In a recent study published in Scientific Reports, Rafaela Jesus Paula and a team of researchers from Brazil investigated the industrial-scale conversion of urban green waste into biochar. Globally, cities generate an average of 47 kilograms of pruning waste per person every year, which is often simply dumped into landfills. This research utilized a pilot-scale continuous reactor to transform these neglected residues—consisting of tree trunks, branches, and leaves—into a stable carbon product. By heating this biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More under specific oxygen-free conditions, the team created a material that serves as both a powerful soil conditioner and a tool for fighting climate change.

The results highlight that urban pruning biochar possesses several unique characteristics that make it ideal for agricultural application. The final product, particularly the sample processed with larger particle sizes, showed a very high carbon content of nearly 71 percent and a low ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More fraction. Its alkaline nature makes it particularly effective at neutralizing acidic soils, while its porous structure acts like a sponge, enhancing water retention and providing a habitat for beneficial soil fungi. Furthermore, the study confirmed that this biochar meets strict international safety standards, showing no dangerous levels of heavy metals or organic contaminants.

Despite these clear benefits, the study also points out practical hurdles that must be addressed for large-scale adoption. The natural variety in the waste materials—ranging from fine leaves to thick trunks—can lead to inconsistencies in the biochar’s quality. Additionally, the logistics of collecting and transporting bulky pruning residues from across a city to a central processing facility remain a challenge. The researchers concluded that while urban pruning biochar is a safe and effective climate mitigation tool, future work must focus on optimizing the pre-screening of materials and conducting long-term field trials to prove its effectiveness across different types of crops and climates.

One of the most significant findings involves the long-term environmental impact of this technology. The researchers used thermal analysis to determine that the biochar has a “moderate” recalcitrance index of 0.5, which suggests it is highly resistant to natural decomposition. This stability allows the material to act as a carbon sink. Quantitatively, the team estimated that every single ton of this biochar could sequester approximately 1.62 tons of carbon dioxide equivalent over a 100-year period. This makes urban waste valorization a robust strategy for municipalities looking to reduce their carbon footprint while simultaneously supporting local agriculture.

Source: Jesus Paula, R., Almeida Pereira, V., Latorre, F. L., Souza, C., Almeida, I. A., Freitas e Silva, P. A., Ferreira, O. E., Lima, R. P., Bezerra, A. C. S., & Machado, A. R. T. (2025). 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 converts urban pruning waste into biochar with soil and climate benefits. Scientific Reports.