Integrated co-digestion of sugarcane by-products for synergistic methane production, energy recovery, and GHG mitigation

Efficient co-digestion of sugarcane by-products requires optimization of substrate interactions to maximize methane production while avoiding inhibitory conditions. Previous studies lack a systematic framework to evaluate interactions and determine optimal feed ratios for stable anaerobic digestion. To address this gap, this study employs a D -optimal mixture design to investigate co-digestion performance of filter cake, molasses, and vinasse. Biomethane potential was assessed through mesophilic batch experiments using 60 g VS per mixture, and kinetic modeling was applied to characterize methane production. The mixture containing 5:15:40 g VS of filter cake, molasses, and vinasse produced the highest methane yield of 570 mL CH 4 g −1 VS, while response surface modeling identified 6.42:15:38.57 as the optimal substrate proportion. Molasses acted as the primary enhancer of methane yield, filter cake imposed hydrolytic limitations, and moderate vinasse loading generated synergistic improvements. Synergy index values confirmed positive interactions, particularly in mixtures with higher methane recovery. Based on a reference system processing 1 ton of VS per day, methane from the optimized co-digestion mixtures enabled substantial energy recovery via a combined heat and power system, generating 2.05 MWh day −1 of electricity and 7.49 GJ day −1 of thermal energy. Substitution of grid electricity and natural gas-derived heat corresponded to an estimated 1.58 t CO 2 -eq day −1 of avoided emissions, demonstrating dual benefits of energy production and climate mitigation. Overall, this study presents a data-driven framework for optimizing ternary co-digestion, emphasizing substrate synergy in enhancing methane yield, energy recovery, and greenhouse gas mitigation within a sugarcane biorefinery context.