Acidogenesis characteristics of natural, mixed anaerobes converting carbohydrate-rich synthetic wastewater to hydrogen

The fermentative metabolisms of mixed anaerobic bacteria taken from an anaerobic digester treating dairy manure and stressed in various ways to enhance hydrogen production from a carbohydrate-rich synthetic wastewater were evaluated in batch culture tests by monitoring intermediate metabolites. First, fermentative metabolism was evaluated in batch vial experiments to evaluate various bacterial stresses for enhancing hydrogen production. The results showed that the bacterial stresses tested promoted hydrogen production, and butyric acid was the primary product of acidogenesis. Completely mixed batch reactor (CMBR) experiments were then performed with pH controlled at 4.6, 5.7, and 6.8. Hydrogen-producing species enriched from mixed anaerobic bacteria by stressing with chemical acidification were used because they gave the best result in batch vial tests. The results of the CMBR experiments showed that butyric acid formation was significantly related to higher hydrogen yield. The CMBR operated at pH controlled at 5.7 showed higher hydrogen yield than did the other pH values, and butyric acid (as 50.8–75.8% of total acidogenic liquid products) was dominant. The presence of propionic acid and ethanol indicated decreased hydrogen production.