Voltage-Driven Regulation of Metabolic Flux and Biohydrogen Production in a Dynamic Membrane Bioreactor Coupled with Electro-Fermentation

Dynamic membrane bioreactors (DMBRs) are promising systems for continuous biohydrogen production because they enable effective biomass retention under short hydraulic retention time (HRT) conditions. In this study, a dynamic membrane bioreactor coupled with electro-fermentation (DMBR-EF) was operated for 59 days to investigate the effect of applied voltage on biohydrogen production and metabolic flux regulation. The reactor was sequentially operated at 0 (no applied voltage), 0.2, 0.4, 0.6, 0.8, and 1.0 V using glucose as a model substrate. The highest hydrogen production rate (HPR) and hydrogen yield (HY) were achieved at 0.2 V, reaching 15.35 ± 0.48 L H2/L/d and 1.54 ± 0.05 mol H2/mol glucoseadded, respectively, which were 33.71% and 33.91% higher than those of the 0 V control. At 0.2 V, residual glucose and effluent volatile suspended solids (VSS) were minimized, while butyric acid (HBu) formation was enhanced and lactic acid (HLa) accumulation was suppressed. In contrast, voltages above 0.4 V reduced hydrogen recovery by shifting metabolic flux toward HLa, propionic acid (HPr), formic acid (HFo), and homoacetogenic pathways. Microbial analysis showed that Clostridium dominated under all conditions, but voltage application selectively altered the relative abundance and metabolic output of Clostridium-related amplicon sequence variants (ASVs). These results indicate that mild electrochemical stimulation at 0.2 V effectively enhances continuous biohydrogen production by promoting butyric acid-type fermentation, suppressing lactic acid accumulation, and reducing hydrogen loss through competing metabolic pathways in DMBR-EF systems.