Methane Yield and Microbial Dynamics in Solid-State Anaerobic Codigestion of Sugar Cane Bagasse and Bovine Manure

Solid-state anaerobic digestion (SS-AD) offers a sustainable route for the valorization of agro-industrial residues, yet its efficiency is often constrained by limited mass transfer and process instability. This study investigated the codigestion of sugar cane bagasse (SCB) and bovine manure (BM) under varying substrate-to-inoculum (S/I) ratios (0.5-2.0), total solids (TS, 8.9-17.2%), and carbon-to-nitrogen (C/N, 16-37) ratios to identify optimal operating conditions for methane production. The highest volumetric methane yields (12.6 to 13.9 L CH₄ L^-1 reactor) occurred at intermediate TS (11.6 to 12.5%) and C/N (19 to 26%) values (T1 and T4). Monodigestion of SCB was feasible up to S/I = 1.0, while codigestion with BM enabled higher organic loading (S/I = 1.5) without inhibition. A shift in the microbiological profile was observed from T1 to T4, with a predominance of Clostridium sensu stricto 1 and Solibacillus, both of which are associated with the degradation of lignocellulosic compounds. In T4, the presence of Pseudomonas stood out, indicating a greater microbial diversity in this SCB monodigestion trial. The archaeal community was dominated by Methanosarcina in T4, with a higher diversity of genes associated with the hydrogenotrophic pathway, followed by the acetoclastic pathway. By linking microbial community dynamics to process performance, this study defines operational thresholds that enhance SS-AD efficiency and resilience, supporting the development of robust dry-digestion systems for lignocellulosic biomass valorization.