Waste-to-resource pathway for sewage sludge: Ultra high-surface area activated carbon with net negative carbon...

Sewage sludge is an abundant byproduct of wastewater treatment that presents significant environmental challenges when managed through conventional disposal routes such as landfilling and incineration. In this work, high-surface-area activated carbon was synthesized from sewage sludge via controlled pyrolysis, rigorous chemical purification, and potassium hydroxide (KOH) activation. The resulting material exhibited a Brunauer-Emmett-Teller (BET) surface area of 1979 m²/g with a hierarchical pore structure comprising both micropores and mesopores. Characterization using thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and gas adsorption measurements confirmed effective removal of inorganic impurities and development of a porous carbon framework. Evolved gas analysis (EGA) revealed a multi-stage thermal decomposition process dominated by long-chain fatty acids and oxygenated hydrocarbons, indicating the presence of lipid-derived and polymeric components in the sludge. The adsorption performance was evaluated using representative pollutants, including dyes, pharmaceuticals, and herbicides, and the sewage sludge-derived activated carbon (SSAC) consistently outperformed a commercial activated carbon, attributed to its higher surface area, hierarchical porosity, and surface chemical heterogeneity. A cradle-to-gate life cycle assessment (LCA) showed that while the baseline production cost and carbon footprint were $13.77/kg and 26.36 kg CO₂e/kg, respectively, inclusion of avoided sludge disposal burdens reduced the cost to $6.12/kg and resulted in a net carbon footprint of -17.02 kg CO₂e/kg, indicating a carbon-negative process. These findings demonstrate a sustainable waste-to-resource pathway for producing high-performance activated carbon for environmental applications.