Hydrogen and methane potential based on the nature of food waste materials in a two-stage thermophilic fermentation process

The purpose of this study is to investigate the biological H2 and CH4 potential based on the nature of organic waste materials in a two-stage thermophilic fermentation process. Three varieties of actual waste specifically potato, kitchen garbage and bean curd manufacturing waste (okara) were selected. The production rates for H2 and CH4 were as follows: potato, 2.1 and 1.2 l/l/d; garbage, 1.7 and 1.5 l/l/d; okara, 0.4 and 1.4 l/l/d in the continuous processes. The H2 and CH4 yields were 20–85 ml H2/g VSadded and 329–364 ml CH4/g VSadded, respectively. The H2 yield increased and the CH4 yield decreased in the order of potato, kitchen garbage and okara. The H2 yield was shown to be not only dependent on the proportion of carbohydrate but also on the hydrolysis pH of the organic waste, which was influenced by the nature of the organic waste materials. Higher yields of H2 or CH4 were obtained when the hydrolysis pH of the organic waste was close to the optimum pH range of H2-producing bacteria or methanogenic archaea in the two-stage fermentation processes.