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 H ₂ and CH ₄ 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 H ₂ and CH ₄ 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 H ₂ and CH ₄ yields were 20-85 ml H ₂/g VS _added and 329-364 ml CH ₄/g VS _added, respectively. The H ₂ yield increased and the CH ₄ yield decreased in the order of potato, kitchen garbage and okara. The H ₂ 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 H ₂ or CH ₄ were obtained when the hydrolysis pH of the organic waste was close to the optimum pH range of H ₂- producing bacteria or methanogenic archaea in the two-stage fermentation processes.