Acidic-alkaline shocks in vinasse fermentation shape methanogenesis and sulfate reduction dynamics

Efficient two-phase anaerobic digestion of sugarcane vinasse hinges on effectively suppressing methanogenesis within the initial sulfate-reducing stage, particularly under mesophilic conditions, to maximize downstream methane production. This study investigates the strategic application of sequential acidic and alkaline pH shocks to achieve this critical control. An Anaerobic Structured-Bed Reactor (AnSTBR), reactivated from prolonged storage to mimic off-season conditions, was fed vinasse for 90 days across six operational stages. Our results demonstrate that these pH shocks successfully inhibited hydrogenotrophic methanogenesis, reducing methane content to 3% while restoring sulfidogenesis to 82% (Stage VI) even after the system returned to original conditions. This robust sulfate removal in high-rate fermentative systems yielded an effluent rich in acetate with enhanced buffering capacity, ideal for subsequent acetoclastic methanogenesis. Microbial community analysis identified Desulfovibrio (6.45-16.91%) as the dominant dissimilatory sulfate reducer, while Bacteroides (11.88-15.80%) and Aminobacterium (2.94-8.48%) were key acetate producers driving fermentative metabolism. This work establishes a novel operational strategy to precisely modulate microbial pathways in vinasse biorefineries, advancing sustainable biogas production and waste management.