Production of methane-rich biogas and minimization of sludge by adopting ethanol fermentation for the pretreatment of biomethanation

In this study, the effectiveness of the ethanol fermentation pretreatment for biomethanation was examined. A sequential batch biomethanation experiment was performed for 130 days using artificial food waste, which was saccharized and ethanol fermented without any evaporation of ethanol. This is compared with a control experiment without pretreatment. Methane yields of the control and pretreatment series were 420 and 460 mL/g of the added volatile solids (VS) with 53% and 68% of methane content, 0.082 and 0.014 g of volatile suspended solids/g VS added for sludge yield, and 87% and 94% for VS biodegradability, respectively. In terms of material balance, the generation of carbon dioxide during biomethanation from an ethanol fermented substrate is lower in volume than that without it, because carbon dioxide is released during ethanol fermentation. The lower sludge generation of the ethanol fermented substrate results from the biomass yield of ethanol and free energy obtained from the biomethanation of ethanol, which is lower than that obtained from the biomethanation of starch.