Removal of gaseous volatile organic compounds using zinc chloride-activated cattle manure-derived biochar

Abstract

This study investigates the adsorption performance of cattle manure-derived biochar for volatile organic compound (VOC) removal in a continuous-flow column system. ZnCl₂ pretreatment followed by the pyrolysis at 600 °C produced the most significant increases in both specific surface area and adsorption capacity, as ZnCl₂-enabled dehydration/aromatization, volatilization during pyrolysis, and subsequent ash removal by acid washing collectively developed micropores. The resultant biochar possessed abundant micropores that favor physisorption-dominated VOC uptake through van der Waals interactions and pore filling. As the pyrolysis temperature increased, the unused bed length decreased, indicating improved adsorption efficiency and bed utilization. Kinetic fitting revealed that the intraparticle diffusion model provided the best agreement, confirming that physical adsorption controlled by pore diffusion is the governing mechanism. The Yoon–Nelson and Thomas models precisely predicted the 50 % breakthrough time (τ) and equilibrium adsorption capacity (qₑ), validating their applicability for column design and process scale-up. Moreover, a 10 g biochar column sustained sub-breakthrough VOC concentrations for over two days, demonstrating robust long-term adsorption stability. Overall, these findings highlight that waste-derived ZnCl₂-activated biochar can serve as a sustainable, high-performance, and viable adsorbent for on-site air quality management in livestock environments.