Recent developments and prospects of sustainable remediation treatments for major contaminants in soil: A review

Intercropping Pteris cretica and Spinacia oleracea L. with peanut enhances arsenic removal and soil remediation

Arsenic (As) exposure through agricultural soil contamination poses significant health risks and threatens food security. This study explored the efficacy of hyperaccumulator plant diversity and intercropping systems in enhancing As removal from contaminated soil while simultaneously reducing As uptake in peanuts (Arachis hypogaea L.). Thus, a pot experiment was conducted using As-contaminated soil, peanut plants, and hyperaccumulator species as the experimental materials. The experimental treatments included monocultured peanuts (Ck) and peanuts intercropped with Pteris cretica. (P*Pc), intercropped peanut with Spinacia oleracea L. (P*So), and intercropped peanut with P. cretica and S. oleracea L. (P*Pc*So). Our findings revealed that the intercropping system significantly reduced soil As levels compared to monocropping. In addition, peanut As uptake was significantly decreased in hyperaccumulator plants, with enhanced effects under hyperaccumulator plant diversity, minimizing the risk of As transfer to the food chain. Moreover, the As removal rate was higher under intercropping than under monocropping, with the highest removal rate of 88% under intercropped peanut/P. cretica/S. oleracea L., followed by peanut/S. oleracea L. (81%) and peanut/P. cretica (80%). The results demonstrate the potential of using diverse hyperaccumulator plants and intercropping systems as sustainable and effective methods for remediating As-contaminated soils, while simultaneously ensuring food safety. However, further research is needed to elucidate the underlying mechanisms driving these effects and to optimize the phytoremediation of As-contaminated soil and crop production.

Innovative Approaches and Evolving Strategies in Heavy Metal Bioremediation: Current Limitations and Future Opportunities

Decades of technological advancements have led to major environmental concerns, particularly the bioaccumulation of heavy metals, which pose persistent risks to ecosystems and human health. Consequently, research has increasingly shifted from conventional remediation techniques toward more sustainable, environmentally friendly solutions. This review explores recent advancements, ongoing challenges, and future perspectives in the field of bioremediation, emphasizing its potential as a green technology for heavy metal decontamination. Despite significant progress, key challenges remain, including scalability limitations and the management of bioremediation by-products, along with the influence of regulatory policies and public perception on its large-scale implementation. Emerging approaches such as genetic engineering and nanotechnology show promise in overcoming these limitations. Gene editing allows the tailoring of specific metabolic traits for bioprocesses targeted towards increased tolerance to pollutants and higher biodegradation efficiency, higher enzymatic specificity and affinity, and improved yield and fitness in plants. Nanotechnologies, particularly biogenic nanostructures, open up the possibility of repurposing waste materials as well as harnessing the advantages of the biosynthesis of NPs with higher stability, biocompatibility, and biostimulant capacities. Furthermore, biopolymers and bio-based nanocomposites can improve the efficiency and costs of bioremediation protocols. Even so, further research is essential to evaluate their long-term risks and feasibility.

Comparative effectiveness of pristine and H3PO4-modified biochar in combination with bentonite to immobilize cadmium in a calcareous soil

Some agricultural soils are contaminated with potentially toxic elements (PTEs) like Cd, necessitating remediation to safeguard the food chain. However, a research gap exists regarding the combined use of biochar and clay minerals, particularly phosphoric acid-modified biochar and bentonite (an abundant and cost-effectiveness mineral in Iran) for Cd immobilization in contaminated calcareous soils. A 90-day factorial incubation study tested three bentonite levels (0% wt. (B0), 1% wt. (B1), 2% (B2) wt.) and five biochars treatments (control, unmodified/H3PO4-modified coffee grounds [G/GH] and municipal solid waste [M/MH], 2% wt.) for Cd immobilization in a contaminated calcareous soil. The results of analytical techniques (SEM-EDX, FTIR, sequential extraction, EDTA-desorption kinetics) indicated that the application of G biochar with bentonite (B1, B2) increased the concentration of Cd in the water-soluble and exchangeable fraction (WsEx) by 12.9% and 60.3% compared to using G biochar alone. In contrast, a synergistic effect on Cd immobilization was observed between M biochar and bentonite. The M + B2 treatment reduced EDTA-desorbed Cd by 18.7% and exhibited the slowest release rate according to the power function kinetic model. This was due to Cd transfer from bioavailable form (WsEx) to more stable fractions like iron-manganese oxides and residual forms, through increased soil pH and phosphorus levels. Overall, unmodified biochars were more effective at stabilizing soil Cd than those modified by phosphoric acid, likely due to an increase in soil pH. In conclusion, the combination of M biochar and B2 bentonite level was the most effective for Cd immobilization in contaminated calcareous soils. Long-term field-scale research with plants is needed to confirm these results.

Bio-chelation for sustainable heavy metal remediation in municipal solid waste compost: A critical review of chelation technologies

Municipal solid waste (MSW) compost is a promising solution for sustainable urban waste management, widely used as a soil amendment and for carbon sequestration. However, heavy metals in MSW compost pose risks to ecosystems, food safety and human health. This review critically examines three decades of research (1994-2024) on heavy metal contamination in MSW compost and household hazardous waste (HHW), identifying gaps in managing these pollutants, particularly regarding hazardous waste co-disposal. It evaluates existing remediation strategies for heavy metal removal, with a focus on chemical-assisted leaching using chelating agents. Key treatment parameters-such as chelating agent concentration, pH, contact time, liquid/solid ratio, temperature and flow rate-are analysed in both batch and continuous modes. The study advocates for biodegradable chelating agents as an effective approach to enhancing MSW compost quality, with applications in landfill reclamation and agriculture. Emphasizing the need for eco-friendly heavy metal mitigation, the review underscores the importance of safe urban composting practices. The findings contribute to the circular economy and Sustainable Development Goals by promoting sustainable and safe MSW compost applications, fostering environmental protection and public health and guiding research and industry toward scalable, marketable remediation solutions.

Theoretical Study on Adsorption of Halogenated Benzenes on Montmorillonites Modified With M(I)/M(II) Cations

Halogenated benzenes (HBs) are hydrophobic organic chemicals belonging to persistent organic pollutants. Owing to their persistence, they represent a serious problem in environmental contamination, specifically of soils and sediments. One of the most important physical processes determining the fate of HBs in soils is adsorption to main soil components such as soil organic matter and soil minerals. Smectites, layered clay minerals of the 2:1 type, are common minerals in clay-rich soils, of which montmorillonite (Mt) is a typical representative. This work focuses on a systematic modeling study of the adsorption mechanism of selected HBs interacting with the basal (001) surface, which is the dominant surface of Mt particles. The HB···Mt interactions were studied by means of a quantum chemical approach based on the density functional theory method. HBs were represented by five molecules, particularly C6F6, C6Cl3F3, C6Cl6, C6Br3Cl3, and C6Br6. In mixed HBs (C6Cl3F3 and C6Br3Cl3) Cl atoms are in 1,3,5 or rather 2,4,6 positions. The effect of a different cation type on adsorption was investigated for M+/M2+-Mt models with cations from alkali group (M+: Li, K, Na, Rb, Cs) and alkaline earth metal group (M2+: Mg, Ca, Sr., Ba). The calculations were also performed on the gas phase HB···M+/M2+ complexes for comparison. Adsorption energies and distances of the main HB molecular plane from the Mt surface were calculated as a measure of the adsorption strength. The results showed that the strongest HB adsorption is for the Na+-Mt and Ca2+-Mt surfaces. The strongest affinity was observed for hexabromobenzene, while the weakest adsorption was found for hexafluorobenzene. The decomposition of the adsorption energy showed that its dominant component is dispersion energy and less important is the cation-π interaction. The calculated adsorption energies showed a good correlation with experimentally determined log Kd values.

Microbial adaptation and genetic modifications for enhanced remediation in low-permeability soils

Low-permeability soils, characterized by fine texture and high clay content, pose significant challenges to traditional soil remediation techniques due to limited hydraulic conductivity, restricted nutrient flow, and reduced oxygen availability. These unique properties enable low-permeability soils to function as natural barriers in environmental protection; however, they also trap contaminants, making traditional remediation efforts challenging. This review synthesizes current knowledge on microbial adaptation and genetic engineering approaches that enhance the effectiveness of bioremediation in such environments. Key microbial adaptations, including anaerobic metabolism, extracellular enzyme production, and stress response mechanisms, allow individual microbes to adapt in low-permeability soils. Additionally, community-level strategies like microhabitat creation, biofilm formation, and functional redundancy further support microbial resilience. Advancements in genetic engineering now enable the modification of microbial traits-such as soil adhesion, nutrient utilization, and stress tolerance-to enhance bioremediation efficacy. Synthetic biology techniques further allow for the design of tailored microbial consortia that work cooperatively to degrade contaminants in complex soil matrices. This review highlights the integration of microbial and genetic engineering strategies, offering a comprehensive overview that informs current practices and guides future research in low-permeability soil remediation.

Microbial Electrochemical Technologies: Sustainable Solutions for Addressing Environmental Challenges

Addressing global challenges of waste management demands innovative approaches to turn biowaste into valuable resources. This chapter explores the potential of microbial electrochemical technologies (METs) as an alternative opportunity for biowaste valorisation and resource recovery due to their potential to address limitations associated with traditional methods. METs leverage microbial-driven oxidation and reduction reactions, enabling the conversion of different feedstocks into energy or value-added products. Their versatility spans across gas, food, water and soil streams, offering multiple solutions at different technological readiness levels to advance several sustainable development goals (SDGs) set out in the 2030 Agenda. By critically examining recent studies, this chapter uncovers challenges, optimisation strategies, and future research directions for real-world MET implementations. The integration of economic perspectives with technological developments provides a comprehensive understanding of the opportunities and demands associated with METs in advancing the circular economy agenda, emphasising their pivotal role in waste minimisation, resource efficiency promotion, and closed-loop system renovation.

Insights into the Relationship between Temperature Variation and NAPL Removal during In Situ Thermal Remediation of Soil in the Presence of NAPL-Water Co-boiling: A Two-Dimensional Visualized Sandbox Study

Thermal remediation effectively treats sites contaminated with nonaqueous phase liquids (NAPL) by heating soil. A key process is the co-boiling at the water-NAPL interface, which lowers the boiling point due to combined vapor pressures, potentially reducing energy needs. However, determining the optimal end time for heating is challenging due to the invisible nature of underground NAPL, often resulting in excessive energy use. The initial NAPL pool size and distance from the heat source influence the spatiotemporal evolution of the NAPL-water interface, defining three zones: the co-boiling equilibrium zone, a nonequilibrium zone, and an unaffected zone. The temperature data collected by fixed temperature sensors can reflect the spatiotemporal evolution of these zones, offering valuable insights into NAPL removal. This study tackles these challenges using a two-dimensional visualized sandbox integrated with real-time image processing and an array of temperature sensors to monitor the NAPL removal and temperature variation. The results reveal semiquantitatively the impact of different initial NAPL amounts and spatial distributions on temperature variations. An optimized strategy is proposed for temperature sensor positioning, and a qualitative relationship is established between the temperature increase and NAPL removal. These findings can enhance our understanding of subsurface temperature dynamics, supporting more efficient, decarbonized remediation practices.

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.

Quantitative expression of LNAPL pollutant concentrations in capillary zone by coupling multiple environmental factors based on random forest algorithm

The capillary zone plays a crucial role in migration and transformation of pollutants. Light nonaqueous liquids (LNAPLs) have become the main organic pollutant in soil and groundwater environments. However, few studies have focused on the concentration distribution characteristics and quantitative expression of LNAPL pollutants within capillary zone. In this study, we conducted a sandbox-migration experiment using diesel oil as a typical LNAPL pollutant, with the capillary zone of silty sand as the research object. The variation characteristics of LNAPL pollutants (total petroleum hydrocarbon) concentration and environmental factors (moisture content, electrical conductivity, pH, and oxidationreduction potential) were essentially consistent at different locations with the same height. These characteristics differed within range of 10.0-50.0 cm and above 60.0 cm from groundwater. A model for quantitative expression of concentrations was constructed by coupling multiple environmental factors of 968 sets-7744 data via random forest algorithm. The goodness of fit (R2) for both training and test sets was greater than 0.90, and the mean absolute percentage error (MAPE) was less than 16.00 %. The absolute values of relative errors in predicting concentrations at characteristic points were less than 15.00 %. The constructed model can accurately and quantitatively express and predict concentrations in capillary zone.

Luminescent Silver Nanoparticles Biosynthesis Using Couroupita guianensis Flower Extract: Antibacterial and Anticancer Potential

Green synthesis of nanoparticles has become a significant area of research, driven by the demand for sustainable, economical, and environmentally friendly processes, particularly in biomedical applications. In this study, silver nanoparticles (AgNPs) were produced using 10 g of Couroupita guianensis flower extract through a straightforward and environmentally friendly method. The biosynthesized AgNPs were characterized using UV-Vis spectroscopy, XRD, FTIR, SEM, and EDS techniques, confirming their successful formation and structural properties. The antibacterial efficacy of the AgNPs was assessed against Escherichia coli and Listeria monocytogenes, achieving 99.5% inactivation for E. coli and 99.3% inactivation for L. monocytogenes after 120 min of visible light exposure. Additionally, the AgNPs showed notable anticancer effects against breast cancer cells (MDA-MB-231), displaying a dose-dependent decrease in cell viability, with reductions of 15%, 30%, 72%, and 86% observed at concentrations of 25, 50, 75, and 100 μg/mL, respectively. The spherical morphology of the synthesized AgNPs contributed to enhanced interactions with bacterial and cancer cells, underpinning their effectiveness. Furthermore, the mechanisms underlying these antibacterial and anticancer effects were analyzed, highlighting the unique phytochemical properties of the extract that assist in biosynthesis and activity enhancement. These findings suggest that green-synthesized AgNPs derived from C. guianensis flower extract hold significant potential for use in biomedical applications, particularly in antibacterial and anticancer therapies.

Understanding Nanoscale Interactions between Minerals and Microbes: Opportunities for Green Remediation of Contaminated Sites

In situ contaminant degradation and detoxification mediated by microbes and minerals is an important element of green remediation. Improved understanding of microbe-mineral interactions on the nanoscale offers promising opportunities to further minimize the environmental and energy footprints of site remediation. In this Perspective, we describe new methodologies that take advantage of an array of multidisciplinary tools─including multiomics-based analysis, bioinformatics, machine learning, gene editing, real-time spectroscopic and microscopic analysis, and computational simulations─to identify the key microbial drivers in the real environments, and to characterize in situ the dynamic interplay between minerals and microbes with high spatiotemporal resolutions. We then reflect on how the knowledge gained can be exploited to modulate the binding, electron transfer, and metabolic activities at the microbe-mineral interfaces, to develop new in situ contaminant degradation and detoxication technologies with combined merits of high efficacy, material longevity, and low environmental impacts. Two main strategies are proposed to maximize the synergy between minerals and microbes, including using mineral nanoparticles to enhance the versatility of microorganisms (e.g., tolerance to environmental stresses, growth and metabolism, directed migration, selectivity, and electron transfer), and using microbes to synthesize and regenerate highly dispersed nanostructures with desired structural/surface properties and reactivity.

Bio-chelate assisted leaching for enhanced heavy metal remediation in municipal solid waste compost

Municipal solid waste compost, the circular economy's closed-loop product often contains excessive amounts of toxic heavy metals, leading to market rejection and disposal as waste material. To address this issue, the study develops a novel approach based on: (i) utilizing plant-based biodegradable chelating agent, L-glutamic acid, N,N-diacetic acid (GLDA) to remediate heavy metals from contaminated MSW compost, (ii) comparative assessment of GLDA removal efficiency at optimal conditions with conventional nonbiodegradable chelator EDTA, and (iii) enhanced pre- and post-leaching to evaluate the mobility, toxicity, and bioavailability of heavy metals. The impact of treatment variables, such as GLDA concentration, pH, and retention time, on the removal of heavy metals was investigated. The process was optimized using response surface methodology to achieve the highest removal effectiveness. The findings indicated that under optimal conditions (GLDA concentration of 150 mM, pH of 2.9, retention time for 120 min), the maximum removal efficiencies were as follows: Cd-90.32%, Cu-81.96%, Pb-91.62%, and Zn-80.34%. This process followed a pseudo-second-order kinetic equation. Following GLDA-assisted leaching, the geochemical fractions were studied and the distribution highlighted Cd, Cu, and Pb's potential remobilization in exchangeable fractions, while Zn displayed integration with the compost matrix. GLDA-assisted leaching and subsequent fractions illustrated transformation and stability. Therefore, this process could be a sustainable alternative for industrial applications (agricultural fertilizers and bioenergy) and social benefits (waste reduction, urban landscaping, and carbon sequestration) as it has controlled environmental footprints. Hence, the proposed remediation strategy, chemically assisted leaching, could be a practical option for extracting heavy metals from MSW compost, thereby boosting circular economy.

Socio-economic baseline for oil-impacted communities in Ogoniland: towards a restoration framework in Niger Delta, Nigeria

This study documents the socio-economic baselines in selected oil-impacted communities prior to the commencement of the Ogoni clean-up and restoration project. Adopting mixed approach consisting of semi-structured interviews, focus group discussions (FGDs), key informant interviews (KIIs), and household surveys, we surveyed the pre-remediation socio-economic conditions in the Ogoniland communities between July 2018 and March 2019. Results indicated that almost all respondents (99.6%) agreed that the smell of petroleum products or crude oil was evident in the air they breathed even as there were visible black particles (soot) in the respondents' nostrils, on their clothes, and in water. The respondents described the ambient air as smoky and choked with an offensive smell. The household waters were smelly, brownish, or oily, and most respondents (76%) cannot afford to treat their water. Forty-two percent of the respondents who relied on fishing and farming for a living sought for alternative means of subsistence and acknowledged that oil pollution caused stunted growth and low crop yield. The majority of respondents (91%) reported falling fish catches, while the fish caught smell and taste of oil, lowering their market value and posing a potential health risk to consumers. It is evident that oil pollution has impacted the socio-ecological values and sustainable livelihood in Ogoniland. This study provides baseline data for monitoring post-remediation socio-economic improvements in Ogoniland. It also highlights areas of urgent intervention to improve livelihood, and access to basic amenities (e.g., potable drinking water), waste management infrastructure, and statutory policy changes for sustainable development in Ogoniland.