Hydrogen and organic acids production from mesophilic and thermophilic dark fermentation of sugarcane vinasse without buffers

The main objective of this study was to evaluate the valorization of vinasse dark fermentation (DF) through bioH2 and value-added metabolites production without buffers in two similar Upflow Anaerobic Sludge Blanket (UASB) reactors under mesophilic (U30) and thermophilic (U55) conditions. An average organic acids yield of (376 ± 52 and 248 ± 122) mg-CODOA.g−1CODtin, and productivity of (17396 ± 5220 and 14024 ± 1642) mg-CODOA.L−1.d−1 was obtained for U30 and U55 reactors, respectively, with only vinasse as substrate. BioH2 production was feasible with sucrose and pH below 3.0, but it ceased with substrate replacement by vinasse along with natural pH increase. A change in the structure of the microbial community was also observed: Ethanoligenens, Clostridium sensu stricto 12, and Liquorilactobacillus using sucrose, under pH <3.0 were replaced by Prevotella, Megasphaera, Pectinatus, Clostridium sensu stricto 11 and Lactobacillus using vinasse, under pH>4.0.