Turning biogas waste into a powerful tool for cleaning ammonium pollution

Researchers in China have developed a modified biochar made from biogas residue that can efficiently remove ammonium nitrogen from water, offering a low-cost and sustainable solution to agricultural pollution.

Ammonium nitrogen, a common pollutant from fertilizers and livestock operations, often leaches into waterways, contributing to eutrophication and groundwater contamination. Using biochar—a carbon-rich material produced by heating organic waste—scientists have long sought to trap these pollutants before they reach the environment. However, traditional biochar has shown limited adsorption capacity.

A new study published in Biochar reports that chemical modification of biogas residue biochar using potassium permanganate, hydrogen peroxide, and sodium hydroxide dramatically enhances its ability to capture ammonium. The team led by Dr. Xuebo Zheng and Dr. Wenjing Song at the Tobacco Research Institute, Chinese Academy of Agricultural Sciences, found that potassium-permanganate-modified biochar achieved an adsorption capacity up to four times greater than unmodified biochar.

“By improving the pore structure and surface chemistry of biochar, we created more active sites for ammonium ions to attach,” said Dr. Zheng. “This simple modification transforms agricultural waste into an efficient adsorbent for water purification.”

Microscopic analysis revealed that potassium permanganate treatment produced a richer network of micro- and mesopores, substantially increasing surface area and enhancing pore-based adsorption. In contrast, hydrogen peroxide and sodium hydroxide primarily boosted oxygen-containing functional groups on the biochar surface, contributing to electrostatic attraction of ammonium ions.

Among all treatments, the potassium permanganate-modified biochar showed the highest performance, achieving a maximum adsorption capacity of 68.15 milligrams per gram under laboratory conditions. This improvement highlights the importance of optimizing pore structure over merely increasing surface functional groups.

The findings demonstrate a promising strategy to recycle biogas residues—a byproduct of renewable energy production—into high-value materials for environmental remediation. “Our work offers a pathway to manage waste and mitigate water pollution at the same time,” said Dr. Song.

The research underscores how small chemical changes to biochar can significantly influence its environmental applications. With further testing in field conditions, the modified biogas residue biochar could provide farmers and wastewater managers a practical tool to prevent nitrogen loss and protect freshwater ecosystems.

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Journal Reference: Cong, P., Song, S., Zhu, Y. et al. Improved adsorption capacity of ammonium from aqueous solution by modified biogas residue biochar. Biochar 7, 97 (2025). https://doi.org/10.1007/s42773-025-00500-z 

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About Biochar

Biochar 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. 

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