Thermal hydrolysis pretreatment for anaerobic digestion of cotton textile waste

Abstract Cotton textile waste is challenging to digest and convert to biogas during anaerobic digestion (AD) due to high crystallinity of cellulose. This study investigated thermal hydrolysis pretreatment (THP) at 120–200 °C for 30 and 60 min to enhance cotton biodegradability prior 21 days of mesophilic AD at a substrate-to-inoculum ratio of 0.5 volatile solids (VS) basis. THP increased cotton solubilisation up to 98% VS removal, at the most sever condition (200 °C, 60 min), crystallinity decreased by 11.84% and COD solubilisation reached 51. However, the highest methane yield was achieved under moderate conditions (140 °C, 60 min), producing 17.92 mL CH 4 /g VS, representing a 123% increase over untreated cotton, indicating an optimal balance between solubilisation and process inhibition. Gompertz modelling showed excellent agreement ( R 2 ≥ 0.99), with a reduced lag phase (2.3 days) and ~2-fold higher biodegradability than untreated cotton. Digestate pH, ammonia nitrogen, and volatile fatty acid (VFA) remained within non-inhibitory ranges under the optimal THP condition, supporting stable and efficient methane production. These results identify cotton-specific THP operating conditions and demonstrate THP-AD as a pathway for valorising cotton textile waste.