Net energy gain from solid organic wastes by dark fermentation and its end products

This study evaluated the feasibility of improving net energy gain from solid organic wastes by dark fermentation (DF) and its aqueous end products. Batch experiments were conducted with dairy cattle manure as a typical solid waste blended with sucrose at different sucrose:manure ratios. This study differs from previous DF studies in two aspects; these experiments were conducted at ambient temperature without any external nutrient supplements or pH control measures while previous studies had resorted to mesophilic conditions, nutrient supplements, and external pH control; this study evaluated the feasibility of DF in terms of net energy yield rather than in terms of hydrogen yield as in previous studies. Hydrogen yields (2.9–5.3 M H₂/M sucrose) and net energy gains (2.0–3.7 kJ/g COD) demonstrated in this study are higher than in previous reports. Based on this study, sucrose:manure ratio of 4.5% is suggested as the optimal ratio.