The global push toward a circular economy is driving researchers to find cost-effective methods for recycling industrial and agricultural waste. One widespread waste stream, agricultural biomass, offers tremendous potential as a raw material for producing value-added products like sorbents. Unfortunately, the common practice of incinerating this biomass negates this potential, wasting valuable resources. In an article for Scientific Reports, Maryna Zhylina, Denis Miroshnichenko, and colleagues detail their investigation into creating structurally optimized biochar from agricultural waste, specifically barley straw and bran. The goal was to demonstrate that controlled pyrolysis of pre-pelletized material could create effective sorbent precursors for water purification and environmental remediation.

The first step involved granulation to create durable pellets, a crucial pre-treatment step often overlooked in previous biochar research that traditionally used unprocessed or loose feedstocks. The study found that a composition of 90% barley straw and 10% barley bran (BSB) resulted in the most durable pellets, with intact pellets and no visible microcracks. Barley bran served as a natural binder, contributing polysaccharides and phenolics that aided in densification and improved mechanical strength without the need for chemical additives. This pre-pelletization is vital because carbon materials made from powdery biomass are typically fragile, have low bulk density, and are prone to attrition, making them unsuitable for continuous-flow systems like packed-bed columns and filtration systems. The dense, uniform pellets, by contrast, maintain their shape and integrity even after high-temperature treatment.

The researchers then performed slow pyrolysis on the BSB pellets, systematically testing three final temperatures—600^∘C, 700^∘C, and 800^∘C—each with holding times of one, two, and three hours. The primary objective was to observe how these thermal treatment parameters influenced the material’s pore structure development. The results demonstrated a clear, positive correlation between increasing temperature, extended holding time, and the resulting specific surface area (SBET​) and total pore volume. The most favorable structural development was consistently observed at 800^∘C. Raising the temperature dramatically increased the surface area and boosted the porosity. This suggests that extended thermal treatment facilitates the further rearrangement of the carbon matrix, promoting the formation of highly desirable microporous structures (pores less than 2 nanometers). This decrease in average pore size at higher temperatures is due to the intense devolatilization of organic compounds, leading to the collapse or narrowing of larger pores and the emergence of smaller, highly effective micropores. The study classified the resulting materials as micro- and mesoporous biochars, characterized by Type IV adsorption isotherms with hysteresis loops. Morphological analysis using SEM also confirmed that the 800^∘C pellets had a far more pronounced, porous structure than the 600^∘C samples, reinforcing the quantitative findings. While the study successfully produced biochar precursors with tailored, stable structures, the researchers acknowledge that the SBET​ values achieved are still far below those of high-performance sorbents obtained after chemical or steam activation.

Therefore, the next stage of the research will focus on activating the most promising pellets and directly testing their adsorption performance for contaminants like heavy metals and organic pollutants in real-world wastewater treatment applications. This integrated process—granulation, optimized pyrolysis, and activation—represents a robust, scalable, and environmentally sustainable pathway for valorizing agricultural waste and supporting the EU’s strategic vision for a low-carbon, circular bioeconomy.

Source: Zhylina, M., Miroshnichenko, D., Melnykov, A., Stepanova, V., Lazdovica, K., Zemcenkovs, V., Sterna, V., & Ozolins, J. (2025). Biochar structure development during slow pyrolysis of pellets from barley straw and bran. Scientific Reports, 15(42624).