Hydrogen and organic acid production from dark fermentation of sugarcane vinasse without buffers in mesophilic and thermophilic conditions

BACKGROUND Sugarcane vinasse has a low pH and several studies report that alkalinity supplementation is essential to the stability of its dark fermentation (DF). In the context of biorefineries, the reduction, or even elimination, of alkalinizing agents could be extremely environmentally and economically advantageous. The main objective of this study was to evaluate the valorisation of vinasse DF through bioH2 and value‐added metabolite production without buffers in two similar Upflow Anaerobic Sludge Blanket (UASB) under mesophilic (U30) and thermophilic (U55) conditions. RESULTS Average organic acid yields of 376 ± 52 and 248 ± 122 mg‐CODOA.g−1CODtin, and productivities of 17 396 ± 5220 and 14 024 ± 1642 mg‐CODOA.L−1 day−1 were obtained for U30 and U55 reactors, respectively, with only vinasse as substrate (CODOA stands for organic acids chemical oxygen demand (COD) and CODin influent COD). BioH2 production was feasible with sucrose as substrate and pH below 3.0, but it ceased with substrate replacement by vinasse along with a natural pH increase. A change in microbial community was also observed: Ethanoligenens, Clostridium sensu stricto 12, and Liquorilactobacillus (using sucrose and with a pH 4.0). CONCLUSION Results showed that DF of sugarcane vinasse without any buffering addition might be a promising approach for the valorization of real wastewater through the production of organic acids. Nevertheless, bioH2 production was not favored and further strategies would be needed to maintain hydrogen‐producing bacteria when sucrose is replaced by real effluent with a natural pH increase. © 2021 Society of Chemical Industry (SCI).