Sunday, May 3, 2009
6-25
Ethanol production from Sugarcane bagasse by Zymomonas mobilis using Simultaneous Saccharification and Fermentation (SSF) Process
During past decades, considerable efforts have been made to utilize agricultural and forest residues as biomass feedstock for the production of bio-ethanol as an alternative fuel. Sugarcane bagasse, composed of 38.1 w% cellulose, 28.4 w% hemicellulose and 18.4 w% lignin, represents the main lignocellulosic material to be considered by most of tropical countries. Compared with Saccharomyces cerevisiae, the ethanol yield and specific productivity of Zymomonas mobilis are higher, because less biomass is produced and a higher metabolic rate of glucose is maintained through its special Entner–Doudoroff pathway. Fermentation utilizing strains of Z. mobilis instead of traditional yeasts and the use of simultaneous saccharification and fermentation (SSF) process has been proposed. Initially, to make easier the accessibility of cellulases to the cellulose microfibrils, the bagasse suffered a pretreatment with diluted acid to extract the hemicellulose sugars fraction and to generate cellulignin. This solid residue was pretread using NaOH (4%), aims at its partial deslignification. Then, the cellulignin suffered the action of a commercial celulolytic preparation, allowing the conversion of cellulose to glucose. This enzymatic pretreatment occurs under temperature of for 12 hours. Thereafter, the temperature was reduced to and the system was inoculated with cells of Z.mobilis. Statistical experimental design was used to optimize the conditions of SSF, evaluating solid content, enzymatic load and cell concentration from by submerged fermentation. The optimum conditions were found to be: solid content (30%), enzymatic load (25 FPU/g) and cell concentration (4 g/L), resulting in a maximum ethanol concentration of 60 g/L.
PDF file