquire a new biological identity due to interactions with biomolecules. In this present study, we performed in vitro characterization in biological fluids for lipid nanocapsules (LNCs) with varying means sizes (50 nm and 100 nm), different electrical surface charges and different Poly Ethylene Glycol (PEG) compositions. Then, different methods were applied to show the impact of the protein corona formation on LNCs. Even if all formulations attached to plasmatic proteins, a higher thickness of corona and highest protein binding was observed for certain LNC50 formulations. A better knowledge of the phenomenon of protein adsorption over NPs in the plasmatic media is a cornerstone of clinical translation. In fact, after short blood circulation time, it is not the initially designed nanoparticle but the complex nanoparticle bearing its protein corona which circulates to reach its target.

Numerical solutions for the treatment brine by diffusive and migration flux using new brine-clay-seawater system

With the growing world population and industrial production, the demand for water has been continuously increasing. By 2030, 60.0% of the world population will not have access to freshwater, which is ∼2.50% of the total global water. For this, a total of over 17,000 operational desalination plants have been constructed worldwide. However, the key barrier to desalination expansion is brine production, which is 50.0% higher than the freshwater, generating 5.0-33.0% of total desalination cost. In this paper, a new theoretical approach for brine treatments has been proposed. It consists in combining electrokinetic and electrochemical mechanisms by using an alkaline clay with high buffering power. Advanced numerical model has been carried out to estimate the ions concentrations in the brine-clay-seawater system. Analytical analyses have been also carried out to estimate the global system efficiency. Results show the feasibility of the theoretical system, its size, and usability of the clay. This model not only should clean the brine to produce new treated seawater but also it should recover useful minerals thank to the electrolysis and precipitations effects.

An investigation into the efficiency of electrokinetic and electrokinetic coupled with calcium peroxide permeable reactive barriers techniques for soil remediation using a statistical analysis

The current study emphasizes on the applicability of combining the electrokinetic (EK) and permeable reactive barriers (PRB) techniques compared to the simple EK technique. For this purpose, a statistical analysis is conducted using the Fractional Factorial Design statistical method. Also, General Linear Model and Two-sample T-Test analyzes are considered to clarify which type of soil remediation technique represents the highest efficiency. Calcium peroxide, an affordable material with easy capability for cultivation, is utilized in the PRB process to eliminate the soil from diesel contamination. The experiments were performed for 3 days and 10 days, according to which the initial contamination rates of 10 and 20% were selected, and the applied voltages were 20 V and 30 V. Using the innovative remediation technique, the experiments were conducted for 10 days with 20% initial pollution content and the applied voltage of 30 V, the initial gasoil content was about 190.5 mg/g, and after applying the proposed technique, the average final pollution content throughout soil reached approximately 37 mg/g. This experiment was also conducted for the approximately initial gasoil content of 185, 206, and 191 mg/g, which led to the removal efficiency of 79.59%, 78.93%, and 79.15%, respectively. The main novelty of this paper is attributed to the use of calcium peroxide in the EK-PRB technique and the statistical analysis conducted in this study that indicates the remarkable efficiency of the proposed approach. It was also revealed that the efficiency of the proposed technique is on par with the other state-of-art ones presented in the literature and even sometimes outperforms them.

Effects of the presence of phosphate buffer solution on removal efficiency of Pb and Zn in soil by solid phase microbial fuel cells

Simple, effective and environment-friendly ways for remediating toxic metal pollution are necessary. In this study, the effect of different concentrations phosphate buffer solution (PBS) on removal efficiency of Pb and Zn in soil by solid phase microbial fuel cell (SMFC) was investigated. During 100 days of operation, the SMFC with 150 mM PBS generated the highest power density of 21.7 mW m^-2 and the lowest internal resistance of 161 Ω. The addition of PBS can also increase soil conductivity and maintain a suitable pH for microbial activity. Furthermore, the removal rate of Pb and Zn in the SMFC with 150 mM PBS can reach 14.7% and 22.3%, respectively. The microbial community analyses demonstrated that Anditalea as an exoelectrogen in alkaline-saline conditions was significantly enriched in the SMFC with 150 mM PBS. This study provides an effective strategy for strengthening SMFC to remove toxic metals in soil.

Insights into enhanced electrokinetic remediation of copper-contaminated soil using a novel conductive membrane based on nanoparticles

Electrokinetic remediation is a process in which a direct electric current is applied across a section of contaminated soil to remove metals. To improve the electrokinetic remediation in this study, a conductive membrane was fabricated via in situ chemical polymerization employing pyrrole and copper oxide nanoparticles. The fabricated membrane was placed in an electric field as part of the electrode structure. A physical model was constructed and filled with copper-contaminated kaolinite in the concentration of 200 mg/kg. To control the pH, 0.1 M citric acid and 0.01 M potassium chloride were used as the electrolyte solutions. Experimental parameters such as voltage, current, pH, EC, drained flow, and copper concentration were measured. The results showed that the minimum surface resistivity of the fabricated membrane under a maximum pressure of 8.2 kPa was 2.55 kΩ/m². The experimental results demonstrated that the use of citric acid as an electrolyte was more useful to desorb the copper due to the formation of the copper-citrate complex. When employing the fabricated membrane, the copper removal increased from 13% (in CT-2) to 63% (in GM-2), while the removal of copper using potassium chloride electrolyte increased from 42% (in CT-1) to 52% (in GM-1). The highest power consumption was obtained in experiments using citric acid. Due to the higher removal efficiency of copper in GM-2, the energy utilization efficiency (β) increased and reached 29.9 near β value of GM-1 with the lowest power consumption.

Microscale electrokinetic-based analysis of intact cells and viruses

Miniaturized electrokinetic methods have proven to be robust platforms for the analysis and assessment of intact microorganisms, offering short response times and higher integration than their bench-scale counterparts. The present review article discusses three types of electrokinetic-based methodologies: electromigration or motion-based techniques, electrode-based electrokinetics, and insulator-based electrokinetics. The fundamentals of each type of methodology are discussed and relevant examples from recent reports are examined, to provide the reader with an overview of the state-of-the-art on the latest advancements on the analysis of intact cells and viruses with microscale electrokinetic techniques. The concluding remarks discuss the potential applications and future directions.

Emerging on-chip electrokinetic based technologies for purification of circulating cancer biomarkers towards liquid biopsy: A review

Early detection of cancer can significantly reduce mortality and save lives. However, the current cancer diagnosis is highly dependent on costly, complex, and invasive procedures. Thus, a great deal of effort has been devoted to exploring new technologies based on liquid biopsy. Since liquid biopsy relies on detection of circulating biomarkers from biofluids, it is critical to isolate highly purified cancer-related biomarkers, including circulating tumor cells (CTCs), cell-free nucleic acids (cell-free DNA and cell-free RNA), small extracellular vesicles (exosomes), and proteins. The current clinical purification techniques are facing a number of drawbacks including low purity, long processing time, high cost, and difficulties in standardization. Here, we review a promising solution, on-chip electrokinetic-based methods, that have the advantage of small sample volume requirement, minimal damage to the biomarkers, rapid, and label-free criteria. We have also discussed the existing challenges of current on-chip electrokinetic technologies and suggested potential solutions that may be worthy of future studies.

The combination of phytoremediation and electrokinetics remediation technology on arsenic contaminated remediation in tailing storage facilities from gold mine

This research aims to study the effects of combining Mott dwarf Napier grass cultivation and electrokinetic (EK) treatment on arsenic (As) mobility and remediation of As-contaminated mine tailings. Experimental groups were treated with 0, 1, 2, and 4 V/cm for 15 days–120 days. Groups treated with 1 and 2 V/cm electromagnetic field had better As remediation efficiency than the control group with no electromagnetic field treatment. However, electromagnetic field treatment at 4 V/cm inhibited plant growth and had an effect on As uptake in the form of solution at a low level. Plants in experimental group treated with 1 V/cm electromagnetic field for 90 days had significantly high As accumulation (7.69 ± 0.16 mg/kg) in their roots. Their relative growth rate was close to that of the control group with the highest biomass (15.09 ± 0.65 g) recorded on day 120. Mobility and accumulation of As and other elements in the plants were investigated using micro-X-ray fluorescence technique (Beamline BL6b). It was found that very low As concentrations could not be detected although energy emitted from its innermost electron shell (K alpha (Kα1&2) and K beta (Kβ1)) were equal to 10.54 and 11.72 keV. In general, As accumulation in plants occurs primarily in the roots and stems, with greater accumulation around the cortex, epidermis, and xylem. This is similar to the patterns of iron and phosphate accumulation, which occurs through phosphate transporters. In addition, high aluminum mobility and accumulation were found in the stems and leaves of Mott dwarf Napier grass. However, As accumulation in the roots of Mott dwarf Napier grass was higher than in the stem and leaves.

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Plants treated with 1 V/cm electromagnetic field for 120 days had the highest arsenic accumulation.

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Treatment with 4 V/cm electromagnetic field can inhibit plant growth.

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Napier grass accumulated more arsenic in its roots than in its stems and leaves.

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Treatment with 1 V/cm electromagnetic field stimulated toxin uptake by plants.

The influence of electrokinetic bioremediation on subsurface microbial communities at a perchloroethylene contaminated site

There is an increased interest in finding remedies for contamination in low permeability and advection-limited aquifers. A technology applicable at these sites, electrokinetic-enhanced bioremediation (EK-BIO), combines traditional bioremediation and electrokinetic technologies by applying direct current to transport bioremediation amendments and microbes in situ. The effect of this technology on the native soil microbial community has only been previously investigated at the bench scale. This research explored the influence of EK-BIO on subsurface microbial communities at a field-scale demonstration site. The results showed that, similar to the findings in laboratory studies, alpha diversity decreased and beta diversity differed temporally, based on treatment phase. Enrichments in specific taxa were linked to the bioaugmentation culture and electron donor. Overall, findings from our study, one of the first field-scale investigations of the influence of electrokinetic bioremediation on subsurface microbial communities, are very similar to bench-scale studies on the topic, suggesting good correlation between laboratory and field experiments on EK-BIO and showing that lessons learned at the benchtop are important and relevant to field-scale implementation. KEY POINTS: • Microbial community analysis of field samples validates laboratory study results • Bioaugmentation cultures and electron donors have largest effect on microbial community.

Time-resolved particle image velocimetry analysis and computational modeling of transient optically induced electrothermal micro vortex

Trapping, sorting, transportation, and manipulation of synthetic microparticles and biological cells enable investigations in their behavior and properties. Microfluidic techniques like rapid electrokinetic patterning (REP) provide a non-invasive means to probe into the nature of these micro and nanoparticles. The opto-electrically induced nature of a REP micro vortex allows tuning of the trap characteristics in real-time. In this work, we studied the effects of transient optical heating on the induced electrothermal vortex using micro-particle image velocimetry (μ-PIV) and computational modeling. A near infra-red (980 nm) laser beam was focused on a colloidal suspension of 1 μm polystyrene beads sandwiched between two parallel-plate electrodes. The electrodes were subjected to an AC current. The laser spot was scanned back-and-forth in a line, at different frequencies, to create the transient vortex. This phenomenon was also studied with a computational model made using COMSOL Multiphysics. We visualize fluid flow in custom-shaped REP traps by superposing multiple axisymmetric (spot) vortices and discuss the limitations of using superposition in dynamically changing traps.

Review of nonlinear electrokinetic flows in insulator-based dielectrophoresis: From induced charge to Joule heating effects

Insulator-based dielectrophoresis (iDEP) has been increasingly used for particle manipulation in various microfluidic applications. It exploits insulating structures to constrict and/or curve electric field lines to generate field gradients for particle dielectrophoresis. However, the presence of these insulators, especially those with sharp edges, causes two nonlinear electrokinetic flows, which, if sufficiently strong, may disturb the otherwise linear electrokinetic motion of particles and affect the iDEP performance. One is induced charge electroosmotic (ICEO) flow because of the polarization of the insulators, and the other is electrothermal flow because of the amplified Joule heating in the fluid around the insulators. Both flows vary nonlinearly with the applied electric field (either DC or AC) and exhibit in the form of fluid vortices, which have been utilized to promote some applications while being suppressed in others. The effectiveness of iDEP benefits from a comprehensive understanding of the nonlinear electrokinetic flows, which is complicated by the involvement of the entire iDEP device into electric polarization and thermal diffusion. This article is aimed to review the works on both the fundamentals and applications of ICEO and electrothermal flows in iDEP microdevices. A personal perspective of some future research directions in the field is also given.

Insulator-based dielectrophoretic focusing and trapping of particles in non-Newtonian fluids

Insulator-based dielectrophoretic (iDEP) microdevices have been limited to work with Newtonian fluids. We report an experimental study of the fluid rheological effects on iDEP focusing and trapping of polystyrene particles in polyethylene oxide, xanthan gum, and polyacrylamide solutions through a constricted microchannel. Particle focusing and trapping in the mildly viscoelastic polyethylene oxide solution are slightly weaker than in the Newtonian buffer. They are, however, significantly improved in the strongly viscoelastic and shear thinning polyacrylamide solution. These observed particle focusing behaviors exhibit a similar trend with respect to electric field, consistent with a revised theoretical analysis for iDEP focusing in non-Newtonian fluids. No apparent focusing of particles is achieved in the xanthan gum solution, though the iDEP trapping can take place under a much larger electric field than the other fluids. This is attributed to the strong shear thinning-induced influences on both the electroosmotic flow and electrokinetic/dielectrophoretic motions.

Remediation of lead (II)-contaminated soil using electrokinetics assisted by permeable reactive barrier with different filling materials

Removal of lead (II) (Pb²⁺) from contaminated soil was investigated using a new-type switchable-array-electrode electrokinetics assisted by permeable reactive barrier (SAE/EK-PRB). The soil pH after treatments with SAE/EK-PRB ranged from 3.5 to 4.8, and the peak values of current density was highest with 3.01 mA/cm² at voltage gradient 2.5 V/cm. Both voltage gradient and moisture content promoted the removal of Pb²⁺. Moisture content 35% and 2.5 V/cm were considered as the optional operating conditions. Different PRB filling materials including zeolite, fly ash, active carbon alone and the combination of fly ash and graphene oxide were, therefore, investigated under the optional operating conditions. The highest removal reached 92.6% with the combination of fly ash and graphene oxide. Pb²⁺ forms in the soil with different PRB filling materials showed the percentages of weak bindings, such as exchangeable and carbonate forms decreased. However, strong binding, residual form increased largely, indicating the SAE/EK-PRB could effectively reduce the environmental risk of Pb²⁺ to a great extent. Fly ash and the combination of zeolite and fly ash as PRB filling materials demonstrated to be highly promising for the effective EK remediation of Pb²⁺-contaminated soil, taking the economic and environmental principles and remediation efficiency into consideration.

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.

Enhanced copper removal from contaminated kaolinite soil by electrokinetic process using compost reactive filter media

Electrokinetic (EK) remediation is a promising technology for soil decontamination, although basic pH in the soil close to cathode has constrained EK effectiveness due to heavy metal precipitation. This study aimed to enhance copper removal from kaolinite soil by integrating EK with compost (C) as recyclable reactive filter media (RFM) for the first time. Compost placed near the cathode served as an adsorbent to bind copper ions while buffering the advancement of the alkaline front in soil. The total copper removal rate increased from 1.03% in EK to 45.65% in EK-100%C under an electric potential of 10 V. Further experiments conducted by using biochar (BC) and compost/biochar (C + BC) mixture RFM at different ratios showed total Cu removal efficiency decreasing as EK-100%C > EK-(10%BC + 90%C) > EK-(20%BC + 80%C) > EK-(30%BC + 70%C) > EK. The application of a constant electric current of 20.00 mA further enhanced copper removal to 84.09% in EK-100%C although did not show significant enhancement in EK-(BC + C). The compost RFM was regenerated by acid extraction and then reused twice, achieving a total removal of 74.11%. The findings demonstrated compost as a promising and reusable RFM for the efficient removal of copper in contaminated soil.

Effects of electric fields on Cd accumulation and photosynthesis in Zea mays seedlings

Phytoremediation enhanced by electrokinetic has been considered as a potential technology for remediating contaminated soils. However, the effects of electric fields on Cd accumulation and photosynthesis in Zea mays (as a cathode) is still unclear. In the present study, Zea mays seedlings were exposed to various doses of Cd²⁺ (10, 50, 100 μM) to explore the impact of electric fields on Cd accumulation and photosynthesis of Zea mays. Results showed that upon exposure to a concentration of 100 μM Cd, electric fields significantly altered the Cd contents in maize shoots, whereas the concentration of 50 μM Cd increased the Cd contents in maize roots as well as affected the Cd transport from roots to shoots. Uptake index (UI) increased by 1.34%-66.16% with the application of electric fields. The variation of photosynthetic rates attributed to the open or closure of stoma was similar to the change of shoot fresh weight, particularly in maize exposed to high Cd stress. This study proposes a new technology in Cd phytoremediation and provides important information on physiological processes in maize when exposed to Cd stress and electric fields.

Influence of electrode configuration on electrokinetic-enhanced persulfate oxidation remediation of PAH-contaminated soil

Electrokinetic (EK) remediation combined with in situ chemical oxidation (ISCO) can be applied to low permeability organic contaminated soil. However, the effects of electrode configuration on EK-oxidation remediation remain unclear. In this study, EK-ISCO remediation of real polycyclic aromatic hydrocarbon (PAH)-contaminated soil under different electrode configurations was conducted. The results showed that increasing the number of anodes and electrode pairs in one-dimensional (1D) and two-dimensional (2D) electrode configuration was conducive to migration of oxidants into the system. The change in soil pH after remediation in 2D electrode configuration was not obvious, but the increase of soil electrical conductivity (EC) was higher than that of the 1D electrode configuration. The removal rates of PAHs in 2D electrode configurations (35.9-40.9%) were relatively higher than those of the 1D electrode configurations (0.54-31.6%), and the hexagonal electrode configuration yielded the highest pollutant removal efficiency, reaching 40.9%. The energy consumption under 2D electrode configuration was smaller than that under 1D electrode configuration, and the energy consumption of per gram removed PAHs in the hexagon configuration (66.74 kWh (g PAHs)^-1) was lowest in all electrode configurations. Overall, the results of this study suggest that 2D electrode configuration is better than 1D and hexagonal electrode configuration is an optimal electrode configuration.

Application of enhanced electrokinetic approach to remediate Cr-contaminated soil: Effect of chelating agents and permeable reactive barrier

Enhanced electrokinetic (EK) technique was employed to remediate Cr-contaminated soil using a permeable reactive barrier (PRB) and chelating agents. Synthesized nanomagnetic Fe₃O₄ was used as a reactive material in PRB. Moreover, EDTA and citric acid (CA) were used as chelating agents. Sequential extraction method (SEM) was employed to determine Cr-elimination mechanism during the EK process. The results revealed that EDTA (78% Cr removal) was more effective than CA (54% Cr removal) in eliminating Cr from the contaminated soil during the EK process. The application of PRB in combination with EDTA was able to reduce the Cr removal rate to 70 and 66% by locating PRB in the middle section and near the anode/cathode reservoir, respectively. The use of PRB coupled with EDTA near the anode and cathode led to a more uniform Cr removal from the soil during the EK process. The highest energy consumption was 0.12 KWh during the EK remediation using PRB. Traditional EK remediation could only remove exchangeable and carbonate fractions of Cr. The use of chelating agents led to a significant (more than 90%) increase in Cr removal from the following fractions: exchangeable phase, carbonate phase, and bond to Fe-Mn oxides. In addition to electromigration (EM) mechanism, electroosmotic flow (EOF) played an important role in Cr removal during the EK process, especially when coupled with PRB.

Electrokinetic potential reduction of fine particles induced by gas nucleation

Electrokinetic potential of particles has been extensively studied in colloidal systems over the past century, while up to date, the influence of gas on electrokinetic behaviors of particles has not been fully understood yet. In this study, the electrokinetic response of particles to gas nucleation was systematically investigated with coal as the object. The results showed that the nucleation of gas (both on particle surfaces and in water) significantly changed the particle' electrokinetic behaviors. Higher gas content and particle's surface hydrophobicity normally trigger more intensive gas nucleation, thus inducing more significant reduction of particle zeta potential. After gas nucleation, numerous nanobubbles (NBs) appear in the suspensions mainly in two forms: NBs adhering onto solid surfaces (ANBs) and NBs stagnating in bulk solutions (BNBs). ANBs not only enhance the surface heterogeneity, but also cause the "steric hindrance" effect, and electric double layer (EDL) overlapping and associated ions shielding towards charged particles, which significantly decrease their electrokinetic potentials. Although BNBs can also reduce the zeta potential of particles by EDL compressing, their functions are rather limited.

Joule heating-enabled electrothermal enrichment of nanoparticles in insulator-based dielectrophoretic microdevices

Insulator-based dielectrophoresis (iDEP) exploits the electric field gradients formed around insulating structures to manipulate particles for diverse microfluidic applications. Compared to the traditional electrode-based dielectrophoresis, iDEP microdevices have the advantages of easy fabrication, free of water electrolysis, and robust structure, etc. However, the presence of in-channel insulators may cause thermal effects because of the locally amplified Joule heating of the fluid. The resulting electrothermal flow circulations are exploited in this work to trap and concentrate nanoscale particles (of 100 nm diameter and less) in a ratchet-based iDEP microdevice. Such Joule heating-enabled electrothermal enrichment of nanoparticles are found to grow with the increase of alternating current or direct current electric field. It also becomes more effective for larger particles and in a microchannel with symmetric ratchets. Moreover, a depth-averaged numerical model is developed to understand and simulate the various parametric effects, which is found to predict the experimental observations with a good agreement.

Insights into the remediation of cadmium-pyrene co-contaminated soil by electrokinetic and the influence factors

The remediation of cadmium-pyrene co-contaminated soil by electrokinetic (EK) and the influence factors were investigated in this study. The artificial contaminated soils were treated for 20 days in EK experimental setups without electrolyte solution reservoirs, to simulate in-situ remediation of unsaturated soil. The results indicated that polarity-reversing electric field had maintained soil pH in the range of 7.27-7.67. Cadmium (Cd) contaminant would aggregate near electrodes, and the average Cd concentration in these areas had reached 72.21 mg/kg (original 51.6 mg/kg), while the value in soil farthest away from electrodes was 33.58 mg/kg. The reasons for Cd aggregated were: the insoluble hydroxide formations attribute to the frequently alternation of acid-base environment, and the decrease of pH and water holding capacity in soil away from electrodes would promote the dissolved Cd movement by electro-osmosis flow. Although the applied electric field could promote the growth and activity of pyrene-degrading microorganisms (PDM), the soluble Cd would be the restriction factor, especially in soil near electrodes. However, the highest (56.38%) pyrene removal efficiency (PRE) was achieved near electrodes due to the synergistic effect of electric filed and PDM, and PRE was positively correlated with the PDM number in soil away from electrodes.

Copper removal from contaminated soil through electrokinetic process with reactive filter media

Electrokinetic (EK) remediation has been used in the removal of metal ions from contaminated soil. This study focused on integrating the EK technique with different reactive filter media (RFM) of activated carbon (AC) and biochar (BC) for the first time without adding chemicals to facilitate the removal of copper ions from the contaminated kaolinite soil. Tests based on EK, EK coupled with AC (EK-AC), and EK combined with BC (EK-BC) were performed under an electric potential of 10 V, and the overall removal efficiency of copper ions decreased as EK-BC > EK-AC > EK. The results show that 27% of copper in the soil was captured by BC, compared with only 10% by AC. Additional EK-BC test performed under a constant current (20 mA) revealed that the acid front swept across the soil, resulting in 70.6-95.0% copper removal from soil sections 4 to 1 close to the anode region with more copper accumulation in section 5. Similar to the EK-BC test under a fixed voltage, 26% of copper in the soil was captured by BC during EK-BC treatment under a constant current although with a higher energy consumption. Moreover, RFM was regenerated by flushing with an acid solution, achieving 99.3% of copper recovery in BC and 78.4% in AC. Although the permeability of AC-RFM was higher than that of BC-RFM, copper contaminant was more easily leached out from the BC-RFM. The findings demonstrated the feasibility of contaminant entrapment in BC-RFM and recovery by acid leaching, with potential for sustainable soil remediation.

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.

Effect of amino acid chiral ionic liquids

A chiral methodology was developed for the first time to ensure the quality control of ivabradine, a novel anti-ischemic and heart rate lowering drug commercialized as a pure enantiomer. With this aim, electrokinetic chromatography (EKC) was employed and the enantiomeric separation of ivabradine was investigated using different anionic and neutral cyclodextrins (CDs) and amino acid-based chiral ionic liquids (CILs) as sole chiral selectors. Baseline separation was only achieved with sulfated CDs, and the best enantiomeric resolution was obtained with sulfated-γ-CD. Under the optimized conditions, ivabradine enantiomers were separated in 6 min with a resolution of 2.7. Nuclear magnetic resonance experiments showed a 1:1 stoichiometry for the enantiomer-CD complexes and apparent and averaged equilibrium constants were determined. The combined use of sulfated-γ-CD and different CILs as dual separation systems was investigated, resulting in a significant increase in the resolution. The use of 5 mM tetrabutylammonium-aspartic acid ([TBA][L-Asp]) in 50 mM formate buffer (pH 2.0) containing 4 mM sulfated-γ-CD were considered the best conditions in terms of resolution and migration times for ivabradine enantiomers. Nevertheless, as no inversion of the enantiomer migration order was observed when combining CILs and sulfated-γ-CD and a good enantiomeric resolution and efficiency were obtained using just sulfated-γ-CD as the sole chiral selector, the analytical characteristics of this method were evaluated, showing good recovery (98% and 103% for S- and R-ivabradine, respectively) and precision values (RSD < 5% for instrumental repeatability, < 6% for method repeatability and < 7% for intermediate precision). The limits of detection (LODs) were 0.22 and 0.28 μg mL^-1 for S- and R-ivabradine, respectively, and the method enabled to detect a 0.1% of the enantiomeric impurity, allowing to accomplish the requirements of the International Conference on Harmonisation (ICH) guidelines. Finally, the method was applied to the analysis of a pharmaceutical formulation of ivabradine. The content of R-ivabradine was below the LOD and the amount of S-ivabradine was in agreement to the labeled content.

Emerging sustainable technologies for remediation of soils and groundwater in a municipal solid waste landfill site -- A review

Remediation of soils and groundwater in a municipal solid wastes (MSW) landfill site emerges as a global challenge to the living environment on earth with significant market potential. Unlike contaminants in an industry or agricultural site, contaminants from MSW landfills are diverse, primarily consisting of chemical oxygen demand (COD), inorganic matter (ammonia-nitrogen, nitrate-nitrogen, total phosphorus) and heavy metals. This renders new challenges to remediation contaminants of different characters altogether. A status quo of existing technologies, including permeable reactive barriers, electrokinetic remediation, microbial remediation, and injection of either solubilizing agents or micro or nanobubbles were thoroughly reviewed, with an emphasis on removal efficiency based on existing projects at lab, pilot or field scales. A design chart tailored for the remediation of a landfill contaminated site was developed, verified by a few case studies, which supplement the chart. Future trends of technical innovation (such as multi-layer permeable reactive barriers (PRBs)) and challenges (such as flow pattern) were identified.

Electrokinetic-enhanced phytoremediation of uranium-contaminated soil using sunflower and Indian mustard

Electrokinetic-enhanced phytoremediation is an effective technology to decontaminate heavy metal contaminated soil. In this study, we examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of U from soils with various U sources. Redistribution of uranium in soils as affected by planting and electrokinetic treatments was investigated. The soil was spiked with 100 mg kg^-1 UO₂, UO₃, and UO₂(NO₃)₂. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct-current was applied across the soils for 9 days. The results indicated that U uptake in both plants were significantly enhanced by electrokinetic treatments from soil with UO₃ and UO₂(NO₃)₂. U was more accumulated in roots than in shoots. Electrokinetic treatments were effective on lowering soil pH near the anode region. Overall, uranium (U) removal efficiency reached 3.4-4.3% from soils with UO₃ and uranyl with both plants while that from soil with UO₂ was 0.7-0.8%. Electrokinetic remediation treatment significantly enhanced the U removal efficiency (5-6%) from soils with UO₃ and uranyl but it was 0.8-1.3% from soil with UO₂, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation. This study implies the potential feasibility of electrokinetic-enhanced phytoremediation of U soils with sunflower and Indian mustard.

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.

The lift force on a charged sphere that translates and rotates in an electrolyte

The distortion of the charge cloud around a uniformly charged, dielectric, rigid sphere that translates and rotates in an unbounded binary, symmetric electrolyte at zero Reynolds number is examined. The zeta potential of the particle ζ is assumed small relative to the thermal voltage scale. It is assumed that the equilibrium structure of the cloud is slightly distorted, which requires that the Péclet numbers characterizing distortion due to particle translation, Pe t = U a / D , and rotation, Pe r = Ω a 2 / D , are small compared to unity. Here, a is radius of the particle; D is the ionic diffusion coefficient; U = | U | and Ω = | Ω | , where U and Ω are the rectilinear and angular velocities of the particle, respectively. Perturbation expansions for small Pe t and Pe r are employed to calculate the nonequilibrium structure of the cloud, whence the force and torque on the particle are determined. In particular, we predict that the sphere experiences a force orthogonal to its directions of translation and rotation. This "lift" force arises from the nonlinear distortion of the cloud under the combined actions of particle translation and rotation. The lift force is given by F lift = L ( κ a ) ( ε a 3 ζ 2 / D 2 ) U × Ω [ 1 + O ( Pe t , Pe r ) ] . Here, ε is the permittivity of the electrolyte; κ - 1 is the Debye length; and L ( κ a ) is a negative function that decreases in magnitude with increasing κ a . The lift force implies that an unconstrained particle would follow a curved path; an electrokinetic analog of the inertial Magnus effect. Finally, the implication of the lift force on cross-streamline migration of an electrophoretic particle in shear flow is discussed.

Comparing the risk of metal leaching in phytoremediation using Noccaea caerulescens with or without electric field

Hyperaccumulators can mobilize all metals in soil through secreting exudates to form soluble compounds but only hyperaccumulate part of them. Metals that cannot be accumulated are defined as non-hyperaccumulated metals and can increase the leaching risk in phytoremediation. Cd and Zn hyperaccumulator Noccaea caerulescens (formerly Thlaspi caerulescens) was utilized to remediate multi-metal polluted soil in the present study, and the leaching risk of non-hyperaccumulated metals including Cu and Pb was investigated during the phytoremediation process. Comparing with Thlaspi arvense, a non-hyperaccumulator, N. caerulescens significantly decreased the concentrations of Cd and Zn in leachate gathered from precipitation simulation experiments without electric field, but meanwhile dramatically increased the concentrations of Cu and Pb in soil solution. Electric field with low (2 V) and moderate (4 V) voltages increased the biomass yield and metal uptake capacity of N. caerulescens simultaneously and therefore further reduced the concentrations of Cd and Zn in the leachate. Although the volume of leachate decreased significantly in pots with electric field, the leaching risk of Pb and Cu was deteriorated. Thus, decontaminating multi-metal polluted soil with electric field and hyperaccumulator should be conducted with caution due to potential secondary environmental risk caused by activated non-hyperaccumulated metals.

Comparing storage battery and solar cell in assisting Eucalyptus Globulus to phytoremediate soil polluted by Cd, Pb, and Cu

Metal decontamination and leaching alleviation capacity of Eucalyptus globulus with and without electric field were investigated using ICP-MS. The biomass production of the chosen plant increased from 0.87 kg in planting control without electrokinetic treatment to 1.16 and 1.42 kg in experiments with electric field supplied by storage battery and solar cell, respectively. Under the influence of electric field with a voltage of 6.5 V, significantly more Cd, Pb and Cu were extracted by the species. Precipitation simulation was performed to evaluate the capacity of battery and solar panel to intercept leaching. The total volume of leachate gathered from the control decreased from 1012 mL to 299 and 336 mL in containers treated by storage battery and solar cell, respectively. In addition to reduction of leachate, the leaching mass of Cd, Pb and Cu was decreased significantly by electric fields (both battery and solar cell) treatments. The effect of remediation and environmental risk alleviation by solar cell was comparable with storage battery, at least during the 30-day experimental period. On the basis of the present study, solar cell should be a suitable substitute for conventional power supply to improve metal polluted soil when considering phytoremediation efficiency and energy consumption.

Using solar cell to phytoremediate field-scale metal polluted soil assisted by electric field

Eucalyptus globulus were used to remediate a real scale site endangered by e-waste with electric fields supplied by solar cell and conventional storage battery. The capacity of the species to produce biomass, absorb pollutants and decontaminate metals, as well as the soil moisture of various layers under different treatments was compared. During the 3-month experiment, the output potential of solar cell influenced by weather conditions was less stable (ranging from 0 to 8.3 V) comparing with traditional power supply. Solar cell and storage battery stimulated the growth of the species from 5.92 in control to 7.21 and 7.38 kg per plant, respectively, demonstrating their similar improvement effect. Electric fields of either power source increased the metal concentrations of plant roots and shoots in equal proportions and subsequently greatly promoted the efficiency to decontaminate pollutants. Relative to the control without electric field, solar cell and storage battery treatments reduced the soil moisture of each corresponding layer and consequently, alleviated the leaching risk. At the termination of the experiment, metals tended to distribute in the surface layer under electric field assisted phytoremediation either by solar cell or storage battery. Comparing with conventional battery, solar cell has similar effect on improving remediation and mitigating leaching risk, but is less energy consuming and easier to manage, especially under real scale field. Solar cell treatment was suggested to be a suitable supplementary means to improve phytoremediation efficiency.

Factors influencing the removal of antibiotic-resistant bacteria and antibiotic resistance genes by the electrokinetic treatment

The performance of the electrokinetic remediation process on the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) was evaluated with different influencing factors. With chlortetracycline (CTC), oxytetracycline (OTC), and tetracycline (TC) as template chemicals, the removal of both ARB and ARGs was enhanced with the increase of voltage gradient (0.4-1.2 V cm^-1) and prolonged reaction time (3-14 d). The greatest removal (26.01-31.48% for ARB, 37.93-83.10% for ARGs) was obtained applying a voltage of 1.2 V cm^-1, leading to the highest electrical consumption. The effect of polarity reversal intervals on the inactivation ratio of ARB followed the order of 0 h (66.06-80.00%) > 12 h (17.07-24.75%) > 24 h (10.44-13.93%). Lower pH, higher current density, and more evenly-distributed voltage drop was observed with a polarity reversal interval of 12 h compared with that of 24 h, leading to more efficient electrochemical reactions in soil. Compared with sul genes, tet genes were more vulnerable to be attacked in an electric field. It was mainly attributed to the lower abundance of tet genes (except tetM) and the varied effects of electrokinetic remediation process on different ARGs. Moreover, a relatively less removal ratio of tetC and tetG was obtained mainly due to the mechanism of the efflux pump upregulation. Both tet and sul genes were positively correlated with TC-resistant bacteria. The efflux pump genes like tetG and the cellular protection genes like tetM showed different correlations with ARB. This study enhances the current understanding on the removal strategies of ARB and ARGs, and it provides important parameters for their destruction by the electrokinetic treatment.

Comparison of constant, pulsed, incremental and decremental direct current applications on solid-liquid phase separation in oil sediments

Phase separation of oil wastes can mitigate the effects on the environment, by decreasing the volume of hazardous materials and regenerate energy. This study focused on the advanced electrokinetic method as a treatment technology to treat oil sediments from oil refineries and separate them into their individual phase components. The effects of four types of electrical field on the phase separation of oil sediments from an oil refinery were investigated namely constant direct current (CDC), pulsed direct current (PDC), incremental direct current (IDC) and decremental direct current (DDC). The results showed that the extent and quality of phase separation differed based on the type of electrical current applied, and indicated that different mechanisms such as electroosmosis, electrophoresis, electro-demulsification, and electro-sedimentation might have been involved in the separation process depending on the type of electrical supply. The application of DDC and IDC was found to cause a significant separation of solids by electrophoresis with the movement of almost 70% of solids to the anode of the reactors. The DDC and IDC regimes resulted in the most efficient phase separation of the oil sediments, and even incurred a highly resolved separation of light hydrocarbons at the top anode.

Remediation of nitrate-contaminated groundwater by PRB-Electrokinetic integrated process

Activated carbon is used as a reactive media in Permeable Reactive Barrier (PRB) for the removal of inorganic contaminants such as nitrate from groundwater. Since removal rate by this media decreases by time and due to the high costs of excavation and replacement of new media, the usage of activated carbon as an adsorbent in PRB is limited. The present study aimed to solve this defect by integrating electrokinetic process and PRB, using in-situ regeneration of activated carbon. This research was carried out on a laboratory scale using synthetically contaminated water and modified activated carbon as a reactive media in PRB. The effects of pH, nitrate concentration, carbon to sand ratio, and also electric gradient on the performance of the process were evaluated, and optimal conditions were determined, to increase the system longevity. According to the results, by applying an electric gradient of 1.25 V cm^-1 to the PRB alone process in optimum operating condition (135 mg L^-1 initial nitrate concentration, flow rate of 2.3 L min^-1, pH = 6.8, and carbon to sand ratios of 1:1) the adsorbent capacity increased by 90%. Under these conditions, the integrated process could keep nitrate concentration in the effluent below the standard limit for about 111 h, while the PRB alone process could do the same job for about 59 h. Also, SEM analysis showed that by applying electrokinetic process, activated carbon was regenerated. Integration of electrokinetic process and PRB was also caused nitrate to transfer from activated carbon media into the soil layer above the system. This nitrate-rich soil has the potential for reuse in agricultural activities.

A statistical approach of zinc remediation using acidophilic bacterium via an integrated approach of bioleaching enhanced electrokinetic remediation (BEER) technology

The aim of the present study was to isolate an indigenous acidophilic bacterium from tannery effluent contaminated sludge (TECS) sample and evaluate its potentiality towards the removal of zinc using an integrated approach of bioleaching enhanced electrokinetic remediation (BEER) technology in zinc spiked soil at an initial concentration of 1000 mg/kg. The isolated acidophilic bacterium was characterized by biochemical and 16S rRNA molecular identification and was named as Serratia marcescens SMAR1 bearing an accession no. MG742410 in NCBI database. The effect of pH and inoculum dosage of SMAR 1 strain showed an optimal growth at pH 5.0 and 4% (v/v) respectively. Based on these experimental data, a statistical analysis was done using Design Expert computer software, v11 to study the interaction between the process parameters with respect to zinc reduction as an output response. Electrokinetic experiments were conducted in a customised EK cell under optimised process conditions, employing titanium electrodes. Experiments for zinc removal were demonstrated for bioleaching, electrokinetic (EK) and BEER technology. On comparing, the integrated process was found to evidence as an excellent metal remediation option with a maximum zinc removal of 93.08% in 72 h than plain bioleaching (72.86%) and EK (56.67%) in 96 h. This is the first report of zinc removal in a short period of time using Serratia marcescens. It is therefore concluded that the BEER approach can be regarded as an effective technology in cleaning up the metal contaminated environment with an easy recovery and reuse option within short period of time.

Effect of various electrokinetic treatment regimes on solids surface properties and thermal behavior of oil sediments

The electrokinetic process has shown its ability to separate the different material phases. However, not much is known about the effect of the electric fields on the surface properties of solids in the oil sediments and their behavior under different electrical regimes. In this study, the effect of four different types of electrical current on the surface properties of oil sediments was investigated, namely constant direct current (CDC), pulsed direct current (PDC), incremental direct current (IDC) and decremental direct current (DDC). X-ray photoelectron spectroscopy (XPS) analyses showed a decrease in the concentration of carbon from 99% in centrifuged samples to 63% on the surface of the solids in the PDC-treated oil sediment. Wettability alteration and contact angle studies showed an enhance in hydrophilicity of the solids following electrokinetic treatment. A significant change in carbon and oxygen-containing functionalities at the surface solids of the DDC-treated sediment was also observed. Thermogravimetric analyses (TGA) confirmed the ability of electrokinetic treatment in separating the phases by shifting the thermogram profiles towards lower temperatures. The findings showed that the electrokinetic process exerts its effect by altering the surface properties of the sediment solids and destabilizing water-in-oil emulsions to facilitate phase separation of this complex waste.

Changes in metal speciation and mobility during electrokinetic treatment of industrial wastes: Implications for remediation and resource recovery

Industrial waste deposits contain substantial quantities of valuable metals and other resources, although often in a recalcitrant form that hinders their recovery. This paper reports an experimental programme on the application of electrokinetic (EK) processing to two different waste materials (a mine tailings deposit and a metallurgical furnace dust), with the aim of exploring the effect of EK on metal speciation and extractability, with a focus on Pb and Zn due to their prevalence in these materials. The speciation of metals within the waste was determined based on a selective sequential extraction (SSE) procedure which was applied to the materials before, during and after the application of the EK treatment. The results demonstrate the generation of an acidic front in the mine tailings, which enhanced the transport of ions associated with the more labile fractions, a behaviour typical of materials characterized by a lower buffering capacity. The application of the EK in the furnace dust showed much less effect due to a very high starting pH (10) with the higher buffering capacity posing an obstacle to transport. It is shown that EK has altered the geochemical speciation of the metals in both materials, typically redistributing them from less available SSE fractions to the more labile fractions. Zn was redistributed with the SSE fractions and mobilised to a greater extent than Pb in both samples. The changes in pH and redox potential arising as a result of the application of an electric field are likely to be the main causes of the changes in speciation of both Zn and Pb. The considerable changes in metal fractionation, including removal from more recalcitrant fractions, suggest that EK may facilitate metal recovery processes. This, combined with its applicability to fine grained materials and heterogeneous environments, demonstrates that the technique may be particularly suited to both remediation of, and in-situ resource recovery from, such materials.

Ultrasound-enhanced electrokinetic remediation for removal of Zn, Pb, Cu and Cd in municipal solid waste incineration fly ashes

Low-frequency ultrasound generated by a transducer was investigated to activate the raw municipal solid waste incineration (MSWI) fly ashes in the electrokinetic process, aiming at enhancing heavy metal (HM) removal and achieving better remedial efficacy. The maximum removal efficiencies of 69.84%, 64.24%, 67.74% and 59.93% were obtained in the orthogonal tests of ultrasonication for Zn, Pb, Cu and Cd, respectively. The acoustic time of 30 min and controlling temperature of 45 °C in the operating parameters were quantitatively determined to optimize the ultrasonication of the MSWI fly ash matrices. The changes of acoustic time had a significant effect on the extraction efficiencies of all the four heavy metal elements in the sonication optimal experiments. The longer running time was preferred for the pretreatment of the fly ashes in according to the marginal mean removal results. The voltage gradient of 2 V/cm was most likely to improve the removals of four HMs during the electrokinetics in the range of 0.5-2 V/cm. The synergetic application of acidification and ultrasonication for the media treatment was demonstrated to be most effective in enhancing the remedial efficiencies in the further electrokinetic experiments compared with the other activation systems. Correspondingly, the leaching concentrations of Zn, Pb, Cu and Cd in the samples were reduced by 85.92%, 98.22%, 88.53% and 98.34%, respectively. The contaminants were continuously extracted from the solid grains of the fly ashes by the protonic attack and bubble implosion. The obtained risk-assessment-code values indicated the adoption of AUS-EKR system reduced the environmental toxicity for the fly ashes to the maximum extent.