Effect of pyrolysis temperature on potential toxicity of biochar if applied to the environment

Biochar amendment affects the microbial genetic profile of the soil, its community structure and phospholipid fatty acid contents

Biochar (BC) amendment has been proposed as a promising strategy for mitigating greenhouse gas (GHG) emissions, specifically carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Conducting a meta-analysis to evaluate the impact of biochar on microbial genetic profile, community structure, and phospholipid fatty acid (PLFA) contents can aid in identifying key microbial groups involved in GHG production and consumption, and assessing the overall effectiveness of biochar in reducing GHG emissions. The present meta-analysis revealed that the addition of biochar resulted in a 22 % and 41 % reduction in pmoA and mcrA genes of methanogenic microorganisms, respectively. The mcrA/pmoA ratio significantly increased by 81 %. Gene abundances exhibited a positive response to biochar amendment, with increases observed in nifH, nirK, nirS, nosZ, and nosZ (nirS + nirK) genes by 13 %, 32 %, 37 %, 42 %, and 79 %, respectively. Moreover, biochar amendment influenced the microbial community structure accordingly. The concentration of PLFAs increased in response to BC treatment in the following order: A-bacteria (+49 %) < Fungi (+30 %) < Gram-pb (+21 %) < G-bacteria (+17 %) < Gram-nb (+11 %). These findings indicate that biochar amendment shapes the microbial community structure, further emphasizing its significance in enhancing soil fertility.

"Active carbon" is more advantageous to the bacterial community in the rice rhizosphere than "stable carbon"

Carbon materials are commonly used for soil carbon sequestration and fertilization, which can also affect crop growth by manipulating the rhizosphere bacterial community. However, the comparison of the differences between active carbon (e.g., organic fertilizers) and stable carbon (e.g., biochar) on rhizosphere microdomains is still unclear. Hence, a trial was implemented to explore the influence of control (CK, no fertilizer; NPK, chemical fertilizer), organic fertilizer (CF-O, organic fertilizer; CF-BO, biochar-based organic fertilizer) and biochar material (CF-B, perishable garbage biochar; CF-PMB, pig manure biochar) on the diversity, composition, and interaction of rice rhizosphere bacterial community through 16 S rRNA gene high-throughput sequencing. Our results demonstrate that organic fertilizer increases bacterial alpha-diversity compared to no-carbon supply treatment to the extend, whereas biochar has the opposite effect. The rhizosphere bacterial community composition showed pronounced variations among the various fertilization treatments. The relative abundance in Firmicutes decreased with organic fertilizer application, whereas that in Chloroflexi and Actinobacteria decreased with biochar application. Bacterial network analysis demonstrate that organic fertilizer enhances the complexity and key taxa of bacterial interactions, while biochar exhibits an opposing trend. The findings of our study indicate that organic fertilizer may contribute to a positive and advantageous impact on bacterial diversity and interaction in rice rhizosphere, whereas the influence of biochar is not as favorable and constructive. This study lays the foundation for elucidating the fate of the rhizosphere bacterial community following different carbon material inputs in the context of sustainable agricultural development.

A review on influence of biochar amendment on soil processes and environmental remediation

Biochar is the thermal degradation product of biomass generated in an oxygen-limited environment under different pyrolysis conditions. Biochar characteristics are functions of the feedstock material and pyrolysis temperature. Depending on pyrolysis conditions biochar concentrates varying quantities of recalcitrant and labile carbon along with nutrients which in turn affect soil physiochemical properties and microbial processes. Biochar in soil balances carbon content encourages nitrogen fixation and solubilize phosphorus along with enhancing soil enzyme activity. It serves as a microhabitat for microorganisms present in soil thus influences the diversity, composition, and distribution of soil microbial communities by affecting their intra- and interspecific communication. This review provides an overview of the current knowledge about biochar characteristics, its interactions with soil, and associated biota and its role in soil remediation. In addition, this paper also discussed the factors affecting the capacity of biochar to adsorb organic pollutants following different mechanisms. Being an effective adsorbent due its high specific surface area, large porosity, and numerous surface functional groups biochar has been explored extensively in field of environment to remediate contaminated soils.

Recent advances in the removal of psychoactive substances from aquatic environments: A review

Psychoactive substances (PS) have become emerging contaminants in aquatic environments, characterized by their wide distribution, high persistence, bioaccumulation and toxicity. They are difficult to be completely removed in sewage treatment plants due to their high stability under different conditions. The incomplete removal of PS poses a threat to the aquatic animals and can also lead to human health problems through accumulation in the food chain. PS has become a huge burden on global health systems. Therefore, finding an effective technology to completely remove PS has become a "hot topic" for researchers. The methods for removal PS include physical techniques, chemical methods and biological approaches. However, there is still a lack of comprehensive and systematic exploration of these methods. This review aims to address this gap by providing a comprehensive overview of traditional strategies, highlighting recent advancements, and emphasizing the potential of natural aquatic plants in removing trace PS from water environments. Additionally, the degradation mechanisms that occur during the treatment process were discussed and an evaluation of the strengths and weaknesses associated with each method was provided. This work would help researchers in gaining a deeper understanding of the methodologies employed and serve as a reference point for future research endeavors and promoting the sustainable and large-scale application of PS elimination.

Biomass-activated carbon-based superhydrophobic sponge with photothermal properties for adsorptive separation of waste oil

The increasing discharge of oily wastewater from life poses a serious threat to the ecological environment and human health. To develop green, efficient, and low-cost materials for oil-water separation, a superhydrophobic photothermal oil-absorbing sponge (CAC-PDA@MF) was prepared by using nanoscale coconut shell activated carbon (CAC) loaded on a melamine sponge in this study. The sponge had excellent superhydrophobicity (WCA of 159.53°) due to the reduction of surface energy by grafting long-chain silanes. The adsorption capacity of the sponge was 69.04 g/g-158.27 g/g for a wide range of oils and organic solvents, and the sponge had excellent mechanical properties for multiple adsorption and recovery of oil. After 50 cycles of oil-water separation, its separation efficiency was maintained at over 98 %. In addition, the material had high acid, alkali, and salt resistance as well as excellent photothermal conversion properties. Its surface temperature rose rapidly to 100 °C and above, at a light intensity of 1.0 kW/m2. The material was capable of adsorbing and recovering high-viscosity oils that were solid or semi-solid at room temperature. Its versatility and commercial value made it a promising candidate for a wide range of applications.

Increased oxygen content in biochar lowered bioavailability of polycyclic aromatic hydrocarbons-related toxicity to various organisms

Agricultural or environmental application of biochar (BC) is connected with the introduction of biochar-derived components among which polycyclic aromatic hydrocarbons (PAHs) and heavy metals are the most toxic. Their presence and bioavailability are crucial considering biochar toxicity. The effect of feedstock and pyrolysis temperature on the physicochemical properties of produced biochar and contaminant content was established and combined with toxicity to a broad range of living organisms. The obtained data revealed that predicting the bioavailability of PAHs using the total content is misleading. The toxicity was influenced by factors in the following way: the bioavailable PAHs > ash > total PAHs content in BC stressing the role of BC physicochemical characteristics. Among tested BC properties, surface functionalization, e.g. presence of oxygen-containing functional groups was crucial in revealing the toxicity. The data clearly indicate that additional research is required to determine BC's impact on various organisms and performing one ecotoxicity test is not sufficient.

A comprehensive review of the "black gold catalysts" in wastewater treatment: Properties, applications and bibliometric analysis

A significant amount of effort has been devoted to the utilization of biochar-based catalysts in the treatment of wastewater. By virtue of its abundant functional groups and high specific surface area, biochar holds significant promise as a catalyst. This article presents a comprehensive systematic review and bibliometric analysis covering the period from 2009 to 2024, focusing on the restoration of wastewater through biochar catalysis. The production, activation, and functionalization techniques employed for biochar are thoroughly examined. In addition, the application of advanced technologies such as advanced oxidation processes (AOPs), catalytic reduction reactions, and biochemically driven processes based on biochar are discussed, with a focus on elucidating the underlying mechanisms and how surface functionalities influence the catalytic performance of biochar. Furthermore, the potential drawbacks of utilizing biochar are also brought to light. To emphasize the progress being made in this research field and provide valuable insights for future researchers, a scientometric analysis was conducted using CiteSpace and VOSviewer software on 595 articles. Hopefully, this review will enhance understanding of the catalytic performance and mechanisms pertaining to biochar-based catalysts in pollutant treatment while providing a perspective and guidelines for future research and development efforts in this area.

A critical review of biochar as an environmental functional material in soil ecosystems for migration and transformation mechanisms and ecological risk assessment

At present, biochar has a large application potential in soil amelioration, pollution remediation, carbon sequestration and emission reduction, and research on the effect of biochar on soil ecology and environment has made positive progress. However, under natural and anthropogenic perturbations, biochar may undergo a series of environmental behaviors such as migratory transformation, mineralization and decomposition, and synergistic transport, thus posing certain potential risks. This paper outlines the multi-interfacial migration pathway of biochar in "air-soil-plant-animal-water", and analyzes the migration process and mechanism at different interfaces during the preparation, transportation and application of biochar. The two stages of the biochar mineralization process (mineralization of easily degradable aliphatic carbon components in the early stage and mineralization of relatively stable aromatic carbon components in the later stage) were described, the self-influencing factors and external environmental factors of biochar mineralization were analyzed, and the mineral stabilization mechanism and positive/negative excitation effects of biochar into the soil were elucidated. The proximity between field natural and artificially simulated aging of biochar were analyzed, and the change of its properties showed a trend of biological aging > chemical aging > physical aging > natural aging, and in order to improve the simulation and prediction, the artificially simulated aging party needs to be changed from a qualitative method to a quantitative method. The technical advantages, application scope and potential drawbacks of different biochar modification methods were compared, and biological modification can create new materials with enhanced environmental application. The stability performance of modified biochar was compared, indicating that raw materials, pyrolysis temperature and modification method were the key factors affecting the stability of biochar. The potential risks to the soil environment from different pollutants carried by biochar were summarized, the levels of pollutants released from biochar in the soil environment were highlighted, and a comprehensive selection of ecological risk assessment methods was suggested in terms of evaluation requirements, data acquisition and operation difficulty. Dynamic tracing of migration decomposition behavior, long-term assessment of pollution remediation effects, and directional design of modified composite biochar materials were proposed as scientific issues worthy of focused attention. The results can provide a certain reference basis for the theoretical research and technological development of biochar.

Treatment of aqueous per- and poly-fluoroalkyl substances: A review of biochar adsorbent preparation methods

Per- and poly-fluoroalkyl substances (PFAS) are synthetic chemicals widely used in everyday products, causing elevated concentrations in drinking water and posing a global challenge. While adsorption methods are commonly employed for PFAS removal, the substantial cost and environmental footprint of commercial adsorbents highlight the need for more cost-effective alternatives. Additionally, existing adsorbents exhibit limited effectiveness, particularly against diverse PFAS types, such as short-chain PFAS, necessitating modifications to enhance adsorption capacity. Biochar can be considered a cost-effective and eco-friendly alternative to conventional adsorbents. With abundant feedstocks and favorable physicochemical properties, biochar shows significant potential to be applied as an adsorbent for removing contaminants from water. Despite its effectiveness in adsorbing different inorganic and organic contaminants from water environments, some factors restrict its effective application for PFAS adsorption. These factors are related to the biochar properties, and characteristics of PFAS, as well as water chemistry. Therefore, some modifications have been introduced to overcome these limitations and improve biochar's adsorption capacity. This review explores the preparation conditions, including the pyrolysis process, activation, and modification techniques applied to biochar to enhance its adsorption capacity for different types of PFAS. It addresses critical questions about the adsorption performance of biochar and its composites, mechanisms governing PFAS adsorption, challenges, and future perspectives in this field. The surge in research on biochar for PFAS adsorption indicates a growing interest, making this timely review a valuable resource for future research and an in-depth exploration of biochar's potential in PFAS remediation.

Conversion of locally available materials to biochar and activated carbon for drinking water treatment

For environmental sustainability and to achieve sustainable development goals (SDGs), drinking water treatment must be done at a reasonable cost with minimal environmental impact. Therefore, treating contaminated drinking water requires materials and approaches that are inexpensive, produced locally, and effortlessly. Hence, locally available materials and their derivatives, such as biochar (BC) and activated carbon (AC) were investigated thoroughly. Several researchers and their findings show that the application of locally accessible materials and their derivatives are capable of the adsorptive removal of organic and inorganic contaminants from drinking water. The application of locally available materials such as lignocellulosic materials/waste and its thermo-chemically derived products, including BC and AC were found effective in the treatment of contaminated drinking water. Thus, this review aims to thoroughly examine the latest developments in the use of locally accessible feedstocks for tailoring BC and AC, as well as their features and applications in the treatment of drinking water. We attempted to explain facts related to the potential mechanisms of BC and AC, such as complexation, co-precipitation, electrostatic interaction, and ion exchange to treat water, thereby achieving a risk-free remediation approach to polluted water. Additionally, this research offers guidance on creating efficient household treatment units based on the health risks associated with customized adsorbents and cost-benefit analyses. Lastly, this review work discusses the current obstacles for using locally accessible materials and their thermo-chemically produced by-products to purify drinking water, as well as the necessity for technological interventions.

Formation mechanisms and degradation methods of polycyclic aromatic hydrocarbons in biochar: A review

Biochar has been widely used in soil amendment and environmental remediation. Polycyclic aromatic hydrocarbons (PAHs) could be produced in preparation of biochar, which may pose potential risks to the environment and human health. At present, most studies focus on the ecotoxicity potential of biochar, while there are few systematic reviews on the formation mechanisms and mitigation strategies of PAHs in biochar. Therefore, a systematical understanding of the distribution, formation mechanisms, risk assessment, and degradation approaches of PAHs in biochar is highly needed. In this paper, the distribution and content of the total and bioavailable PAHs in biochar are reviewed. Then the formation mechanisms, influencing factors, and potential risk assessment of PAHs in biochar are systematically explored. After that, the effective strategies to alleviate PAHs in biochar are summarized. Finally, suggestions and perspectives for future studies are proposed. This review provides a guide for reducing the formation of biochar-associated PAHs and their toxicity, which is beneficial for the development and large-scale safe use of environmentally friendly biochar.

Alteration of biomass toxicity in torrefaction - A XDS-CALUX bioassay study

Torrefaction constitutes one of the promising technologies for the management of waste biomass and the production of high-carbon products for combustion, gasification, adsorption of pollutants or soil treatment. Unfortunately, waste biomass may be contaminated with toxic persistent organic pollutants, such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) and dioxin-like biphenyls (dl-PCB). Literature does not provide consistent measurements on how the low-temperature thermochemical processing, such as torrefaction, affects the toxicity of biomass. This contribution assesses how a torrefaction treatment, conducted at 200 °C, modifies the toxicity due to PCDD/PCDF/dl-PCB in biomass. We deploy the XDS-CALUX biotest on five types of waste biomass (sewage sludge, tree bark, cattle manure, spent coffee ground, common reed), before and after treatment. The content of total dioxin- & biphenyl fraction compounds in the raw biomass, investigated in this study, varies from 0.14 to 3.67 pg BEQ·g-1d.m., and in the torrefied biomass between 0.17 and 6.00 pg BEQ·g-1d.m.; BEQ stands for bioanalytical equivalent. This increase is statistically insignificant at p = 0.05, taking into account all types of examined biomass. This proves that low-temperature torrefaction cannot detoxify biomass, i.e., chars, produced from biomass characterized by elevated concentration of PCDD/PCDF/dl-PCB, will reflect the contamination of the feedstocks. With respect to heavy metals, we conclude that only the content of Cd in biomass, and, to a lesser extent, the abundance of Cu and Fe, modify the toxicity of this material during its thermochemical treatment at low temperature.

Biochar modulating soil biological health: A review

Biochar can be used for multifunctional applications including the improvement of soil health and carbon storage, remediation of contaminated soil and water resources, mitigation of greenhouse gas emissions and odorous compounds, and feed supplementation to improve animal health. A healthy soil preserves microbial biodiversity that is effective in supressing plant pathogens and pests, recycling nutrients for plant growth, promoting positive symbiotic associations with plant roots, improving soil structure to supply water and nutrients, and ultimately enhancing soil productivity and plant growth. As a soil amendment, biochar assures soil biological health through different processes. First, biochar supports habitats for microorganisms due to its porous nature and by promoting the formation of stable soil micro-aggregates. Biochar also serves as a carbon and nutrient source. Biochar alters soil physical and chemical properties, creating optimum soil conditions for microbial diversity. Biochar can also immobilize soil pollutants and reduce their bioavailability that would otherwise inhibit microbial growth. However, depending on the pyrolysis settings and feedstock resources, biochar can be comprised of contaminants including polycyclic aromatic hydrocarbons and potentially toxic elements that can inhibit microbial activity, thereby impacting soil health.

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.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge. The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Ensuring safety standards in sewage sludge-derived biochar: Impact of pyrolysis process temperature and carrier gas on micropollutant removal

The application of sewage sludge to agricultural land is facing increasing restrictions due to concerns about various micropollutants, including polycyclic aromatic hydrocarbons (PAHs), dioxins and furans (PCDD/Fs), polychlorinated biphenyls (PCBs), per- and poly-fluoroalkyl substances (PFAS), and heavy metals (HMs). As an alternative approach to manage this residue, the use of pyrolysis, a process that transforms sludge into biochar, a carbon-rich solid material, is being explored. Despite the potential benefits of pyrolysis, there is limited data on its effectiveness in removing micropollutants and the potential presence of harmful elements in the resulting biochar. This study aims to evaluate the impact of the temperature and the use of a carrier gas (N2) during a two-stage pyrolysis and cooling on micropollutant removal. Pilot-scale tests showed that a higher temperature (650 °C) and the use of a carrier gas (0.4 L/min N2) during the pyrolysis and the cooling process led to a reduction of PAHs, PCDD/Fs, PCBs and PFAS below their detection limits. As such, the generated biochar aligns with the guidelines set by the International Biochar Initiative (IBI) and the European Biochar Certificate (EBC) for all micropollutants, except for zinc and copper. Additional investigation is required to determine whether the micropollutants undergo destruction or transition into other pyrolysis end-products, such as the gas or liquid phase.

Revealing the generation of reactive oxygen species in hydrochar and pyrochar: Insight into rational regulation of free radicals and catalytic mechanism

The removal of organic pollutants by biochar has been extensively studied. However, the differences in the removal mechanisms of contaminants by biochar obtained from different preparation techniques have not been thoroughly elucidated. In this study, the catalytic performances of hydrochar (HC) and pyrochar (PC) were compared in the dark and light. Owing to more persistent free radicals (PFRs), greater defects and stronger charge transfer ability on the surface, PC could produce a certain concentration of superoxide radicals (•O2-) even in the dark, making its degradation efficiency for benzoic acid (BA) 11% higher than that of HC. On the contrary, when the light was turned on, HC rather than PC can generate a higher amount of hydroxyl radical (•OH), resulting in an 11% higher degradation efficiency of BA compared to PC. The improvement of catalytic performance in HC originated from its oxygen-containing functional groups (OFGs), which was beneficial for its effective production of singlet oxygen (1O2) and ·OH under light exposure. For PC, its photocatalytic activity depended mainly on the formation of 1O2 induced by the triplet of DOM (dissolved organic matter), but the lack of oxidative ·OH in its system leads to a lower degradation efficiency than that of HC. To prove the universal applicability of this rule for biochar materials, HC and PC materials obtained from soybean residue were also prepared for degrading BA. This work is devoted to an in-depth exploration of the catalytic activation mechanism of biochar obtained by different technological methods, and can create conditions for the generation of more dominant reactive oxygen species (ROS) on biochar, thus providing the guidance for environmental remediation.

Effect of chemical aging on phosphate adsorption and ecotoxicological properties of magnesium-modified biochar

Using magnesium-biochar composites (Mg-BC) in adsorption allows for the efficient and economically relevant removal of phosphate (PO43-) from water and wastewater. Applying Mg-BC for pollutant removal requires evaluating the adsorption capacity of composites and their ecotoxicological properties. Investigating the composite aging during the application of these composites into the soil is also essential. In the present study, nonaged and aged (at 60 or 90 °C) Mg-BC composites were investigated in the context of pyrolysis temperature (500 or 700 °C). All analyzed biochars were examined by Fourier transform infrared spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and surface area. The content of polycyclic aromatic hydrocarbons (PAHs) (bioavailable Cfree and organic solvent-extractable Ctot), heavy metals (HMs), and environmentally persistent free radicals (EPFRs) were determined. Ecotoxicity was evaluated using tests with Folsomia candida and Allivibrio fischeri. The dependence of adsorption on pyrolysis temperature and composite aging time was observed. Changes in physicochemical properties occurring as a result of aging reduced the adsorption of PO43- on Mg-BC composites. It was found that nonaged Mg-BC700 was more effective (9.55 mg g -1) in the adsorption of PO43- than Mg-BC500 (5.75 mg g-1). The adsorption capacities of aged composites were from 21 to 61% lower than those of the nonaged composites. Due to aging, the content of Cfree PAHs increased by 3-5 times depending on the pyrolysis temperature. However, aging reduced the Ctot PAHs in all composites from 24 to 35% depending on the pyrolysis temperature. Ecotoxicological evaluation of Mg-BC composites showed increased toxicity after aging to both organisms. The use of aged BC potentially increases the contaminant content and toxicity of Mg-BC composites.

Combined microbe-plant remediation of cadmium in saline-alkali soil assisted by fungal mycelium-derived biochar

Cadmium contamination in saline-alkali soil is becoming a great concern. Combined microbe-plant remediation is an economic way to treat this contamination, but is compromised by its low cadmium-removing capacity. In this study, the novel fungus-derived biochar was prepared to enhance the salt-tolerant bacterium-plant remediation of cadmium-contaminated saline-alkali soil. This biochar was prepared by pre-incubation of living Trichoderma atroviride hyphae with imidazole and further heating at 500 °C for 1 h. The obtained fungus-derived nitrogen-doped biochar (FBioCN) exhibited the high affinity to bacterial cells, leading to efficient colonization of exogenous salt-tolerant bacteria (e.g., Rhizobacter sp. and Sphingomonas sp.) on Amaranthus hypochondriacus roots. During culturing of the plants in the cadmium-contaminated saline-alkali soil, FBioCN drastically remodeled the rhizosphere microbiome, leading to enhance colonization of the exogeneous salt-tolerant bacteria, and increase bacterial diversity. The combination of FBioCN and the exogeneous bacteria further improved the activity of rhizosphere functional enzymes, protected the plants from the multiple stress, and promoted cadmium transport from the soil to the plants. Consequently, FBioCN together with the salt-tolerant bacteria drastically improved cadmium removal from the saline-alkali soil, with the percent of cadmium removal at the rhizosphere region increasing from 35.1% to 95.1%. This study sheds a light on the application of fungus-derived biochar in combined microbe-plant remediation in saline-alkali soil.

Nitrogen-enriched biochar co-compost for the amelioration of degraded tropical soil

Tropical soils are often deeply weathered and vulnerable to degradation having low pH and unfavorable Al/Fe levels, which can constrain crop production. This study aims to examine nitrogen-enriched novel biochar co-composts prepared from rice straw, maize stover, and gram residue in various mixing ratios of the biochar and their feedstock materials for the amelioration of acidic tropical soil. Three pristine biochar and six co-composts were prepared, characterized, and evaluated for improving the chemical and biological quality of the soil against a conventional lime treatment. The pH, cation exchange capacity (CEC), calcium carbonate equivalence (CCE) and nitrogen content of co-composts varied between 7.78-8.86, 25.3-30.5 cmol (p+) kg-1, 25.5-30.5%, and 0.81-1.05%, respectively. The co-compost prepared from gram residue biochar mixed with maize stover at a 1:7 dry-weight ratio showed the highest rise in soil pH and CEC, giving an identical performance with the lime treatment and significantly better effect (p < .05) than the unamended control. Agglomerates of calcite and dolomite in biochar co-composts, and surface functional groups contributed to pH neutralization and increased CEC of the amended soil. The co-composts also significantly (p < .05) increased the dehydrogenase (1.87 µg TPF g-1 soil h-1), β-glucosidase (90 µg PNP g-1 soil h-1), and leucine amino peptidase (3.22 µmol MUC g-1 soil h-1) enzyme activities in the soil, thereby improving the soil's biological quality. The results of this study are encouraging for small-scale farmers in tropical developing countries to sustainably reutilize crop residues via biochar-based co-composting technology.

Integrated microbiome and multi-omics analysis reveal the molecular mechanisms of Eisenia fetida in response to biochar-derived dissolved and particulate matters

At present, most ecotoxicological studies are still confined to focusing on the harmful effects of biochar itself on soil fauna. However, the potential ecotoxicity of different components separated from biochar to terrestrial invertebrates remains poorly understood. In this study, the dissolved matter (DM) and particulate matter (PM) were separated from biochar (BC) and then introduced into the soil-earthworm system to investigate the response mechanism of earthworms at the molecular level. The results showed that BC and DM exposure caused an increase in the abundance of Proteobacteria in the cast bacterial community, suggesting the dysbiosis of intestinal microbiota. It was also observed that the cast bacterial communities were more sensitive to DM exposure than PM exposure. Transcriptomic analysis showed that BC and DM exposure induced significant enrichment of functional pathways related to infectious and neuropathic diseases. Metabolomic profiling manifested that DM exposure caused metabolic dysfunction, antioxidant and detoxification abilities recession. Furthermore, significant differences in the responses of earthworms at transcriptomic and metabolic levels confirmed that DM exhibited greater ecotoxicity than PM. This study highlighted the significant contributions of dissolved matter to the ecotoxicity of biochar from the perspective of transcriptomic and metabolomic profiles.

Succession of biochar addition for soil amendment and contaminants remediation during co-composting: A state of art review

This paper aimed to highlight the succession of biochar addition for soil amendment and contaminants remediation during composting process. Biochar incorporated into the compost mixture promotes composting performance and enhances contaminants reduction. Co-composting with biochar for soil biota has been demonstrated via modified soil biological community abundance and diversity. On the other hand, adverse alterations to soil properties were noted, which had a negative impact on the communication of microbe-to-plant interactions within the rhizosphere. As a result, these changes influenced the competition between soilborne pathogens and beneficial soil microorganisms. Co-composting with biochar promoted the heavy metals (HMs) remediation efficiency in contaminated soils by around 66-95%. Notably, applying biochar during composting could improve nutrient retention and mitigate leaching. The adsorption of nutrients such as nitrogen and phosphorus compounds by biochar can be applied to manage environmental contamination and presents an excellent opportunity to enhance soil quality. Additionally, the various specific functional groups and large specific surface areas of biochar allow for excellent adsorption of persistent pollutants (e.g., pesticides, polychlorinated biphenyls (PCBs)) and emerging organic pollutants, such as microplastic, phthalate acid esters (PAEs) during co-composting. Finally, future perspectives, research gaps, and recommendations for further studies are highlighted, and potential opportunities are discussed.

Unveiling the Role of Dissolved Organic Matter on the Hg Phytoavailability in Biochar-Amended Soils

Biochar can effectively reduce the phytoavailability of mercury (Hg) in soil, but the mechanisms are not fully understood. In this study, the dynamic changes in Hg content adsorbed by the biochar (BC-Hg), Hg phytoavailability in the soil (P-Hg), and soil dissolved organic matter (DOM) characteristics were determined over a 60-day treatment period. Biochar obtained at 300 °C, 500 °C and 700 °C reduced the P-Hg concentration assessed by MgCl2 extraction by 9.4%, 23.5% and 32.7%, respectively. However, biochar showed a very limited adsorption on Hg, with the maximum BC-Hg content only accounting for 1.1% of the total amount. High-resolution scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the proportion of Hg atoms in biochar after 60 d was barely detectable. Biochar treatment can shift soil DOM toward higher aromatic content and molecular weight. Additionally, the addition of high-temperature biochar increased more humus-like components, but low-temperature biochar increased more protein-like components. Correlation analysis and partial least squares path modeling (PLS-PM) showed that biochar promoted humus-like fractions formation to reduce the Hg phytoavailability. This research has deepened the understanding of the mechanisms by which biochar stabilizes Hg in agricultural soils.

Physicochemical properties of nanosized biochar regulated by heat treatment temperature dictates algal responses: From the perspective of fatty acid metabolism

Nanosized biochar (NBC) is an important fraction of biochar (BC) as it can exert nano-scale effects on aquatic organisms, attracting increasing research attention. However, effects of different physicochemical properties of NBC on biological responses at the metabolic and gene expression level are not comprehensively understood. Here, biological effects of NBCs pyrolyzed at different heat treatment temperatures (HTTs, 350-700 °C) were evaluated using freshwater algae Chlorella vulgaris, from the perspectives of growth and fatty acid (FA) profile changes. NBC pyrolyzed at 700 °C (N700) induced the greatest algal growth inhibition and oxidative stress than N350 and N500. In addition, NBC exposure to 50 mg/L increased saturated and monounsaturated FAs, along with a decrease in polyunsaturated FAs (PUFAs). Exposure to NBC also significantly influenced the expression of key FA metabolism genes (3fad, sad, kasi and accd), demonstrating the potential role of reactive oxygen species-mediated PUFA reduction accompanied by increased membrane permeability in algal toxicity upon NBC exposure. The observed differences in response to N700 were attributed to its smaller particle size and higher abundance of -COOH. These findings reveal the underlying mechanisms in the algal response to NBCs and provide valuable guidance for the safe design and application of BC materials.

Conversion of quinoa and lupin agro-residues into biochar in the Andes: An experimental study in a pilot-scale auger-type reactor

In the last decades, the cultivation of quinoa and lupin became an important source of income for Andean farmers due to the demand for high nutrient-density foods from the Global North. The increase in the cultivation intensity caused by this exogenous demand led to the overexploitation of local ecosystems and a decrease in soil fertility. As an alternative to recover and improve soil quality, this work uses a pilot-scale auger pyrolysis reactor, implemented in the Andes, to assess the conversion of the agro residues generated in the post-harvesting processes of quinoa and lupin into biochar for soil amendment. Following the European Biochar Certificate guidelines, the pyrolyzed quinoa stems can be classified as biochar while the pyrolyzed quinoa husks can be classified as pyrogenic carbonaceous material. Both can be used for soil amendment considering their molar ratios (H/C_org, O/C_org) and carbon content. It was not possible to carbonize lupin stems and seedcases. Despite the altitude (2,632 m.a.s.l), the CO concentration during the carbonization of quinoa stems and husks were 1,024.4 and 559 mg/Nm³, this last, near the European eco-design standard of 500 mg/Nm³. A subsequent SWOT analysis showed the need to explore low-cost and low-complexity pyrolysis reactors that allow the decentralized conversion of agro residues at the farm-scale. The development of local standards to regulate the production and use of biochar is also essential to grant the safety of the processes, the quality of the products, and mobilize funds that allow implementation at relevant scales.

Biochar application strategies for polycyclic aromatic hydrocarbons removal from soils

Polycyclic aromatic hydrocarbons (PAHs) are known as a hazardous group of pollutants in the soil which causes many challenges to the environment. In this study, the potential of biochar (BC), as a carbonaceous material, is evaluated for the immobilization of PAHs in soils. For this purpose, various bonding mechanisms of BC and PAHs, and the strength of bonds are firstly described. Also, the effect of impressive criteria including BC physicochemical properties (such as surface area, porosity, particle size, polarity, aromaticity, functional group, etc., which are mostly the function of pyrolysis temperature), number of rings in PAHs, incubation time, and soil properties, on the extent and rate of PAHs immobilization by BC are explained. Then, the utilization of BC in collaboration with biological tools which simplifies further dissipation of PAHs in the soil is described considering detailed interactions among BC, microbes, and plants in the soil matrix. The co-effect of BC and biological remediation has been authenticated by previous studies. Moreover, recent technologies and challenges related to the application of BC in soil remediation are explained. The implementation of a combined BC-biological remediation method would provide excellent prospects for PAHs-contaminated soils.

Carbon-based catalyst for environmental bioremediation and sustainability: Updates and perspectives on techno-economics and life cycle assessment

Global rise in the generation of waste has caused an enormous environmental concern and waste management problem. The untreated carbon rich waste serves as a breeding ground for pathogens and thus strategies for production of carbon rich biochar from waste by employing different thermochemical routes namely hydrothermal carbonization, hydrothermal liquefaction and pyrolysis has been of interest by researchers globally. Biochar has been globally produced due to its diverse applications from environmental bioremediation to energy storage. Also, several factors affect the production of biochar including feedstock/biomass type, moisture content, heating rate, and temperature. Recently the application of biochar has increased tremendously owing to the cost effectiveness and eco-friendly nature. Thus this communication summarized and highlights the preferred feedstock for optimized biochar yield along with the factor influencing the production. This review provides a close view on biochar activation approaches and synthesis techniques. The application of biochar in environmental remediation, composting, as a catalyst, and in energy storage has been reviewed. These informative findings were supported with an overview of lifecycle and techno-economical assessments in the production of these carbon based catalysts. Integrated closed loop approaches towards biochar generation with lesser/zero landfill waste for safeguarding the environment has also been discussed. Lastly the research gaps were identified and the future perspectives have been elucidated.

Adsorptive removal of synthetic plastic components bisphenol-A and solvent black-3 dye from single and binary solutions using pristine pinecone biochar

The existing study deals with adsorptive removal of the endocrine-disrupting chemical bisphenol-A and toxic azo dye solvent black-3 from single and binary solutions. These two chemicals are commonly used as an additive in the synthetic plastic industries. Among the tested twenty pristine and modified biochars, the pristine pinecone biochar produced at 750 °C revealed greater bisphenol-A removal. Simulation of the experimental data obtained for bisphenol-A and dye removal from the single-component solution offered a best-fit to Elovich (R² > 0.98) and pseudo-second-order (R² > 0.99) kinetic models, respectively. Whereas for the bisphenol-A + dye removal from binary solution, the values for bisphenol-A adsorption were best suited to Elovich (R² > 0.98), while pseudo-second-order (R² > 0.99) for dye removal. Similarly, the two-compartment model also demonstrated better values (R² > 0.92) for bisphenol-A and dye removal from single and binary solutions with greater F_fast values (except for bisphenol-A in binary solution). The Langmuir isotherm model demonstrated the highest regression coefficient values (R² > 0.99) for bisphenol-A and dye removal with the highest adsorption capacity of 38.387 mg g^-1 and 346.856 mg g^-1, correspondingly. Besides, the co-existence of humic acid revealed a positive impact on bisphenol-A removal, while the dye removal rate was slightly hindered in presence of humic acid. The absorption process showed monolayer coverage of biochar surface with contaminants using a chemisorption mechanism with fast reactions between functional groups on the adsorbate and adsorbent. Whereas the adsorption mechanism was primarily controlled by hydrogen bonding, hydrophobic and π-π electron-donor-acceptor interactions as confirmed by FTIR, XPS, and pH investigations.

Influence of Miscanthus Rhizome Pyrolysis Operating Conditions on Products Properties

Waste from the Miscanthus production cycle may be a promising source of material for the pyrolysis and biochar production. The biochar can be used to enrich the soil on which the crop grows, thus increasing productivity. A sample of Miscanthus rhizomes was used as a raw material in a series of experiments in order to find the most suitable conditions for the preparation of biochar. Miscanthus biochar was prepared in a laboratory unit using four different temperatures (i.e., 400, 500, 600 and 700 °C). All pyrolysis products were subsequently evaluated in terms of their quality and product yields were determined. For a temperature of 600 °C and a residence time of 2 h, the appropriate properties of biochar were achieved and the process was still economical. The biochar contained a minimal number of polycyclic aromatic hydrocarbons and a high percentage of carbon. Surface area was measured to be 217 m2/g. The aqueous extract of biochar was alkaline.

Aryl hydrocarbon reporter gene bioassay for screening polyhalogenated dibenzo-p-dioxins/furans and dioxin-like polychlorinated biphenyls in hydrochar and sewage sludge

The suitability of the AhR reporter gene bioassays to screen the presence of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in sewage sludge (SL) and related hydrochar (HC) was here investigated. Samples of SL obtained from six WWTPs were processed by hydrothermal carbonization to obtain the resultant HCs and both tested with DR-CALUX® bioassay. Levels of PCDD/Fs and dl-PCBs were also determined analytically in the same samples by GC-MS/MS. Bioanalytical Toxicity Equivalent values (BEQ) resulted in one order of magnitude higher in HC compared to SL samples and those obtained from the dl-PCBs fraction higher than those from PCDD/Fs. BEQ and TEQ_WHO values, the latter obtained by GC-MS/MS analysis on the same matrices, were highly correlated showing also a similar trend in the six WWTPs (R_S= 0.8252, p < 0.001; Pearson's R R_P =0.8029, p < 0.01). The suitability of AhR bioassays and in particular of the DR-CALUX® to screen the presence and biological activity of legacy organohalogen compounds in both SL and HC matrices was demonstrated for the first time which support their usage for the assessment of potential risks associated with their further environmental applications.

Interactions between biochar, arbuscular mycorrhizal fungi and photosynthetic processes in potato (Solanum tuberosum L.)

Pyrolyzed biomass, generating biochar for use as soil amendment, is recognized as a promising strategy for carbon sequestration. Current understanding of the interactions between biochar, arbuscular mycorrhizal (AM), and plant photosynthesis, in terms of biochemical processes and CO₂ uptake, is fragmentary. The aim of this study was to investigate the effects on photosynthesis in potato including maximum rate of carboxylation by Rubisco (V_cmax), maximum rate of electron transport rate for RuBP-regeneration (J_max), mesophyll conductance (g_m) and other plant traits. Four types of biochar (wheat or miscanthus straw pellets pyrolyzed at temperatures of either 550 °C or 700 °C) were amended into low phosphorus soil. Potato plants were inoculated with the AM fungus Rhizophagus irregularis (M+) or not (M-). The results showed that four types of biochar generally decreased nitrogen and phosphorus content of potato, especially the biochars pyrolyzed at high temperature. This negative effect of biochar on nutrient content was alleviated by AM. It was found that V_cmax was limited by low plant nitrogen content as well as leaf area and phosphorus content. Plant phosphorus content also limited J_max, which was mutually constrained by V_cmax of leaves. Low g_m was an additional limiting factor for photosynthesis. The g_m was positively correlated to nitrogen content, which influenced the leaf anatomical structure by alteration of leaf mass per area. In conclusion, the influence of interactions between quality of biochar and AM symbiosis on photosynthesis of potato seems to relate to effects on plant nutrient content and leaf structures. Accordingly, a model for the dependence of V_cmax on nitrogen and phosphorus content and their interactive effect exhibited a high correlation coefficient. As potato plants form AM symbiosis under natural field conditions, the extent and interaction with the quality of amended biochar can be a determining factor for plant nutrient content, growth and yield.

Biochar aging: Impact of pyrolysis temperature on sediment carbon pools and the availability of arsenic and lead

Arsenic (As) and lead (Pb) are potentially toxic elements capable of developing several diseases in human beings such as cancer. Several adsorbent materials, including biochars, have been adopted as alternative measures designed to reduce the availability of As and Pb in water. The retention capacity of potentially toxic elements in biochars varies according to time, feedstock, and the pyrolysis temperature to produce the biochar. Our objectives in this study were to evaluate i) the aging effect of sugarcane straw pyrolyzed biochars at 350 (BC350), 550 (BC550), and 750 °C (BC750) and their ability to immobilize As and Pb; and ii) how the pyrolysis temperature and biochar aging alter the carbon content and quality of the solution and sediment. Biochars were applied at 5% (w/w), and their aging together with As and Pb immobilization effects were evaluated every 45 days over a total period of 180 days. The results were obtained using visible ultraviolet spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy combined with physical fractionation of organic matter and multivariate statistics. The groups formed in the Principal Component Analysis indicated that the change in the availability of As and Pb was related to the aging of the biochar and the temporal changes in the content and quality of organic carbon in the sediment and solution. The pyrolysis temperature was a key factor in the (im)mobilization capacity of As and Pb during the aging of the biochar. The increase in polysaccharides and organic matter associated with the particulate fraction can enhance the release of As in solution (24%). Increasing the fraction of organic matter associated with minerals reduced the availability of Pb by 58%. These findings may provide new insights into understanding the dynamics of organic matter and its role in the immobilization of As and Pb during biochar aging.

Biochars intended for water filtration: A comparative study with activated carbons of their physicochemical properties and removal efficiency towards neutral and anionic organic pollutants

Seven biochars (BCs) obtained from pyrolysis or gasification of different vegetal feedstocks were thoroughly characterized in comparison with three commercial activated carbons (ACs) routinely used in drinking water treatment plants. BCs and ACs characterization included the determinations of ash, iodine and methylene blue adsorption indexes, and the release of metals and polycyclic aromatic hydrocarbons, which were performed according to international standards applied for adsorption media to be used in drinking waters. Total specific surface area, micropore and mesopore specific surface area, pH of the point of zero charge, and the release of polychlorinated biphenyls were also determined in all chars. Principal component analysis and cluster analysis were performed in order to summarize the complex set of information deriving from the aforementioned characterizations, highlighting the BC most similar (BC6 from high temperature gasification of woody biomass) and most different (BC7 from low-temperature pyrolysis of corn cob) from ACs. These BCs were studied for their adsorption in ultrapure water towards diiodoacetic acid (an emergent disinfection by-product), benzene, and 1.2-dichlorobenzene, in comparison with ACs, and results obtained were fitted by linearized Freundlich equation. Overall, BC6 showed higher sorption performances compared to BC7, even though both BCs were less performing sorbents than ACs. However, the sorption properties of BCs were maintained also in real water samples collected from drinking water treatment plants.

Biochar-induced priming effects in soil via modifying the status of soil organic matter and microflora: A review

Biochar (BC) application has the potential to be integrated into a carbon-trading framework owing to its multiple environmental and economic benefits. Despite the increasing research attention over the past ten years, the mechanisms of BC-induced priming effects on soil organic carbon mineralization and their influencing factors have not been systematically considered. This review aims to document the recent progress in BC research by focusing on (1) how BC-induced priming effects change the soil environment, (2) the factors governing the mechanisms underlying BC amendment effects on soils, and (3) how BC amendments alter soil microbial communities and nutrient dynamics. Here, we carried out a detailed examination of the origins of different biochar, its pyrolysis conditions, and potential interactions with various factors that affect BC characteristics and mechanisms of C mineralization in primed soil. These findings clearly addressed the strong linkage between BC properties and abiotic factors that leads to change the soil microclimate, priming effects, and carbon stabilization. This review offers an overview of a fragmented body of evidence and the current state of understanding to support the application of BC in different soil environments with the aim of sustaining or improving the agricultural crop production.

Investigating the effects of biochar colloids and nanoparticles on cucumber early seedlings

Understanding about the influence of biochar colloidal and nanoscale particles on plant is limited. We therefore extracted the colloids and nanoparticles from hot pepper stalk biochar (CB600 and NB600), and examined physiological responses of cucumber early seedlings through hydroponic culture and pot experiment. CB600 had no significant effect on shoot at 500 mg/L, while it decreased root biomass and inhibited lateral root development. The biomass and root length, area, and tip number dramatically reduced after 500 mg/L NB600 treatment. Water content of NB600-exposed shoot was lower, suggesting water uptake and transfer might be hindered. For resisting exposure stress, root hair number and length increased. Even, the study observed swelling and hyperplasia of root hairs after direct exposure of CB600 and NB600. These adverse effects might be associated with the contact and adhesion of CB600 and NB600 with sharp edges to root surface. For a low concentration of 50 mg/L, NB600 did not influence cucumber early seedlings. In soil, CB600 and NB600 did not cause inhibitory effect at relatively high contents of 500 mg/kg and 2000 mg/kg. This study provides useful information for understanding phytotoxicity and environmental risk of biochar colloids and nanoparticles, which has significant implications with regard to biochar application safety.

Ozonized biochar filtrate effects on the growth of Pseudomonas putida and cyanobacteria Synechococcus elongatus PCC 7942

BACKGROUND

Biochar ozonization was previously shown to dramatically increase its cation exchange capacity, thus improving its nutrient retention capacity. The potential soil application of ozonized biochar warrants the need for a toxicity study that investigates its effects on microorganisms.

RESULTS

In the study presented here, we found that the filtrates collected from ozonized pine 400 biochar and ozonized rogue biochar did not have any inhibitory effects on the soil environmental bacteria Pseudomonas putida, even at high dissolved organic carbon (DOC) concentrations of 300 ppm. However, the growth of Synechococcus elongatus PCC 7942 was inhibited by the ozonized biochar filtrates at DOC concentrations greater than 75 ppm. Further tests showed the presence of some potential inhibitory compounds (terephthalic acid and p-toluic acid) in the filtrate of non-ozonized pine 400 biochar; these compounds were greatly reduced upon wet-ozonization of the biochar material. Nutrient detection tests also showed that dry-ozonization of rogue biochar enhanced the availability of nitrate and phosphate in its filtrate, a property that may be desirable for soil application.

CONCLUSION

Ozonized biochar substances can support soil environmental bacterium Pseudomonas putida growth, since ozonization detoxifies the potential inhibitory aromatic molecules.

A comprehensive assessment on bioavailability, leaching characteristics and potential risk of polycyclic aromatic hydrocarbons in biochars produced by a continuous pyrolysis system

Biochar application as a soil amendment has attracted worldwide attention. Nevertheless, polycyclic aromatic hydrocarbons (PAHs) formed during biochar production might enter into ecosystems and threaten human health after application to soil. Continuous pyrolysis systems tend to cause an accumulation of PAHs in biochar owing to short residence time and rapid cooling. This study conducted a comprehensive assessment regarding potential risk of PAHs in biochars produced by a continuous pyrolysis system based on bioavailability, leaching behavior, toxic equivalent quantity, health risk and phytotoxicity of PAHs. Results showed that the concentrations of total PAHs in biochars were in the range of 93.40-172.40 mg/kg, exceeding the European Biochar Certificate standard. 3-rings PAHs were the predominant groups. The percentages of total freely dissolved and leachable PAHs were lower than 1%. RH contained the least bioavailable and leachable PAHs concentration and phytotoxicity compared with CS and PS, which might attribute to the characteristic of three biochars. CS and PS were acidic and exhibited high levels of DOC and VFAs, while RH was strongly alkaline and presented greater aromaticity and higher surface area, which might have resulted in high adsorptive capacity and decreased bioavailability of PAHs. When the biochar application rate was higher than 0.6 t/ha, the incremental lifetime cancer risk value for human exposure to biochar-borne PAHs through the biochar-amended soil was over 10^-6, suggesting carcinogenic risks. Germination index values of biochars ranged from 25.66 to 88.95%. Phytotoxicity mainly was caused by bioavailable PAHs and dissolved organic compounds. Overall, these findings highlighted that although the percentage of bioavailable PAHs was low, the potential health risk and phytotoxicity of PAHs in biochars produced by a continuous pyrolysis system was of a great concern. High biochar application rates should be avoided without processing both for soil safety and human health.

Temporal changes in arsenic and lead pools in a contaminated sediment amended with biochar pyrolyzed at different temperatures

Globally, tons of soils and sediments are experiencing degradation due to the presence of high concentrations of potentially toxic elements (PTEs), such as arsenic (As) and lead (Pb), in areas in the vicinity of metal mining activities. The addition of biochar to contaminated sediments is a promising in situ remediation approach, and the effects of pyrolysis temperature and biochar aging are important factors for the immobilization and fate of PTEs. In this study, we evaluated the temporal changes in pools of As and Pb in sediment amended with biochars produced from sugarcane (Saccharum officinarum) pyrolyzed at 350 (BC350), 550 (BC550), and 750 °C (BC750). Biochars were aged by natural process (without additional acid or heat), and changes in As and Pb pools were evaluated every 45 days until completing 180 days of incubation. Changes in the As and Pb pools were extracted with water (bioavailable), magnesium chloride (exchangeable), nitric acid (active geochemical fraction), and exchangeable Mehlich-3 (associated with organic matter). As and Pb available contents have increased over time. BC750 was more effective in reducing the bioavailable and exchangeable As contents, while BC550 and BC350 were more effective in reducing the contents of bioavailable and exchangeable Pb.

Fabrication and environmental applications of metal-containing solid waste/biochar composites: A review

The resource utilization of industrial solid waste has become a hot issue worldwide. Composites of biochar with metal-containing solid wastes (MCSWs) can not only improve the adsorption performance, but also reduce the cost of modification and promote the recycling of waste resources. Thus, the synthesis and applications of biochar composites modified by MCSWs have been attracting increasing attention. However, different MCSWs may result in metal-containing solid waste/biochar composites (MCSW-BCs) with various physicochemical properties and adsorption performance, causing distinct adsorption mechanisms and applications. Although a lot of researches have been carried out, it is still in infancy. In particular, the explanation on the adsorption mechanisms and influencing factors of pollutant onto MCSW-BCs are not comprehensive and clear enough. Therefore, a systematic review on fabrication and potential environmental applications of different MCSW-BCs is highly needed. Here we summarize the recent advances on the utilization of typical metal-containing solid wastes, preparation of MCSW-BCs, adsorption mechanisms and influencing factors of pollutants by MCSW-BCs as well as their environmental applications. Finally, comments and perspectives for future studies are proposed.

A critical review of the possible adverse effects of biochar in the soil environment

Biochar has received extensive attention because of its multi-functionality for agricultural and environmental applications. Despite its many benefits, there are concerns related to the long-term safety and implications of its application, mainly because the mechanisms affecting soil and organism health are poorly quantified and understood. This work reviews 259 sources and summarises existing knowledge on biochar's adverse effects on soil from a multiangle perspective, including the physicochemical changes in soil, reduced efficiency of agrochemicals, potentially toxic substances in biochar, and effects on soil biota. Suggestions are made for mitigation measures. Mixed findings are often reported; however, the results suggest that high doses of biochar in clay soils are likely to decrease available water content, and surface application of biochar to sandy soils likely increases erosion and particulate matter emissions. Furthermore, biochar may increase the likelihood of excessive soil salinity and decreased soil fertility because of an increase in the pH of alkaline soils causing nutrient precipitation. Regarding the impact of biochar on (agro)chemicals and the role of biochar-borne toxic substances, these factors cannot be neglected because of their apparent undesirable effects on target and non-target organisms, respectively. Concerning non-target biota, adverse effects on reproduction, growth, and DNA integrity of earthworms have been reported along with effects on soil microbiome such as a shift in the fungi-to-bacteria ratio. Given the diversity of effects that biochar may induce in soil, guidelines for future biochar use should adopt a structured and holistic approach that considers all positive and negative effects of biochar.

Preparation, characterization and agri applications of biochar produced by pyrolysis of sewage sludge at different temperatures

Sewage sludge (SS) is an abundantly available feedstock, which is generally considered as potential threat to human health and environment. Its utilization in any process would be of great help for environmental sustainability. Accordingly, this work aimed to prepare and characterize the sewage sludge biochar (SSB) at temperatures, i.e. (500, 450, 400, and 350 °C), and further analyze the available nutrients and contaminants as well as agri application potential. The results indicated that the total nitrogen (TN), electrical conductivity (EC), and total organic carbon (TOC) content in SSBs decreased with increasing pyrolysis temperature. The overall concentration of polycyclic aromatic hydrocarbons (PAHs) in SSBs was substantially lower (1.8-9.7-fold depending on pyrolysis temperature) than in SS. Pyrolysis of SS enriched the heavy metals content in SSBs and the relative enrichment factor (RE) factor varied between 1.1 and 2.1 depending on the pyrolysis temperature. Furthermore, compared to SS, the leaching rate of heavy metals was significantly decreased in SSBs (1.1-100-fold depending on the pyrolysis temperature) and the pyrolysis temperature of 400-450 °C prevented the Ni, Pb, Cr, and Zn leaching in SSB. The total PAH and heavy metals content in biochars were below the control standard for land application. Finally, testing of the growth-promoting effect of biochar extracts on fenugreek plants revealed that SSB prepared at 350 °C significantly stimulated the root and shoot length of 5-days old seedlings. This study provides important data for potential environmental risks of SSB applications.

Potential hazards of biochar: The negative environmental impacts of biochar applications

Biochar has been widely used as an environmentally friendly material for soil improvement and remediation, water pollution control, greenhouse gas emission reduction, and other purposes because of its characteristics such as a large surface area, porous structure, and abundant surface O-containing functional groups. However, some surface properties (i.e., (i) some surface properties (i.e., organic functional groups and inorganic components), (ii) changes in pH), and (iii) chemical reactions (e.g., aromatic C ring oxidation) that occur between biochar and the application environment may result in the release of harmful components. In this study, biochars with a potential risk to the environment were classified according to their harmful components, surface properties, structure, and particle size, and the potential negative environmental effects of these biochars and the mechanisms inducing these negative effects were reviewed. This article presents a comprehensive overview of the negative environmental impacts of biochar on soil, water, and atmospheric environments. It also summarizes various technical methods of environment-related risk detection and evaluation of biochar application, thereby providing a baseline reference and guiding significance for future biochar selection and toxicity detection, evaluation, and avoidance.

Enrichment of potential degrading bacteria accelerates removal of tetracyclines and their epimers from cow manure biochar amended soil

The excessive usage of tetracyclines in animal husbandry and aquaculture invariably leads to deterioration of the microbial quality of nearby soils. We previously reported the accelerated removal of tetracyclines and their intermediates from the cow manure biochar amended soil (CMB). However, little is known about the underlying changes in the microbial community that mediate the accelerated removal of tetracyclines from the CMB. Here, we compared the concentration of parent tetracyclines along with their intermediates, microbial biomass, and microbial (fungal and bacterial) community in CMB and the control soil (CK) on the day of 1, 5, 10, 20, 30, 45, and 60. The biochar amendment accelerated the removal of tetracyclines and their epimers from the soil. Bacterial community composition varied between the CMB and CK. The relative abundance and richness of the bacteria that correlated with the degradation of tetracyclines and their epimers was significantly higher in the CMB as compared to the CK. Specifically, the CMB had a more intricate network of the degrading bacteria with the three keystone genera viz. Acidothermus sp., Sphingomonas sp., and Blastococcus sp., whereas, the CK had a simple network with Sphingomonas sp. as the keystone genus. Overall, the biochar amendment accelerated the removal of tetracyclines and their epimers through the enrichment of potential tetracycline degrading bacteria in the soil; thus, it can be applied for the in situ remediation of soils contaminated with tetracyclines.

Review of organic and inorganic pollutants removal by biochar and biochar-based composites

Biochar (BC) has exhibited a great potential to remove water contaminants due to its wide availability of raw materials, high surface area, developed pore structure, and low cost. However, the application of BC for water remediation has many limitations. Driven by the intense desire of overcoming unfavorable factors, a growing number of researchers have carried out to produce BC-based composite materials, which not only improved the physicochemical properties of BC, but also obtained a new composite material which combined the advantages of BC and other materials. This article reviewed previous researches on BC and BC-based composite materials, and discussed in terms of the preparation methods, the physicochemical properties, the performance of contaminant removal, and underlying adsorption mechanisms. Then the recent research progress in the removal of inorganic and organic contaminants by BC and BC-based materials was also systematically reviewed. Although BC-based composite materials have shown high performance in inorganic or organic pollutants removal, the potential risks (such as stability and biological toxicity) still need to be noticed and further study. At the end of this review, future prospects for the synthesis and application of BC and BC-based materials were proposed. This review will help the new researchers systematically understand the research progress of BC and BC-based composite materials in environmental remediation.

Adsorptive removal of crude petroleum oil from water using floating pinewood biochar decorated with coconut oil-derived fatty acids

The present investigation deals with the adsorptive removal of crude petroleum oil from the water surface using coconut oil-modified pinewood biochar. Biochar generated at higher pyrolysis temperature (700 °C) revealed higher fatty acid-binding efficiency responsible for the excellent hydrophobicity of the biochar. Fatty acids composition attached to the biochar produced at 700 °C was (mg g^-1 BC) lauric acid (9.024), myristic acid (5.065), palmitic acid (2.769), capric acid (1.639), oleic acid (1.362), stearic acid (1.114), and linoleic acid (0.130). Simulation of the experimental adsorption data of pristine and modified pinewood biochar generated at 700 °C offered the best fit to pseudo-first-order kinetics (R² > 0.97) and Langmuir isotherm model (R² > 0.99) based on the highest regression coefficients. Consequently, the adsorption process was mainly driven by surface hydrophobic interactions including π-π electron-donor-acceptor between electron-rich (π-donor) polycyclic aromatic hydrocarbons from the crude oil and biochar (π-acceptor). A maximum adsorption capacity (Q_max) of 5.315 g g^-1 was achieved by modified floating biochar within 60 min. Whereas the reusability testing revealed 49.39% and 51.40% was the adsorption efficiency of pristine and modified biochar at the fifth adsorption-desorption cycle.

Superhydrophobic-superoleophilic biochar-based foam for high-efficiency and repeatable oil-water separation

Leakage accidents occurring during oil production and transportation are currently one of the most serious environmental problems worldwide. Developing efficient and environmentally friendly oil-water separation methods is the key to solve this problem. In this work, a facile method to fabricate a high-performance oil absorbent through the loading of ball-milled biochar (BMBC) and octadecylamine on the skeleton of melamine foam (MF) is reported. The resulting ball-milled biochar-based MF (BMBC@MF) displayed a complex three-dimensional porous structure. The BM biochar on the surface of BMBC@MF forms nano/μm-scale folds, which reduced the surface energy of BMBC@MF after grafted octadecylamine. These structures resulted in the conversion of the hydrophilic surface of MF to hydrophobic surface. These characteristics made the modified foam an excellent oil absorbent with a high oil absorption capacity (43-155 times its own weight) and extraordinary recyclability. Furthermore, the BMBC@MF could maintain high hydrophobicity and adsorption stability in a wide pH range (from 1 to 11). More importantly, BM biochar is a cheap and readily available material to make BMBC@MF possible for large-scale production. Therefore, this work provides an effective way for low-cost, environmentally friendly, and large-scale production of superhydrophobic adsorbents for oil-water separation.

Combined Effects of Microplastics and Biochar on the Removal of Polycyclic Aromatic Hydrocarbons and Phthalate Esters and Its Potential Microbial Ecological Mechanism

Microplastics (MPs) have been attracting wide attention. Biochar (BC) application could improve the soil quality in the contaminated soil. Currently, most studies focused on the effect of MPs or BC on the soil properties and microbial community, while they neglected the combined effects. This study investigated the combined effects of BC or ball-milled BC (BM) and polyethylene plastic fragments (PEPFs) and degradable plastic fragments (DPFs) on the removal of polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) from the PAH-contaminated soil and the potential microbial ecological mechanisms. The results showed that BC or BM combined with PEPF could accelerate the removal of PAHs and PAEs. PEPF combined with BM had the most significant effect on the removal of PAHs. Our results indicating two potential possible reasons contribute to increasing the removal of organic pollutants: (1) the high sorption rate on the PEPF and BC and (2) the increased PAH-degrader or PAE-degrader abundance for the removal of organic pollutants.

THE DARK SIDE OF BLACK GOLD: Ecotoxicological aspects of biochar and biochar-amended soils

Biochar, a product of biomass pyrolysis, is characterized by significant surface area, porosity, high water holding capacity, and environmental persistence. It is perceived as a material that can counteract climate change due to its high carbon stability and is also considered suitable for soil amendment (fertility improvement, soil remediation). However, biochar can have a toxic effect on organisms as harmful substances may be present in it. This paper reviews the literature regarding the current knowledge of harmful substances in biochar and their potential negative impact on organisms from different trophic levels. The effects of biochar on the content and toxicity of harmful substances in biochar-amended soils are also reviewed. Application of biochar into soil does not usually have a toxic effect and very often stimulate plants, bacteria activity and invertebrates. The effect however is strictly determined by type of biochar (especially the feedstock used and pyrolysis temperature) as well as contaminants content. The pH, electrical conductivity, polycyclic aromatic hydrocarbons as well as heavy metals are the main factor usually responsible for biochar toxicity.

High pyrolysis temperature biochar reduced the transport of petroleum degradation bacteria Corynebacterium variabile HRJ4 in porous media

Biochar has been widely applied for the remediation of petroleum-contaminated soil. However, the effect of biochar on the transport of petroleum degradation bacteria has not been studied. A typical Gram-positive petroleum degradation bacteria-Corynebacterium variabile HRJ4 was used to study the effect of different biochars on bacterial transport and retention. Results indicated that the addition of biochar in sand was effective for reducing the transport of bacteria and poplar sawdust biochar (PSBC) had a stronger hinder effect than corn straw biochar (CSBC). The hindrance was more evident with pyrolysis temperature of biochar raised from 300°C to 600°C, which was attributed to the increase of specific surface area (309 times). The hindrance effect also enhanced with higher application rate of biochar. Furthermore, the reduction of HRJ4 transport was more obvious in higher (25 mmol/L) concentration of NaCl solution owing to electrostatic attraction enhancement. The adsorption of biochar to HRJ4 was defined to contribute to the hindrance of HRJ4 transport mainly. Combining the influence of feedstocks and pyrolysis temperature on HRJ4 transport, it suggested that specific surface area had the greatest effect on HRJ4 transport, and pore-filling, electrostatic force also contributed to HRJ4 retained in quartz sand column. At last, phenol transportation experiment indicated that the restriction of biochar on HRJ4 enhanced the phenol removal rate in the column. This study provides a theoretical basis for the interaction of biochar and bacteria, which is vital for the remediation of oil-contaminated soil and groundwater in the field.