MILD ALKALINE PRETREATMENT APPLIED IN THE BIOREFINERY OF SORGHUM BIOMASS FOR ETHANOL AND BIOGAS PRODUCTION

Production of bioenergy from lignocellulosic biomass has gained more and more interest over the past years. Due to its high content in carbohydrates, Sorghum bicolor is one of the best suited candidate for bioenergy production. However, the lignocellulosic nature of the sorghum biomass raises difficulties to the access of the microbial enzymes to cellulose and hemicellulose and inhibits processes such as hydrolysis, fermentation and anaerobic digestion of biomass to produce biofuels. In this study, the effects of thermo - chemical pretreatment (mild alkaline pretreatment), applied to improve biodegradability of three different hybrids of sorghum biomass were investigated. Alkaline pretreatment have positive effects on the production of lignocellulosic ethanol, increasing both cellulose and hemicellulose content while breaking the lignocellulosic bonds and reducing lignin content. The achieved methane yields ranged from 320 to 345 l(n) CH4/kg VS for the pretreated biomass, approximately 22% higher than the yields obtained from the untreated biomass. Important increase of methane production has been noticed as well in the case of anaerobic digestion of spent bagasse resulted after ethanol fermentation. Mild alkaline pretreatment is a suitable pretreatment method for conversion of sorghum biomass to ethanol and biogas.