Energy storage devices (e.g., supercapacitors and rechargeable Li-ion batteries (LIBs)) play a critical role in meeting the growing energy demand and reducing the consumption of fossil fuels-based exergy. Recently, increasing attention is given worldwide to use biomass-derived carbon materials (BCMs) for clean energy storage technologies due to their tunable physicochemical properties, excellent surface chemistry, good electrical conductivity, low-cost, and environmental sustainability. This review critically analyzes the latest advancements in the application of BCMs for the development of energy storage devices namely supercapacitors and LIBs. Biomass from plants, microorganisms and animals are used as the low-cost precursor for synthesis of BCMs. Different biomass conversion technologies (e.g., pyrolysis, hydrothermal carbonization and physicochemical activation) are used for synthesis and enhancement of the electrochemical characteristics of BCMs. Carbon materials are categorized into four different types of materials namely zero-dimensional, one-dimensional, two-dimensional and three-dimensional materials based on their dimensionality. Different types of carbon materials including activated carbons, heteroatoms doped carbons, nano-carbons, biochars and carbon composites are used as electrodes (cathode and anode) in energy storage devices. BCMs-based electrodes offer promising electrochemical performance (high energy density, high specific capacitance, promising rate performance and long cycling stability). Life cycle assessment (LCA) shows that production of biomass-based electrodes is sustainable, environmentally benign and cost-effective than commercial electrodes. The key challenges associated with the large-scale production and practical application of BCMs are highlighted. This comprehensive review would contribute to developing advanced high performance and sustainable energy storage technologies using renewable biomass-derived electrode materials.

The application of biomass-derived carbon materials (e.g., biochar) into soil is considered as an attractive and sustainable strategy to enhance carbon sequestration in soil and to mitigate climate change. Our comprehensive literature analysis shows that the carbon sequestration potential of biochar in soil systems varies between 0.7 and 1.8 Gt CO2-C(eq)/year. Biochar with high stability and C/N ratios is effective to achieve significant carbon sequestration in soil. Furthermore, carbon sequestration is usually favourable at high biochar application rate in soil with high porosity and alkaline pH (>7.5). The dominant bacterial communities enriched in the biochar-amended soil include Proteobacteria and Acidobacteria, while Ascomycota dominates the fungal communities. The impact of biochar amendment on soil microbial biomass and communities depends on the biochar particle size, porosity and application rate. Life cycle assessment (LCA) of biochar-amended soil reveals that biochar produced from waste biomass is found to be environmentally friendly with the acceptable level of economic feasibility in terms of large-scale applications. The recommended future research directions to seek practical applications of biochar amendment in soil include (1) development of biochar-microbe co-engineering strategies to stabilize labile carbon fractions in soil, (2) exploration of machine learning tools to optimize biochar properties for adoption of biochar treatment under region-specific soil conditions, and (3) standardization of carbon accounting methodologies to address and resolve discrepancies in LCA studies. We believe that this comprehensive review would help for development of novel biochar to achieve optimum carbon sequestration efficiency in soil and to develop practical climate change mitigation strategies.

Biodegradable plastics have received considerable attention as an eco-friendly material to replace non-biodegradable plastics. This paper critically reviews recent studies on the occurrence, fate, transport, and ecotoxicity of biodegradable and non-biodegradable microplastics (MPs) in the aquatic environment. The fate and transport of MPs largely depend on their properties, hydrodynamic conditions, and climatic factors. MPs show various levels of ecotoxicity toward aquatic biota. The overall aim of this review is to improve the current understanding on the fate and transport of MPs and help regulatory agencies to develop effective strategies for mitigation of pollution, caused by MPs in the aquatic environment.

This study explores the use of water treatment residuals (WTR) and construction waste (CW) in bioretention systems (BRS) for managing stormwater in urban areas. Using life cycle assessment and cost analysis, we compared the performance of an engineered media mix of WTR and CW in BRS (called BRS2) with that of a conventional soil mix (called BRS1) in Singapore's context, with due consideration of local climatic conditions and precipitation patterns. Our findings indicate that the environmental impacts of BRS are primarily due to the acquisition (30-90%) and transportation (3-66%) of materials, followed by the operation and maintenance (1-40%) of BRS. Integrating WTR and CW in BRS2 media offers superior environmental benefits (reducing environmental impacts by up to 10%) and proves to be more cost-effective (increasing net monetized profit by about 3%) than the conventional BRS1 media. Our study demonstrates that implementing BRS on a large-scale network can effectively manage water resources, mitigate air pollution and climate change, promote the circular economy, and enhance environmental sustainability. While these results are based on conditions in Singapore, we believe that the general approach toward stormwater management based on nature-based systems is scalable and adaptable to other urban environments with similar climatic conditions.

Vehicular traffic is a major source of urban air pollution in Southeast Asia (SEA), posing significant health risks to pedestrians due to exposure to fine particulate matter (PM2.5), black carbon (BC), and ultrafine particles (UFPs). Despite this issue of health concern, limited data exists linking the spatial and temporal variations of these pollutants and related pedestrian exposure in the region. Due to the unique urban topography, road infrastructure, and meteorological conditions in SEA, high-resolution air quality monitoring studies are essential to better understand pedestrian exposure patterns. This study addresses this knowledge gap by conducting a comprehensive real-time mobile measurement campaign in Singapore as a case study, using portable instruments to assess pedestrian exposure to the traffic-derived air pollutants across diverse urban road categories. We developed three land-use regression (LUR) models to identify the determinants and spatial distributions of PM2.5, BC, and UFP concentrations along the pedestrian pathways. Unlike previous stationary or vehicular-based LUR studies, our walking-based approach represents an effective assessment of pedestrian exposure. The results showed mean levels of PM2.5, BC and UFPs ranged from 16.4 to 20.0 mu g m(-3), 2.2-5.8 mu g m(-3) and 11.3 x 10(3) to 31.7 x 10(3) # cm(-3), respectively, with BC and UFPs more strongly correlated with vehicular traffic emissions than PM2.5, particularly near highways and major arterial roads. Urban greenery, including tree density and park areas, was found to significantly reduce pedestrian exposure. These findings provide insights into the relationship between urban design, traffic patterns, and pedestrian health, offering strategies to mitigate traffic-related air pollution and promote healthier cities in SEA.

Lithium-ion batteries (LIBs) are widely used as power storage systems in electronic devices and electric vehicles (EVs). Recycling of spent LIBs is of utmost importance from various perspectives including recovery of valuable metals (mostly Co and Li) and mitigation of environmental pollution. Recycling methods such as direct recycling, pyrometallurgy, hydrometallurgy, bio-hydrometallurgy (bioleaching) and electrometallurgy are generally used to resynthesise LIBs. These methods have their own benefits and drawbacks. This manuscript provides a critical review of recent advances in the recycling of spent LIBs, including the development of recycling processes, identification of the products obtained from recycling, and the effects of recycling methods on environmental burdens. Insights into chemical reactions, thermodynamics, kinetics, and the influence of operating parameters of each recycling technology are provided. The sustainability of recycling technologies (e.g., life cycle assessment and life cycle cost analysis) is critically evaluated. Finally, the existing challenges and future prospects are presented for further development of sustainable, highly efficient, and environmentally benign recycling of spent LIBs to contribute to the circular economy. A critical review of the recent developments in the recycling of spent Li-ion batteries using five major technologies (direct recycling, pyrometallurgy, hydrometallurgy, bioleaching and electrometallurgy) and evaluation of their sustainability.

Soil pollution, caused by potentially toxic elements (PTEs), is a significant problem worldwide. This study has investigated the key factors that control the mobility and fate of six PTEs (Pb, Cd, Cr, Cu, Zn, and Ni) which are frequently detected in contaminated soils. The findings of this study demonstrate that smaller particles present in soil show stronger adsorption capacity compared to larger particles because of the higher specific surface area. Moreover, soil with higher organic matter content (e.g., humic acid) exhibits stronger adsorption capacity due to the presence of abundant functional groups namely hydroxyl (OH) and carboxyl (COOH). Notably, these functional groups possess high affinity for Pb adsorption, followed by Cd > Cu > Cr > Zn > Ni. The adsorption of most of the PTEs by soil with and without humic acid is better described by the Langmuir isotherm model and pseudo-second-order kinetic model. Overall, the experimental results illustrate that soil with high contents of humic acid can restrict the mobility of PTEs. This mechanistic evaluation predicts how soils with different organic matter contents respond to PTEs pollution. This study outcome will be helpful in developing sustainable remediation strategies to tackle pollution caused by PTEs in the soil environment.

Visible-light-driven photocatalytic oxidation by photogenerated holes has immense potential for environmental remediation applications. While the electron-mediated photoreduction reactions are often at the spotlight, active holes possess a remarkable oxidation capacity that can degrade recalcitrant organic pollutants, resulting in nontoxic byproducts. However, the random charge transfer and rapid recombination of electron-hole pairs hinder the accumulation of long-lived holes at the reaction center. Herein, a novel method employing defect-engineered indium (In) single-atom photocatalysts with nitrogen vacancy (Nv) defects, dispersed in carbon nitride foam (In-Nv-CNF), is reported to overcome these challenges and make further advances in photocatalysis. This Nv defect-engineered strategy produces a remarkable extension in the lifetime and an increase in the concentration of photogenerated holes in In-Nv-CNF. Consequently, the optimized In-Nv-CNF demonstrates a remarkable 50-fold increase in photo-oxidative degradation rate compared to pristine CN, effectively breaking down two widely used antibiotics (tetracycline and ciprofloxacin) under visible light. The contaminated water treated by In-Nv-CNF is completely nontoxic based on the growth of Escherichia coli. Structural-performance correlations between defect engineering and long-lived hole accumulation in In-Nv-CNF are established and validated through experimental and theoretical agreement. This work has the potential to elevate the efficiency of overall photocatalytic reactions from a hole-centric standpoint.

Spent lithium-ion batteries (LIBs) are increasingly generated due to their widespread use for various energy-related applications. Spent LIBs contain several valuable metals including cobalt (Co) and lithium (Li) whose supply cannot be sustained in the long-term in view of their increased demand. To avoid environmental pollution and recover valuable metals, recycling of spent LIBs is widely explored using different methods. Bioleaching (biohydrometallurgy), an environmentally benign process, is receiving increased attention in recent years since it utilizes suitable microorganisms for selective leaching of Co and Li from spent LIBs and is cost-effective. A comprehensive and critical analysis of recent studies on the performance of various microbial agents for the extraction of Co and Li from the solid matrix of spent LIBs would help for development of novel and practical strategies for effective extraction of precious metals from spent LIBs. Specifically, this review focuses on the current advancements in the application of microbial agents namely bacteria (e.g., Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans) and fungi (e.g., Aspergillus niger) for the recovery of Co and Li from spent LIBs. Both bacterial and fungal leaching are effective for metal dissolution from spent LIBs. Among the two valuable metals, the dissolution rate of Li is higher than Co. The key metabolites which drive the bacterial leaching include sulfuric acid, while citric acid, gluconic acid and oxalic acid are the dominant metabolites in fungal leaching. The bioleaching performance depends on both biotic (microbial agents) and abiotic factors (pH, pulp density, dissolved oxygen level and temperature). The major biochemical mechanisms which contribute to metal dissolution include acidolysis, redoxolysis and complexolysis. In most cases, the shrinking core model is suitable to describe the bioleaching kinetics. Biological-based methods (e.g., bioprecipitation) can be applied for metal recovery from the bioleaching solution. There are several potential operational challenges and knowledge gaps which should be addressed in future studies to scale-up the bioleaching process. Overall, this review is of importance from the perspective of development of highly efficient and sustainable bioleaching processes for optimum resource recovery of Co and Li from spent LIBs, and conservation of natural resources to achieve circular economy.

The direct impacts of climate change involve a multitude of phenomena, including rising sea levels, intensified severe weather events such as droughts and flooding, increased temperatures leading to wildfires, and unpredictable fluctuations in rainfall. This comprehensive review intends to examine firstly the probable consequences of climate change on extreme weather events such as drought, flood and wildfire. This review subsequently examines the release and transformation of contaminants in terrestrial, aquatic, and atmospheric environments in response to extreme weather events driven by climate change. While drought and flood influence the dynamics of inorganic and organic contaminants in terrestrial and aquatic environments, thereby influencing their mobility and transport, wildfire results in the release and spread of organic contaminants in the atmosphere. There is a nascent awareness of climate change's influence of climate change-induced extreme weather events on the dynamics of environmental contaminants in the scientific community and decision-making processes. The remediation industry, in particular, lags behind in adopting adaptive measures for managing contaminated environments affected by climate change-induced extreme weather events. However, recognizing the need for assessment measures represents a pivotal first step towards fostering more adaptive practices in the management of contaminated environments. We highlight the urgency of collaboration between environmental chemists and climate change experts, emphasizing the importance of jointly assessing the fate of contaminants and rigorous action to augment risk assessment and remediation strategies to safeguard the health of our environment.

Biodegradable microplastics (BMPs) are considered to be environmentally friendly compared to non-biodegradable plastics (NMPs). However, BMPs are likely to become toxic during their transport because of the adsorption of pollutants (e.g., heavy metals) onto them. This study investigated the uptake of six heavy metals (Cd2+, Cu2+, Cr3+, Ni2+, Pb2+, and Zn2+) by a common BMPs (polylactic acid (PLA)) and compared their adsorption characteristics to those of three types of NMPs (polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)) for the first time. The order of heavy metal adsorption capacity among the four MPs was PE > PLA > PVC > PP. The findings suggest that BMPs contained more toxic heavy metals than some NMPs. Among the six heavy metals, Cr3+ showed considerably stronger adsorption than other heavy metals in both BMPS and NMPs. The adsorption of heavy metals on MPs can be well explained using the Langmuir isotherm model, while the adsorption kinetic curves showed the best fit to the pseudo-second-order kinetic equation. Desorption experiments revealed that BMPs released a higher percentage of heavy metals (54.6–62.6

Silver (Ag), a naturally occurring, rare and precious metal, is found in major minerals such as cerargyrite (AgCl), pyrargyrite (Ag3SbS3), proustite (Ag3AsS3), and stephanite (Ag5SbS4). From these minerals, Ag is released into soil and water through the weathering of rocks and mining activities. Silver also enters the environment by manufacturing and using Ag compounds in electroplating and photography, catalysts, medical devices, and batteries. With >400 t of Ag NPs produced yearly, Ag NPs have become a rapidly growing source of anthropogenic Ag input in the environment. In soils and natural waters, most Ag is sorbed to soil particles and sediments and precipitated as oxides, carbonates, sulphides, chlorides and hydroxides. Silver and its compounds are toxic, and humans and other animals are exposed to Ag through inhalation of air and the consumption of Ag-contaminated food and drinking water. Remediation of Ag-contaminated soil and water sources can be achieved through immobilization and mobilization processes. Immobilization of Ag in soil and groundwater reduces the bioavailability and mobility of Ag, while mobilization of Ag in the soil can facilitate its removal. This review provides an overview of the current understanding of the sources, geochemistry, health hazards, remediation practices and regulatory mandates of Ag contamination in complex environmental settings, including soil and aquatic ecosystems. Knowledge gaps and future research priorities in the sustainable management of Ag contamination in these settings are also discussed.

Recently, increasing attention is given on the resource and energy recovery (e.g. short-chain fatty acids (SCFAs) and phosphorus (P)) from waste active sludge (WAS) under the "Dual carbon goals". This study compared four thiosulfate-assisted Fe2+/persulfate (TAFP) pretreatments of WAS, i.e. in-situ TAFP pretreatment (R1), ex-situ TAFP pretreatment (R2), in-situ TAFP pretreatment + pH adjustment (R3) and ex-situ TAFP pretreatment + pH adjustment (R4), followed by anaerobic fermentation over 20 days for SCFA production and P recovery. The results showed that the maximal SCFA yields in R1-4 were 730.2 ± 7.0, 1017.4 ± 13.9, 860.1 ± 40.8, and 1072.0 ± 33.2 mg COD/L, respectively, significantly higher than Control (365.2 ± 17.8 mg COD/L). The findings indicated that TAFP pretreatments (particularly ex-situ TAFP pretreatment) enhanced WAS disintegration and provided more soluble organics and subsequently promoted SCFA production. The P fractionation results showed the non-apatite inorganic P increased from 11.6 ± 0.2 mg P/g TSS in Control to 11.8 ± 0.5 (R1), 12.4 ± 0.3 (R2), 13.2 ± 0.7 (R3) and 12.7 ± 0.7 mg P/g TSS (R4), suggesting TAFP pretreatments improved P bioavailability due to formation of Fe-P mineral (Fe(H2PO4)2·2H2O), which could be recycled through magnetic separators. These findings were further strengthened by the analysis of microbial community and related marker genes that fermentative bacteria containing SCFA biosynthesis genes (e.g. pyk, pdhA, accA and accB) and iron-reducing bacteria containing iron-related proteins (e.g. feoA and feoB) were enriched in R1-4 (dominant in ex-situ pretreatment systems, R2 and R4). Economic evaluation further verified ex-situ TAFP pretreatment was cost-effective and a better strategy over other operations to treat WAS for SCFA production and P recovery.

In recent years, the removal of heavy metals from water and wastewater systems remains a challenging issue globally. Adsorption technology is widely used for the removal of heavy metals from aquatic systems due to several advantages including its simple operation, low cost and high efficiency. Biochar, which is an environmental benign and low-cost adsorbent, is increasingly used for remediation of heavy metal pollution in aquatic systems. This review critically analyzes recent developments on the biochar-based adsorptive removal of heavy metals from water and wastewater. Biochar is effective for the removal of several toxic metals (As, Cr and Mn) from groundwater and drinking water. Biochar also shows promising performance for the removal of various heavy metals (Cr, Pb, Cu, Cd and Zn) from wastewater. The heavy metal adsorption capacity of the biochar largely depends on the water/wastewater chemistry (pH, competing ions and initial concentrations of adsorbates), contact time between adsorbates and the adsorbent, adsorbent dose and environmental parameters (temperature). The adsorption isotherms and kinetics can be well explained by the Langmuir and pseudo-second order models, respectively. The key mechanisms which drive the heavy metal adsorption onto biochar include precipitation and ion exchange. Biochar-based adsorptive decontamination of heavy metal pollution is sustainable due to low environmental impacts, low energy consumption and low-costs. The key knowledge gaps and future research directions for improvement of biochar-based sorption capacities are highlighted. This review would help for the development of effective biochar-based adsorption technology for the removal of heavy metals from aquatic environments.

Hydrothermal process is an emerging technology that contributes to sustainable production of biomass-derived chemicals, fuels, and materials. This technology uses hot compressed water to convert various biomass feedstocks including recalcitrant organic compounds in biowastes into desired solid, liquid, and gaseous products. In recent years, considerable progress has been made in the hydrothermal conversion of lignocellulosic as well as nonlignocellulosic biomass to value-added products and bioenergy to fulfill the principles of circular economy. However, it is important to assess hydrothermal processes in terms of their capabilities and limitations from different sustainability aspects so that further advances can be made toward improvement of their technical maturity and commercialization potential. The key aims of this comprehensive review are to (a) explain the inherent properties of biomass feedstocks and physio-chemical characteristics of their bioproducts, (b) elucidate related transformation pathways, (c) clarify the role of hydrothermal process for biomass conversion, (d) evaluate the capability of hydrothermal treatment coupled with other technologies for producing novel chemicals, fuels and materials, (e) explore different sustainability assessments of hydrothermal processes for potential large-scale applications, and (f) offer our perspectives to facilitate the transition from a primarily petro-based to an alternative biobased society in the context of changing climate.

In recent years, increasing attention has been given to the application of Nature-based systems (NbS) for mitigation of environmental pollution in cities. NbS namely bioretention systems, green roofs and constructed wetlands are widely adopted in urban environments for stormwater hydrology management and treatment, while roadside vegetation is utilized for mitigating air pollution of local traffic origin. Both bioretention systems and wetlands are capable of removing diverse pollutants such as total suspended solids, nutrients (nitrogen and phosphorous) and potentially toxic elements from runoff. Green roofs can act as a sink, or a source of pollutants to roof runoff outflow depending on the composition of engineered media used in support of vegetation growth. A holistic understanding of NbS in terms of their wide range of ecosystem services, multi-functionality nature, and contribution to circularity in cities is currently lacking. NbS can improve public health by providing clean air to breathe and natural waters of better quality for various purposes, but this application is not fully elucidated with an integrated approach involving both air and water quality assessments. For effective use of NbS, fundamental laboratory studies on the relative importance of phytoremediation versus bioremediation, laboratory studies to assess their actual performance under diverse weather conditions, and numerical simulations of hydrology and airflow should be conducted in tandem. Furthermore, it is important to develop guidelines for the design, installation, operation and maintenance of NbS for effective removal of environmental pollutants in the context of sustainable urban development.

Enhancement of dissimilatory nitrate/nitrite reduction to ammonium (DNRA) in agricultural soils has recently gained attention as a means to decelerate nitrogen loss. Here, the potential effects of plant root exudates on the DNRA activity of a model organism Shewanella loihica and agricultural soil consortia were examined. The chemical composition of the root exudate collected from Arabidopsis thaliana (Col-0) plant was analyzed by gas chromatography time-of-flight mass spectrometry (GC TOF-MS) and applied to S. loihica cultures grown on lactate and $${\text{NO}}_{3}^{{^{ - } }}$$ to examine the effects on the $${\text{NO}}_{3}^{{^{ - } }}$$ fate. Additionally, artificial root exudate was synthesized consisting of the major root exudate constituents, and its impacts on denitrification vs. DNRA competition in agricultural soil extracts, as well as S. loihica cultures, were investigated. Incubation of S. loihica in media amended with A. thaliana root exudates or artificial root exudates both resulted in a significant enhancement of DNRA activity. The agricultural soil consortia amended with root exudates did not exhibit significant DNRA enhancement; however, artificial root exudates addition had significant DNRA enhancement effect, which was confirmed with $$^{{{15}}} {\text{NH}}_{4}^{ + }$$ production from added $$^{{{15}}} {\text{NO}}_{3}^{{^{ - } }}$$ . The findings of this study suggest that plants’ root exudates may have stimulatory impact on the environmentally beneficial DNRA pathway.