Synergetic effects of conductive materials and bacterial population in inoculum on mixed-culture biohydrogen production

This study examined the effect of conductive materials (softwood pellet biochar pyrolyzed at 550 °C and 700 °C, powdered activated carbon and stainless-steel) on the two series of batch biohydrogen production inoculated with three types of heated-treated anaerobic digester sludge. Biochar pyrolyzed at 550 °C and stainless-steel exhibited the highest enhanced hydrogen yield up to 117 % in the first and second series of experiments, respectively. Importantly, the enhancement effect by the introduction of conductive materials was significantly affected by the microbial population in inoculum, particularly the relative abundance of electroactive H ₂-producing Clostridium sp. Metabolic flux analysis revealed that the enhanced H ₂ yield was concurrent with the decrease of lactate production and the increase of H ₂-producing acetogenesis. Conductive materials also improved electron transport system activity and NADH/NAD ⁺ ratio, which are related with the metabolic activity. This study shows that introducing conductive material can control intracellular redox environment, thereby reinforcing the metabolic activity selectively.