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

Permeable reactive nanofiber barrier integrated with electrokinetic geosynthetics for the remediation of copper contaminated soil under cyclic loading conditions

Permeable reactive barrier (PRB) integrated with electrokinetic geosynthetic (EKG) is an enhancement technique to improve the efficiency of in-situe heavy metal contaminated soil remediation. In this study, EKG-PRB was considered under cyclic loading conditions to remediate copper contaminated soil. Also, the basis of remediation is the implementation of electrokinetic geosynthetic (EKG) materials as electrodes and fabricated composite nanofibers as a permeable reactive barrier. Therefore, nanofibers electrospun with graphene nanoparticle inclusion were designed and constructed. To assess the performance of EKG-PRNB technique on remediation of a copper contaminated soil, an experimental apparatus was designed, and various tests were categorized into EKG and EKG-PRNB groups. All tests were carried out under the similar conditions, cyclic loading (7-113 kPa), drainage condition (open cathode-closed anode), duration (60 h), and a voltage gradient of 1 V cm-1 with a tolerance of ±0.1. The EKG was carried out without utilizing the PRB, while EKG-PRNB experiments were conducted using a permeable reactive nanofiber barrier in different positions, adjacent to cathode (PRNB0) and at a distance of 4 cm from the cathode (PRNB1). According to the results, PRNB were fabricated with a specific surface area of 19.423 m2 g-1 and a maximum adsorption capacity of 81.43 mg g-1. Copper removal efficiency in drainage water reached 97.4 %, with copper immobilization efficiency approximately 14 %. Results demonstrated that the positioning of the reactive barrier had no statistically significant impact on the electrokinetic remediation system performance, removal efficiency, settlement, and consolidation degree.

Advancements in Biochar Research Methods for Soil Pollution Remediation: Development and Applications

This review primarily focuses on the advancement of biochar research methods and their application in treating soil pollution and agriculture. Biochar, a novel material for soil treatment, shows great potential because of its high specific surface area, abundant functional groups, and well-developed pore structure. This work first introduces the current state and hazards of soil pollution and the limitations of traditional remediation technologies. It then discusses biochar research methods and advancements in biochar preparation techniques. This paper also discussed the application of biochar in the agricultural field. Although biochar has shown many advantages in soil remediation, technical and economic issues in its production remain to be resolved, and long-term environmental impacts and ecological safety need to be further evaluated. Future research should focus on the functional modification and application optimization of biochar to fully realize its potential in soil remediation and sustainable agricultural development.

Black tea waste/iron slag reactive filter media-electrokinetic for mixed heavy metals treatment from contaminated site

Electrokinetic (EK) remediation is a cutting-edge technique used for extracting heavy metals from soils by applying an electric field. This study explores the integration of EK remediation with reactive filtration media (RFM) composed of recycled waste materials of powder iron slag/black tea waste (PIS/BTW) and granular iron slag/black tea waste (GIS/BTW) to improve the removal efficiency of single and mixed heavy metals from kaolinite and natural soils. Results demonstrated that PIS/BTW significantly outperformed GIS/BTW in heavy metal extraction, achieving 98.75 % copper removal compared to 90.06 % with GIS/BTW. Recycled RFMs achieved excellent copper removal, reaching 91.28 % for PIS/BTW and 84.90 % for GIS/BTW over 3 weeks. Specific energy consumption (SEC) increased with treatment durations, ranging from 0.055 to 0.254 kWh kg-1 in kaolin soil, while 0.344 kWh kg-1 increased in natural soil. For a heavy metals mixture in kaolinite soil, the removal of copper, nickel, and zinc achieved 97.15 %, 98.30 %, and 96.68 %, respectively, after 4 weeks, while in natural soil, the removal rates for copper, nickel, and zinc were 16.39 %, 89.22 %, and 84.38 % after 5 weeks. The alkaline pH of the RFMs facilitated the adsorption and precipitation of metal ions, contributing to their immobilization. The research study demonstrated the effectiveness of using recyclable and eco-friendly RFMs to optimize EK remediation, providing a sustainable and efficient solution for addressing heavy metal contamination in soils.

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.

PFOA remediation from kaolinite soil by electrokinetic process coupled with activated carbon/iron coated activated carbon - permeable reactive barrier

This study applied electrokinetic (EK) in situ soil remediation for perfluorooctanoic acid (PFOA) removal from kaolinite soil. The kaolinite soil was spiked with 10 mg/kg PFOA for the EK treatment using Sodium Cholate bio-surfactant coupled with Activated Carbon (AC) or iron-coated Activated Carbon (FeAC) permeable reactive barrier (PRB). The study also evaluated the impact of AC and FeAC PRBs' position on the EK process performance. In the EK with the PRB in the middle section, PFOA removal from kaolinite was 52.35 % in the AC-EK tests and 59.55 % in the FeAC-EK. Experimental results showed the accumulation of PFOA near the cathode region in FeAC PRB tests, hypothesising that Fe from the PRB formed a complex with PFOA ions and transported it to the cathode region. Spent PRBs were regenerated with methanol for PFOA extraction and reuse in the EK experiments. Although FeAC PRB achieved better PFOA removal than AC PRB, the EK tests with regenerated AC-EK and FeAC-EK PRBs achieved 40.37 % and 20.62 % PFOA removal. For EK with FeAC PRB near the anode, PFOA removal was 21.96 %. Overall, using PRB in conjunction with the EK process can further enhance the removal efficiency. This concept could be applied to enhance the removal of various PFAS compounds from contaminated soils by combining a suitable PRB with the EK process. It also emphasizes the feasibility of in-situ soil remediation technologies for forever chemical treatment.

Effect of Electrode Positioning on Electrokinetic Remediation of Contaminated Soft Clay with Surface Electrolyte

Soft clay contamination is an increasingly global issue with significant implications for land development and human health. Electrokinetic remediation (EKR) has demonstrated significant potential for cleaning contaminated soils. It is crucial to develop efficient processes that minimize environmental impact and reduce costs. A series of citric acid (CA)-enhanced EKR tests were conducted using a novel experimental setup, with the electrolyte positioned above the soil surface, to examine the impact of four different electrode arrangements on the effectiveness of EKR. The position of the electrode end had a significant impact on the migration of ions in the anolyte and catholyte, which in turn affected the volume reduction in the anolyte, the magnitude of the current, and the migration of heavy metals. The electrode arrangement mode c (electrodes suspended in the electrolytes) can enhance the migration of the anolyte and reduce the drainage of the soil, making it an effective measure for improving the removal rate of heavy metals. After the heavy metal remediation is complete, the bearing capacity of the soil should be increased. Changing the electrode arrangement to mode d (anode suspended in the anolyte, a very small part of the cathode inserted into the soil) is an effective measure for reducing the soil water content and improving soil strength.

Iodide- and electrochemical assisted removal of mercury by Cirsium arvense from gold tailings in the Amansie West District, Ghana

Mercury (Hg) pollution in Ghana through mining has become a serious environmental challenge. This study investigates the potential of Cirsium arvense to photostabilize Hg using electrokinetic current with or without an iodide solution in gold mine tailings heavily contaminated through mining activities in southern Ghana. An initial Hg concentration of 9.60 mg/kg using cold vapor atomic absorption spectrometry (CVAAS) was determined. The biological absorption coefficient, bioconcentration factor, and translocation factor of Hg have been presented. Cirsium arvense therefore had a higher bioconcentration factor (BCF) of 2.6-5.15 mg/kg, and a transfer factor (TF) of 0.24-0.36 indicating a higher efficiency for phytostabilization. Both the rate and time of extractions of Hg from the tailings by Cirsium arvense are efficiently improved in the combined electric current and iodide treatment. Plant and electric current combined treatment and plant and iodide combined treatment had only 60 and 50% phytostabilization rates, respectively. The combined plant, iodide, and electric current treatment has proven to be superior with about >90% Hg removal rate. Therefore, the combined plant, iodide, and electric current treatment resulted in a higher Hg removal efficiency by Cirsium arvense in a shorter period due to higher solubilization rate and electromigration effects on Hg species.

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.

On the electrokinetic remediation of Pb-contaminated soil: A coupled electro-transport-reaction modelling study based on chemical reaction kinetics

The accumulation of lead (Pb) in soil resulted from industrialization and urbanization poses a threat to human health and the ecosystem. This study proposes a mathematical model for Pb migration and transformation in soil porous media, aiming to guide the design of electrokinetic remediation schemes for Pb-contaminated soils. To improve the validity of the model, the chemical reactions considered in the model are all based on chemical reaction kinetics, which were usually overlooked for model simplification. The model quantitatively describes various physical and chemical processes of Pb at the soil-pore fluid interface and in the pore fluid, including diffusion, electromigration, electroosmosis, electrolytic water reaction, precipitation, adsorption/desorption, protonation/deprotonation reaction, and water self-ionization reaction. The numerical results show that the pH value is a key factor affecting the distribution of Pb in the soil and determining the removal efficiency of Pb. The effects of different enhancement methods on Pb concentration distribution and removal efficiency were evaluated with this model. It was found that placing a cation exchange membrane at the cathode boundary while using 0.01 M nitric acid as anode electrolyte can effectively improve Pb removal efficiency from 3.9% to 93.6%. The developed model can be used to guide the design of the enhanced electrokinetic remediation schemes.

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.

Electrokinetic remediation of estuarine sediments using a large reactor: spatial variation of physicochemical, mineral, and chemical properties

The treatment and beneficial use of polluted or contaminated environmental matrices have become major issues, especially as the world strives toward a zero-waste policy. In this regard, dredged sediments need to be treated before they can be used in an environmentally safe and sustainable manner. Therefore, this work aims to treat estuarine sediments and, more importantly, use physicochemical, mineral, organic, and chemical information to understand the reactions that occur upon treatment. Dredged estuarine sediments were collected from Tancarville (Seine River estuary, France) and subjected to electrokinetic (EK) remediation using a 128-L laboratory-scale reactor. The sediments were treated 8 h per day for 21 days. The electric (voltage and current) and physicochemical (pH and electric conductivity) parameters were monitored during treatment. Sediments were collected from various sections in the reactor at the end of the experiment (lengthwise, widthwise, and depthwise). The spatial variation was investigated in terms of organic, mineral, and metal contents. Statistical analyses proved that the variation occurred only in the lengthwise direction. Furthermore, three main phases described the treatment, which were mainly linked to carbonate dissolution and pH variation. The results also showed that the trace elements Ni and Zn were reduced by 21% and 19%, respectively, without a direct link to pH, while Ca and Mg were only redistributed. The buffering capacity of the anodic sediment was reduced due to carbonate dissolution. The treated sediments showed reduced contents in trace metals without affecting major elements that can be useful in agriculture (i.e., Ca and Mg).

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.

Applying a nanocomposite hydrogel electrode to mitigate electrochemical polarization and focusing effect in electrokinetic remediation of a Cu- and Pb-contaminated loess

Inappropriate handling of copper (Cu) and lead (Pb)-containing wastewater resulting from metallurgical and smelting industries in Northwest China encourages their migration to surrounding environments. Their accumulation causes damage to liver and kidney function. The electrokinetic (EK) technology is considered to be an alternative to traditional remediation technologies because of its great maneuverability. The EK remediation is accompanied by the electrode polarization and the focusing effect toward affecting removal efficiency. In this study, a nanocomposite hydrogel (NCH) electrode was proposed and applied to the EK remediation of Cu- and Pb-contaminated loess. The mechanical, adsorption capacity, adsorption kinetics, and electrochemical properties of the NCH electrode were investigated in detail, followed by microscopic analyses of Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Raman spectrometer. Results showed that the enhancement of the mechanical properties of the NCH electrode was attributed to the crosslinks of graphene nanoparticles, calcium alginate, and hydrogen bonds, while the Cu or Pb adsorption by the NCH electrode was in a chemisorption manner. The second layer formation might address the increase in adsorption capacity with increasing temperature. These results highlight the relative merits of the NCH electrode and verify the potential of applying the NCH electrode to the EK remediation of Cu- and Pb-contamianted loess.

Removal mechanisms of Cd from water and soil using Fe-Mn oxides modified biochar

The development of remediation materials simultaneously suitable for Cd-contaminated water and soil is of great significance. In this study, the functional biochar (FM-RBC and FM-DBC) was prepared using branch and durian shell biochar (RBC and DBC, respectively) with iron-manganese oxide (Fe-Mn oxide) modification. The behaviors and mechanisms of Cd adsorption and stabilization in water and alkaline soil treated with FM-RBC and FM-DBC were explored. The results showed that the adsorption capacities of RBC and DBC for Cd had increased by 40-80 mg/g after the Fe-Mn oxide modification. The Cd adsorption was conformed to pseudo-second-order kinetic and the Langmuir isothermal models. After 35 days of soil cultivation, the maximum reduction rate of DTPA-Cd occurred in 3% FM-DBC treatments (37.73%), followed by in 3% FM-RBC (30.08%), all of which were significantly higher than that observed in 3% BC treatments (12.55-18.91%). Notably, the FM-RBC and FM-DBC treatments promoted the conversion of the exchangeable to the carbonate-bound and Fe/Mn oxyhydroxide fractions of Cd. The XRD, FTIR, and XPS analyses demonstrated that the loading amount of Fe-Mn oxide was positively correlated with the oxygen-containing functional group of biochar. CdO, Cd₂Mn₃O₈ and CdCO₃ were loaded on the FM-BC, indicating the existence of two main adsorption mechanisms: (1) the complexation with M-O (M: Fe, Mn) and acid oxygen-containing functional groups, (2) the precipitation with carbonate of Cd. In this work, we prepared two functional biochar that rapidly removes Cd from water and effectively fixes Cd in alkaline soil, thus, debasing the risk of Cd entry into the food chain.

Experimental investigation on a combination of soil electrokinetic consolidation and remediation of drained water using composite nanofiber-based electrodes

A novel electrokinetic geosynthetic (EKG) can be efficient in achieving multiple objectives. In this study, a new EKG as an electrode and a drainage channel in the electro-osmotic consolidation was fabricated by electrospun nanofibers containing graphene nanoparticles (GNs) attached to a carbon fiber substrate. To investigate the effectiveness of the fabricated electrodes in electro-osmotic consolidation and remediation of water drained from the system, an experimental apparatus was constructed while considering loading capability in expanded ranges and applying the electric field, and was filled with copper (Cu)-contaminated kaolinite. Experiments were divided into control (CT) and EKG groups, and three categories, C-EK, ES₁-EK, and ES₂-EK (using carbon fiber, electrospun nanofibers containing 1 wt% GNs, and electrospun nanofibers consisting of 2 wt% GNs, respectively). All the experiments were conducted with the same conditions, loading, drainage condition, and duration. However, EKG experiments were performed by employing the electric field under the vertical pressure in the range of 7-113 kPa, while the CT was conducted without the electric field. According to experimental results, 18 wt% polymethyl methacrylate in the dimethylformamide solvent containing 1 and 2 wt% GNs was selected for making a nanofibrous layer on the carbon fiber. The average diameters of the fibers were 404 ± 36 and 690 ± 62 nm and yielded at 1 and 2 wt% GNs, respectively. The results revealed that using the EKG accelerated kaolinite consolidation. The average degree of consolidation was 68 and 85% in the CT and EKG experiments, respectively. Furthermore, the fabricated electrodes were highly effective as a drainage channel for remediating water drained from the system. Moreover, the highest Cu removal efficiency was obtained in ES₂-EK (97%) and ES₁-EK (92%), respectively. Conversely, the lowest Cu removal efficiency was observed in the C-EK group (85%).

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

Bioaugmentation, the addition of cultured microorganisms to enhance the currently existing microbial community, is an option to remediate contaminated areas. Several studies reported the success of the bioaugmentation method in treating heavy metal contaminated soil, but concerns related to the applicability of this method in real-scale application were raised. A comprehensive analysis of the mechanisms of heavy metal treatment by microbes (especially bacteria) and the concerns related to the possible application in the real scale were juxtaposed to show the weakness of the claim. This review proposes the use of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil. The performance of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil as well as the mechanisms of removal and interactions between plants and microbes are also discussed in detail. Bioaugmentation-assisted phytoremediation shows greater efficiencies and performs complete metal removal from soil compared with only bioaugmentation. Research related to selection of hyperaccumulator species, potential microbial species, analysis of interaction mechanisms, and potential usage of treating plant biomass after treatment are suggested as future research directions to enhance this currently proposed topic.

Enhanced remediation of Cd-contaminated soil using electrokinetic assisted by permeable reactive barrier with lanthanum-based biochar composite filling materials

Electrokinetic remediation (EK) combined with a permeable reactive barrier (PRB) is a relatively new technique for efficiently remediating Cd-contaminated soil in situ. Eupatorium adenophorum, which is a malignant invasive plant, was used to synthesise biochar and a novel lanthanum-based biochar composite (LaC). The biochar and LaC were used as cheap and environmentally benign PRB filling materials to remediate simulated and real Cd-contaminated soils. The pH and residual Cd concentration in the simulated contaminated soil during remediation gradually increased from the anode to the cathode used to apply an electric field to the EK-PRB system. However, the soil conductivity changed in the opposite way, and the current density first increased and then decreased. For simulated contaminated soils with initial Cd concentrations of 34.9 and 100.6 mg kg^-1, the mean Cd removal rates achieved using LaC were 90.6% and 89.3%, respectively, which were significantly higher than those of biochar (P < 0.05). Similar results were achieved using natural soils from mining area and polluted farmland, and the Cd removal rates were 66.9% and 72.0%, respectively. Fourier-transform infrared and X-ray photoelectron spectroscopy indicated that there were many functional groups on the LaC surfaces. The removal mechanism of EK-PRB for Cd in contaminated soil includes electromigration, electroosmotic flow, surface adsorption, and ion exchange. The results indicated that the LaC could be used in the EK-PRB technique as a cheap and 'green' material to efficiently decontaminate soil polluted with heavy metals.

Effects of ecohydrological interfaces on migrations and transformations of pollutants: A critical review

With the rapid development of society, the soil and water environments in many countries are suffering from severe pollution. Pollutants in different phases will eventually gather into the soil and water environments, and a series of migrations and transformations will take place at ecohydrological interfaces with water flow. However, it is still not clear how ecohydrological interfaces affect the migration and the transformation of pollutants. Therefore, this paper summarizes the physical, ecological, and biogeochemical characteristics of ecohydrological interfaces on the basis of introducing the development history of ecohydrology and the concept of ecohydrological interfaces. The effects of ecohydrological interfaces on the migration and transformation of heavy metals, organic pollutants, and carbon‑nitrogen‑phosphorus (C-N-P) pollutants are emphasized. Lastly, the prospects of applying ecohydrological interfaces for the removal of pollutants from the soil and water environment are put forward, including strengthening the ability to monitor and simulate ecohydrological systems at micro and macro scales, enhancing interdisciplinary research, and identifying main influencing factors that can provide theoretical basis and technical support.

Advances in As contamination and adsorption in soil for effective management

Arsenic (As) is a heavy metal that causes widespread contamination and toxicity in the soil environment. This article reviewed the levels of As contamination in soils worldwide, and evaluated how soil properties (pH, clay mineral, organic matter, texture) and environmental conditions (ionic strength, anions, bacteria) affected the adsorption of As species on soils. The application of the adsorption isotherm models for estimating the adsorption capacities of As(III) and As(V) on soils was assessed. The results indicated that As concentrations in contaminated soil varying significantly from 1 mg/kg to 116,000 mg/kg, with the highest concentrations being reported in Mexico with mining being the dominating source. Regarding the controlling factors of As adsorption, soil pH, clay mineral and texture had demonstrated the most significant impacts. Both Langmuir and Freundlich isotherm models can be well fitted with As(III) and As(V) adsorption on soils. The Langmuir adsorption capacity varied in the range of 22-42400 mg/kg for As(V), which is greater than 45-8901 mg/kg for As(III). The research findings have enhanced our knowledge of As contamination in soil and its underlying controls, which are critical for the effective management and remediation of As-contaminated soil.