Valorization of pyroligneous acids from agricultural waste: Assessment of their potential use as organic herbicide

Agricultural waste is produced in significant quantities worldwide, with 258 million tons of crop residues generated annually in the European Union alone. Improper management of these residues can result in environmental issues, including soil and water contamination and greenhouse gas emissions, exacerbating climate change. Pyrolysis of residual biomass offers a sustainable solution by converting agricultural waste into valuable products: syngas (a methane-rich gas), biochar (a porous carbonaceous solid), bio-oil, and pyroligneous acid (also called wood vinegar). While syngas and biochar have well-established applications, pyroligneous acid, remains underutilized, with its agricultural potential still being explored.

This study investigates the properties and composition of pyroligneous acid obtained from the pyrolysis of mixed wood biomass, abundant in Mediterranean agriculture. The biomass was pyrolyzed at 500 °C in a continuous-feed cylindrical reactor at the Euthenia Energy Center (Puente Genil, Spain). For comparison, a commercial organic herbicide was also used. Physical properties (pH, electrical conductivity, density, and dry residue) were measured, while elemental composition (carbon and nitrogen) was determined using a TOC analyzer. Nutrients, micronutrients, and toxic elements were quantified via ICP-OES, and organic molecular composition was assessed using GC/MS.

To evaluate its potential agronomic use as herbicide, germination tests were conducted with Lepidium sativum seeds exposed to varying pyroligneous acid concentrations (0%, 25%, 50%, 100%). Preliminary results reveal the absence of persistent contaminants and significant reductions in seed germination, highlighting its potential as a natural herbicide. Current field trials aim to confirm these findings under real-world conditions. This research demonstrates a pathway for agricultural waste valorization, aligning with circular economy principles and promoting sustainable agricultural practices.

Acknowledgements: This study received support of the Projects RES2SOIL (PID2021-126349OB-C22) and RICE4CHANGE (grant TED2021-130964B-I00) funded by the Spanish Agency of Research (MCIN/AEI/10.13039/501100011033) and the European Union (Next Generation EU/PRTR funding). We also appreciate the support from the Junta de Andalucía, the EU (EAFRD), and the AEI association through the Operative Group Resioliva (agreement GOPO-CO-23-0004). Euthenia Energy Center is acknowledged for its collaboration in this study.