Development of a novel three-stage fermentation system converting food waste to hydrogen and methane

In this study, a novel three-stage (lactate- + photo-H2 + CH4) fermentation system was developed, which converts food waste to H2 and CH4, with an emphasis on achieving high H2 yield. The system begins by first fermenting food waste to lactate, rather than acetate and butyrate, using indigenous lactic acid bacteria. Lactate fermentation effluent was then centrifuged, and the supernatant was used for H2 production by photo-fermentation, while the residue was used for CH4 production by anaerobic digestion. Overall, via the three-stage fermentation system, 41% and 37% of the energy content in the food waste was converted to H2 and CH4, respectively, corresponding to the electrical energy yield of 1146 MJ/ton-food waste, which is 1.4 times higher value than that of previous two-stage dark (H2 + CH4) fermentation system. The H2 yield based on hexose input was 8.35 mol H2/mol hexoseadded, the highest value ever reported from actual organic waste.