Co-fermentation of liquid and solid sugarcane byproducts in thermophilic anaerobic compartmented fixed-bed reactors:...

Two thermophilic (55 °C) Anaerobic Compartmented Fixed-Bed Reactors (ACFBR; R1 and R2) were operated for 198 days using sugarcane vinasse and bagasse hydrolysate. Hydrothermally pretreated bagasse (200 °C, 16 bar, 10 min) filled 13 modular sections per reactor, serving as both substrate and support. Glass beads (5 mm) were placed between bagasse compartments only in R1. Biohydrogen evolved up to 356 ± 341 and 628 ± 348 NmL H₂ L^-1 d^-1 in R1 and R2, respectively, even at OLR<18 kg COD m^-3 d^-1. Hemicellulose degradation by Caldanaerobius supplied additional substrate for fermentative bacteria. Butyric (Thermoanaerobacterium, Caproiciproducens) and valeric (Clostridium) acids dominated through chain elongation. Although bagasse alone supported biomass growth, glass beads enhanced biomass retention and acidogenic stability, improving hemicellulose conversion while slightly restricting H₂ transfer. The ACFBR configuration demonstrates potential for integrating sugarcane byproducts into biohydrogen and carboxylate production, with higher OLR and mixed substrates offering routes for process intensification.