Efficient ethanol production from kitchen and garden wastes and biogas from the residues

Kitchen and garden wastes were used for ethanol production and the residue was applied for biogas production. The wastes were pretreated with dilute acid to improve the yield of ethanol production. The pretreatments were carried out with 0.05 M sulfuric acid at 120, 150, and 180 °C for 0, 10, 30, and 60 min, resulting in a liquor mainly containing starchy materials and hemicellulosic sugars and a solid mainly containing cellulose. In order to remove the inhibitors from the liquor, a detoxification step with lime (overliming) was performed. Furthermore, the starch contents of the liquor were enzymatically hydrolyzed before fermentation. Then, the liquor was fermented with ethanolic fungus Mucor indicus, which is a highly inhibitor-tolerant strain of Zygomycetes. After that, the biomasses obtained from aerobic and anaerobic fermentation along with the dilute acid–pretreated solids were subjected to anaerobic digestion for biogas production. The results showed that the addition of fermentation biomass to the pretreated solid significantly improved the biomethane production yield. After pretreatment at 150 °C for 30 min and without detoxification, the maximum amounts of gasoline equivalent of 162.1 and 120.6 L were obtained with and without starch hydrolysis, respectively, where methane production yield was 157.4 mL/g VS and ethanol yields were 75.9% and 94.2%.