Valorization of agricultural residues through their transformation into sustainable filters for water treatment

The sustainable management of escalating volumes of organic waste, alongside the mitigation of air, soil, and water pollution, presents a critical global environmental challenge. Agriculture plays a pivotal role in addressing these issues. Within this context, the current study investigates the valorisation of abundant agricultural by-products by transforming them into activated carbon (AC), a versatile material for remediating water contaminated with both organic and inorganic pollutants.

Rice husks (RH) and almond shells (AS) were selected as feedstock owing to their availability and transformative potential. They underwent pyrolysis and subsequently activated using chemical (potassium hydroxide, KOH) and physical (water vapour) methods to enhance their adsorption properties. The characterisation of these materials revealed favourable physicochemical properties, including an alkaline pH, substantial water retention capacity, high carbon content, and an elevated iodine adsorption index. Physical activation of pyrolysed RH significantly increased the specific surface area (SSA-BET), achieving values up to 600 m²/g.

The efficacy of the derived ACs was assessed through adsorption experiments targeting pharmaceutical contaminants, specifically anti-inflammatory drugs and antibiotics. ACs derived from RH achieved complete removal (up to 100%) of these persistent pollutants, performing comparably to commercial activated carbons. Furthermore, the study explored the adsorption of heavy metals, confirming the efficacy of these materials in sequestering inorganic pollutants from aqueous systems. These findings highlight the potential of agricultural waste-derived ACs for dual-purpose applications in treating both organic and inorganic contaminants in wastewater.

Acknowledgements:

This study received financial support in the framework of the Project RICERES4CHANGE (grant TED2021-130964B-I00), by the Spanish Ministry of Science, the Spanish Agency of Research (MCIN/AEI/10.13039/501100011033) and the European Union (Next Generation EU/PRTR funding). A. Sánchez-Martín thanks The Spanish Ministry of Science and Innovation (MICIN) for her contract as Technical Support Personnel (PTA2021-020000-I). M. Arenas and Sergio Gómez are thanked for this technical and analytical support.