Effect of Wet, Hemi-Solid, and Solid-State Conditions and Substrate to Inoculum Ratio on Methane Production from Sugarcane Bagasse

Sugarcane bagasse (SCB) constitutes up to 28% of the weight of crushed sugarcane, with significant potential for bioenergy production. Solid-state anaerobic digestion with total solids (TSs) over 15% is an interesting technology that can be used to treat agricultural wastes such as SCB, resulting in smaller reactor sizes and lower water consumption. This study investigates methane production from SCB under wet (10% TS), hemi-solid (15% TS), and solid-state (20% TS) anaerobic digestion with substrate-to-inoculum ratios (SIR) of 1, 2, 3, and 4. Batch experiments were conducted under mesophilic conditions (37 °C) to evaluate methane yields, volumetric methane productivity, and kinetic parameters. Results revealed that the highest methane yields—125, 115, and 106 L CH 4 kg VS −1 —were achieved for wet, hemi-solid, and solid-state digestion, respectively. Despite similar methane yields across TS conditions, volumetric methane productivities increased by 118% and 128% from hemi-slid and solid-state digestion, demonstrating their potential for scaling up in commercial biogas plants. The first-order kinetic model best-predicted methane production (R 2 > 0.984), with hydrolysis identified as the limiting step (K hyd ≤ 0.05 d −1 ). These findings highlight the advantages of solid-state anaerobic digestion for lignocellulosic feedstocks like SCB, contributing to bioenergy sustainability and the circular economy.