Waste-derived biochar could help remove troublesome natural organic matter from water
image: Review of modified biochar for removing humic acid from water: analysis of structure-activity relationship
Credit: Yiting Li, Ying Zhu, Jianguo Liu, Wenhong Fan, Yingnan Cao, Yaoqiang Huo & Jingting Wei
Humic acid is a common part of natural organic matter in rivers, lakes, groundwater, and wastewater. Although it comes from the natural decomposition of plant and animal residues, too much humic acid in water can create serious challenges for water treatment. It can affect the color, taste, and smell of drinking water, bind with metals, promote corrosion in pipe networks, and react with chlorine during disinfection to form potentially harmful byproducts such as trihalomethanes and haloacetic acids.
A review published in Biochar examines how biochar and modified biochar can be used to remove humic acid from water. The article, “Review of modified biochar for removing humic acid from water: analysis of structure-activity relationship,” summarizes recent progress in adsorption, Fenton reactions, photocatalysis, electrochemical oxidation, and combined treatment methods.
Biochar is a carbon-rich material produced by heating biomass, such as agricultural waste, forestry residues, food waste, or sludge, under low-oxygen conditions. Because it can be made from abundant waste resources, biochar offers a low-cost and potentially sustainable tool for water purification. Its porous structure and surface chemical groups allow it to trap pollutants, while further modification can improve its adsorption and catalytic performance.
“Humic acid is difficult to remove because it has a complex and variable structure,” said corresponding author Ying Zhu. “Our review shows that modified biochar can be designed to target humic acid through both adsorption and oxidative degradation, providing a promising pathway for cleaner and safer water treatment.”
The review explains that the performance of biochar depends strongly on its source material, pyrolysis temperature, and modification strategy. Biochars made from different biomass sources can vary widely in pore structure, aromaticity, ash content, and surface functional groups. Higher pyrolysis temperatures often improve pore development and surface area, which can enhance humic acid adsorption. Modification with metals, metal oxides, acids, alkalis, or polymers can further tune the surface charge, active sites, and catalytic properties of biochar.
According to the review, humic acid can be adsorbed by biochar through several mechanisms, including pore filling, electrostatic interactions, pi-pi stacking, and hydrogen bonding. However, adsorption alone may not fully solve the problem because humic acid can desorb once equilibrium is reached. For this reason, researchers are increasingly exploring biochar-assisted oxidation methods.
In Fenton and Fenton-like systems, modified biochar can help generate highly reactive species such as hydroxyl radicals and sulfate radicals, which attack and degrade humic acid molecules. In photocatalytic systems, biochar can improve light-driven electron transfer and support the formation of reactive oxygen species. In electrochemical systems, biochar-based electrodes can combine adsorption with oxidation, helping mineralize humic acid into carbon dioxide and water. Synergistic systems that combine adsorption with advanced oxidation processes may offer even higher removal efficiency.
The authors also emphasize that practical application requires careful safety evaluation. Some biochars may contain potentially toxic elements or generate harmful byproducts during pyrolysis. More research is also needed on the recycling, regeneration, and safe disposal of spent biochar after water treatment.
“Biochar-based materials show great potential because they can turn waste into a useful water treatment resource,” Zhu said. “The next step is to develop safer, more efficient, and recyclable modified biochars that can work in real water systems.”
The review provides a framework for understanding how biochar structure controls humic acid removal and offers guidance for designing multifunctional biochar materials for future water purification technologies.
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Journal Reference: Li, Y., Zhu, Y., Liu, J. et al. Review of modified biochar for removing humic acid from water: analysis of structure-activity relationship. Biochar 7, 1 (2025).
https://doi.org/10.1007/s42773-024-00387-2
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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.