Delignification of Rice Husk and Production of Bioethanol

Lignocellulose is a generic term for describing the main constituents in most plants, namely cellulose, hemicelluloses, and lignin. Lignocellulose is a complex matrix, comprising many different polysaccharides, phenolic polymers and proteins. Cellulose, the major component of cell walls of land plants, is a glucan polysaccharide containing large reservoirs of energy that provide real potential for conversion into biofuels. Lignocellulosic biomass consists of a variety of materials with distinctive physical and chemical characteristics. The conversion of Lignocellulosic biomass to ethanol involves pretreatment followed by polysaccharide hydrolysis to simple sugars followed by sugar fermentation to ethanol. The presence of lignin in cell walls negatively impacts these conversion steps. Sodium hydroxide treatment is one of the highly effective lignin removal methods due to their strong alkanity. The chemical pretreatments of rice husk were carried out with sodium hydroxide and sodium chlorite concentration (15%) with the best results at 5% for both the solutions. This greatly enhanced its susceptibility to enzymatic hydrolysis at 30 °C. The chemical pretreatments caused deep deacetylation and milder delignification of rice husk and did not cause an apparent loss of cellulose. In addition fungal treatment (Trichoderma reesei) of pretreated samples has been applied to improve the conversion of cellulosic material in sugar. The method of alkali pretreatment and subsequent fungal treatment (in different concentrations) results the highest conversion of lignocelluloses in rice husk to sugar and consequently, highest ethanol yields were 250 mg/gram dry biomass after 6 days fermentation with Saccharomyces cerevisiae.