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

Hybrid and enhanced electrokinetic system for soil remediation from heavy metals and organic matter

The electrokinetic (EK) process has been proposed for soil decontamination from heavy metals and organic matter. The advantages of the EK process include the low operating energy, suitability for fine-grained soil decontamination, and no need for excavation. During the last three decades, enhanced and hybrid EK systems were developed and tested for improving the efficiency of contaminants removal from soils. Chemically enhanced-EK processes exhibited excellent efficiency in removing contaminants by controlling the soil pH or the chemical reaction of contaminants. EK hybrid systems were tested to overcome environmental hurdles or technical drawbacks of decontamination technologies. Hybridization of the EK process with phytoremediation, bioremediation, or reactive filter media (RFM) improved the remediation process performance by capturing contaminants or facilitating biological agents' movement in the soil. Also, EK process coupling with solar energy was proposed to treat off-grid contaminated soils or reduce the EK energy requirements. This study reviews recent advancements in the enhancement and hybrid EK systems for soil remediation and the type of contaminants targeted by the process. The study also covered the impact of operating parameters, imperfect pollution separation, and differences in the physicochemical characteristics and microstructure of soil/sediment on the EK performance. Finally, a comparison between various remediation processes was presented to highlight the pros and cons of these technologies.

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 remediation for the removal of heavy metals in soil: Limitations, solutions and prospection

Electrokinetic remediation (EKR) technology is a promising method to remove heavy metals from low permeability soil, because it is environmentally friendly, efficient and economical, and can realize in-situ remediation. In this paper, the basic principles and related physical and chemical phenomena of EKR are systematically summarized, and three limiting problems of EKR technology are put forward: the weak ability of dissolving metals, focusing effect, and energy consumption. There are many methods to solve these technical problems, but there is a lack of systematic summary of the causes of problems and solutions. Based on various enhanced EKR technologies, this paper summarizes the main ideas to solve the limiting problems. The advantages and disadvantages of each technology are compared, which has guiding significance for the development of new technology in the future. This paper also discusses the dissolution of residual heavy metals, which is rare in other articles. The energy consumption of EKR and the remediation effect are equally important, and both can be used as indicators for evaluating the feasibility of new technologies. This paper reviews the influence of various electric field conditions on power consumption, such as renewable energy supply, new electrode materials and electrode configurations, suitable voltage values and functional electrolytes. In addition, a variety of energy consumption calculation methods are also introduced, which are suitable for ohmic heat loss, energy distribution when there is non-target ion competition, and power consumption of specific ions in various metal ions. Researchers can make selective reference according to their actual situations. This paper also systematically introduces the engineering design and cost calculation of EKR, lists the research progress of some engineering cases and pilot-scale tests, analyzes the reasons why it is difficult to apply EKR technology in large-scale engineering at present, and puts forward the future research direction.

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.

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.

Microbiome-based enrichment pattern mining has enabled a deeper understanding of the biome-species-function relationship

Microbes live in diverse habitats (i.e. biomes), yet their species and genes were biome-specific, forming enrichment patterns. These enrichment patterns have mirrored the biome-species-function relationship, which is shaped by ecological and evolutionary principles. However, a grand picture of these enrichment patterns, as well as the roles of external and internal factors in driving these enrichment patterns, remain largely unexamined. In this work, we have examined the enrichment patterns based on 1705 microbiome samples from four representative biomes (Engineered, Gut, Freshwater, and Soil). Moreover, an "enrichment sphere" model was constructed to elucidate the regulatory principles behind these patterns. The driving factors for this model were revealed based on two case studies: (1) The copper-resistance genes were enriched in Soil biomes, owing to the copper contamination and horizontal gene transfer. (2) The flagellum-related genes were enriched in the Freshwater biome, due to high fluidity and vertical gene accumulation. Furthermore, this enrichment sphere model has valuable applications, such as in biome identification for metagenome samples, and in guiding 3D structure modeling of proteins. In summary, the enrichment sphere model aims towards creating a bluebook of the biome-species-function relationships and be applied in many fields.

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.

Biochar as a potential strategy for remediation of contaminated mining soils: Mechanisms, applications, and future perspectives

Soil heavy metal contamination caused by mining activities is a global issue. These heavy metals can be enriched in plants and animals through the food chain, and eventually transferred to the human system and threatening public health. Biochar, as an environmentally friendly soil remediation agent, can effectively immobilize heavy metals in soil. However, most researchers concern more about the remediation effect and mechanism of biochar for industrial and agricultural contaminated soil, while related reviews focusing on mining soil remediation are limited. Furthermore, the remediation effect of soil in mining areas is affected by many factors, such as physicochemical properties of biochar, pyrolysis conditions, soil conditions, mining environment and application method, which can lead to great differences in the remediation effect of biochar in diverse mining areas. Therefore, it is necessary to systematically unravel the relevant knowledge of biochar remediation, which can also provide a guide for future studies on biochar remediation of contaminated soils in mining areas. The present paper first reviews the negative effects of mining activities on soil and the advantages of biochar relative to other remediation methods, followed by the mechanism and influencing factors of biochar on reducing heavy metal migration and bioavailability in mining soil were systematically summarized. Finally, the main research directions and development trends in the future are pointed out, and suggestions for future development are proposed.

Chelating surfactant N-lauroyl ethylenediamine triacetate enhanced electrokinetic remediation of copper and decabromodiphenyl ether co-contaminated low permeability soil: Applicability analysis

In this study, chelating surfactant N-lauroyl ethylenediamine triacetate (N-LED3A) was used as strengthening agent for electrokinetic (EK) remediation of copper (Cu) and decabromodiphenyl ether (BDE209) co-contaminated low permeability soil. The results indicated that negligible amount of N-LED3A would be adsorbed on the experimental soil. The synchronous elution efficiencies (SEEs) of Cu and BDE209 had reached 65.4% and 49.9%, respectively, when the concentration of N-LED3A was 4000 mg/L, and they kept almost unchanged as the concentration of N-LED3A further increased. Meanwhile, the optimal SEEs were obtained at the pH condition within 6-8. The removal efficiencies of Cu (55.3%-65.8%) and BDE209 (31.4%-46.4%) would be increased with the applied voltage gradient and concentration of N-LED3A. In addition, BDE209 and Cu contaminants were also detected in the catholyte and anolyte, respectively, and their concentrations still showed an uptrend by the end of the experiments. While in the control experiments, the removal efficiency of Cu was in the range of 18.2%-23.6%, and almost no BDE209 was migrated out. The electric current would be increased with N-LED3A concentration increased, further resulting in the enhancement of cumulative electro-osmotic flow (EOF). However, the increment of EOF was limited after an 8-day treatment due to the declined capacity of the soil water supply, and the removal efficiency of BDE209 did not change proportionally to the cumulative EOF as a consequence. The accumulated (21 days) energy consumption under the optimal operation conditions (voltage gradient 1 V/cm, N-LED3A 1 g/L) was 377.28 KWh/m³. Efficiently synchronous removal of BDE209 and Cu could be achieved by the N-LED3A enhanced EK technique, exhibiting a promising application potential in the organic pollutant and heavy metal co-contaminated soil remediation.

Effective remediation of heavy metals in contaminated soil by electrokinetic technology incorporating reactive filter media

Soil contamination is increasingly a global problem with serious implications for human health. Among different soil decontamination approaches, electrokinetic (EK) remediation is a relatively new technology for treating organic and inorganic contaminants in soil. This research aims to develop an enhanced EK treatment method incorporating a compost-based reactive filter media (RFM) with the advantages of low-cost and strong affinity for heavy metals and test and improve the treatment efficiency for multiple heavy metals in natural soil. A series of EK operations were performed to investigate the performance of EK-RFM under different operating conditions such as the electric current and voltage, processing time, and the amount of RFM. The electric current and treatment time demonstrated a significant positive impact on removing Zn, Cd and Mn ions while changing the amount of RFM had an insignificant impact on the efficiency of heavy metals removal. Overall, 51.6%-72.1% removal of Zn, Cd, and Mn was achieved at 30.00 mA of electric current and 14 days of treatment duration. The energy consumption of the EK process was 0.17 kWh kg^-1. The soil organic matter adversely affected the mobilization and migration of heavy metals such as Cu and Pb during EK treatment. The results are valuable in optimizing the design of the EK-RFM system, which will extend its application to field-scale soil decontamination practices.