This study evaluated a two-stages bioprocess for biohythane (H 2 and CH 4 ) and valuable metabolites production from brewery spent grain and brewery wastewater. The first stage employs a fermentative compartmentalized fixed-bed anaerobic reactor (CFBAR) for H 2 and valuable metabolites, while in the second stage the effluent from CFBAR is used to feed anaerobic batch reactors for methane production. Then, the biogas from both reactors can be blended to generate biohythane. Altering the hydraulic retention time (HRT) of CFBAR from 48 h to 24 h revealed high potential for simultaneous H 2 production (499 mL H 2 L⁻¹d⁻¹) and valuable metabolites such as acetate, caproate and butyrate. The fermented effluent from 24h-HRT CFBAR provided a maximum CH 4 yield rate ( Rm ) of 10.1 ± 0.4 mL CH 4 .L -1 .h -1 . The system enabled simultaneous production of hydrogen and value-added carboxylic acids in the first stage, followed by methane production in the second stage, and chemical organic demand removal of 85.6%, forming an integrated biohythane production approach. Clostridium , Bacteroidaceae , and Bifidobacterium were the main bacteria associated with lignocellulose degradation and H 2 production in CFBAR, while Syntrophales and Methanolinea syntropy were the key driver for CH 4 in the second stage batch reactors.
Gomes et al. (2026) studied this question.