Valorization of wastewater sludge into carbon materials for energy storage applications: feasibility and economic assessment

Abstract

The increasing accumulation of sewage sludge from wastewater treatment presents both environmental and economic concerns. This study proposes a sustainable valorization approach by converting sludge into porous carbon materials for lithium metal battery applications. Sludge underwent chemical pretreatment, pyrolysis at 800 degrees C, and KOH activation to yield carbon (Sludge C) with tailored structure and functionality. Physicochemical characterization confirmed a microporous structure, oxygen-rich surface groups, and partial crystallinity due to residual inorganic elements such as Si, Al, and Fe. Compared to commercial Super P, Sludge C exhibited lower lithium nucleation overpotential and improved cycling stability, attributed to its lithiophilic species and high surface area. A techno-economic analysis compared sludge carbonization with incineration, composting, and biohydrogen production. Despite higher capital costs, sludge carbonization offered promising value recovery through electrode material production. This study highlights a scalable and eco-friendly pathway for transforming sewage sludge into functional materials for energy storage, supporting waste minimization and circular bioeconomy goals.