Formation and characterization of H₂-producing granule in a pilot-scale dynamic membrane bioreactor

This study aimed to achieve high-rate continuous biohydrogen production in a pilot-scale dynamic membrane bioreactor (DMBR), continuously fed with a 20 g/L mixture of glucose, xylose, and arabinose at flow rates ranging from 40 to 160 L/d. The highest average hydrogen production (HP), hydrogen production rate (HPR), and hydrogen yield (HY) were 570 ± 17 L H₂/d, 28.52 ± 0.85 L H₂/L-d, and 1.48 ± 0.03 mol H₂/mol hexose equivalent_consumed, respectively. The high-rate performance was achieved along with the formation of H₂-producing granules after 29 days of the continuous operation. The low-cost polyester mesh in DMBR properly acted as a carrier for granule formation. Granulation increased the retention of bacterial concentrations (g VSS) more than twice, which contributed to the high volumetric HPR. It also increased the HY due to the shift of the metabolic flux distribution from lactic acid production and homoacetogenesis to H₂-producing butyric and acetic pathways. H₂-producing granules exhibited an average size of 1215 μm, settling velocity of 25.8 to 77.0 m/h, porosity of 0.67 to 0.93, and fluid collection efficiency of 0 to 0.29. Extracellular polymeric substances (EPS) secreted by hydrogen-producing bacteria partially covered the pores of the granules, but the substrate transfer was not severely retarded due to the high porosity over 0.7. Clostridium pasteurianum dominated the microbial population in the granules, similar to the microbial population of the biofilm. This study demonstrates the feasibility of high-rate biohydrogen production via the formation of H₂-producing granule in pilot-scale.