As the world searches for better ways to manage waste biomass and clean up polluted environments, a growing body of research is focusing on biochar, a carbon-rich material made by heating organic waste in low-oxygen conditions. A new review published in Biochar offers a comprehensive comparison of conventional pyrolysis and microwave-assisted pyrolysis, two major routes for producing biochar, and explains how the choice of heating method can shape biochar's structure, chemistry, and pollution-removal performance.
Biochar can be made from agricultural residues, forestry by-products, sewage sludge, animal manure, and other organic wastes. Instead of being burned or landfilled, these materials can be converted into porous carbon materials that help adsorb contaminants, improve soil quality, and store carbon. However, not all biochars are the same. Their effectiveness depends strongly on how they are produced.
"Biochar is not simply charcoal from waste. It is a tunable environmental material, and the production method determines how well it can capture pollutants, stabilize metals, and support circular resource use," said lead author Atta Rasool. "Our review shows that microwave-assisted pyrolysis offers unique opportunities to design biochars with more active surfaces and improved pore structures."
In conventional pyrolysis, heat is transferred from the outside of the biomass inward. This process is widely used and can produce stable biochar, but it often requires longer residence times and may create uneven heating across the material. Such thermal gradients can limit pore development and reduce certain surface functional groups that are important for pollutant binding.
By contrast, microwave-assisted pyrolysis uses electromagnetic energy to heat biomass volumetrically from within. This can accelerate thermal decomposition, reduce processing time, and promote more uniform pore formation. The review reports that microwave-derived biochars often show higher surface area, stronger mesoporosity, enhanced graphitization, and greater retention of oxygen-containing functional groups compared with conventionally produced biochars.
These structural differences matter for environmental cleanup. The review highlights multiple mechanisms by which biochar can capture or transform contaminants, including ion exchange, electrostatic attraction, surface complexation, precipitation, redox reactions, hydrogen bonding, hydrophobic interactions, and physical entrapment. Microwave-derived biochars have shown promise for removing heavy metals such as Pb, Cd, Cu, Cr, and Tl, as well as organic pollutants including dyes, pharmaceuticals, phenols, pesticides, PFAS, and microplastics.
The authors also emphasize that biochar is more than a water-treatment material. Beyond remediation, it has potential roles in soil amendment, composting, catalysis, carbon sequestration, and electrode materials. These uses place biochar at the intersection of pollution control, waste valorization, and climate action.
However, the review cautions that microwave-assisted pyrolysis is not yet a plug-and-play solution for industry. Key challenges remain, including reactor scale-up, non-uniform electromagnetic fields, hotspot formation, feedstock variability, energy balance, safety design, and the need for more life cycle and techno-economic assessments.
"Microwave-assisted pyrolysis is promising, but its benefits must be proven under realistic operating conditions," Rasool said. "Future work should connect reactor design, biochar structure, contaminant-removal mechanisms, regeneration, and long-term environmental safety."
By integrating production methods, material properties, adsorption mechanisms, and application prospects, the review provides a roadmap for developing next-generation biochars that can help address waste disposal, water pollution, soil contamination, and carbon-neutral resource recovery.
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Journal Reference: Rasool, A., Brožová, K., Chromíková, J. et al. Conventional and microwave-assisted pyrolysis biochars: comparative mechanistic insights, structural evolution, and environmental remediation applications. Biochar 8, 98 (2026).
https://doi.org/10.1007/s42773-026-00601-3
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
