Reclaiming cigarette butts: biorefinery technologies toward circular waste valorization

Cigarette butts (CBs) are among the most abundant forms of anthropogenic litter, with about 5 trillion units discarded each year, corresponding to more than 800,000 tons of waste. Composed primarily of cellulose acetate (CA), accounting for 95% of the filter mass, CBs exhibit low biodegradability and act as carriers of toxic substances such as nicotine, heavy metals, and polycyclic aromatic hydrocarbons. Their persistence in the environment has raised growing concerns across terrestrial and aquatic ecosystems. This review critically examines the potential integration of CBs into circular waste management strategies through biorefinery technologies. Key processes include deacetylation to increase hydrolytic accessibility, enabling conversion into fermentable sugars for bioethanol production, as well as thermochemical routes like pyrolysis for fuel and activated carbon generation. Additional valorization options, such as enzymatic degradation and transformation into nanostructured carbon materials, are discussed with respect to their feasibility and environmental impact. Legislative gaps, technological barriers, and limited scalability are identified as major constraints to industrial implementation. Nonetheless, the inclusion of CBs as a non-conventional feedstock offers a promising opportunity to reduce the environmental footprint of CBs while recovering energy and materials within a biorefinery loop.