Effect of pH in fermentation of vegetable kitchen wastes on hydrogen production under a thermophilic condition

A series of tests on the fermentation of vegetable kitchen wastes to produce hydrogen were conducted at pHs of 5.5, 6.0, 6.5, and 7.0 under a thermophilic condition. Microorganisms used in fermentation were enriched from kitchen-waste composts, and a high vegetable-content kitchen-waste was utilized. The initial substrate to microorganism ratio was kept at 10 g COD/g VSS under a thermophilic (55 °C) condition. A maximum specific hydrogen production rate of 0.48 mmol H2/g VSS/h was achieved at pH = 6.0, and the highest hydrogen yield of 0.57 mmol H2/g COD occurred at pH = 7.0. No hydrogen production occurred at pH = 5.5. At pHs controlled at 6.0, 6.5, and 7.0, the major volatile acid produced was butyrate. Using a terminal restriction fragment length polymorphism (TRFLP) analysis for microbial identification, T-RFs of 227 bps were found to be a dominant population when hydrogen was produced efficiently at pHs of 6.0, 6.5, and 7.0.