High-rate dark fermentative hydrogen production in a UASB reactor with granular activated carbon and Clostridium pasteurianum bioaugmentation.

The combined application of granular activated carbon (GAC) and Clostridium pasteurianum bioaugmentation was evaluated in an up-flow anaerobic sludge blanket (UASB) reactor for high-rate dark fermentative hydrogen production under progressively shortened hydraulic retention times (HRTs). Two parallel reactors were operated: a control reactor (UASB-C) and a modified reactor incorporating both GAC and repeated bioaugmentation (UASB-ACBA). Compared with UASB-C, UASB-ACBA achieved a 26% higher maximum hydrogen yield (1.94 moL H2/moL glucose consumed) and an approximately fourfold higher hydrogen production rate (83.08 L/L/d), while maintaining hydrogen production at an HRT of 1 h. Metabolite profiles suggested that UASB-ACBA maintained a more balanced lactate-associated fermentation pattern under shortened HRT conditions, whereas UASB-C showed lactate, acetate, and residual glucose accumulation under intensified loading. Microbial community analysis indicated the persistence of the ASV assigned to C. pasteurianum and the coexistence of hydrogen-producing Clostridium species and lactic acid-producing bacteria. Overall, GAC addition and C. pasteurianum bioaugmentation may support high-rate UASB dark fermentation.