A new study shows how leftover lavender distillation residue can be converted into useful biochar through a science-guided process that balances product quality, energy use, and environmental impacts.
Lavender is widely known for its essential oil, used in fragrances, foods, cosmetics, and traditional products. Yet the oil extraction process leaves behind large amounts of solid plant residue. Much of this material is burned, landfilled, or used in low-value applications, despite its potential as a renewable carbon resource.
Now, researchers have developed a mechanism-resolved framework to help turn this underused lavender waste into biochar, a carbon-rich material with potential uses in soil improvement, carbon storage, renewable solid fuels, and environmental applications.
The study, published in Biochar, evaluated how different pyrolysis conditions affect biochar production from lavender distillation residue. Pyrolysis is a heating process carried out in limited oxygen. The team tested 13 operating conditions under nitrogen, covering temperatures from 200 to 600 °C, heating rates from 10 to 40 °C per minute, and holding times from 0 to 30 minutes.
Rather than choosing the "best" condition only by looking at final biochar yield, the researchers connected thermal behavior, kinetic analysis, energy demand, and life-cycle environmental indicators into one decision framework.
"Lavender distillation residue is often treated as a waste, but it still contains a valuable lignocellulosic structure," said corresponding author Ahsanullah Soomro. "Our goal was to show not only that this residue can become biochar, but also how to choose production conditions in a transparent and defensible way."
The results showed a clear trade-off. Higher temperatures generally reduced biochar yield but increased fixed carbon, meaning the material became more carbonized and potentially more stable. Across the experimental matrix, final temperature was the dominant factor controlling this balance. For example, raising the temperature from 200 to 600 °C lowered yield while increasing fixed carbon, reflecting stronger devolatilization and carbon formation.
Thermogravimetric analysis revealed how the lavender residue decomposes during heating. The main decomposition peak shifted from about 327 to 364 °C as the heating rate increased from 5 to 40 °C per minute, showing that heating history strongly affects the thermal pathway. Kinetic analysis further indicated that activation energy remained relatively stable during early to mid conversion, then rose sharply at high conversion, consistent with late-stage carbonization and structural rearrangement.
The team also examined the resulting biochar using chemical and structural characterization. The optimized biochar showed strong carbon enrichment, reduced oxygen and hydrogen content, increased fixed carbon, and a higher heating value. Scanning electron microscopy showed that pyrolysis transformed the dense plant structure into a more porous carbon skeleton, while FTIR analysis confirmed the loss of oxygen-rich functional groups and growth of more aromatic carbon structures.
To support practical decision-making, the researchers applied entropy-weighted TOPSIS, a multi-criteria ranking method, using yield, fixed carbon, electricity intensity, and five Environmental Footprint 3.0 midpoint indicators. This analysis identified Run 5 as the best overall compromise, with 48.94% yield, 0.85 kWh per kg biochar, and 2.05 kWh per kg fixed carbon. When a minimum fixed carbon requirement of 60% was imposed, the preferred condition shifted to Run 4, which reached 61.67% fixed carbon.
"This approach helps avoid selecting conditions that look good by one metric but are less attractive when energy and environmental burdens are included," said Soomro. "It provides a pathway for designing biochar production that is both technically meaningful and sustainability-oriented."
The study offers a reproducible strategy for converting aromatic-plant residues into value-added carbon materials and may support circular bioeconomy efforts in regions where lavender processing generates large quantities of biomass waste.
By linking how biochar forms with how production choices affect energy and environmental performance, the work provides a practical roadmap for lavender-residue valorization.
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Journal Reference: Soomro, A., Koçer, A.T., Hassan, M. et al. Mechanism-resolved operating windows for biochar production from lavender distillation residue. Biochar 8, 105 (2026).
https://doi.org/10.1007/s42773-026-00617-9
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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.
