Bioenergy production in anaerobic thermophilic / mesophilic two-phase process using food waste

Abstract

The recent rise in oil and natural gas prices forced to drive the current economy toward alternative energy sources. Since oil and natural gas are finite resources, the combustion of these fossil fuels contributes to air pollution and the greenhouse effect, hydrogen has been considered as a promising alternative to fossil fuels due to its clean, renewable and high energy yield. Hydrogen production from anaerobic fermentation is an environmentally friendly, energy saving process and reduces wastes to be treated as well. Food waste, which has C/N ratio of 13.6-26.7, is a carbohydrate-rich organic solid waste meaning that it is a promising feedstock to produce hydrogen from anaerobic fermentation. In this study, therefore, hydrogen production from food waste in anaerobic fermentation was studied. To find out the feasibility of hydrogen production from food waste, hydrogen production by the mesophilic and thermophilic acidogenic culture acclimated directly from food waste at organic loading rate (OLR) of $3gVSl^{-1}d^{-1}$, HRT of 5 days, and pH of 5.6±0.2 was evaluated by batch experiments on the effect of pH and volatile solid (VS) concentrations. The amounts of hydrogen produced from the thermophilic acidogenic culture were much higher than those from the mesophilic culture at all tested pHs due to free of methane and negligible propionate production. The optimum pH of hydrogen production in the thermophilic and mesophilic acidogenic culture was 5.5. The effect of VS concentrations on hydrogen production from the thermophilic acidogenic culture was conducted at pH 5.5. Increase of VS concentrations from 3 to $10 gVSl^{-1}$ resulted in the increase of quantity and quality of hydrogen production. Hydrogen producing microorganisms of Thermoanaerobacterium thermosaccharolytium and Desulfotomaculum geothermicum were detected from the thermophilic acidogenic culture, whereas Thermotogales strain and Bacillus species were detected from the mesophilic acidogenic cultur...