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

In-situ growth of FeSx nanosheets on iron foam as three-dimensional electrode for electrokinetic remediation of copper, lead and zinc co-contaminated soil

The combined contamination of heavy metals, such as copper, lead, and zinc, in soil poses a global environmental challenge, threatening soil quality, ecosystems, and human health. A novel three-dimensional electrokinetic (3D EK) system utilizing FeSx nanosheets loaded on iron foams (FeS@IF) as the third electrode was developed to enhance the electrokinetic remediation of co-contaminated soils. The application of this system achieved significantly higher removal efficiencies for Cu (34.73 % vs 15.79 %), Pb (36.85 % vs 26.14 %), and Zn (47.79 % vs 29.43 %) compared to traditional two-dimensional electrokinetic remediation. Soil pH was maintained within a near-neutral range (6.37-7.34), while the stability of residual heavy metals was enhanced, increasing the proportion of Zn in the residual fraction from 50.3 % to ∼75.0 %. The system electrolytes were reusable, and the recyclable FeS@IF electrode avoided the release of heavy metals back into the soil. The synergistic effects of high electrical conductivity, soluble iron content, and adsorption capacity of the FeS@IF electrode were key to its superior performance. Additionally, microbial community analysis revealed an increase in bacterial abundance. In conclusion, this work demonstrates an efficient and environmental-friendly 3D electrode system for soil remediation, offering a sustainable solution for reducing heavy metal pollution and protecting the environment and human health.

Geochemistry of arsenic in soils with a focus on calcareous soils: control strategies and perspectives

Arsenic (As) contamination has become a significant environmental challenge due to the global expansion of industrial, agricultural, and mining activities, which contribute to the contamination of water, air, soils, and biota with As and other metals and metalloids. This review elucidates the geochemical behavior of As in soils, focusing on the factors influencing its dynamics and the effectiveness of various remediation techniques, particularly in calcareous soils. Calcareous soils, characterized by their unique properties, exhibit intricate interactions with As, necessitating a deeper understanding of the mechanisms driving these processes. Compared to other soil types, the bioavailability of As in calcareous soils is generally lower, largely due to their elevated pH and the presence of calcium carbonate (CaCO3). These factors contribute to the enhanced adsorption of As by soil organic and mineral components, forming less soluble As-CaCO3 complexes and decreasing As solubility. Despite this, research on As geochemistry in calcareous soils and the development of effective removal techniques still needs to be completed, emphasizing the need for further study. Additionally, this review explores future research directions in the context of As contamination and remediation, integrating case studies and advanced technologies to highlight innovative approaches for mitigating As contamination in calcareous soils.

Soil total nitrogen content and pH value estimation method considering spatial heterogeneity: Based on GNNW-XGBoost model

Soil nitrogen content and pH value are two pivotal factors that critically determine soil fertility and plant growth. As key indicators of soil health, they each play distinct yet complementary roles in the soil ecosystem. Nitrogen is one of the essential nutrients for plant growth, while soil pH directly influences the activity of soil microorganisms. These microbes are essential for breaking down minerals and organic materials, which in turn affects the availability and conversion of key nutrients like nitrogen and phosphorus. A comprehensive understanding of the distribution of total nitrogen content and pH value is crucial for ensuring the sustainability of agricultural production and maintaining soil and ecosystem health. Existing models for estimating soil property based on near-infrared (NIR) spectral data often overlook the spatial non-stationarity of the relationship between soil spectra and composition content. Therefore, we proposed a new model for estimating soil total nitrogen content and pH value, which combined geographically neural network weighted regression (GNNWR) with extreme gradient boosting (XGBoost), utilizing neural networks to improve the accuracy of predicting total nitrogen content and pH value, efficiently captured the spatial heterogeneity between spectral reflectance and soil total nitrogen content and pH value in different regions. Using the soil nutrient and visible near-infrared spectral samples collected by Eurostat in 2009 for the land use and coverage area frame survey of the 23 members of the European Union, the Geographically Neural Network Weighted-eXtreme Gradient Boosting (GNNW-XGBoost) model was used to estimate total nitrogen content and pH value. The spatial correlation between reflectance of spectral characteristic bands and soil total nitrogen content, pH value was trained in the model to verify its robustness and superiority, and the experimental process was improved by 10-fold cross-validation. In terms of model evaluation, compared to the standalone XGBoost and GNNWR models, the GNNW-XGBoost model demonstrated superior predictive accuracy. It achieved a highest coefficient of determination (R2) of 0.84 for total nitrogen and 0.80 for pH. Additionally, it reduced the root mean square error (RMSE) by 7.64 %, 7.61 % for total nitrogen, and 8.96 %, 4.69 % for pH, respectively. This study not only provides a new method for accurate prediction of soil total nitrogen content and pH value, but also has significant reference value for other estimation issues involving geographic data, which can help to improve the accuracy of environmental monitoring, optimize resource management strategies, and promote the development of sustainable agriculture.

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.

Immobilisation of arsenic and simultaneous degradation of polycyclic aromatic hydrocarbons in soil in situ by modified electrooxidation

Improper management of wood impregnation chemicals and treated wood has led to soil contamination at many wood treatment sites, particularly with toxic substances like creosote oil and chromated copper arsenate (CCA). The simultaneous presence of these pollutants complicates the choice of soil remediation technologies, especially if they are to be applied in situ. In this laboratory study, we attempted to immobilise arsenic (As) and simultaneously degrade polycyclic aromatic hydrocarbons (PAHs) (constituents of creosote oil) by applying a modified electrochemical oxidation method. The supply of iron (Fe) amendments in contaminated soil was done using corroding Fe electrodes as an Fe source and applying an alternating polarity electrical current. Soil with a large fraction of organic matter (25%) and containing 505 mg kg-1 As and 5160 mg kg-1 16-PAHs was placed in Plexiglas cells equipped with porewater samplers and an iron electrode pair connected to a power supply unit. The porewater and percolating solution were periodically sampled and analysed over an 8-week period. The modified electrochemical soil treatment led to a decrease in the total concentration of 16-PAHs in soil by 56-68%. The amount of poorly crystalline Fe oxides in the soil substantially increased, especially close to the electrodes, enabling 76-89% of As to be bound to this most reactive Fe fraction. Nevertheless, over 10% of soil As remained in the most soluble and available fraction (exchangeable), most likely due to the decline in soil redox potential over time. This study suggests that electrochemical oxidation of organic soil with mixed contaminants could be used for in situ soil remediation but needs further improvement to achieve more efficient As immobilisation.

Sustainable heavy metal removal from sewage sludge: A review of bioleaching and other emerging technologies

By 2050, global sewage sludge production is expected to increase by 51 %, rising from its current level of over 45 million tons of dry solids to nearly 68 million tons. This growth is primarily driven by population growth and the implementation of increasingly stringent environmental regulations. This increase in sewage sludge volume poses substantial challenges for sustainable management due to its complex composition. While sewage sludge contains valuable nutrients such as nitrogen (N), phosphorus (P), and potassium (K) that make it suitable for agriculture use, the presence of heavy metals (HMs), including cadmium (Cd), lead (Pb), mercury (Hg), chrome (Cr), copper (Cu), nickel (Ni) and zinc (Zn) creates significant barriers to its safe reuse. Inadequately treated sewage sludge, when repeatedly applied to agricultural soils, can lead to the accumulation of HMs, posing risks to long-term soil fertility, crop productivity, and broader environmental health. This review discusses various techniques for de-metallization of sewage sludge, including aerobic- and anaerobic bioleaching, chemical leaching, electrokinetic treatment, and supercritical fluid extraction. Among these techniques, anaerobic bioleaching is identified as the most environmentally sustainable option, as it offers a lower-energy, less chemically intensive approach to decrease HM content in the solid fraction of sewage sludge. This approach utilizes microbial activity under anaerobic conditions to solubilize and remove HMs, while minimizing nutrient loss and preserving the ecological integrity of the treated sewage sludge. Future research should prioritize the optimizing of anaerobic bioleaching processes to enhance both HM removal efficiency and nutrient retention. Additionally, integrating anaerobic bioleaching with air-assisted ultrasonication as a post treatment technology could further improve metal removal efficiency. This review aims to provide a comprehensive reference for researchers and practitioners seeking environmentally friendly solutions for HM removal from sewage sludge, ensuring its safe reuse in land applications and contributing to a circular agro-economy.

Composites Based on Natural Zeolites and Green Materials for the Immobilization of Toxic Elements in Contaminated Soils: A Review

Soil contamination by toxic elements is a global problem, and the remediation of contaminated soils requires complex and time-consuming technology. Conventional methods of soil remediation are often inapplicable, so an intensive search is underway for innovative and environmentally friendly ways to clean up ecosystems. The use of amendments that stabilize the toxic elements in soil by reducing their mobility and bioavailability is one of the simplest and most cost-effective ways to remediate soil. This paper provides a summary of studies related to the use of composites based on natural zeolites and green materials for the immobilization of toxic elements in contaminated soils and highlights positive examples of returning land to agricultural use. The published literature on natural zeolites and their composites has shown that combinations of zeolite with biochar, chitosan and other clay minerals have beneficial synergistic effects on toxic element immobilization and soil quality. The effects of zeolite properties, different combinations, application rates, or incubation periods on toxic elements immobilization were tested in laboratory scale or field experiments, whereas the mobility of toxic elements in soil was evaluated by chemical extractions of toxic elements transferred to the plants. This review highlights the excellent potential of natural zeolites to be used as single or combined sustainable green materials to solve environmental pollution problems related to the presence of toxic elements.

A novel test set up to study three-dimensional electrokinetic dewatering of dredged soil

The dredged soil obtained from maintenance activities of water bodies has emerged as a potential alternate fill material for infrastructure development. However, dredged soil requires stabilization due to high initial water content, low shear strength and high compressibility. Among several methods, stabilization of dredged soil by using electrokinetics is one of the effective ground improvement techniques that uses electric field to dewater and strengthen the soil. In this context, a series of experiments were conducted on dredged soil by using a combination of electrokinetic treatment with and without 6 kPa seating pressure (viz., low surcharge). A customized and patented electrokinetic dewatering (EKD) test set up was used for the three-dimensional electrokinetic treatment of soil. The potential difference (in the range of 6 V-48 V) within the soil was achieved by inserting stainless steel pipes of 21.4 mm outer diameter, 1.2 mm thickness, and 170 mm length. Two control tests (with and without seating pressure of 6 kPa) also were performed to understand the effectiveness of EKD. From the study, up to 1057% and 427% increase in dewatering was noted in EKD tests due to application of 24 V (optimum voltage noted in EKD tests) as compared to control tests, without and with seating pressure, respectively. Further, seating pressure with EKD resulted in effective control of crack formation in the dredged soil and uniform improvement in shear strength along the depth (up to 95 kPa). The combination of low surcharge with EKD, adopted in the study, is also expected to yield lower differential settlement, and hence better performance of geotechnical structures built on improved dredged soil. The novel 3-dimensional patented EKD test setup with Arduino-programmed automatic water pumping enables collecting and accurately measuring dewatered effluent volume, performing cone penetration tests on undisturbed soil, and collecting soil samples for determination of water content/physiochemical properties from different locations. Overall, the developed EKD setup can be utilized for evaluating the effectiveness and adopting real-time progress management for EKD or other ground improvement methods, and remediation of sludge, mine tailings, dredged sediments, and contaminated soils.

Bioelectrochemical technologies for soil and sediment remediation: Recent advances and future perspectives

Soil and sediment serve as the ultimate repositories of pollutants, presenting a significant environmental concern on a global scale. However, there is no effective measure due to the low mobility, high resistance and high cost of contaminated soil or sediment. The bioelectrochemical systems (BESs) combine microbial and electrochemical technology to achieve efficient and rapid degradation of pollutants by enriching electroactive microbial membranes with electrodes. Specifically, BESs offer an ideal solution for in-situ remediation, eliminating the secondary pollution and high energy consumption issues associated with traditional technologies. However, in soil or sediment bioelectrochemical systems (SBESs), further summarization and improvement are required to address the influencing factors during the process of pollutant remediation, given the fragility of complex geographical and natural environments. This paper provides a comprehensive overview and analysis of the removal mechanisms of organic pollutants, heavy metals and emerging contaminants within contaminated soil or sediment, elucidating the influential factors and strategies aimed at enhancing pollutant removal processes within SBESs. The current emerging problems and limitations of microbial electrochemical remediation technology are summarized, and it is suggested that future development should focus on microorganisms, reactors and practical applications.

Effective and green in-situ remediation strategies based on TEMPO-nanocellulose/lignin/MIL-100(Fe) hydrogel nanocomposite adsorbent for lead and copper in agricultural soils

Hydrogel adsorbents are promising tools for reducing heavy metals' bioavailability in contaminated soil. However, their practical feasibility remains limited by the low stability, inefficient removal efficiency, and potential secondary pollution. Optimizing the adsorption operation and the functional properties of hydrogel adsorbents could eliminate this method's drawbacks. Herein, three innovative in-situ remediation strategies for Pb/Cu-contaminated soil were adopted based on the concept of novel TEMPO-cellulose (TO-NFCs)/lignin/acrylamide@MIL-100(Fe) nanocomposite hydrogel adsorbent (NCLMH). Characteristic analyses revealed ideal Pb/Cu adsorption mechanisms by swelling, complexation, electrical attraction, and ion exchange via carboxyl/hydroxyl/carbonyl groups and unsaturated Fe(III) sites on ANCMH besides FeOOH formation. The highest maximum theoretical adsorption capacities of Pb(II) and Cu(II) on ANCMH were 416.39 and 133.98 mg/g, under pH 6.5, governed by pseudo-second-order/Freundlich models. Greenhouse pot experiments with contaminated soils amended with two-depth layers of 0.5% NCLMHs (SA@NCLMH) displayed a decline in Pb and Cu bioavailability up to 85.9% and 74.5% within 45 d. Soil column studies simulating continuous water soil flushing coupled with NCLMH layers, instead of conventional extractant fluids, and connected to NCLMH-sand column as purification unit (CF@NCLMH) achieved higher removal rates for Pb, and Cu of 89.5% and 77.2% within 24 h. Alternatively, conducting multiple-pulse soil flushing mode (MF@NCLMH) gained the highest Pb and Cu removal of 96.5% and 85.4%, as the water flushing-stop flux events allowed adequate water movement/residence period, promoting Pb/Cu desorption-adsorption from soil to NCLMH. Also, the NCLMH-sand column conducting and easy separation of the stable/reusable NCLMHs prevented the potential secondary pollution. Interestingly, the three remediated soils reached the corresponding regulation of the permissible limits for Pb and Cu residential scenarios in medium-to-heavily agricultural polluted soils, alleviating the Pb/Cu bioaccumulation and phytotoxicity symptoms in cultivated wheat, especially after MF@NCLMH treatment. This study introduces promising alternative remediation strategies with high sustainability and feasibility in acidic-to-neutral heavy metal-contaminated agricultural soil.

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.

Electrokinetic Remediation of Cu- and Zn-Contaminated Soft Clay with Electrolytes Situated above Soil Surfaces

Electrokinetic remediation (EKR) has shown great potential for the remediation of in situ contaminated soils. For heavy metal-contaminated soft clay with high moisture content and low permeability, an electrokinetic remediation method with electrolytes placed above the ground surface is used to avoid issues such as electrolyte leakage and secondary contamination that may arise from directly injecting electrolytes into the soil. In this context, using this novel experimental device, a set of citric acid (CA)-enhanced EKR tests were conducted to investigate the optimal design parameters for Cu- and Zn-contaminated soft clay. The average removal rates of heavy metals Cu and Zn in these tests were in the range of 27.9-85.5% and 63.9-83.5%, respectively. The results indicate that the Zn removal was efficient. This was determined by the migration intensity of the electro-osmotic flow, particularly the volume reduction of the anolyte. The main factors affecting the Cu removal efficiency in sequence were the effective electric potential of the contaminated soft clay and the electrolyte concentration. Designing experimental parameters based on these parameters will help remove Cu and Zn. Moreover, the shear strength of the contaminated soil was improved; however, the degree of improvement was limited. Low-concentration CA can effectively control the contact resistance between the anode and soil, the contact resistance between the cathode and soil, and the soil resistance by increasing the amount of electrolyte and the contact area between the electrolyte and soil.

Waves of change: Electrochemical innovations for environmental management and resource recovery from water - A review

Environmental electrochemistry and water resource recovery are covered in this review. The study discusses the growing field's scientific basis, methods, and applications, focusing on innovative remediation tactics. Environmental electrochemistry may solve water pollution and extract resources. Electrochemical methods may effectively destroy or convert pollutants. This method targets heavy metals, organic compounds, and emerging water contaminants such as pharmaceuticals and microplastics, making it versatile. Environmental electrochemistry and resource recovery synergize to boost efficiency and sustainability. Innovative electrochemical methods can extract or synthesise metals, nutrients, and energy from wastewater streams, decreasing treatment costs and environmental effect. The study discusses electrocoagulation, electrooxidation, and electrochemical advanced oxidation processes and their mechanics and performance. Additionally, it discusses current electrode materials, reactor designs, and process optimisation tactics to improve efficiency and scalability. Resource recovery in electrochemical remediation methods is also examined for economic and environmental feasibility. Through critical examination of case studies and techno-economic evaluations, it explains the pros and cons of scaling up these integrated techniques. This study covers environmental electrochemistry and resource recovery's fundamental foundations, technology advances, and sustainable water management consequences.

Oceanobacillus picturae alleviates cadmium stress and promotes growth in soybean seedlings

Cadmium (Cd) is a heavy metal that significantly impacts human health and the environment. Microorganisms play a crucial role in reducing heavy metal stress in plants; however, the mechanisms by which microorganisms enhance plant tolerance to Cd stress and the interplay between plants and microorganisms under such stress remain unclear. In this study, Oceanobacillus picturae (O. picturae) was isolated for interaction with soybean seedlings under Cd stress. Results indicated that Cd treatment alone markedly inhibited soybean seedling growth. Conversely, inoculation with O. picturae significantly improved growth indices such as plant height, root length, and fresh weight, while also promoting recovery in soil physiological indicators and pH. Metabolomic and transcriptomic analyses identified 157 genes related to aspartic acid, cysteine, and flavonoid biosynthesis pathways. Sixty-three microbial species were significantly associated with metabolites in these pathways, including pathogenic, adversity-resistant, and bioconductive bacteria. This research experimentally demonstrates, for the first time, the growth-promoting effect of the O. picturae strain on soybean seedlings under non-stress conditions. It also highlights its role in enhancing root growth and reducing Cd accumulation in the roots under Cd stress. Additionally, through the utilization of untargeted metabolomics, metagenomics, and transcriptomics for a multi-omics analysis, we investigated the impact of O. picturae on the soil microbiome and its correlation with differential gene expression in plants. This innovative approach unveils the molecular mechanisms underlying O. picturae's promotion of root growth and adaptation to Cd stress.

Restoration of degraded estuarine and marine ecosystems: A systematic review of rehabilitation methods in Europe

This article provides a comprehensive study of ecosystem rehabilitation methods widely used in the 21st century, focusing on Europe. The review covers the evolution and trends in scientific article publication, identification of European countries demonstrating high publication outputs, collaboration patterns, leading journals, and thematic areas. Additionally, it examines primary stressors in European aquatic ecosystems, and different methods and treatments commonly employed for remediation purposes. The analysis of selected articles revealed a significant increase in studies over time, driven by public awareness and financial incentives from national, European and global organizations. Italy, Portugal and Spain were the leading countries in degraded ecosystem rehabilitation studies, mainly focusing on remediating contaminated areas where metals were identified as the primary stressor (chemical pollution). Chemical remediation method emerged as the most used, closely followed by biological remediation method, which have gained prominence in recent years due to their ecological, economic, and social combined benefits. Furthermore, recent studies demonstrate a growing trend towards the combined use of more than one treatment/method to rehabilitate ecosystems, particularly with biological treatments. This combined approach has the potential for synergistic effects in achieving more effective rehabilitation and their sustainability in the long term, thus, a focus for future research.

Biochar as a partner of plants and beneficial microorganisms to assist in-situ bioremediation of heavy metal contaminated soil

Synergistic remediation of heavy metal (HM) contaminated soil using beneficial microorganisms (BM) and plants is a common and effective in situ bioremediation method. However, the shortcomings of this approach are the low colonisation of BM under high levels of heavy metal stress (HMS) and the poor state of plant growth. Previous studies have overlooked the potential of biochar to mitigate the above problems and aid in-situ remediation. Therefore, this paper describes the characteristics and physicochemical properties of biochar. It is proposed that biochar enhances plant resistance to HMS and aids in situ bioremediation by increasing colonisation of BM and HM stability. On this basis, the paper focuses on the following possible mechanisms: specific biochar-derived organic matter regulates the transport of HMs in plants and promotes mycorrhizal colonisation via the abscisic acid signalling pathway and the karrikin signalling pathway; promotes the growth-promoting pathway of indole-3-acetic acid and increases expression of the nodule-initiating gene NIN; improvement of soil HM stability by ion exchange, electrostatic adsorption, redox and complex precipitation mechanisms. And this paper summarizes guidelines on how to use biochar-assisted remediation based on current research for reference. Finally, the paper identifies research gaps in biochar in the direction of promoting beneficial microbial symbiotic mechanisms, recognition and function of organic molecules, and factors affecting practical applications.

Experimental Study of Electroosmosis in Rock Cores Based on the Dual Pressure Sensor Method

Electroosmotic experiments obtain the electroosmotic pressure coefficient of a rock sample by measuring the excitation voltage at both ends of the sample and the pressure difference caused by the excitation voltage. The electroosmotic pressure is very weak and buried in the background noise, which is the most difficult signal to measure in the dynamic-electric coupling experiment, so it is necessary to improve its signal-to-noise ratio. In this paper, for the low signal-to-noise ratio of electroosmotic pressure, the dual pressure sensor method is proposed, i.e., two pressure sensors of the same type are used to measure electroosmotic pressure. Two different data extraction methods, Fast Fourier Transform and Locked Amplification, are utilized to compare the dual pressure sensor method of this paper with the existing single pressure sensor method. The relationship between the electroosmotic pressure coefficient and the excitation frequency, mineralization, permeability, and porosity is analyzed and discussed.

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.

Rapid immobilization of arsenic in contaminated soils by microwave irradiation combined with magnetic biochar: Microwave-induced electron transfer for oxidation and immobilization of arsenic (III)

Biochar with adjustable redox activity is an effective strategy for immobilization of excess arsenic (As(III)) contaminated soil. However, biochar exhibits limitations in terms of electron transfer efficiency and immobilization efficiency due to insufficient activation energy. In this study, As(III) in the soil was rapidly immobilized by adding magnetic biochar (Fe-BC) and introducing microwave irradiation energy to enhance electron transport efficiency. The results showed that the pore structure and iron species (ZVI, Fe3O4) loaded onto the biochar could be modulated by controlling the temperature and time of microwave pyrolysis, which enhanced the microwave absorption capacity and the immobilization performance of As. After adding Fe-BC (10 wt%) and treating with microwave irradiation for 3 h, the content of As(III) in the soil was reduced to 54.56 %. Compared with the conventional heating treatment, the percentage of stabilized As (residual form) increased by 11.21 %. The localized hot spots formed through the absorption of microwave energy by biochar promote the formation of arsenic-containing mineral crystals (FeAsO4 and Fe3AsO7), thus enhancing the immobilization efficiency. In addition, microwave-induced electron transfer facilitated the oxidation of As(III) to As(V) by surface quinone and carbonyl groups on the Fe-BC. Density functional theory calculation further proved that the surface groups of the Fe-BC had a stronger electron-withdrawing ability under microwave irradiation, thereby promoting the adsorption and immobilization of As(III). This work provided a new perspective on the technology of rapid remediation of heavy metals contaminated soil using biochar.

Techno-economic feasibility and life cycle assessment analysis for a developed novel biosorbent-based arsenic bio-filter system

Significant aquifers around the world is contaminated by arsenic (As), that is regarded as a serious inorganic pollution. In this study, a biosorbent-based bio-filter column has been developed using two different plant biomasses (Colocasia esculenta stems and Artocarpus heterophyllus seeds) to remove total As from the aqueous system. Due to its natural origin, affordability, adaptability, removal effectiveness, and possibility for integration with existing systems, the biosorbent-based bio-filter column presents an alluring and promising method. It offers a practical and eco-friendly way to lessen the damaging impacts of heavy metal contamination on ecosystems and public health. In this system, As (III) is oxidized to As (V) using chlorine as an oxidant, after this post-oxidized As-contaminated water is passed through the bio-filter column to receive As-free water (or below World Health Organization permissible limit for As in drinking water). Optimization of inlet flow rate, interference of co-existing anions and cations, and life cycle of the column were studied. The maximum removal percent of As was identified to be 500 µg L-1 of initial concentration at a flow rate of 1.5 L h-1. Furthermore, the specifications of the biosorbent material was studied using elemental analysis and Zeta potential. The particle size distribution, morphological structures, and chemical composition before and after binding with As were studied using dynamic light scattering (DLS), scanning electron microscope-energy dispersive X-Ray spectroscopy (SEM-EDX), and fourier's transform infrared spectroscopy (FTIR) analysis, respectively. SuperPro 10 software was used to analyze the techno-economic viability of the complete unit and determine its ideal demand and potential. Life cycle assessment was studied to interpret the environmental impacts associated alongside the process system. Therefore, this bio-filtration system could have a potential application in rural, urban, and industrial sectors.

Magnetic biochar enhanced copper immobilization in agricultural lands: Insights from adsorption precipitation and redox

Biochar has exceeded expectations for heavy metal immobilization and has been prepared from widely available sources and inexpensive materials. In this research, coconut shell biochar (CSB), bamboo biochar (BC), magnetic coconut shell charcoal (MCSB), and magnetic bamboo biochar (MBC) were manufactured via co-pyrolysis, and their adsorption properties were tested. The pseudo-secondary (R2 = 0.980-0.985) adsorption kinetic fittings for the four biochas were superior to the pseudo-primary kinetics (R2 = 0.969-0.982). Unmodified biochar adsorption isotherms were more consistent with the Freundlich model, while magnetic biochar fitted Langmuir models better. The maximum adsorption capacity of MCSB for Cu(Ⅱ) reached 371.50 mg g-1. The adsorption mechanisms quantitatively analysis of the biochar indicated that chemical precipitation and ion exchange contributed to the adsorption, in which the magnetic biochar metal-π complexation also enhanced the adsorption. The pot experiment revealed that MCSB (2.0 %DW) significantly enhanced the biomass of lettuce, and facilitated the immobilization of DTPA-Cu (p < 0.05). SEM-EDS, XPS, and FTIR were utilized for morphological characterization and functional group identification, and the increased active adsorption sites (-OH, -COOH, CO, and Fe-O) of MCSB enhanced chemisorption and π-π EDA complexation with Cu(Ⅱ). EEM-PARAFAC and RDA analysis further elucidated that magnetic biochar immobilized copper and reduced biotoxicity (efficiency: 76.12%) by adjusting soil pH, phosphate, and SOM release (negative correlation). The presence of iron oxides (FeOx) promoted in situ adsorption of metallic copper and offered new insights into soil remediation.

Removal of Pb from Contaminated Kaolin by Pulsed Electrochemical Treatment Coupled with a Permeable Reactive Barrier: Tuning Removal Efficiency and Energy Consumption

Lead contamination in soil has emerged as a significant environmental concern. Recently, pulse electrochemical treatment (PECT) has garnered substantial attention as an effective method for mitigating lead ions in low-permeability soils. However, the impact of varying pulse time gradients, ranging from seconds to hours, under the same pulse duty cycle on lead removal efficiency (LRE) and energy consumption in PECT has not been thoroughly investigated. In this study, a novel, modified PECT method is proposed, which couples PECT with a permeable reaction barrier (PRB) and adds acetic acid to the catholyte. A comprehensive analysis of LRE and energy consumption is conducted by transforming pulse time. The results show that the LREs achieved in these experiments were as follows: PCb-3 s (89.5%), PCb-1 m (91%), PCb-30 m (92.9%), and PCb-6 h (91.9%). Importantly, these experiments resulted in significant reductions in energy consumption, with decreases of 68.5%, 64.9%, 51.8%, and 47.4% compared to constant voltage treatments, respectively. It was observed that LRE improved with an increase in both pulse duration and voltage gradient, albeit with a corresponding rise in energy consumption. The results also revealed that corn straw biochar as a PRB could enhance LRE by 6.1% while adsorbing migrating lead ions. Taken together, the present data highlights the potential of modified PECT technology for remediation of lead-contaminated soil, which provides an optimal approach to achieve high LRE while minimizing energy consumption.

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).