Conversion of abundant lignocellulosic biomass to biofuels and replacing them with fossil fuels is a viable option to reduce greenhouse emissions. It has been reported that cellulosic ethanol and ethanol produced from other biomass resources have the potential to cut greenhouse gas emissions by 86%. Lignocellulosic materials such as agricultural residues (e.g., wheat straw, sugarcane bagasse, corn stover), forest products (hardwood and softwood), and dedicated crops (switchgrass, salix) are renewable sources of energy. These wastes are mostly left in the field, causing a disposal problem for the local producing agro-industries. However, lignocellulosic biomass actually has a great potential as feedstock for production of more value-added products such as low price chemicals, e.g. xylitol, xylose, glucose, furfural, fuels, biofibres, ruminant feed, biopulp, or even for enzyme production. In this study Biological pretreatment of three types of lignocelluloses including rice straw, hardwood sycamore and softwood pine with anaerobic digestion (AD) was investigated for efficient ethanol production. The effects of ultrasonication on AD-treated and untreated lignocelluloses were studied prior to their separated hydrolysis and fermentation (SHF). The pretreated and untreated samples were analyzed using Compositional Analysis, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) methods. The biological pretreatment significantly reduced the hemicellulose content of the samples and showed a slight reduction in the amount of cellulose with no effect on the lignin content. In the case of the rice straw holocellulose loss was more than the case of sycamore and pine woods. The highest yield of glucose after 72h enzymatic hydrolysis was 65.83% obtained after pretreatment of the rice straw with AD process followed by ultrasonication at 60°C for 1h. After 24h fermentation, the yield of ethanol for pretreated rice straw at the best conditions was 69.55% while one it was 44% approximately for untreated. Furthermore, the pretreatment of sycamore and pine woods at the best conditions improved the ethanol yield up to 38.7% and 30.6%, respectively. Keywords: Biological Pretreatment, Lignocelluloses, Anaerobic Digestion, ethanol
