Anaerobic co-digestion of textile and food waste: methane production and process performance

Anaerobic digestion (AD) of textile waste is limited by the complex structure of fibers that resist microbial degradation. This study investigated the mono- and co-digestion of common textile wastes (cotton, polycotton, and wool) with food waste (FW) under mesophilic conditions. Digestion performance was evaluated at substrate-to-inoculum (S/I) ratios of 0.5 and 1 and various feedstock mixing ratios. Methane yields increased with decreasing S/I ratios. Among the textiles, cotton showed the highest methane yield (103 mL/g volatile solids (VS)) and biodegradability (BD) of 25.87% at an S/I ratio of 0.5 due to its favorable composition. Overall, in co-digestion, increasing the FW proportion enhanced methane production. However, the highest yield (129.7 mL/g VS) was achieved from a cotton-to-wool ratio of 6:1 due to a balanced carbon-to-nitrogen (C/N) ratio of 20.63. Synergistic effects were most substantial when FW comprised over 80% of the blend, particularly with cotton, as indicated by a co-digestion performance index (CI) exceeding 1. Kinetic analysis using the modified Gompertz model closely fit the experimental data, showing that more FW reduced lag phases and accelerated biogas production. In contrast, polycotton and wool showed antagonistic effects (CI<1) due to the non-biodegradability of polyester and the complexity of wool keratin, which limited methane output. This study highlights the importance of co-substrate selection, optimal S/I ratios, and an increase in FW proportion within the optimal C/N ratio, which enhances co-digestion performance. Future work should explore pretreatment strategies, such as thermal hydrolysis for organic fabrics and synthetic separation from blended fabrics, which can help improve textile digestibility and biogas yields. Graphical abstract