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This study aimed to better understand the role of different microbial groups and the determining fermentation pathways in a biohydrogen (bioH 2 )-producing reactor fed with sugarcane vinasse by using next-generation sequencing and principal component analysis (PCA). Both microbial structure and dynamics were characterized. The highest bioH 2 production levels were associated with the Thermoanaerobacterium genus, whilst lactate-producing bacteria comprised the dominant genera (e.g. Lactobacillus and Leuconostoc ) within the reactor at both stable and unstable bioH 2 -producing periods. PCA further revealed that the fermentation of lactate played a dual role in the reactor, as both bioH 2 -producing (acetate + lactate → butyrate + bioH 2 ) and non-bioH 2 -producing (lactate → propionate + acetate) routes could be observed. Overall, the results suggested that lactate is the primary alternative carbon source in vinasse-fed systems subjected to carbohydrate-shortage conditions. [ABSTRACT FROM AUTHOR]

This study considered the application of anaerobic digestion (AD) with phase separation combined with the use of an anaerobic structured-bed reactor (ASTBR) as the methanogenic phase for the treatment of sugarcane vinasse, a high-strength wastewater resulting from ethanol production. Two combined thermophilic acidogenic-methanogenic systems formed by one single acidogenic reactor followed by two methanogenic reactors operated in parallel were compared, namely, a conventional UASB reactor and an upflow ASTBR reactor. Increasing organic loading rate (OLR) conditions (15–30 kg COD m −3 d −1 ) were applied to the methanogenic reactors. The results highlighted the feasibility of applying the ASTBR to vinasse, indicating a global COD removal higher than 80%. The ASTBR exhibited a stable long-term operation (240 days), even for OLR values as high as 30 kg COD m −3 d −1 . The application of similar conditions to the UASB reactor indicated severe performance losses, leading to the accumulation of acids for every increase in the OLR. An energetic potential of 181.5 MJ for each cubic meter of vinasse was estimated from both hydrogen and methane. The provision of bicarbonate alkalinity proved to be a key factor in obtaining stable performance, offsetting the limitations of relatively low hydraulic retention times (<24 h). [ABSTRACT FROM AUTHOR]