Fenton oxidation for soil remediation: A critical review of observations in historically contaminated 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.

Efficient PFAS removal from contaminated soils through combined washing and adsorption in soil effluents

This study investigates soil washing as a viable strategy to remove poly- and perfluoroalkyl substances (PFAS) from contaminated soils using various washing agents including water, methanol, ethanol, and cyclodextrin ((2-Hydroxypropyl)-β-cyclodextrin HPCD)). Water was less effective (removing only 30 % of PFAS), especially for long-chain hydrophobic PFAS. Methanol (50 % v/v) or HPCD (10 mg g-1 soil) achieved > 95 % PFAS removal regardless of PFAS type, soil size fraction (0-400 µm or 400-800 µm), or experimental setups (batch or column, at liquid/solid (L/S) = 1). Column optimization studies revealed improved efficiency at L/S = 10 with diluted washing solutions, where HPCD exhibited rapid PFAS mobilization even at lower concentrations (1 mg mL-1). We then applied a first-order decay model to effectively predict PFAS breakthrough curves and mobilization within soil columns. Subsequent treatment of wash effluents by activated carbon and biochar effectively reduced PFAS concentrations below detection limits. The performance of both soil washing and subsequent adsorption was found to depend strongly on the specific characteristics of PFAS compounds. These findings highlight the significant potential of methanol and HPCD in soil washing and the effectiveness of integrated soil washing and adsorption for optimizing PFAS removal.

Organic radicals driving polycyclic aromatic hydrocarbon polymerization with peracetic acid activation in soil

The use of peracetic acid (PAA) in advanced oxidation processes has gained significant attention recently, but the knowledge of activating PAA to degrade polycyclic aromatic hydrocarbons (PAHs) is limited due to the variety and selectivity of reactive substances in PAA oxidation system. This paper presented the first systemically study on the degradation of PAHs by PAA activation in soil. It was found that heat-activated peracetic acid (heat/PAA) was capable of degrading phenanthrene (PHE) efficiently with degradation efficiency > 90 % within 30 min. Experimental results demonstrated that a series of reactive oxygen species (ROS) including organic radicals (RO•), hydroxyl radicals (HO•) and singlet oxygen (1O2) were generated, while acetylperoxyl (CH3C(O)OO•) and acetyloxyl (CH3C(O)O•) radicals were primarily responsible for PHE degradation in soil. Further analysis shows that polymerization products such as diphenic acid, 2'-formyl-2-biphenylcarboxylic acid and other macromolecules were dominant products of PHE degradation, suggesting polymerization driving PHE degradation instead of the conventional mineralization process. Toxicity analysis shows that most of the polymerization products had less toxicity than that of PHE. These results indicate that PAA activation was a highly effective remediation method for PAHs contaminated soil, which also provided a novel mechanism for pollutant degradation with the PAA activation process for environmental remediation.

New strategy to optimize in-situ fenton oxidation for TPH contaminated soil remediation via artificial neural network approach

In-situ remediation of total petroleum hydrocarbon (TPH) contaminated soils via Fenton oxidation is a promising approach. However, determining the proper injection amount of H2O2 and Fe source over the Fenton reaction in the complex geological conditions for in-situ TPH soil remediation remains a daunting challenge. Herein, we introduced a practical and novel approach using soft computational models, a multilayer perception artificial neural network (MPLNN), for predicting the TPH removal performance. In this study, we conducted 48 sets of TPH removal experiments using Fenton oxidation to determine the TPH removal performance of a wide range of different ground conditions and generated 336 data points. As a result, a negative Pearson correlation coefficient was obtained in the Fe injection mass and the natural presence of Fe mineral in the soil, indicating that the excess of Fe could significantly retarded the TPH removal performance in the Fenton reaction. In addition, the MPLNN model with 6-6-1 training using Scaled conjugate gradient backpropagation (SCG) with tangent sigmoid as the transfer function demonstrated a high accuracy for TPH removal prediction with the correlation determination of 0.974 and mean square error value of 0.0259. The optimized MPLNN model achieved less than 20% error for predicting TPH removal performance in actual TPH-contaminated soil via Fenton oxidation. Hence, the proposed MPLNN can be useful in improving the Fenton oxidation of TPH removal performance in-situ soil remediation.

Emerging contaminants: A One Health perspective

Environmental pollution is escalating due to rapid global development that often prioritizes human needs over planetary health. Despite global efforts to mitigate legacy pollutants, the continuous introduction of new substances remains a major threat to both people and the planet. In response, global initiatives are focusing on risk assessment and regulation of emerging contaminants, as demonstrated by the ongoing efforts to establish the UN's Intergovernmental Science-Policy Panel on Chemicals, Waste, and Pollution Prevention. This review identifies the sources and impacts of emerging contaminants on planetary health, emphasizing the importance of adopting a One Health approach. Strategies for monitoring and addressing these pollutants are discussed, underscoring the need for robust and socially equitable environmental policies at both regional and international levels. Urgent actions are needed to transition toward sustainable pollution management practices to safeguard our planet for future generations.

Nanotechnology Approaches for the Remediation of Agricultural Polluted Soils

Soil pollution from various anthropogenic and natural activities poses a significant threat to the environment and human health. This study explored the sources and types of soil pollution and emphasized the need for innovative remediation approaches. Nanotechnology, including the use of nanoparticles, is a promising approach for remediation. Diverse types of nanomaterials, including nanobiosorbents and nanobiosurfactants, have shown great potential in soil remediation processes. Nanotechnology approaches to soil pollution remediation are multifaceted. Reduction reactions and immobilization techniques demonstrate the versatility of nanomaterials in mitigating soil pollution. Nanomicrobial-based bioremediation further enhances the efficiency of pollutant degradation in agricultural soils. A literature-based screening was conducted using different search engines, including PubMed, Web of Science, and Google Scholar, from 2010 to 2023. Keywords such as "soil pollution, nanotechnology, nanoremediation, heavy metal remediation, soil remediation" and combinations of these were used. The remediation of heavy metals using nanotechnology has demonstrated promising results and offers an eco-friendly and sustainable solution to address this critical issue. Nanobioremediation is a robust strategy for combatting organic contamination in soils, including pesticides and herbicides. The use of nanophytoremediation, in which nanomaterials assist plants in extracting and detoxifying pollutants, represents a cutting-edge and environmentally friendly approach for tackling soil pollution.

Biodegradation of pyrene by bacterial consortia: Impact of natural surfactants and iron oxide nanoparticles

Polycyclic aromatic hydrocarbons (PAHs) are potentially hazardous compounds that could cause a severe impact on many ecosystems. They are very challenging to remove using conventional methods due to their hydrophobic nature. However, this issue can be resolved by utilizing surface-active molecules to increase their bioavailability. In this study, pyrene was chosen as the PAH compound to explore its degradability by the effect of individual bacterial strains (Pseudomonas stutzeri NA3 and Acinetobacter baumannii MN3) and mixed consortia (MC) along with natural surfactant derived from Sapindus mukorossi and iron oxide nanoparticles (NPs). Additionally, fatty acids esters, dipeptides, and sugar derivative groups were identified as potent bioactive components of natural surfactants. Various techniques, such as XRD, VSM, TEM, and FE-SEM with EDX, were utilized to characterize the pristine and Fenton-treated iron oxide NPs. The analytical results confirmed that the Fe3O4 crystal phase and spherical-shaped NPs exhibited excellent magnetic properties. The impact of natural surfactants and iron oxide NPs has significantly contributed to the biodegradation process, resulting in a prominent decrease in chemical oxygen demand (COD) levels. Gas chromatography-mass spectrometry (GC-MS) analysis showed that biodegradation systems produced primary hydrocarbon intermediates, which underwent oxidative degradation through Fenton treatment. Interestingly, synthesized iron oxide NPs effectively produced hydroxyl radical (•OH) during the Fenton reaction, which was confirmed by electron paramagnetic resonance (EPR) spectra, and the pristine iron oxide NPs underwent a material transformation observed. The study demonstrated an integrated approach for biodegradation and the Fenton reaction process to enhance the pyrene degradation efficiency (90%) compared to other systems. Using natural surfactants and iron oxide NPs in aquatic environments serves as a crucial platform at the interface of microorganisms and contaminated oil products. This interaction offers a promising solution for PAHs bioremediation.

Development of a Multifaceted Perspective for Systematic Analysis, Assessment, and Performance for Environmental Standards of Contaminated Sites

Contaminated soil and groundwater can pose significant risks to human health and ecological environments, making the remediation of contaminated sites a pressing and sustained challenge. It is significant to identify key performance indicators and advance environmental management standards of contaminated sites. The traditional study currently focuses on the inflexible collection of related files and displays configurable limitations regarding integrated assessment and in-depth analysis of published standards. In addition, there is a relative lack of research focusing on the analysis of different types of standard documents. Herein, we introduce a cross-systematic retrospective and review for the development of standards of the contaminated sites, including the comprehensive framework, multifaceted analysis, and improved suggestion of soil and groundwater standards related to the environment. The classification and structural characteristics of different types of files are systematically analyzed of over 300 national, trade, local, and group standards for the contaminated sites. It exhibits that trade standards are the main types and testing methods are the important format within numerical considerations of soil standards. The guide standard serves as a crucial component in environmental management for investigating, assessing, and remediating of contaminated sites. Future improvement plans and development directions are proposed for advancing robust technical support for effective soil contamination prevention and control. This multidimensional analysis and the accompanying suggestions can provide improved guidance for Chinese environmental management of contaminated sites and sparkle the application of standards in a wide range of countries.

Recent trends in the use of fly ash for the adsorption of pollutants in contaminated wastewater and soils: Effects on soil quality and plant growth

Fly ash is one of the largest types of industrial wastes produced during the combustion of coal for energy generation. Finding efficient and sustainable solutions for its reuse has been the subject of substantial research worldwide. Here, we review the recent research data related to (i) the use of fly ash as a low-cost adsorbent for pollutants in wastewater and soils and (ii) its implications in soil-plant system. Fly ash showed prominent adsorption capacity for pollutants in water especially when it was activated or applied in composites. In addition to direct pollutant binding in soils, fly ash can enhance the soil pH indirectly increasing metals' immobilization reducing their plant uptake. Its non-selective adsorptive nature may lead to the co-adsorption of nutrients with pollutants which merits to be considered. Owing to its considerable nutrient contents, fly ash can also improve soil fertility and plant growth. The effects of fly ash on soil physico-chemical properties, microbial population and plant growth are critically evaluated. Fly ash can also contain potentially toxic contaminants (toxic metals, hydrocarbons, etc.) which could have harmful impacts on soil health and plant growth. Identifying the levels of inherent pollutants in fly ash is crucial to evaluate its suitability as a soil amendment. Negative effects of fly ash can also be addressed by using co-amendments, biological agents, and most importantly by an adequate calibration (dose and type) of fly ash based on site-specific conditions. Research directions are identified to promote the research regarding its use in wastewater treatment and agriculture.

The Usability of Sorbents in Restoring Enzymatic Activity in Soils Polluted with Petroleum-Derived Products

Due to their ability to adsorb or absorb chemical pollutants, including organic compounds, sorbents are increasingly used in the reclamation of soils subjected to their pressure, which results from their high potential in eliminating xenobiotics. The precise optimization of the reclamation process is required, focused primarily on restoring the condition of the soil. This research are essential for seeking materials sufficiently potent to accelerate the remediation process and for expanding knowledge related to biochemical transformations that lead to the neutralization of these pollutants. The goal of this study was to determine and compare the sensitivity of soil enzymes to petroleum-derived products in soil sown with Zea mays, remediated using four sorbents. The study was conducted in a pot experiment, with loamy sand (LS) and sandy loam (SL) polluted with VERVA diesel oil (DO) and VERVA 98 petrol (P). Soil samples were collected from arable lands, and the effects of the tested pollutants were compared with those used as control uncontaminated soil samples in terms of Zea mays biomass and the activity of seven enzymes in the soil. The following sorbents were applied to mitigate DO and P effects on the test plants and enzymatic activity: molecular sieve (M), expanded clay (E), sepiolite (S), and Ikasorb (I). Both DO and P exerted a toxic effect on Zea mays, with DO more strongly disturbing its growth and development and the activities of soil enzymes than P. In sandy clay (SL), P was found to be a significant inhibitor of dehydrogenases (Deh), catalase (Cat), urease (Ure), alkaline phosphatase (Pal), and arylsulfatase (Aryl) activities, while DO stimulated the activity of all enzymes in this soil. The study results suggest that the sorbents tested, mainlya molecular sieve, may be useful in remediating DO-polluted soils, especially when alleviating the effects of these pollutants in soils of lower agronomic value.

Soil physiochemical properties and bacterial community changes under long-term polycyclic aromatic hydrocarbon stress in situ steel plant soils

In situ soils were collected at two depths in Jinan and Hangzhou steel plants, which both have a long history of operation and polycyclic aromatic hydrocarbons (PAHs) contamination. The richness of 16 S rRNA gene and bacterial community of the soil were determined by real-time PCR and high-throughput sequencing. Soil physicochemical properties, PAHs contamination characteristics, and their interrelationships were also analyzed. In general, the PAHs contamination decreased with increasing soil depths. The physicochemical properties and PAH concentration of soil had synergistic impacts on the composition of the bacterial community. The long-term higher PAHs stress in Hangzhou contaminated soil (982 mg kg^-1) increased the bacterial abundance and diversity, while that of Jinan contaminated soil (63 mg kg^-1) decreased bacterial abundance and diversity. The pH value, sand content of the soil were positively correlated (P < 0.05) with the bacterial diversity including Simpson, Shannon, Observed_species and Chao1 indexes., and the other soil properties exhibited negative correlations with different strengths. The abundances of Curvibacter, Pseudomonas, Thiobacillus, Lysobacter, and Limnobacter were positively correlated with the PAHs concentration (P < 0.01). Additionally, the network structure of the PAHs-contaminated soils was more complex compared to that of uncontaminated soils, with stronger linkages and correlations between the different bacteria. These findings provide a theoretical basis for microbial remediation of PAHs-polluted soil.

Remediation of benzo[a]pyrene contaminated soils by moderate chemical oxidation coupled with microbial degradation

Chemical oxidation is a promising technology for the remediation of organics-contaminated soils. However, residual oxidants and transformation products have adverse effects on microbial activities. This work aimed at moderate chemical oxidation coupled with microbial degradation (MOMD) for the removal of benzo[a]pyrene (BaP) by optimizing the type and dosage of oxidants. Potassium permanganate (KMnO₄), Fe²⁺ + sodium persulfate (Fe²⁺ + PS), Fenton's reagent (Fe²⁺ + H₂O₂), and hydrogen peroxide (H₂O₂) were compared for BaP removal from loam clay and sandy soils. Overall, the removal efficiency of BaP by a moderate dose of oxidant coupled indigenous microorganism was slightly lower than that by a high dose of relevant oxidant. The contributions of microbial degradation to the total removal of BaP varied for different oxidants and soils. The removal efficiency of BaP from loam clay sandy soil by a moderate dose of KMnO₄ (25 mmol/L) was 94.3 ± 1.1 % and 92.5 ± 1.8 %, respectively, which were both relatively higher than those under other conditions. The indirect carbon footprint yielded by the moderate dose of oxidants was 39.2-72.8 % less than that by the complete oxidation. A moderate dose of oxidants also reduced disturbances to soil pH and OC. The microbial communities after MOMD treatment were dominated by Burkholderiaceae, Enterobacteriaceae, Alicyclobacillaceae, and Oxalobacteraceae. These dominant microorganisms promoted the removal of BaP through the expression of polycyclic aromatic hydrocarbon-ring hydroxylated dioxygenase gene. Compared with complete chemical oxidation, MOMD is also a promising technique with the utilization of indigenous microorganism for remediating BaP-contaminated soils.

Raman spectroscopic and microscopic monitoring of on-site and in-situ remediation dynamics in petroleum contaminated soil and groundwater

The mechanistic study of soil and groundwater remediation in petroleum contaminated lands significantly demands rapid qualitative and quantitative identification of petroleum substances. However, most traditional detection methods cannot provide the on-site or in-situ information of petroleum compositions and contents simultaneously even with multi-spot sampling and complex sample preparation. In this work, we developed a strategy for the on-site detection of petroleum compositions and in-situ monitoring of petroleum contents in soil and groundwater using dual-excitation Raman spectroscopy and microscopy. The detection time was 0.5 h for the Extraction-Raman spectroscopy method and one minute for the Fiber-Raman spectroscopy method. The limit of detection was 94 ppm for the soil samples and 0.46 ppm for the groundwater samples. Meanwhile, the petroleum changes at the soil-groundwater interface were successfully observed by Raman microscopy during the in-situ chemical oxidation remediation processes. The results revealed that hydrogen peroxide oxidation released petroleum from the interior to the surface of soil particles and then to groundwater during the remediation process, while persulfate oxidation only degraded petroleum on the soil surface and in groundwater. This Raman spectroscopic and microscopic method can shed light on the petroleum degradation mechanism in contaminated lands, and facilitate the selection of suitable soil and groundwater remediation plans.

Novel insights into the predominant factors affecting the bioavailability of polycyclic aromatic hydrocarbons in industrial contaminated areas using PLS-developed model

Bioavailability is recognized as a useful technical standard for risk assessment and pollution rehabilitation. However, knowledge on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in contaminated site soils is still limited, especially concerning the influential mechanism. With an abundance of soil collections from nine industrial areas in China, the bioavailabilities, as conceptually defined as bioconcentration factors (BCFs) of PAHs were analyzed using biomimetic extraction of hydroxypropyl-β-cyclodextrin (HPCD). Apart from the total content of PAHs varying with the different pyrogenic sources, the BCFs were greatly dependent on the soil physicochemical properties from the spatial scale and inversely proportional to the number of rings. Pearson correlation analysis indicated a weak relationship between bioavailability and the soil dissolved organic matter (DOM), pH and particle size. To incorporate the soil physicochemical properties and structural characteristics of PAHs determined by density functional theory (DFT), the optimum model for bioavailability was developed for BCFs by partial least square (PLS) analysis. The PLS-derived model was shown to be predictive within the applicability domain (AD). The structural characteristics, e.g., molecular polarizability and frontier orbital energy level that favor the soil adsorption of PAH isomers via dispersion interactions, and electron exchanges were indicated to be more impactful on bioavailability than soil environmental factors. However, soil factors should not be neglected, because the pH, DOM, etc. were significantly influential. It makes sense that the higher DOM causes greater bioavailability via increasing the free-dissolved fractions of PAHs. Interestingly, the effect of pH on bioavailability was spectrally validated by excitation-emission matrix (EEM) fluorescence, showing that the interaction between DOM and pyrene strengthened the fluorescence quenching of chromophores with the decline in pH.

Challenges in Recycling Spent Lithium-Ion Batteries: Spotlight on Polyvinylidene Fluoride Removal

In the recycling of retired lithium-ion batteries (LIBs), the cathode materials containing valuable metals should be first separated from the current collector aluminum foil to decrease the difficulty and complexity in the subsequent metal extraction. However, strong the binding force of organic binder polyvinylidene fluoride (PVDF) prevents effective separation of cathode materials and Al foil, thus affecting metal recycling. This paper reviews the composition, property, function, and binding mechanism of PVDF, and elaborates on the separation technologies of cathode material and Al foil (e.g., physical separation, solid-phase thermochemistry, solution chemistry, and solvent chemistry) as well as the corresponding reaction behavior and transformation mechanisms of PVDF. Due to the characteristic variation of the reaction systems, the dissolution, swelling, melting, and degradation processes and mechanisms of PVDF exhibit considerable differences, posing new challenges to efficient recycling of spent LIBs worldwide. It is critical to separate cathode materials and Al foil and recycle PVDF to reduce environmental risks from the recovery of retired LIBs resources. Developing fluorine-free alternative materials and solid-state electrolytes is a potential way to mitigate PVDF pollution in the recycling of spent LIBs in the EV era.

A Mechanistic Study of Goethite-Based Fenton-Like Reactions for Imidacloprid Degradation

Biotic transformation of imidacloprid (IMD) has been widely investigated in the environments. However, little was known about IMD degradation via abiotic pathways, such as reactive oxygen species (ROS)-based oxidation processes. Here we systematically investigated the mechanism of hydroxyl radical (^•OH) production and the associated IMD degradation in the goethite (α-FeOOH)-based Fenton-like systems. Results showed that IMD can be efficiently degraded in the α-FeOOH/H₂O₂ systems, with degradation rate exceeded 80% within 48 h. Based on the examination of electron paramagnetic resonance (EPR) and chemical probes, ^•OH was identified as the key ROS that responsible for IMD degradation. IMD can be decomposed via hydroxylation or removal of -N-NO₂ to produce hydroxylated IMD, cyclic urea and 6-chloronicotinic acid, with the associated toxicities also evaluated. In addition, the increasing H₂O₂ concentration and decreasing solution pH both significantly increased IMD degradation. This study provides theoretical understanding for the implications of soil mineral-based Fenton-like reactions in the abiotic transformation of pesticide pollutants.

The era of low-permeability sites remediation and corresponding technologies: A review

Rational utilization of soil resources and remediation of contaminated soils are imperative due to the rapidly growing demand for clean soils. Currently, many in-situ remediation technologies are less suitable at low-permeability sites due to the limitations of soil permeability. This work defines a low-permeability site as a site with hydraulic conductivity less than 10^-4 cm/s, and summarizes the migration characteristics of representative contaminants at low-permeability sites, and discusses the principles and practical applications of different technologies suitable for the remediation of low-permeability sites, including electrokinetic remediation technology, polymer flushing technology, fracturing technology, and in-situ thermal remediation technology. Enhanced and combined remediation technologies are further described because one remediation technology cannot remediate all contaminants. The prospects for the application of remediation technologies to low-permeability sites are also proposed. This work highlights the necessity of low-permeability sites remediation and the urgent need for new remediation technologies, with the hope to inspire future research on low-permeability sites.

Emerging bio-dispersant and bioremediation technologies as environmentally friendly management responses toward marine oil spill: A comprehensive review

Marine oil spills emanating from wells, pipelines, freighters, tankers, and storage facilities draw public attention and necessitate quick and environmentally friendly response measures. It is sometimes feasible to contain the oil with booms and collect it with skimmers or burn it, but this is impracticable in many circumstances, and all that can be done without causing further environmental damage is adopting natural attenuation, particularly through microbial biodegradation. Biodegradation can be aided by carefully supplying biologically accessible nitrogen and phosphorus to alleviate some of the microbial growth constraints at the shoreline. This review discussed the characteristics of oil spills, origin, ecotoxicology, health impact of marine oils spills, and responses, including the variety of remedies and responses to oil spills using biological techniques. The different bioremediation and bio-dispersant treatment technologies are then described, with a focus on the use of green surfactants and their advances, benefits/drawbacks. These technologies were thoroughly explained, with a timeline of research and recent studies. Finally, the hurdles that persist as a result of spills are explored, as well as the measures that must be taken and the potential for the development of existing treatment technologies, all of which must be linked to the application of integrated procedures.

Remediation techniques for elimination of heavy metal pollutants from soil: A review

Contaminated soil containing toxic metals and metalloids is found everywhere globally. As a consequence of adsorption and precipitation reactions, metals are comparatively immobile in subsurface systems. Hence remediation techniques in such contaminated sites have targeted the solid phase sources of metals such as sludges, debris, contaminated soils, or wastes. Over the last three decades, the accumulation of these toxic substances inside the soil has increased dramatically, putting the ecosystem and human health at risk. Pollution of heavy metal have posed severe impacts on human, and it affects the environment in different ways, resulting in industrial anger in many countries. Various procedures, including chemical, biological, physical, and integrated approaches, have been adopted to get rid of this type of pollution. Expenditure, timekeeping, planning challenges, and state-of-the-art gadget involvement are some drawbacks that need to be properly handled. Recently in situ metal immobilization, plant restoration, and biological methods have changed the dynamics and are considered the best solution for removing metals from soil. This review paper critically evaluates and analyzes the numerous approaches for preparing heavy metal-free soil by adopting different soil remediation methods.

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

Insights into the recent advances in nano-bioremediation of pesticides from the contaminated soil

In the present scenario, the uncontrolled and irrational use of pesticides is affecting the environment, agriculture and livelihood worldwide. The excessive application of pesticides for better production of crops and to maintain sufficient food production is leading to cause many serious environmental issues such as soil pollution, water pollution and also affecting the food chain. The efficient management of pesticide use and remediation of pesticide-contaminated soil is one of the most significant challenges to overcome. The efficiency of the current methods of biodegradation of pesticides using different microbes and enzymes depends on the various physical and chemical conditions of the soil and they have certain limitations. Hence, a novel strategy is the need of the hour to safeguard the ecosystem from the serious environmental hazard. In recent years, the application of nanomaterials has drawn attention in many areas due to their unique properties of small size and increased surface area. Nanotechnology is considered to be a promising and effective technology in various bioremediation processes and provides many significant benefits for improving the environmental technologies using nanomaterials with efficient performance. The present article focuses on and discusses the role, application and importance of nano-bioremediation of pesticides and toxic pollutants to explore the potential of nanomaterials in the bioremediation of hazardous compounds from the environment.

Oxidative leaching of V-Cr-bearing reducing slag via a Cr(III) induced Fenton-like reaction in concentrated alkaline solutions

V-Cr-bearing reducing slag (VCRS) is considered a hazardous waste that can create ecosystem disasters if handled improperly. It consists of a considerable amount of heavy metals, such as vanadium (V) and chromium (Cr). In this study, we propose a novel process featuring a VCRS self-induced Cr(III)-Fenton-like reaction to efficiently recover V and Cr from hazardous VCRS. The generation of hydroxyl radicals (·OH) and determination of their effect on V and Cr oxidation were examined via electron spin resonance detection, free radical quenching, and terephthalic acid fluorescence probe methods. The V and Cr oxidative leaching processes were directly controlled by the amount of added H₂O₂ and generated·OH from the Cr(III)-Fenton-like reaction, which in turn was dependent on the amount of dissolved Cr(OH)₄^-. In a single oxidative leaching process, the leaching efficiencies of V and Cr reached 97.5 ± 0.6 % and 85.2 ± 0.8 %, respectively, and reached 99.4 ± 0.5 % and 94.6 ± 0.9 %, respectively, from circular leaching owing to a continuous supply of dissolved Cr(OH)₄^- from fresh VCRS. This study identifies a novel approach to discovering deep oxidation of the VCRS while minimizing environmental contamination via a waste control strategy and can be considered an attractive alternative approach for the green treatment of VCRS.

Development of a new methodology for multifaceted assessment, analysis, and characterization of soil contamination

It is important to identify key performance and core progress features of soil contamination management practices. Traditional research currently focuses on numerical statistics of contaminated sites but exhibits structural limitations regarding cross-assessment and in-depth analysis of published findings. Herein, we report a multidimensional perspective to assess the environmental management performance of soil contamination via systematic and historical development of construction land risk control and remediation lists (RCRLs). The considered contaminated sites are mainly concentrated in Northern China, Yangtze River Delta, Pearl River Delta, and Sichuan-Chongqing regions. Monthly historical overviews indicate that most lists are updated 4-5 times within 32 months. Direct chemical-related industrial production results in the largest number of contaminated sites. Arsenic and lead are the most common heavy metals of concern in soil contamination. The fiscal revenue index exhibits the best positive performance in terms of the number of contaminated sites. By employing the site number, update frequency, and published contents of different calculation proportions, ten types of integrated assessment indicators (IAIs) are established to evaluate the environmental achievements in various provincial regions in regard to soil contamination protection. This multifaceted strategy can provide advanced guidance for Chinese environmental management and expand the application of soil pollution risk control and remediation in a wide range of countries.

Coupling surfactants with ISCO for remediating of NAPLs: Recent progress and application challenges

Non-aqueous phase liquids (NAPLs) pose a serious risk to the soil-groundwater environment. Coupling surfactants with in situ chemical oxidation (ISCO) technology is a promising strategy, which is attributed to the enhanced desorption and solubilization efficiency of NAPL contaminants. However, the complex interactions among surfactants, oxidation systems, and NAPL contaminants have not been fully revealed. This review provides a comprehensive overview on the development of surfactant-coupled ISCO technology focusing on the effects of surfactants on oxidation systems and NAPLs degradation behavior. Specifically, we discussed the compatibility between surfactants and oxidation systems, including the non-productive consumption of oxidants by surfactants, the role of surfactants in catalytic oxidation systems, and the loss of surfactants solubilization capacity during oxidation process. The effect of surfactants on the degradation behavior of NAPL contaminants is then thoroughly summarized in terms of degradation kinetics, byproducts and degradation mechanisms. This review demonstrates that it is crucial to minimize the negative effects of surfactants on NAPL contaminants oxidation process by fully understanding the interaction between surfactants and oxidation systems, which would promote the successful implementation of surfactant-coupled ISCO technology in remediation of NAPLs-contaminated sites.

Managing Fenton-treated sediment with biochar and sheep manure compost: Effects on the evolutionary characteristics of bacterial community

Fenton oxidation is a widely used method for the fast and efficient treatment of contaminated sediment, but few studies have investigated the management of Fenton-treated sediment for resource utilization. In this study, the evolutionary characteristics of bacterial community composition in Fenton-treated riverine sediment were investigated using 16S rRNA gene sequencing after the incorporation of rice straw biochar and sheep manure compost. The Fenton treatment caused a decline in the relative abundance of Bacteroidetes from 39% to 8% on the 7th day, and using biochar and compost rapidly increased the relative abundance of Firmicutes from 13% to 61% and 57%, respectively. Applying 1.25 wt% biochar after the Fenton treatment contributed to high Shannon diversity indices of 4.80, 4.69, and 4.76 on the 7th, 28th, and 56th day, respectively. The reduced differences of Shannon indexes on the 56th day indicated that the bacterial diversity among different treatments tended to be similar over time. The genera Flavisolibacter and Bacillus were representatively detected on the 7th day in the untreated sediment and Fenton/biochar-treated sediment, respectively. The number of feature bacteria decreased significantly from 88 on the 7th day to 29 on the 56th day. The community functions for the carbon, nitrogen, and sulfur cycles were sensitive to the Fenton-treatment and the subsequent treatment with biochar and compost. This study may provide a useful reference for follow-up work on the remediation of contaminated sediment using advanced oxidation processes, and promote the development of resource utilization of amended sediment.

Thermally enhanced bioremediation: A review of the fundamentals and applications in soil and groundwater remediation

Thermally enhanced bioremediation (TEB), a new concept proposed in recent years, explores the combination of thermal treatment and bioremediation to address the challenges of the low efficiency and long duration of bioremediation. This study presented a comprehensive review regarding the fundamentals of TEB and its applications in soil and groundwater remediation. The temperature effects on the bioremediation of contaminants were systematically reviewed. The thermal effects on the physical, chemical and biological characteristics of soil, and the corresponding changes of contaminants bioavailability and microbial metabolic activities were summarized. Specifically, the increase in temperature within a suitable range can proliferate enzymes enrichment, extracellular polysaccharides and biosurfactants production, and further enhancing bioremediation. Furthermore, a systematic evaluation of TEB applications by utilizing traditional in situ heating technologies, as well as renewable energy (e.g., stored aquifer thermal energy and solar energy), was provided. Additionally, TEB has been applied as a biological polishing technology post thermal treatment, which can be a cost-effective method to address the contaminants rebounds in groundwater remediation. However, there are still various challenges to be addressed in TEB, and future research perspectives to further improve the basic understanding and applications of TEB for the remediation of contaminated soil and groundwater are presented.

Decrypting the synergistic action of the Fenton process and biochar addition for sustainable remediation of real technogenic soil from PAHs and heavy metals

The objective of this study was to demonstrate the feasibility and the relevance of combining biochar with the Fenton process for the simultaneous improvement of polycyclic aromatic hydrocarbons (PAHs) degradation and immobilization of heavy metals (HMs) in real soil remediation processes at circumneutral pH. The evaluation of PAHs degradation results was performed through multivariate statistical tools, including principal component analysis (PCA) and partial least squares (PLS). PCA showed that the level of biochar amendment decisively affected the degree of degradation of total PAHs, highlighting the role of biochar in catalyzing the Fenton reaction. Moreover, the PLS model was used to interpret the important features of each PAH's physico-chemical properties and its correlation to degradation efficiency. The electron affinity of PAHs correlated positively with the degradation efficiency only if the level of biochar amendment sat at 5%, explained by the ability of biochar to transfer the electrons to PAHs, improving the Fenton-like degradation. Moreover, the addition of biochar reduced the mobilization of HMs by their fixation on their surface, reducing the Fenton-induced metal leaching from the destruction of metal-organic complexes. In overall, these results on the high immobilization rate of HMs accompanied with additional moderate PAHs degradation highlighted the advantages of using a biochar-assisted Fenton-like reaction for sustainable remediation of technogenic soil.

Remediation of phenol contaminated soil using persulfate activated by ball-milled colloidal activated carbon

The degradation of phenolic compounds through persulfate (PS) activation is a valuable approach for soil/groundwater remediation. Several reports have been made related to PS activation and contaminant degradation using carbo-catalysts; however, there is no detailed study on soil remediation by colloidal activated carbon. This study demonstrates the phenol (PhOH) degradation efficiency in spiked and field-contaminated soils by a novel and low-cost ball-milled colloidal activated carbon (CAC_BM) catalyst. The CAC_BM/PS system exhibited outstanding degradation performance for PhOH in both spiked and field-contaminated soils. Optimum condition for degradation of 5.63 mmol PhOH kg soil^-1 was achieved at 2.5 mg CAC_BM g soil^-1, 5 mM PS, and a solid-liquid ratio of 1:5 at 25 °C in the wide pH range of 3-11. Radical scavenger experiments and electron spin resonance (ESR) spectroscopy revealed that both radical (^•OH and SO₄^•-) and non-radical (¹O₂) species were involved in the CAC_BM/PS system. PhOH degradation in soil phase followed several degradation pathways, resulting in various intermediate byproducts such as acetic acid, maleic acid, p-benzoquinone, fumaric acid, and ferulic acid as analyzed by ultra-high-performance liquid chromatography with mass spectroscopy (UPLC-MS). The CAC_BM/PS system showed a promising potential in the remediation of organic-contaminated soil.

Remediation of soil polluted with petroleum hydrocarbons and its reuse for agriculture: Recent progress, challenges, and perspectives

Petroleum hydrocarbons (PHs) are used as raw materials in many industries and primary energy sources. However, excessive PHs act as soil pollutants, posing serious threats to living organisms. Various ex-situ or in-situ chemical and biological methods are applied to restore polluted soil. However, most of the chemical treatment methods are expensive, environmentally unfriendly, and sometimes inefficient. That attracts scientists and researchers to develop and select new strategists to remediate polluted soil through risk-based analysis and eco-friendly manner. This review discusses the sources of PHs, properties, distribution, transport, and fate in the environment, internal and external factors affecting the soil remediation and restoration process, and its effective re-utilization for agriculture. Bioremediation is an eco-friendly method for degrading PHs, specifically by using microorganisms. Next-generation sequencing (NGS) technologies are being used to monitor contaminated sites. Currently, these new technologies have caused a paradigm shift by giving new insights into the microbially mediated biodegradation processes by targeting rRNA are discussed concisely. The recent development of risk-based management for soil contamination and its challenges and future perspectives are also discussed. Furthermore, nanotechnology seems very promising for effective soil remediation, but its success depends on its cost-effectiveness. This review paper suggests using bio-electrochemical systems that utilize electro-chemically active microorganisms to remediate and restore polluted soil with PHs that would be eco-friendlier and help tailor-made effective and sustainable remediation technologies.