In a study published in Molecules, researchers Sylwia Stegenta-Dąbrowska, Marta Galik, Magdalena Bednik-Dudek, Ewa Syguła, and Katarzyna Ewa Kosiorowska explored the potential of using mature compost as a feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More for producing biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More to capture and separate gases. While previous research has focused on pure gases or simple mixtures, this study addressed a critical knowledge gap by testing biochar’s performance against a complex gas mixture that simulates real-world composting emissions, including carbon dioxide (CO2​), carbon monoxide (CO), hydrogen sulfide (H2​S), ammonia (NH3​), and methane (CH4​).

The researchers produced biochar by pyrolyzing mature compost at various temperatures from 400°C to 650°C, with heating rates of 10°C, 15°C, or 20°C per minute. The team’s findings reveal a strong correlation between the pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperature and the sorption characteristics of the resulting biochars. Biochars produced at higher temperatures (550°C, 600°C, and 650°C) with a heating rate of 10°C per minute were most effective at reducing emissions of CO2​, CH4​, and H2​S, achieving reductions of 69%, 69%, and 72%, respectively. This enhanced performance is linked to the increased surface area and the formation of microporous structures at higher temperatures. The highest specific surface area of 39.2 m²/g was observed in biochar produced at 650°C. This is modest compared to commercial activated carbons but represents a reasonable performance for a sustainable, waste-derived material.

In contrast, the same high-temperature biochars were less effective at adsorbing CO and NH3​. The highest CO adsorption was found in biochars produced at lower temperatures, specifically 400°C and 450°C. The 400°C variant showed the highest CO reduction, ranging from 46% to 50%. Similarly, lower temperatures, particularly around 400°C, led to superior NH3​ adsorption, with the 450°C variant initially adsorbing 87% of the gas. The different adsorption behaviors are due to varying mechanisms: CO2​ and H2​S primarily undergo physical adsorption, which is enhanced by a higher surface area, and chemisorption with basic metal oxides that concentrate at higher temperatures. However, CO and NH3​ require oxygen-containing functional groups for chemical interaction, and these groups are more abundant in biochars produced at lower pyrolysis temperatures and slower heating rates, as confirmed by FTIR analysis.

The study also assessed the economic viability of the process. Producing one ton of biochar from compost at 550°C requires 1.197 tons of compost and 287 MJ of external energy. The research suggests that the energy contained in the gas generated during the pyrolysis process could be reused to improve the system’s efficiency, for example, for drying the substrate. This dual benefit of addressing waste management challenges while creating a sustainable gas cleaning technology makes compost-derived biochar an attractive material for industrial-scale applications. The researchers conclude that while compost biochar’s high CH4​ sorption capacity makes it better suited for mitigating emissions during composting, it also shows strong potential for a variety of gas adsorption applications.

Source: Stegenta-Dąbrowska, S., Galik, M., Bednik-Dudek, M., Syguła, E., & Kosiorowska, K. E. (2025). Applying Compost Biochar for Gas Adsorption—Effects of Pyrolysis ConditionsThe conditions under which pyrolysis takes place, such as temperature, heating rate, and residence time, can significantly affect the properties of the biochar produced.   More. Molecules, 30(16), 3365.