Adsorption of organic micropollutants on biogenic activated carbon: Potential of kitchen waste and woody residues as feedstocks for advanced wastewater treatment

The removal of organic micropollutants (OMPs) in wastewater treatment is crucial for protecting aquatic ecosystems. However, conventional powdered activated carbons (PACs) are typically derived from fossil sources. Utilising biogenic residues as feedstock for PAC production could support a circular carbon economy and contribute to negative greenhouse gas emissions. Yet, the adsorption behaviour of OMPs on biogenic activated carbon (bPAC) remains insufficiently understood. In this study, bPACs were produced from kitchen waste and hedge trimming under varying production conditions, including steam activation, pyrolysis time and pre-treatment, and were compared with two fossil-based PACs. Elemental composition and surface area were characterised including methylene blue number, iodine number and nitrogen gas adsorption. Adsorption experiments with model compounds (nitrobenzene, benzotriazole) and municipal wastewater including different OMPs were conducted. Despite lower maximum specific surface areas (685 m²/g for hedge trimming, 396 m²/g for kitchen waste) and high ash contents (around 20-50 %), bPACs exhibited satisfactory OMP adsorption. To achieve comparable performance to fossil PAC, 0.6-1.5 times the amount of hedge trimming based bPAC and 2.2-3.4 times the amount of kitchen waste based bPAC were required. Beyond surface area, surface chemistry was identified as a key factor influencing adsorption efficiency. A case study examining local availability showed that, even in an urban area, woody residues could meet the local demand for bPAC, whereas kitchen waste availability was a limiting factor. Overall, biogenic residues represent a viable alternative to fossil PAC, though adsorption performance cannot be reliably predicted by surface characterisation alone.