Enhancing compost maturity with biochar: A global meta-analysis reveals key factors
Maximum Academic Press
However, the varied physicochemical properties of biochar and the complexity of composting conditions have led to inconsistent results regarding its effectiveness. A new global meta-analysis of 125 studies offers critical insights into how biochar properties influence compost maturation, gas emissions, and nutrient dynamics. This research aims to provide practical guidelines for optimizing composting strategies by integrating biochar into the process.
Composting, a biotechnological process for organic waste management, faces challenges like inconsistent quality, prolonged processing times, and significant greenhouse gas emissions. The addition of exogenous materials, such as biochar, has gained attention for its ability to enhance composting outcomes by improving microbial habitats, reducing emissions, and speeding up organic matter degradation. Despite these benefits, the effects of biochar on composting vary significantly due to differences in biochar properties, such as feedstock type, pyrolysis temperature, and particle size, as well as initial composting conditions, including C/N ratio and moisture content. This meta-analysis synthesizes 269 observations from 125 studies to clarify these complex interactions and identify the most influential factors.
A study (DOI:10.48130/bchax-0025-0005) published in Biochar X on 16 October 2025 by Fei Shen’s team, Sichuan Agricultural University, highlights the critical role of biochar in enhancing composting efficiency, improving compost quality, and mitigating greenhouse gas emissions.
This study conducted a meta-analysis to examine the impact of biochar properties and initial compost parameters on compost maturation, utilizing 269 observations from 125 peer-reviewed studies. The heterogeneity analysis showed significant between-group differences (p < 0.05), indicating variability in composting outcomes across different biochar properties and conditions. The results also revealed the presence of publication bias, particularly related to biochar size, which influenced gas emissions like CO2, CH4, and N2O, while biochar pH mainly affected N2O emissions. Despite these biases, the analysis maintained reliability, with Pearson correlation analysis confirming that biochar properties—such as feedstock type, pyrolysis temperature, pore volume (PV), and surface area—had significant effects on compost maturity indicators, including the C/N ratio, germination index (GI), and nitrogen content (NH4+−N, NO3−−N). Biochar's role in reducing greenhouse gas emissions was also emphasized, with significant reductions observed in CH4 (51.31%), N2O (43.49%), and NH3 (47.59%). Structural equation modeling (SEM) further highlighted that biochar's PV, feedstock type, and amendment rate were crucial in optimizing composting efficiency, particularly with straw-derived biochar and higher amendment rates (>12%). These findings provide a comprehensive framework for selecting biochar properties and adjusting composting conditions to enhance compost quality and environmental sustainability. The research underscores the importance of biochar in improving composting performance and suggests that future studies should focus on refining data quality and considering additional maturity indicators for more robust conclusions.
This research provides valuable guidelines for optimizing composting processes. By selecting biochar with specific properties—such as straw-based feedstock, a pyrolysis temperature above 400°C, and a high amendment rate—compost producers can enhance the quality and efficiency of their products. The reduction in greenhouse gas emissions during composting not only makes the process more environmentally friendly but also improves the sustainability of waste management systems. These findings are crucial for municipal waste management facilities and agricultural composting operations looking to improve compost quality and reduce environmental impact.
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References
DOI
Original Source URL
https:///doi.org/10.48130/bchax-0025-0005
Funding information
The authors acknowledge funding provided by the National Key Research and Development Program of China - Key Technologies and Equipment for Collaborative Emission Reduction of Ammonia/Greenhouse Gases and New Pollutants (Grant No. 2023YFD1701600).
About Biochar X
Biochar X is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
A holistic assessment of biochar amendment effects on compost maturation: a meta-analysis
Iron fortified hemp biochar helps keep “forever chemicals” out of radishes and the food chain
image:
Iron-fortified hemp-derived biochar reduces per- and poly-fluoroalkyl substances bioaccumulation in radish (Raphanus sativus L.)
view moreCredit: Trung Huu Bui, Mandeep Kaur, Nubia Zuverza-Mena, Sara L. Nason, Christian O. Dimkpa, Jasmine P. Jones & Jason C. White
Iron fortified hemp biochar made from agricultural waste can significantly cut the amount of “forever chemicals” that move from contaminated soil into food crops, according to a new study on radishes grown in PFAS polluted soil.
Plain language overview
Per and polyfluoroalkyl substances (PFAS) are extremely persistent industrial chemicals that can move through soil, water and air and build up in crops and people. In this greenhouse study, researchers tested whether biochar made from hemp plants, and enhanced with iron, could lock PFAS in place and keep them out of edible radish bulbs. They found that iron fortified hemp biochar lowered PFAS levels in radish tissues and reduced overall plant uptake compared with unamended soil and with plain biochar.
What the researchers did
The team collected PFAS contaminated sandy loam soil from a former firefighting training area in Connecticut, where long term use of aqueous film forming foams had left high concentrations of PFOS and related PFAS. They produced biochar from hemp stems and leaves at different temperatures between 500 and 800 degrees Celsius, with some batches “fortified” by soaking the biomass in an iron sulfate solution before pyrolysis to create iron rich sorption sites.
After characterizing surface area, pore structure, and mineral content, the researchers mixed selected biochars into the contaminated soil at low application rates of 2 or 5 percent by weight and incubated the mixtures for 90 days to allow PFAS to interact with the sorbents. Radish seedlings were then grown for four weeks in amended and unamended soils, and PFAS were measured in soil leachates, shoots and edible bulbs using high sensitivity liquid chromatography–mass spectrometry.
Key findings
Soil at the field site contained about 576 nanograms of total PFAS per gram, dominated by PFOS which contributed roughly 60 percent of the total burden. Biochar made at the lowest temperature (500 degrees Celsius) had the highest specific surface area and more oxygen containing functional groups, which favored PFAS retention compared with material made at higher temperatures. Fortifying biochar with iron further increased surface area and pore volume and introduced iron oxide and hydroxide sites that can attract anionic PFAS molecules.
Across all treatments, radishes grown in the contaminated soil without amendments showed strong accumulation of short chain PFAS, with bioaccumulation factors above 1 and particularly high values for short chain carboxylic and sulfonic acids. When the soil was amended with iron fortified hemp biochar produced at 500 degrees, total PFAS in whole radish plants dropped by about 37 percent compared with unamended soil, and by nearly 46 percent relative to plants grown with non fortified biochar. In the edible bulb, iron fortified biochar cut PFAS bioaccumulation by about 25.7 percent and produced especially large reductions for several short chain sulfonic and carboxylic acids.
Why iron fortified hemp biochar works
Analyses showed that increasing pyrolysis temperature shrank the biochar’s surface area and pore volume and reduced the abundance of reactive surface functional groups, all of which limited PFAS sorption. In contrast, iron fortification boosted porosity and created additional positively charged and hydrophilic sites that support electrostatic attraction, ligand exchange, hydrogen bonding and complex formation with PFAS head groups while maintaining a hydrophobic carbon backbone that interacts with the fluorinated chains. The authors conclude that this combination of physical and chemical mechanisms allows iron fortified hemp biochar to hold PFAS more strongly in soil pore spaces, lowering the freely dissolved fraction available for plant uptake.
Public health and environmental significance
The study highlights that even root vegetables like radish can accumulate substantial amounts of short chain PFAS when grown in contaminated fields, raising concerns for food safety in affected farming regions. By demonstrating that a relatively low dose of iron enriched biochar made from an agricultural residue can both improve soil properties and reduce PFAS transfer into edible tissues, the work points to a practical soil management strategy for reducing PFAS exposure through diet. The authors note that future research should examine long term field performance, potential effects on soil microbes and PFAS transformation, and whether similar approaches can protect other crop species and soils with different PFAS mixtures.
Sample author quote for media use
“PFAS do not simply disappear once they reach farmland, and our results show that they can move efficiently from soil into the foods we grow,” said lead author Trung Huu Bui. “Iron fortified hemp biochar offers a promising way to trap these contaminants in the soil and reduce their entry into the food chain without sacrificing plant growth.”
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Journal reference: Bui TH, Kaur M, Zuverza-Mena N, Nason SL, Dimkpa CO, et al. 2025. Iron-fortified hemp-derived biochar reduces per- and poly-fluoroalkyl substances bioaccumulation in radish (Raphanus sativus L.). Environmental and Biogeochemical Processes 1: e010
https://www.maxapress.com/article/doi/10.48130/ebp-0025-0010
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About the Journal:
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
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Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Iron-fortified hemp-derived biochar reduces per- and poly-fluoroalkyl substances bioaccumulation in radish (Raphanus sativus L.)
Unlocking the strength of biochar: Understanding the mechanical anisotropy of monolithic biochar for advanced applications
Maximum Academic Press
This study introduces a multiscale hardness analysis of crack-free monolithic biochar derived from seven wood species pyrolyzed at temperatures ranging from 600 to 1,000 °C.
Biochar, a carbon-based material derived from sustainable biomass, has been increasingly explored for applications in energy storage, water purification, and structural composites. While biochar’s environmental and chemical properties have been widely studied, existing research predominantly focuses on powdered biochar, neglecting the role of its inherent hierarchical architecture. This oversight limits the material’s application in next-generation technologies that demand directional mechanical performance, such as structural composites and flow-through systems. Monolithic biochar, which preserves the natural wood structure, holds unique potential due to its anisotropic mechanical properties—characteristics that arise from the alignment and compaction of carbonized cell walls during pyrolysis. Yet, the understanding of how these properties vary with different wood species and pyrolysis conditions has been underexplored, especially in terms of their nanoscale and macroscale behavior.
A study (DOI:10.48130/bchax-0025-0007) published in Biochar X on 21 October 2025 by Charles Q. Jia’s team, University of Toronto, represents a significant step forward in the design and application of biochar as a versatile material for structural, energy, and environmental technologies.
This study investigates the temperature-dependent hardness anisotropy of biochar derived from various wood species, subjected to pyrolysis at temperatures of 600, 800, and 1,000 °C. The researchers employed micro- and nano-indentation techniques to measure hardness in both axial and transverse directions across biochar samples from maple, pine, hemlock, bamboo, redwood, African ironwood, and yew. The results show that the hardness of both maple and pine biochar increases with pyrolysis temperature. At 600 °C, the hardness values are low due to incomplete carbonization, as the cellular framework remains partially intact. As the temperature rises to 800 °C and 1,000 °C, the hardness significantly increases, reflecting the enhanced carbonization and formation of a more crystalline carbon network. Notably, the axial hardness consistently exceeds transverse hardness across all species and temperatures, with the difference becoming more pronounced at higher pyrolysis temperatures. This increased anisotropy is due to the preferential alignment of carbon structures along the axial direction. For example, at 1,000 °C, the axial hardness of maple biochar nearly doubles compared to 600 °C, emphasizing the impact of pyrolysis temperature on mechanical properties. Furthermore, the study finds that the hardness values vary significantly across wood species at 1,000 °C, with African ironwood exhibiting the highest hardness values in both directions, and hemlock showing the lowest hardness overall. The study also identifies a strong correlation between bulk density and hardness, particularly in the axial direction (R² = 0.84), highlighting the role of density in controlling hardness. Additionally, the carbon fraction, determined through SEM analysis, correlates with increased axial hardness, reinforcing the importance of carbon content in enhancing the material's mechanical strength.
The study provides valuable insights into controlling and enhancing the mechanical performance of monolithic biochar. By optimizing pyrolysis temperatures and selecting appropriate feedstocks, biochar can be tailored for various applications, such as ultra-hard biochar for robust electrodes or structural components that require high load-bearing capacity, and highly anisotropic biochar for directional-flow filters or composites that demand strength along specific axes. This research paves the way for integrating biochar into next-generation technologies, ranging from energy storage devices to environmental filtration systems, by leveraging its unique mechanical properties.
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References
DOI
Original Source URL
https://doi.org/10.48130/bchax-0025-0007
Funding information
This work was supported by the Natural Science and Engineering Research Council of Canada (NSERC), and the Low Carbon Renewable Materials Centre at the University of Toronto.
About Biochar X
Biochar X is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Unlocking extreme anisotropy in monolithic biochar hardness
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