Size Matters: Nano-Biochar Triggers Decomposition and Transformation Inhibition of Antibiotic Resistance Genes in Aqueous Environments

Recent advancement of nano-biochar for the remediation of heavy metals and emerging contaminants: Mechanism, adsorption kinetic model, plant growth and development

Even though researches have shown that biochar can improve soil-health and plant-growth even in harsh environments and get rid of harmful heavy metals and new contaminants, it is still not sustainable, affordable, or effective enough. Therefore, scientists are required to develop nanomaterials in order to preserve numerous aquatic and terrestrial species. The carbonaceous chemical known as nano-biochar (N-BC) can be used to get rid of metal contamination and emerging contaminants. However, techniques to reduce hetero-aggregation and agglomeration of nano-biochar are needed that lead to the emergence of emerging nano-biochar (EN-BC) in order to maximise its capacity for adsorption of nano-biochar. To address concerns in regards to the expanding human population and sustain a healthy community, it is imperative to address the problems associated with toxic heavy metals, emerging contaminants, and other abiotic stressors that are threatening agricultural development. Nano-biochar can provide an effective solution for removal of emerging contaminants, toxic heavy metals, and non-degradable substance. This review provides the detailed functional mechanistic and kinetics of nano-biochar, its effectiveness in promoting plant growth, and soil health under abiotic stress. Nonetheless, this review paper has comprehensively illustrated various adsorption study models that will be employed in future research.

New challenge: Mitigation and control of antibiotic resistant genes in aquatic environments by biochar

With an increase of diverse contaminants in the environment, particularly antibiotics, the maintenance and propagation of antibiotic resistance genes (ARGs) are promoted by co-selection mechanisms. ARGs are difficult to degrade, cause long-lasting pollution, and are widely transmitted in aquatic environments. Biochar is frequently used to remove various pollutants during environmental remediation. Thus, this review provides a thorough analysis of the current state of ARGs in the aquatic environment as well as their removal by using biochar. This article summarizes the research and application of biochar and modified biochar to remove ARGs in aquatic environments, in order to refine the following contents: 1) fill gaps in the research on the various ARG behaviors mediated by biochar and some influence factors, 2) further investigate the mechanisms involved in effects of biochar on extracellular ARGs (eARGs) and intracellular ARGs (iARGs) in aquatic environments, including direct and the indirect effects, 3) describe the propagation process and resistance mechanisms of ARGs, 4) propose the challenges and prospects of feasibility of application and subsequent treatment in actual aquatic environment. Here we highlight the most recent research on the use of biochar to remove ARGs from aquatic environments and suggest future directions for optimization, as well as current perspectives to guide future studies on the removal of ARGs from aquatic environments.

A state-of-art review on the redox activity of persistent free radicals in biochar

Biochar-bound persistent free radicals (biochar-PFRs) attract much attention because they can directly or indirectly mediate the transformation of contaminants in large-scale wastewater treatment processes. Despite this, a comprehensive top-down understanding of the redox activity of biochar-PFRs, particularly consumption and regeneration mechanisms, as well as challenges in redox activity assessment, is still lacking. To tackle this challenge, this review outlines the identification and determination methods of biochar-PFRs, which serve as a prerequisite for assessing the redox activity of biochar-PFRs. Recent developments concerning biochar-PFRs are discussed, with a main emphasis on the reaction mechanisms (both non-free radical and free radical pathways) and their effectiveness in removing contaminants. Importantly, the review delves into the mechanism of biochar-PFRs regeneration, triggered by metal cations, reactive oxygen species, and ultraviolet radiations. Furthermore, this review thoroughly explores the dilemma in appraising the redox activity of biochar-PFRs. Components with unpaired electrons (particular defects and metal ions) interfere with biochar-PFRs signals in electron paramagnetic resonance spectra. Scavengers and extractants of biochar-PFRs also inevitably modify the active ingredients of biochar. Based on these analyses, a practical strategy is proposed to precisely determine the redox activity of biochar-PFRs. Finally, the review concludes by presenting current gaps in knowledge and offering suggestions for future research. This comprehensive examination aims to provide new and significant insights into the redox activity of biochar-PFRs.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

Definitive Review of Nanobiochar

Nanobiochar is an advanced nanosized biochar with enhanced properties and wide applicability for a variety of modern-day applications. Nanobiochar can be developed easily from bulk biochar through top-down approaches including ball-milling, centrifugation, sonication, and hydrothermal synthesis. Nanobiochar can also be modified or engineered to obtain "engineered nanobiochar" or biochar nanocomposites with enhanced properties and applications. Nanobiochar provides many fold enhancements in surface area (0.4-97-times), pore size (0.1-5.3-times), total pore volume (0.5-48.5-times), and surface functionalities over bulk biochars. These enhancements have given increased contaminant sorption in both aqueous and soil media. Further, nanobiochar has also shown catalytic properties and applications in sensors, additive/fillers, targeted drug delivery, enzyme immobilization, polymer production, etc. The advantages and disadvantages of nanobiochar over bulk biochar are summarized herein, in detail. The processes and mechanisms involved in nanobiochar synthesis and contaminants sorption over nanobiochar are summarized. Finally, future directions and recommendations are suggested.

New discovery of extremely high adsorption of environmental DNA on cuttlefish bone pyrolysis derivative via large pore structure and carbon film

Environmental DNA (eDNA) carrying antibiotic resistance gene (ARG) has attracted a great deal of attention because of its threat to the ecology and human health. Traditional porous adsorbents, such as microporous biochar and natural mineral, are low-effective in removing eDNA from sewage. This study used cuttlefish-bone (CB), a fishery waste, as an anticipated material to adsorb a model compound of eDNA from herring sperm (hsDNA). An interesting result was firstly observed that extremely high DNA adsorption on cuttlefish-bone pyrolysis derivative (CCB) was up to 88.7 mg/g, 3-10 folds higher than that of most other adsorbents in the existing literatures, which was attributed to the carbon film and large pores. To achieve an adsorption rate of 75 %, hsDNA adsorption took 96 h on CB but only 24 h on CCB, which was attributed to the fluent channel of CCB. The ligand exchange, Ca2+ bridge and π-π interaction were identified as dominated adsorption mechanisms, based on FTIR and phosphate competition experiments. This study exploited a high-efficient, environmentally friendly, and low-cost adsorbent for treating ARG-contaminated soil and water.

A comprehensive review on the preparation of biochar from digestate sources and its application in environmental pollution remediation

The preparation of biochar from digestate is one of the effective ways to achieve the safe disposal and resource utilization of digestate. Nevertheless, up to now, a comprehensive review encompassing the factors influencing anaerobic digestate-derived biochar production and its applications is scarce in the literature. Therefore, to fill this gap, the present work first outlined the research hotspots of digestate in the last decade using bibliometric statistical analysis with the help of VOSviewer. Then, the characteristics of the different sources of digestate were summarized. Furthermore, the influencing factors of biochar preparation from digestate and the modification methods of digestate-derived biochar and associated mechanisms were analyzed. Notably, a comprehensive synthesis of anaerobic digestate-derived biochar applications is provided, encompassing enhanced anaerobic digestion, heavy metal remediation, aerobic composting, antibiotic/antibiotic resistance gene removal, and phosphorus recovery from digestate liquor. The economic and environmental impacts of digestate-derived biochar were also analyzed. Finally, the development prospect and challenges of using biochar from digestate to combat environmental pollution are foreseen. The aim is to not only address digestate management challenges at the source but also offer a novel path for the resourceful utilization of digestate.

Visible light-driven C/O-g-C3N4 activating peroxydisulfate to effectively inactivate antibiotic resistant bacteria and inhibit the transformation of antibiotic resistance genes: Insights on the mechanism

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) dissemination within water pose a serious threat to public health. Herein, C and O dual-doped g-C3N4 (C/O-g-C3N4) photocatalyst, fabricated via calcination treatment, was utilized to activate peroxydisulfate (PDS) to investigate the disinfection effect on tetracycline-resistant Escherichia coli and the transformation frequency of ARGs. As a result, approximately 7.08 log E. coli were inactivated, and 72.36 % and 53.96 % of antibiotics resistance gene (tetB) and 16 S rRNA were degraded respectively within 80 min. Futhermore, the transformation frequency was reduced to 0.8. Characterization and theoretical results indicated that C and O doping in g-C3N4 might lead to the electronic structure modulation and band gap energy reduction, resulting in the production of more free radicals. The mechanism analysis revealed that C/O-g-C3N4 exhibited a lower adsorption energy and reaction energy barrier for PDS compared to g-C3N4. This was beneficial for the homolysis of O-O bonds, forming SO4•- radicals. The attack of the generated active species led to oxidative stress in cells, resulting in damage to the electron transport chain and inhibition of ATP production. Our findings disclose a valuable insight for inactivating ARB, and provide a prospective strategy for ARGs dissemination in water contamination.

Biochar induces different responses of intracellular and extracellular antibiotic resistance genes and suppresses horizontal transfer during lincomycin fermentation dregs composting

This study aims to indicate the influence of biochar on extracellular and intracellular ARGs (e/iARGs) variation and proliferation during lincomycin fermentation dregs (LFDs) compost. Biochar addition made iARGs keep reducing but eARGs increase to the maximum at the middle thermophilic phase and reduce at the end of the compost. Compared to control 3.15-log and 5.42-log reduction of iARGs and eARGs were observed, respectively. Biochar addition, bacterial community, and MGEs were the major contributors to iARGs and eARGs removal, with the contribution percentages of 38.4%, 31.0%, 23.7%, and 27.2%, 29.1%, and 34.9%, respectively. Moreover, biochar significantly inhibited eARGs transformation and RP4 plasmid conjugative transfer among E. coli DH5α and Pseudomonas aeruginosa HLS-6. The underlying mechanism involved in broken cell membranes of bacteria, and altered expression of oxidative stress genes and save our souls (SOS) response-related genes. The results indicated that biochar addition in composting could limit the dissemination of ARGs.

A review of microbial responses to biochar addition in anaerobic digestion system: Community, cellular and genetic level findings

The biochar is a well-developed porous material with various excellent properties, that has been proven with excellent ability in anaerobic digestion (AD) efficiency promotion. Current research is usually focused on the macro effects of biochar on AD, while the systematic review about the mechanisms of biochar on microbial behavior are still lacking. This review summarizes the effects and potential mechanisms of biochar on microorganisms in AD systems, and found that biochar addition can provide habitats for microbial colonization, alleviate toxins stress, supply essential nutrients, and accelerate interspecies electron transferring. Moreover, it also improves microbial community diversity, facilitates EPS secretion, enhances functional enzyme activity, promotes functional genes expression, and inhibits the antibiotic resistance genes transformation. Future research directions including biochar targeted design, in-depth microbial mechanisms revelation, and modified model development were suggested, which could promote the widely practical application of of biochar-amended AD technology.

Size matters: Powder biochar promotes the elimination of antibiotics resistance genes and potential hosts during swine manure composting

Livestock manure faced acute environmental pollution and ecology risky caused by antibiotic resistance genes (ARGs). This study investigated the effects of biochar particle size including powder biochar (75 μm, PB), and granular biochar (2 mm, GB) on ARGs variation during the aerobic composting. The results showed that the total relative abundance (RA) of the ARGs decreased significantly in all the treatments after composting. While compared to the removal efficiency of total RA in the control (CK), PB decreased by 90.99 % and GB increased by 93.25 %, and both PB and GB removed MGEs completely. Sulfonamide antibiotic resistance genes were the main contributor of the ARGs rebounding. PB addition could hinder the rebounding of sulfonamide antibiotic resistance genes during the later stage of the composting. Co-occurrence network analysis showed that the addition of biochar (both types) increased the complexity of the microbial community the competition of inter-phylum, which was indicated by the higher number of edge and density and lower positive connection. The different ARGs removal efficiency in these two treatments might be that PB promoted the competition both inter-phylum and potential hosts-other microbes, resulted in fewer kinds and abundance of ARGs hosts, while GB increased the stability of ARGs hosts making it more resistant to environment changes. Totally, compared with the global adjustment strategy of microbial communities, more exclusive methods focusing on the controlling of ARGs hosts should be explored to decrease the ecological risk of composting products during composting process.

Waste-derived nanobiochar: A new avenue towards sustainable agriculture, environment, and circular bioeconomy

The greatest challenge for the agriculture sector in the twenty-first century is to increase agricultural production to feed the burgeoning global population while maintaining soil health and the integrity of the agroecosystem. Currently, the application of biochar is widely implemented as an effective means for boosting sustainable agriculture while having a negligible influence on ecosystems and the environment. In comparison to traditional biochar, nano-biochar (nano-BC) boasts enhanced specific surface area, adsorption capacity, and mobility properties within soil, allowing it to promote soil properties, crop growth, and environmental remediation. Additionally, carbon sequestration and reduction of methane and nitrous oxide emissions from agriculture can be achieved with nano-BC applications, contributing to climate change mitigation. Nonetheless, due to cost-effectiveness, sustainability, and environmental friendliness, waste-derived nano-BC may emerge as the most viable alternative to conventional waste management strategies, contributing to the circular bioeconomy and the broader goal of achieving the Sustainable Development Goals (SDGs). However, it's important to note that research on nano-BC is still in its nascent stages. Potential risks, including toxicity in aquatic and terrestrial environments, necessitate extensive field investigations. This review delineates the potential of waste-derived nano-BC for sustainable agriculture and environmental applications, outlining current advancements, challenges, and possibilities in the realms from a sustainability and circular bioeconomy standpoint.

Nano-biochar uptake and translocation by plants: Assessing environmental fate and food chain risk

Nano-biochar (N-BC) is an emerging nanomaterial with potential applications in various fields. Understanding its behavior in the environment and its interaction with plants is crucial for assessing its ecological implications and potential risks to the food chain. In this study, we investigated the absorption and transportation of N-BC by wheat and Chinese cabbage plants using microscopy techniques and stable isotope analysis. Our results revealed that N-BC particles were readily absorbed by the plants through their root systems and transported to the aboveground tissues. Scanning electron microscopy and transmission electron microscopy provided visual evidence of N-BC particles inside the plants, predominantly located in the xylem and cell walls of the cortical tissue. Stable isotope analysis confirmed the uptake and transportation of N-BC, with elevated isotopic values observed in the plant tissues exposed to 13C-N-BC. Our results demonstrated that around 50.2 %-52.4 % of the absorbed N-BC by plants was accumulated in the roots of wheat and Chinese cabbage, and the remaining fraction was transferred to the shoots including steam (31.0 %-32.1 %) and leaf (16.5 %-17.6 %). Importantly, we observed significant accumulation of N-BC in the edible parts of Chinese cabbage, raising concerns about its potential entry into the food chain and associated health risks. These findings highlight the need for further research to explore the specific pathways and modes of N-BC uptake and transport in plants. Monitoring the presence of N-BC in the environment and its potential impact on the food chain is crucial for ensuring food security and safeguarding human health.

Distribution, toxicity, and impacts of nano-biochar in mice following dietary exposure: Insights into environmental risks and mammalian effects

Nano-biochar is a novel material with emerging applications in various fields, including agriculture and environmental remediation. The potential risks of nano-biochar (N-BC) in the food chain necessitate further investigation. We studied the distribution and toxicity of N-BC in mice through dietary exposure. Using Balb/c mice, we assessed N-BC accumulation in organs and its impact on vital organs. Isotope analysis showed significant accumulation of 13C-N-BC in the liver (53.1%-55.9%), kidneys (4.0%-5.9%), and blood (9.2%-13.6%), with lesser amounts in the intestines (0.8%-1.2%) and stool (28.0%-28.1%). N-BC induced liver damage, evident by increased oxidative stress markers and histopathological changes. It disrupted tight junction proteins in the intestine, potentially allowing systemic entry. N-BC also influenced gut microbiota composition and metabolites. Our study provides insights into N-BC's distribution, toxicity, and environmental risks, urging further research on its implications for mammalian health and the ecosystem.

Intrinsic peroxidase-like activity of dissolved black carbon released from biochar

Dissolved black carbon (DBC) is an important constituent of the natural organic carbon pool, influencing the global carbon cycling and the fate processes of many pollutants. In this work, we discovered that DBC released from biochar has intrinsic peroxidase-like activity. DBC samples were derived from four biomass stocks, including corn, peanut, rice, and sorghum straws. All DBC samples catalyze H2O2 decomposition into hydroxyl radicals, as determined by the electron paramagnetic resonance and the molecular probe. Similar to enzymes that exhibit saturation kinetics, the steady-state reaction rates follow the Michaelis-Menten equation. The peroxidase-like activity of DBC is controlled by the ping-pong mechanism, as suggested by parallel Lineweaver-Burk plots. Its activity increases with temperature from 10 to 80 °C and has an optimum at pH 5. The peroxidase-like activity of DBC is positively correlated with its aromaticity as aromatics can stabilize the reactive intermediates. The active sites in DBC also involve oxygen-containing groups, as inferred by increased activity after the chemical reduction of carbonyls. The peroxidase-like activity of DBC has significant implications for biogeochemical processing of carbon and potential health and ecological impacts of black carbon. It also highlights the need to advance the understanding of the occurrence and role of organic catalysts in natural systems.

Dynamics of antibiotic resistance genes and bacterial community during pig manure, kitchen waste, and sewage sludge composting

Organic solid wastes (OSWs) are important reservoirs for antibiotic resistance genes (ARGs). Aerobic composting transforms OSWs into fertilizers. In this study, we investigated ARGs dynamics and their driving mechanisms in three OSW composts: pig manure (PM), kitchen waste (KC), and sewage sludge (SG). The dominant ARGs were different in each OSW, namely tetracycline, aminoglycoside, and macrolide resistance (PM); tetracyclines and aminoglycosides (KC); and sulfonamides (SG). ARGs abundance decreased in PM (71%) but increased in KC (5.9-fold) and SG (1.3-fold). Interestingly, the ARGs abundance was generally similar in all final composts, which was contributed to the similar bacterial community in final composts. In particular, sulfonamide and β-lactam resistant genes removed (100%) in PM, while sulfonamide in KC (38-fold) and tetracycline in SG (5-fold) increased the most. Additionally, ARGs abundance rebounded during the maturation period in all treatments. Firmicutes, Proteobacteria, and Actinobacteria were the main ARGs hosts. Several persistent and high-risk genes included tetW, aadA, aadE, tetX, strB, tetA, mefA, intl1, and intl2. The structural equation models showed ARGs removal was mainly affected by physicochemical parameters and bacterial communities in PM, the ARGs enrichment in KC composting correlated with increased mobile genetic elements (MGEs). In general, thermophilic aerobic composting can inhibit the vertical gene transfer (VGT) of pig manure and horizontal gene transfer (HGT) of sludge, but it increases the HGT of kitchen waste, resulting in a dramatic increase of ARGs in KC compost. More attention should be paid to the ARGs risk of kitchen waste composting.

Recent advancements and challenges in emerging applications of biochar-based catalysts

The sustainable utilization of biochar produced from biomass waste could substantially promote the development of carbon neutrality and a circular economy. Due to their cost-effectiveness, multiple functionalities, tailorable porous structure, and thermal stability, biochar-based catalysts play a vital role in sustainable biorefineries and environmental protection, contributing to a positive, planet-level impact. This review provides an overview of emerging synthesis routes for multifunctional biochar-based catalysts. It discusses recent advances in biorefinery and pollutant degradation in air, soil, and water, providing deeper and more comprehensive information of the catalysts, such as physicochemical properties and surface chemistry. The catalytic performance and deactivation mechanisms under different catalytic systems were critically reviewed, providing new insights into developing efficient and practical biochar-based catalysts for large-scale use in various applications. Machine learning (ML)-based predictions and inverse design have addressed the innovation of biochar-based catalysts with high-performance applications, as ML efficiently predicts the properties and performance of biochar, interprets the underlying mechanisms and complicated relationships, and guides biochar synthesis. Finally, environmental benefit and economic feasibility assessments are proposed for science-based guidelines for industries and policymakers. With concerted effort, upgrading biomass waste into high-performance catalysts for biorefinery and environmental protection could reduce environmental pollution, increase energy safety, and achieve sustainable biomass management, all of which are beneficial for attaining several of the United Nations Sustainable Development Goals (UN SDGs) and Environmental, Social and Governance (ESG).

Nano-biochar: recent progress, challenges, and opportunities for sustainable environmental remediation

Biochar is a carbonaceous by-product of lignocellulosic biomass developed by various thermochemical processes. Biochar can be transformed into "nano-biochar" by size reduction to nano-meters level. Nano-biochar presents remarkable physico-chemical behavior in comparison to macro-biochar including; higher stability, unique nanostructure, higher catalytic ability, larger specific surface area, higher porosity, improved surface functionality, and surface active sites. Nano-biochar efficiently regulates the transport and absorption of vital micro-and macro-nutrients, in addition to toxic contaminants (heavy metals, pesticides, antibiotics). However an extensive understanding of the recent nano-biochar studies is essential for large scale implementations, including development, physico-chemical properties and targeted use. Nano-biochar toxicity on different organisms and its in-direct effect on humans is an important issue of concern and needs to be extensively evaluated for large scale applications. This review provides a detailed insight on nanobiochar research for (1) development methodologies, (2) compositions and properties, (3) characterization methods, (4) potentiality as emerging sorbent, photocatalyst, enzyme carrier for environmental application, and (5) environmental concerns.

Single cobalt atoms anchored on Ti3C2Tx with dual reaction sites for efficient adsorption-degradation of antibiotic resistance genes

The assimilation of antibiotic resistance genes (ARGs) by pathogenic bacteria poses a severe threat to public health. Here, we reported a dual-reaction-site-modified CoSA/Ti3C2Tx (single cobalt atoms immobilized on Ti3C2Tx MXene) for effectively deactivating extracellular ARGs via peroxymonosulfate (PMS) activation. The enhanced removal of ARGs was attributed to the synergistic effect of adsorption (Ti sites) and degradation (Co-O3 sites). The Ti sites on CoSA/Ti3C2Tx nanosheets bound with PO43- on the phosphate skeletons of ARGs via Ti-O-P coordination interactions, achieving excellent adsorption capacity (10.21 × 1010 copies mg-1) for tetA, and the Co-O3 sites activated PMS into surface-bond hydroxyl radicals (•OHsurface), which can quickly attack the backbones and bases of the adsorbed ARGs, resulting in the efficient in situ degradation of ARGs into inactive small molecular organics and NO3. This dual-reaction-site Fenton-like system exhibited ultrahigh extracellular ARG degradation rate (k > 0.9 min-1) and showed the potential for practical wastewater treatment in a membrane filtration process, which provided insights for extracellular ARG removal via catalysts design.

Disintegration of biochar adsorbent under the hydraulic conditions of fixed bed water treatment

Recent studies have provided promising evidence for potential applications of biochar in environmental engineering, including its use as an alternative carbonaceous adsorbent for water and wastewater treatment. Carbonaceous adsorbents, such as activated carbon and biochar, are prone to disintegration and erosion due to water flow, potentially leading to the co-transport of hazardous contaminants with eroded fine particles (1 μm or smaller). Despite its significance in overall performance assessment, the stability and erodibility of biochar as an adsorbent in fixed bed water treatment have received limited research attention. This paper presents the results of a series of filtration tests and microscopic examinations to evaluate the disintegration of activated carbon and three types of biochar filters under the hydraulic conditions of fixed bed filtration. A novel testing design was employed to study the effects of fluid velocities and ionic strengths on disintegration, mass loss, and the morphology of granular adsorbents before and after water flushing. The results indicate that disintegration of both activated carbon and biochar is continuous but exhibits different behaviour with pore volume. Although fluid velocity influenced erosion rates, minimal differences were observed in overall mass loss. Ionic strength had a more pronounced impact on the erodibility and stability of particles in suspension by altering electrical conductivity and Zeta potential. Disintegration of hardwood biochar was found to be comparable to that of activated carbon; however, impurities in biochar (elements other than carbon and oxygen) are more likely to be flushed out, creating additional pathways for co-transport of contaminants.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

What happens when nanoparticles encounter bacterial antibiotic resistance?

Bacterial resistance to antibiotics has become a widespread concern, and poses serious environmental and global health problems. Lots of studies have demonstrated that engineered nanoparticles (NPs) can significantly affect bacterial antibiotic resistance; however, whether NPs promote or inhibit antibiotic resistance remains a complex and well-debated issue. This will constrain environmental antibiotic resistance gene contamination and clinical bacterial resistance problems, resulting in unclear and poorly targeted treatment efficacy. To better understand the relationship between NPs and antibiotic resistance, this review systematically summarizes and reanalyzes published data on the effect of NPs on bacterial antibiotic resistance and related mechanisms. The effects of intrinsic properties of NPs, such as size, concentration, functional groups, and extrinsic properties of NPs on the development of antibiotic resistance were dissected. This review will provide a better understanding of the effects of increasingly released NPs in different environments on bacterial resistance and underlines the direction for employing NPs to control the dissemination of antibiotic resistance genes in the environment. Next, how NPs affect intracellular and extracellular antibiotic resistance needs in-depth exploration. Besides, alternative treatments of NPs and antibiotics in therapy will be a future trend for combating antibiotic resistance, and the follow-up emphasis should determine their dose effects and potential mechanism. This study will expand our understanding of the biosafety of nanomaterials and provides a theoretical reference to guide the proper application of nanomaterials or technologies to environmental pollution control and clinical treatment.

Soil minerals and organic matters affect ARGs transformation by changing the morphology of plasmid and bacterial responses

Soil environment is a vital place for the occurrence and spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Extracellular DNA-mediated transformation is an important pathway for ARGs horizontal transfer and widely exists in soil environment. However, little information is available on how common soil components affect ARGs transformation. Here, three minerals (quartz, kaolinite, and montmorillonite) and three organic matters (humic acid, biochar, and soot) were selected as typical soil components. A small amount in suspension (0.2 g/L) of most soil components (except for quartz and montmorillonite) promoted transformant production by 1.1-1.6 folds. For a high amount (8 g/L), biochar significantly promoted transformant production to 1.5 times, kaolinite exerted a 30 % inhibitory effect. From the perspective of plasmid, biochar induced a higher proportion of supercoiled plasmid than kaolinite; more dissolved organic matter and metal ions facilitated plasmid aggregation under the near-neutral pH, thus promoted transformation. As for the influence of materials on recipient, although biochar and kaolinite both increased reactive oxygen species (ROS) level and membrane permeability, biochar up-regulated more ROS related genes, resulting in intracellular ROS production and up-regulating the expression of carbohydrate metabolism and transformation related genes. While kaolinite inhibited transformation mainly by causing nutrient deficiency.

Adsorption of antibiotic, heavy metal and antibiotic plasmid by a wet-state silicon-rich biochar/ferrihydrite composite to inhibit antibiotic resistance gene proliferation/transformation

Decreasing bioaccessible antibiotics, heavy metals, and antibiotic resistance genes (ARGs) in soil by adsorption is an attractive, but unrealized, approach for ARG risk reduction. This approach has the potential to reduce the (co)selection pressure from antibiotics and heavy metals on bacteria and ARG horizontal gene transformation to pathogens. Here, a wet-state silicon-rich biochar/ferrihydrite composite (SiC-Fe(W)) synthesized by loading ferrihydrite onto rice straw-derived biochar was examined for i) adsorption of oxytetracycline and Cu²⁺ to reduce (co)selection pressure and ii) adsorption of extracellular antibiotic resistance plasmid pBR322 (containing tetA and bla_TEM-1) to inhibit ARG transformation. SiC-Fe(W) gained the adsorption priority of biochar (for Cu²⁺) and wet-state ferrihydrite (for oxytetracycline and pBR322) and showed adsorptive enhancement (for Cu²⁺ and oxytetracycline) from a more wrinkled and exposed surface from biochar silica-dispersed ferrihydrite and a more negatively charged biochar, and the adsorption capacity for SiC-Fe(W) was 17-135 times that of soil. Correspondingly, 10 g/kg SiC-Fe(W) amendment increased the soil adsorption coefficient K_d by 31%-1417% and reduced the selection pressure from dissolved oxytetracycline, co-selection pressure from dissolved Cu²⁺, and transformation frequency of pBR322 (assessed with Escherichia coli). The development of Fe-O-Si bonds on silicon-rich biochar in alkaline enhanced ferrihydrite stability and adsorption capacity (for oxytetracycline), presenting a new potential strategy of biochar/ferrihydrite composite synthesis for adsorptive inhibition of ARG proliferation and transformation in ARG pollution control.

Electron exchange capacity of pyrogenic dissolved organic matter (pyDOM): complementarity of square-wave voltammetry in DMSO and mediated chronoamperometry in water

Pyrogenic dissolved organic matter (pyDOM) is derived from black carbon, which is important in the global carbon cycle and other biogeochemical redox processes. The electron-exchange capacity (EEC) of pyDOM has been characterized in water using mediated chronoamperometry (MCA), which gives precise results under specific operational conditions, but the broader significance of these EECs is less clear. In this study, we described a novel but complementary electrochemical approach to quantify EECs of pyDOM without mediation using square-wave voltammetry (SWV) in dimethyl sulfoxide (DMSO). Using both the SWV and MCA methods, we determined EECs for 10 pyDOMs, 6 natural organic matter (NOM) samples, and 2 model quinones. The two methods gave similar EECs for model quinones, but SWV gave larger EECs than MCA for NOM and pyDOM (by several-fold and 1-2 orders of magnitude, respectively). The differences in the EECs obtained by SWV and MCA likely are due to multiple factors, including the potential range of electrons sampled, kinetics of electron transfer from (macro)molecular structures, and coupling of electron and proton transfer steps. Comparison of the results obtained by these two methods should provide new insights into important environmental processes such as carbon-cycling, wildfire recovery, and contaminant mitigation using carbon-based amendments.

Carbon content determines the aggregation of biochar colloids from various feedstocks

The aggregation kinetics of biochar colloids (BCs) play a crucial role in the fate and transport of contaminants, as well as the carbon (C) cycle in the environment. However, the colloidal stability of BCs from various feedstocks is very limited. In this study, the critical coagulation concentration (CCC) of twelve standard biochars pyrolyzed from various feedstocks (municipal source, agricultural waste, herbaceous residue, and woody feedstock) at 550 °C and 700 °C were investigated, and the relationship between the physicochemical characteristics of biochar and the colloidal stability of BCs was further analyzed. The CCC of BCs in the NaCl solution followed the trend of municipal source < agricultural waste < herbaceous residue < woody feedstock, which was similar to the order of C content in biochar. The CCC of BCs showed a strong positive correlation with the C content of various biochars, especially pyrolyzed at a higher temperature of 700 °C. The BCs derived from lignin-rich feedstock (e.g., woody feedstock) had the highest colloidal stability, followed by cellulose-rich feedstock (e.g., agricultural waste and herbaceous residue). The BCs derived from organic matter-rich feedstock (municipal source) were easy to aggregate in the aqueous environment. This study quantitatively provides new insights into the relationship between BCs stability and biochar characteristics from various feedstocks, which is critical to assess biochar environmental behavior in aqueous environments.

Carbon-defect-driven persulfate activation for highly efficient degradation of extracellular DNA contaminant: Radical oxidation and electron transfer pathways

Extracellular DNA (eDNA), as a dynamic repository for antibiotic-resistant genes (ARGs), is a rising threat to public health. This work used a ball-milling method to enhance defect structures of activated carbon, and carbon defects exhibited an excellent capacity in persulfate (PS) activation for model eDNA and real ARGs degradation. The eDNA removal by defect-rich carbon with PS was 2.3-fold higher than that by unmilled activated carbon. The quenching experiment, electrochemical analysis and thermodynamic calculation showed that carbon defects could not only enhance the generation of SO₄^•- and ^•OH, but formed an electron transfer bridge between eDNA and PS, leading to the non-radical oxidation of eDNA. According to molecular calculations, the nitrogenous bases of DNA were the easiest sites to be oxidized by electron transfer pathway. This research offers a new way using defective carbon materials as PS activator for eDNA pollutants, and an insight into the non-radical mechanism of eDNA degradation.

Recent advances in nanomaterials based sustainable approaches for mitigation of emerging organic pollutants

Emerging organic pollutants (EOPs) are a category of pollutants that are relatively new to the environment and recently garnered a lot of attention. The majority of EOPs includes endocrine-disrupting chemicals (EDCs), antibiotic resistance genes (ARGs), pesticides, dyes and pharmaceutical and personal care products (PPCPs). Exposure to contaminated water has been linked to an increase in incidences of malnutrition, intrauterine growth retardation, respiratory illnesses, liver malfunctions, eye and skin diseases, and fatalities. Consequently, there is a critical need for wastewater remediation technologies which are effective, reliable, and economical. Conventional wastewater treatment methods have several shortcomings that can be addressed with the help of nanotechnology. Unique characteristics of nanomaterials (NMs) make them intriguing and efficient alternative in wastewater treatment strategies. This review emphasis on the occurrence of divers emerging organic pollutants (EOPs) in water and their effective elimination via different NMs based methods with in-depth mechanisms. Furthermore, it also delves the toxicity assessment of NMs and critical challenges, which are crucial steps for practical implementations.

Conjugation-mediated transfer of antibiotic resistance genes influenced by primary soil components and underlying mechanisms

Soil is the main natural reservoir of antibiotic resistant bacteria and antibiotic resistance genes (ARGs). Their dissemination and proliferation were largely motivated by conjugative transfer, while the influence of soil components on bacterial conjugative transfer and the underlying mechanisms remain poorly understood. In the present study, two Escherichia coli strains were exposed to soil minerals (quartz, kaolinite and montmorillonite) and organic matters (humic acid, biochar and soot) respectively to investigate their impact on ARGs conjugation. The results showed that quartz had no significant effect on conjugation; montmorillonite promoted the growth of the donor, but inhibited the recipient and conjugant; kaolinite and three organic matters significantly promoted the production of conjugant, while biochar promoted and then inhibited it with time prolong. Within the range of bacterial concentration involved in this study, the concentration of conjugant increased with the ratio of the concentration of donor and recipient (R_D/R), indicating that the variation of conjugant production was mainly mediated by changing R_D/R. Further observation of biochar treatment group showed that the bacterial responses such as cell membrane permeability, cell surface hydrophobicity and biofilm formation ability shifted with the exposure time, which might be a potential factor affecting conjugative transfer. Collectively, our findings suggest that the type and exposure time of soil components jointly affected conjugation, while the change of R_D/R and related bacterial responses are the main underlying mechanisms.

A review of the impact of conductive materials on antibiotic resistance genes during the anaerobic digestion of sewage sludge and animal manure

The urgent need to reduce the environmental burden of antibiotic resistance genes (ARGs) has become even more apparent as concerted efforts are made globally to tackle the dissemination of antimicrobial resistance. Concerning levels of ARGs abound in sewage sludge and animal manure, and their inadequate attenuation during conventional anaerobic digestion (AD) compromises the safety of the digestate, a nutrient-rich by-product of AD commonly recycled to agricultural land for improvement of soil quality. Exogenous ARGs introduced into the natural environment via the land application of digestate can be transferred from innocuous environmental bacteria to clinically relevant bacteria by horizontal gene transfer (HGT) and may eventually reach humans through food, water, and air. This review, therefore, discusses the prospects of using carbon- and iron-based conductive materials (CMs) as additives to mitigate the proliferation of ARGs during the AD of sewage sludge and animal manure. The review spotlights the core mechanisms underpinning the influence of CMs on the resistome profile, the steps to maximize ARG attenuation using CMs, and the current knowledge gaps. Data and information gathered indicate that CMs can profoundly reduce the abundance of ARGs in the digestate by easing selective pressure on ARGs, altering microbial community structure, and diminishing HGT.

Particle size of biochar significantly regulates the chemical speciation, transformation, and ecotoxicity of cadmium in biochar

The pyrolysis of biomass containing excessive heavy metals is likely to produce heavy metal contaminated biochar (BC). Although multiple lines of evidence indicate that higher charring temperature leads to enhanced immobilization of heavy metals in BC, we find that particle size could also play a critical role in the content of heavy metals in BC and BC ecotoxicity. Here, BC derived from cadmium (Cd) enriched rice straw was prepared at different temperatures (300-600 °C) and divided into macro-, colloidal-, and nano-sized fractions, respectively. The content and chemical forms of Cd in BC fractions as well as related algal toxicity were examined. The results show that for the same temperature BC the content of Cd followed an order of colloidal-BC > macro-BC > nano-BC; and the residual fractions of Cd significantly decreased (3.47-16.08%) while that of acid soluble and reducible fractions significantly increased (4.13-16.51% and 0.24-1.71%, respectively) with decreasing particle size of BC. Consistently, colloidal-BC exhibited the highest ecotoxicity for Scenedesmus obliquus. The acid soluble fractions of Cd in macro- and colloidal-BC played a dominating role in their algal toxicity (p < 0.05). However, the ecotoxicity of nano-BC was more dependent on the total content of Cd than specific fractions probably due to the phagocytosis by algal cells. These results indicate that the chemical forms and ecotoxicity of Cd in BC could be remarkably modified by its particle size, which has profound implications for understanding the behavior and potential risk of heavy metal contaminated BC in the environment.

Recent Advances in the Investigation of Poly(lactic acid) (PLA) Nanocomposites: Incorporation of Various Nanofillers and their Properties and Applications

Poly(lactic acid) (PLA) is considered the most promising biobased substitute for fossil-derived polymers due to its compostability, biocompatibility, renewability, and good thermomechanical properties. However, PLA suffers from several shortcomings, such as low heat distortion temperature, thermal resistance, and rate of crystallization, whereas some other specific properties, i.e., flame retardancy, anti-UV, antibacterial or barrier properties, antistatic to conductive electrical characteristics, etc., are required by different end-use sectors. The addition of different nanofillers represents an attractive way to develop and enhance the properties of neat PLA. Numerous nanofillers with different architectures and properties have been investigated, with satisfactory achievements, in the design of PLA nanocomposites. This review paper overviews the current advances in the synthetic routes of PLA nanocomposites, the imparted properties of each nano-additive, as well as the numerous applications of PLA nanocomposites in various industrial fields.

A review of antibiotics and antibiotic resistance genes (ARGs) adsorption by biochar and modified biochar in water

Antibiotics have been used in massive quantities for human and animal medical treatment, and antibiotic resistance genes (ARGs) are of great concern worldwide. Antibiotics and ARGs are exposed to the natural environment through the discharge of medical wastewater, causing great harm to the environment and human health. Biochar has been widely used as a green and efficient adsorbent to remove pollutants. However, pristine and unmodified biochars are not considered sufficient and efficient to cope with the current serious water pollution. Therefore, researchers have chosen to improve the adsorption capacity of biochar through different modification methods. To have a better understanding of the application of modified biochar, this review summarizes the biochar modification methods and their performance, particularly, molecular imprinting and biochar aging are outlined as new modification methods, influencing factors of biochar and modified biochar in adsorption of antibiotics and ARGs and adsorption mechanisms, wherein adsorption mechanism of ARGs on biochar is found to be different than that of antibiotics. After that, the directions of biochar and modified biochar worthy of research and the issues that need attention are proposed. It can be noted that under the current dual carbon policy, biochar may have wider application prospects in future.

Enhanced Cr(VI) bioreduction by biochar: Insight into the persistent free radicals mediated extracellular electron transfer

Biochar can act as a shuttle to accelerate the extracellular electron transfer (EET) by exoelectrogens. However, it is poorly understood how the persistent free radicals (PFRs) in biochar affected EET and the redox reaction. Herein, the effects of the biochar and chitosan modified biochar (CBC) on the Cr(VI) bioreduction by Shewanella oneidensis MR-1 (MR-1) was investigated. Kinetic study indicated that the Cr(VI) bioreduction rate constant by MR-1 was increased by 1.8-33.7 folds in the presence of biochar, and by 2.7-60.2 folds in the presence of CBC, respectively. Moreover, Cr(VI) bioreduction rates increased with the decreasing pH. Results suggested that the electrostatic attraction between Cr(VI) and redox-active particles could accelerate the EET by c-cytochrome due to the promotion of the Cr(VI) migration from aqueous phase to biochar or CBC. Electron paramagnetic resonance analysis suggested that the PFRs affected the electron transfer from the ·O₂^- generated by MR-1 to Cr(VI) and accelerate the Cr(VI) bioreduction. Remarkably, in the presence of PFRs, this electron shuttling process was dependent on the non-metal-reducing respiratory pathway. Our results offer new insights that free radicals may be widely involved in the EET and strongly impact on the redox reaction in the environment.

Dichotomous Role of Humic Substances in Modulating Transformation of Antibiotic Resistance Genes in Mineral Systems

Widespread antibiotic resistance genes (ARGs) have emerged as a focus of attention for public health. Transformation is essential for ARGs dissemination in soils and associated environments; however, the mechanisms of how soil components contribute to the transformation of ARGs remain elusive. Here we demonstrate that three representative mineral-humic acid (HA) composites exert contrasting influence on the transformation of plasmid-borne ARGs in Bacillus subtilis. Mineral surface-bound HA facilitated transformation in kaolinite and montmorillonite systems, while an inhibitory effect of HA was observed for goethite. The elevated transformation by HA-coated kaolinite was mainly attributed to the enhanced activity of competence-stimulating factor (CSF), while increased transformation by montmorillonite-HA composites was assigned to the weakened adsorption affinity of DNA and enhanced gene expression induced by flagella-driven cell motility. In goethite system, HA played an overriding role in suppressing transformation via alleviation of cell membrane damage. The results obtained offer insights into the divergent mechanisms of humic substances in modulating bacterial transformation by soil minerals. Our findings would help for a better understanding on the fate of ARGs in soil systems and provide potentials for the utilization of soil components, particularly organic matter, to mitigate the spread of ARGs in a range of settings.

Biochar-amended composting of lincomycin fermentation dregs promoted microbial metabolism and reduced antibiotic resistance genes

Improper disposal of antibiotic fermentation dregs poses a risk of releasing antibiotics and antibiotic resistant bacteria to the environment. Therefore, this study evaluated the effects of biochar addition to lincomycin fermentation dregs (LFDs) composting. Biochar increased compost temperature and enhanced organic matter decomposition and residual antibiotics removal. Moreover, a 1.5- to 17.0-fold reduction in antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) was observed. Adding biochar also reduced the abundances of persistent ARGs hosts (e.g., Streptomyces, Pseudomonas) and ARG-related metabolic pathways and genes (e.g., ATP-binding cassette type-2 transport, signal transduction and multidrug efflux pump genes). By contrast, compost decomposition improved due to enhanced metabolism of carbohydrates and amino acids. Overall, adding biochar into LFDs compost reduced the proliferation of ARGs and enhanced microbial community metabolism. These results demonstrate that adding biochar to LFDs compost is a simple and efficient way to decrease risks associated with LFDs composting.

Pyrolysis temperature affects the inhibitory mechanism of biochars on the mobility of extracellular antibiotic resistance genes in saturated porous media

The migration of extracellular antibiotic resistance genes (eARGs) in porous media is an important pathway for ARGs to spread to the subsoil and aquifer. Biochar (BC) has been widely used to reduce the mobility of soil contaminants, however, its effect on the mobility of eARGs in porous media and the mechanisms are largely unknown. Herein, the effects of BCs synthesized from wheat straw and corn straw at two pyrolysis temperatures (300 °C and 700 °C) on the transport of plasmids-carried eARGs in sand column were investigated. The BC amendments all significantly decreased the mobility of eARGs in the porous medium, but the mechanism varied with pyrolysis temperature. The higher temperature BCs had a stronger irreversible adsorption of plasmids and greatly enhanced the attachment and straining effects on plasmids during transport, thus more effectively inhibited the mobility of eARGs. The lower temperature BCs had weaker adsorption, attachment, and straining effects on plasmids, but induced generation of hydroxyl radicals in the porous medium and thereby fragmented the plasmids and hindered the amplification of eARGs. These findings are of fundamental significance for the potential application of BC in controlling the vertical spread of eARGs in soil and vadose zones.

Biochar Effectively Inhibits the Horizontal Transfer of Antibiotic Resistance Genes via Restraining the Energy Supply for Conjugative Plasmid Transfer

Horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) through plasmid-mediated conjugation poses a major threat to global public health. Biochar, a widely used environmental remediation material, has remarkable impacts on the fate of ARGs. However, although biochar was reported being able to inhibit the HGT of ARGs via conjugation and transformation, little is known about the intracellular process that mediates the inhibition effects. On the other hand, as typical natural organic matter, fulvic acid is a common environmental influencer, and how it interferes with the effect of biochar on the HGT of ARGs is unknown. Therefore, this study investigated the effects on the conjugative transfer of ARGs between Escherichia coli MG1655 and E. coli HB101 carrying plasmid RP4, with biochars pyrolyzed at three temperatures and with the corresponding biochars coating with fulvic acid. Results showed that biochar with higher pyrolyzed temperature had a more substantial inhibitory effect on the conjugative transfer of the RP4 plasmid. The inhibitory effect of biochar was mainly attributed to (i) down-regulation of plasmid transfer gene expression, including the formation of conjugative transfer channel and plasmid replication, due to restrained adenosine triphosphate (ATP) energy supply and (ii) decreased cell membrane permeability. Conversely, the fulvic acid coating diminished this inhibition effect of biochar, mainly by providing more ATP and strengthening intracellular reactive oxygen species (ROS) defense. Our findings shed light on the intracellular process that mediates the effects of biochar on the conjugative transfer of ARGs, which would provide support for using biochar to reduce the spread of ARGs.

Coconut shell and its biochar as fertilizer amendment applied with organic fertilizer: Efficacy and course of actions on eliminating antibiotic resistance genes in agricultural soil

Biomass amendments have numerous benefits in reducing antibiotic resistance genes (ARGs) in the soil environment. However, there are debatable outcomes regarding the effect of raw biomass and its pyrolytic biochar on ARGs, and the exploration of the influence mechanism is still in infancy. Herein, we investigated the changes in soil ARGs under the organic fertilizer application with coconut shell and its biochar. The results showed that the coconut shell biochar could effectively diminish ARGs, with 61.54% reduction in target ARGs, which was higher than that adding raw coconut shells (p < 0.05). Structural equation modeling indicated that ARGs were significantly affected by changes in environmental factors, mainly by modulating bacterial communities. Neutral community model and network analysis demonstrated that the coconut shell biochar can restrict the species dispersal, thereby mitigating the spread of ARGs. Also, coconut shell biochar exhibited strong adsorption, with a large specific surface area (476.66 m²/g) and pores (pore diameter approximately 1.207 nm, total pore volume: 0.2451 m³/g), which markedly enhanced soil heterogeneity that created a barrier to limit the resistant bacteria proliferation and ARGs propagation. The outcome gives an approach to control the development of ARGs after organic fertilizer application into soil.

Biochar induced inhibitory effects on intracellular and extracellular antibiotic resistance genes in anaerobic digestion of swine manure

Distribution of intracellular (iARGs) and extracellular ARGs (eARGs) in manure anaerobic digestion (AD) process coupled with two types of biochar (BC and BP) were investigated. And the effects of biochar on the conjugation transfer of ARGs were explored by deciphering the interaction of biochar with bacterial stress responses, physiological metabolism and antibiotic resistances. Results showed that AD process could effectively remove all the detected eARGs with efficiency of 47.4-98.2%. The modified biochar (BP) with larger specific surface area (SSA) was propitious to decrease the absolute copy number of extracellular resistance genes. AD process could effectively remove iARGs by inhibiting the growth of host bacteria. The results of structural equation models (SEM) indicated that biochar put indirect influences on the fate of ARGs (λ = -0.23, P > 0.05). Analysis on oxidative stress levels, antioxidant capacity, DNA damage-induced response (SOS) response and energy generation process demonstrated that biochar induced the oxidative stress response of microorganisms and enhanced the antioxidant capacity of bacteria. The elevated antioxidant capacity negatively affected SOS response, amplified cell membrane damage and further weakened the energy generation process, resulted in the inhibition of horizontal transfer of ARGs.

Application of α-Fe2O3 nanoparticles in controlling antibiotic resistance gene transport and interception in porous media

Metal oxide nanoparticles (MONPs) with a large specific surface area are expected to bind with antibiotic resistance genes (ARGs), thereby controlling ARGs' contamination by reducing their concentration and mobilization. Here, adsorption experiments were carried out and it was found that α-Fe₂O₃ NPs could chemically bind with ARGs (tetM-carrying plasmids) in water with an adsorption rate of 0.04 min^-1 and an adsorption capacity of 7.88 g/kg. Mixing α-Fe₂O₃ NPs into quartz sand column markedly increased the interceptive removal of ARGs from inflow water. The interception rate of 1.0 μg/mL ARGs in ultrapure water (25 mL, 5 pore volumes) through the sand column (plexiglass, length 8 cm, internal diameter 1.4 cm) with 1 g/kg α-Fe₂O₃ NPs was 1.73 times of that through the pure sand column; the interception rate overall increased with increasing addition of α-Fe₂O₃ NPs, reaching 68.8% with 20 g/kg α-Fe₂O₃ NPs. Coexisting Na⁺ (20 mM), Ca²⁺ (20 mM), and acidic condition (pH 4.0) could further increase the interception rate of ARGs by 1 g/kg α-Fe₂O₃ NPs from 21.1% to 86.2%, 90.7%, and 96.2%, respectively. The presence of PO₄^3- and humic acid at environmentally relevant concentrations would not significantly affect the interception of ARGs. In the treatment groups with PO₄^3- and humic acid, the removal rate decreased by only 1.8% and 0.1%, respectively. In addition, the interceptive removal of ARGs by α-Fe₂O₃ NPs-incorporated sand column was even better in actual surface water samples (87.2%) than that in the ultrapure water (21.1%). The findings provide a promising approach to treat ARGs-polluted water.

The effects of biochar on antibiotic resistance genes (ARGs) removal during different environmental governance processes: A review

Antibiotic resistance genes (ARGs) pollution has been considered as one of the most significant emerging environmental and health challenges in the 21st century, many efforts have been paid to control the proliferation and dissemination of ARGs in the environment. Among them, the biochar performs a positive effect in reducing the abundance of ARGs during different environmental governance processes and has shown great application prospects in controlling the ARGs. Although there are increasing studies on employing biochar to control ARGs, there is still a lack of review paper on this hotspot. In this review, firstly, the applications of biochar to control ARGs in different environmental governance processes were summarized. Secondly, the processes and mechanisms of ARGs removal promoted by biochar were proposed and discussed. Then, the effects of biochar properties on ARGs removal were highlighted. Finally, the future prospects and challenges of using biochar to control ARGs were proposed. It is hoped that this review could provide some new guidance for the further research of this field.

New insights into physicochemical properties of different particulate size-fractions and dissolved organic matter derived from biochars and their sorption capacity for phenanthrene

To improve the knowledge of the heterogeneity and sorption behavior of biochars on hydrophobic organic contaminants (HOCs), pristine biochars (PBCs, 400 and 700 °C) were fractionated into four particulate fractions (S_fBCs) and dissolved organic matter derived from biochars (DBC), then the sorption capacities of them towards phenanthrene were examined. Results showed that the OC-normalized sorption distribution coefficients (K_oc) of PBCs were generally at intermediate levels among that of S_fBCs and DBCs. The logK_oc values of S_fBCs increased as particle sizes decreased. By virtue of the higher micropore volume, specific surface area, aromaticity and hydrophobicity, the lowest S_fBCs (0.45-10 µm, BC_0.45-10) exhibited remarkably higher logK_oc. Besides, although S_fBCs from 700 °C generally showed larger logK_oc than counterparts from 400 °C, almost no difference was observed for logK_oc values of BC_0.45-10 fractions from 400 and 700 °C. We thus speculated that particle size might have stronger effect on their sorption capacity than pyrolysis temperature. Although DBCs exhibited dramatically lower logK_oc values than nano-scale S_fBCs, they were interestingly comparable to large-sized S_fBCs. Our findings thus suggested the importance of small particulate biochar species and DBCs on HOCs transport should be both highlighted since these fractions were highly dynamic in the environment.

Nano-biochar: A novel solution for sustainable agriculture and environmental remediation

Currently, the applications of biochar (BC) in agricultural practices and for environmental remediation purposes have demonstrated multifaceted advantages despite a few limitations. Nano-BC offers considerable opportunities especially for the remediation of hazardous contaminants as well as the improvement of crop productivity. Positive outcomes of nano-BC on soil physico-chemical and biological characteristics have indicated its suitability for agricultural applications. Nano-BC may effectively regulate the mobilization and sorption of important micro- and macro-nutrients, along with the hazardous contaminants including potentially toxic metals, pesticides, etc. Additionally, the sorption characteristics of nano-BC depends substantially on feedstock materials and pyrolysis temperatures. Nevertheless, the conducted investigations regarding nano-BC are in infant stages, requiring extensive field investigations. The nano-enhanced properties of BC on one hand dramatically improve its effectiveness and sustainability, on the other hand, there may be associated with toxicity development in diverse aquatic and/or terrestrial environments. Therefore, risk assessment on soil organisms and its indirect impact on human health is another area of concern linked with the field application of nano-BC. The present review delineates the potentiality of nano-BC as an emerging sorbent for sustainable agriculture and environmental applications.

Effect of root exudates on the release, surface property, colloidal stability, and phytotoxicity of dissolved black carbon

In this study, the release of dissolved black carbon (DBC) from bulk-BC, its surface properties, colloidal stability, and oxidative stress to rice seedlings in the presence and absence of rice root exudates were compared. The bulk-BCs were prepared at 550 °C and derived from wood chips and pig manure, respectively. The release of DBC from bulk-BC was significantly enhanced (20.19-23.63%) by the introduction of root exudates, where low molecular weight organic acids played a dominating role in the dissociation of DBC from carbon skeleton. The surface properties of DBC were greatly modified by root exudates including decreases in the surface area (18.13%) and mineral contents (43.90-69.57%). The O-containing groups and graphitization were also enhanced by 11.46% and 18.65%, respectively. Meanwhile, the presence of root exudates not only reduced the colloidal stability of DBC but also lowered the intensity of free radicals (19.44-22.22%) in DBC. Consequently, the oxidative stress of DBC to rice seedlings was significantly (p < 0.05) alleviated, evidenced by reduced antioxidative enzyme activities (5.67-29.25%) and soluble protein content (15.75-46.79%) in rice plants. These results indicate that the interaction between DBC and root exudates could remarkably modify the surface properties and reactivity of DBC, which has profound implications for understanding the behavior and functions of DBC in the environment.

Efficient remediation of antibiotic pollutants from the environment by innovative biochar: current updates and prospects

The increased antibiotic consumption and their improper management led to serious antibiotic pollution and its exposure to the environment develops multidrug resistance in microbes against antibiotics. The entry rate of antibiotics to the environment is much higher than its exclusion; therefore, efficient removal is a high priority to reduce the harmful impact of antibiotics on human health and the environment. Recent developments in cost-effective and efficient biochar preparation are noticeable for their effective removal. Moreover, biochar engineering advancements enhanced biochar remediation performance several folds more than in its pristine forms. Biochar engineering provides several new interactions and bonding abilities with antibiotic pollutants to increase remediation efficiency. Especially heteroatoms-doping significantly increased catalysis of biochar. The main focus of this review is to underline the crucial role of biochar in the abatement of emerging antibiotic pollutants. A detailed analysis of both native and engineered biochar is provided in this article for antibiotic remediation. There has also been discussion of how biochar properties relate to feedstock, production conditions and manufacturing technologies, and engineering techniques. It is possible to produce biochar with different surface functionalities by varying the feedstock or by modifying the pristine biochar with different chemicals and preparing composites. Subsequently, the interaction of biochar with antibiotic pollutants was compared and reviewed. Depending on the surface functionalities of biochar, they offer different types of interactions e.g., π-π stacking, electrostatic, and H-bonding to adsorb on the biochar surface. This review demonstrates how biochar and related composites have optimized for maximum removal performance by regulating key parameters. Furthermore, future research directions and opportunities for biochar research are discussed.

Accumulation of antibiotic resistance genes in pakchoi (Brassica chinensis L.) grown in chicken manure-fertilized soil amended with fresh and aged biochars

Biochar has been used to alleviate the contamination of antibiotic resistance genes (ARGs) in soil and to inhibit ARGs transfer from soil to plants. However, the effect of aged biochar on ARGs abundance in soil and ARGs enrichment in plants are scarcely investigated. In this study, a pot experiment was conducted to compare the effects of fresh and aged biochars on the accumulation of five typical ARGs including tetX, tetW, sul2, ermB, and intI1 in a chicken manure-fertilized soil and in pakchoi (Brassica chinensis L.). Results showed that both biochars significantly decreased the abundance of tetW, sul2, and ermB and increased the abundance of tetX and intI1 in soil. However, the accumulation of all tested ARGs in pakchoi were significantly decreased by both biochars. At the lower addition rate (1%), the fresh biochar was superior to the aged biochar in decreasing the accumulation of some genes (tetW, tetX, and sul2) in pakchoi, whereas an opposite tendency was observed for other genes (ermB and intI1). As the addition rate increased to 2%, the difference between the two biochars diminished, and a similar capacity of decreasing ARGs transfer was observed. The reduction in ARGs accumulation in pakchoi was highly related to the type of ARGs, the biochar addition level, and the aging of biochar. Our results provide insights into the naturally aged biochar on the fate of ARGs in a soil-plant system.

Efficient removal of antibiotic-resistant bacteria and intracellular antibiotic resistance genes by heterogeneous activation of peroxymonosulfate on hierarchical macro-mesoporous Co3O4-SiO2 with enhanced photogenerated charges

Antibiotic resistance genes (ARGs) and their host antibiotic-resistant bacteria (ARB) are widely detected in the environment and pose a threat to human health. Traditional disinfection in water treatment plants cannot effectively remove ARGs and ARB. This study explored the potential of a heterogeneous photo-Fenton-like process utilizing a hierarchical macro-mesoporous Co₃O₄-SiO₂ (MM CS) catalyst for activation of peroxymonosulfate (PMS) to inactivate ARB and degrade the intracellular ARGs. A typical gram-negative antibiotic-resistant bacteria called Pseudomonas sp. HLS-6 was used as a model ARB. A completed inactivation of ARB at ∼10⁷ CFU/mL was achieved in 30 s, and an efficient removal rate of more than 4.0 log for specific ARGs (sul1 and intI1) was achieved within 60 min by the MM CS-based heterogeneous photo-Fenton-like process under visible light and neutral pH conditions. Mechanism investigation revealed that •O₂^- and ¹O₂ were the vital reactive species for ARB inactivation and ARG degradation. The formation and transformation of the active species were proposed. Furthermore, the hierarchical macro-mesoporous structure of MM CS provided excellent optical and photoelectrochemical properties that promoted the cycle of Co³⁺/Co²⁺ and the effective utilization of PMS. This process was validated to be effective in various water matrices, including deionized water, underground water, source water, and secondary effluent wastewater. Collectively, this work demonstrated that the MM CS-based heterogeneous photo-Fenton-like process is a promising technology for controlling the spread of antibiotic resistance in aquatic environments.

Biochar can mitigate co-selection and control antibiotic resistant genes (ARGs) in compost and soil

Heavy metals (HMs) contamination raises the expression of antibiotic resistance (AR) in bacteria through co-selection. Biochar application in composting improves the effectiveness of composting and the quality of compost. This improvement includes the elimination and reduction of antibiotic resistant genes (ARGs). The use of biochar in contaminated soils reduces the bioaccessibility and bioavailability of the contaminants hence reducing the biological and environmental toxicity. This decrease in contaminant bioavailability reduces contaminants induced co-selection pressure. Conditions which favour reduction in HMs bioavailable fraction (BF) appear to favour reduction in ARGs in compost and soil. Biochar can prevent horizontal gene transfer (HGT) and can eliminate ARGs carried by mobile genetic elements (MGEs). This effect reduces maintenance and propagation of ARGs. Firmicutes, Proteobacteria, and Actinobacteria are the major bacteria phyla identified to be responsible for dissipation, maintenance, and propagation of ARGs. Biochar application rate at 2-10% is the best for the elimination of ARGs. This review provides insight into the usefulness of biochar in the prevention of co-selection and reduction of AR, including challenges of biochar application and future research prospects.

Nanobiochar-rhizosphere interactions: Implications for the remediation of heavy-metal contaminated soils

Soil heavy metal contamination has increasingly become a serious environmental issue globally, nearing crisis proportions. There is an urgent need to find environmentally friendly materials to remediate heavy-metal contaminated soils. With the continuing maturation of research on using biochar (BC) for the remediation of contaminated soil, nano-biochar (nano-BC), which is an important fraction of BC, has gradually attracted increasing attention. Compared with BC, nano-BC has unique and useful properties for soil remediation, including a high specific surface area and hydrodynamic dispersivity. The efficacy of nano-BC for immobilization of non-degradable heavy-metal contaminants in soil systems, however, is strongly affected by plant rhizosphere processes, and there is very little known about the role that nano-BC play in these processes. The rhizosphere represents a dynamically complex soil environment, which, although having a small thickness, drives potentially large materials fluxes into and out of plants, notably agricultural foodstuffs, via large diffusive gradients. This article provides a critical review of over 140 peer-reviewed papers regarding nano-BC-rhizosphere interactions and the implications for the remediation of heavy-metal contaminated soils. We conclude that, when using nano-BC to remediate heavy metal-contaminated soil, the relationship between nano-BC and rhizosphere needs to be considered. Moreover, the challenges to extending our knowledge regarding the environmental risk of using nano-BC for remediation, as well as further research needs, are identified.