Novel insights on the versatility of biohydrogen production from sugarcane vinasse via thermophilic dark fermentation: Impacts of pH-driven operating strategies on acidogenesis metabolite profiles

An innovative application of the anaerobic structured-bed reactor (AnSTBR) in thermophilic dark fermentation of sugarcane vinasse targeting biohydrogen (bioH(2)) production was assessed. A detailed metabolite monitoring program identified the major substrates and primary metabolic pathways within the system. Increasing the applied organic loading rate positively affected bioH(2) production, reaching 2074 N mL-H-2 L-1 d(-1) and indicating an optimal load of approximately 70 kg-COD m(-3) d(-1). Controlling the fermentation pH (5.0-5.5) was the primary strategy to maintain bioH(2)-producing conditions, offsetting negative impacts associated with the compositional variability of vinasse. Metabolic correlations pointed out lactate as the primary substrate for bioH(2) production, indicating its accumulation as evidence of impaired reactors. The versatility of the acidogenic system was confirmed by identifying three major metabolic pathways according to the pH, i.e., lactate-producing (pH < 5.0), bioH(2)-/butyrate-producing (pH = 5.0-5.5) and bioH(2)-producing/sulfate-reducing (pH > 6.0) systems, which enables managing the operation of the reactors for diversified purposes in practical aspects.