Characterization of a hydrogen‐producing granular sludge

This study demonstrated that hydrogen‐producing acidogenic sludge could agglutinate into granules in a well‐mixed reactor treating a synthetic sucrose‐containing wastewater at 26°C, pH 5.5, with 6 h of hydraulic retention. A typical matured granule is 1.6 mm in diameter, 1.038 g/mL in density, 11% in ash content, and over 50 m/h in settling velocity. Treating a solution containing 12.15 g/L of sucrose at a volumetric loading rate of 48.6 g/(L · d), the reactor containing 20 g/L of granular sludge degraded 97% of sucrose. Effluent comprised 46% acetate and 49% butyrate and the methane‐free biogas comprised 63% hydrogen, 35% carbon dioxide, and 2% nitrogen. Hydrogen production rate was 13.0 L/(L · d), and the yield was 0.28 L/g‐sucrose. The granule had multiple cracks on the surface and comprised two morphological types of bacteria: fusiform bacilli and a spore‐forming bacterium. Phylogenetic analysis showed that 69.1% of the clones were affiliated with four Clostridium species in the family Clostridiaceae, and 13.5% with Sporolactobacillus racemicus in the Bacillus/Staphylococcus group. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 44–52, 2002; DOI 10.1002/bit.10174