Development and characteristics of rapidly formed hydrogen-producing granules in an acidic anaerobic sequencing batch reactor (AnSBR)

This study investigated the development and characteristics of rapidly formed hydrogen-producing granules (HPGs) in an acidic anaerobic sequencing batch reactor (AnSBR). When subjecting the AnSBR suspended sludge to heat-shock (80 °C for 20 min) and acidic pretreatment (pH 2.0 for 24 h) subsequently, granules were formed within the first 10 days of the AnSBR operation at pH 5.5. After subsequent second time heat-shock of the granules on day 35, hydrogen yield increased significantly to 1.36 mol-H₂/mol-glucose with a headspace content of 65 ± 7% and was stable during the next 60 days running of the AnSBR. A typical mature HPG showed 1.7 ± 0.2 mm in diameter and had an average settling velocity of 43 m/h. The granules were comprised of uniform rod shaped bacteria with a non-layered structure and multiple cracks on the surface. Three pure cultures, Clostridium sp. HP2, HP4 and HP7, were obtained from the enriched HPGs. Among the three isolates, strain HP4 showed the highest hydrogen yield of 1.41 (mol-H₂/mol-glucose) at a rate of 0.85 L-H₂/L/day (34.5 mmol-H₂/L/day). This study suggests that acid pretreatment, combining with the short settling time (30 min) and large exchange ratio (60%) of effluent, is applicable for rapid formation of HPGs in the AnSBR, which provides a promising approach for biological hydrogen production from the organic wastewater.