Conversion of High Biomass/Bagasse from Sorghum and Bermuda Grass into Second-Generation Bioethanol

Abstract

Sorghum (Sorghum bicolor) and Bermuda (Cynodon dactylon) grass are examples of annual and perennial forage crops produced throughout the globe. These crops should be harvested at the peak of biomass production when the levels of lignin are relatively low. The high biomass sorghum, sweet sorghum bagasse (2 cuts or crops year −1 ) or Bermuda grass capable of yielding up to 50, 60 and 27 tons of dry forage ha −1 year −1 rich in cellulose and hemicellulose can be efficiently transformed into bioethanol using second-generation technologies consisting of milling, pretreatment (chemical and/or enzymatic) and fermentation with microorganisms capable of transforming C5/C6 sugars to obtain ethanol. An alternative process contemplates the extrusion aimed toward the physical disruption of cell walls minimizing the use of considerable amounts of water and chemicals commonly used during pretreatment. Extruded feedstocks treated with fiber-degrading enzyme cocktails had conversion efficiencies between 60 and 78% of the hemicellulose and cellulose similar to the ones achieved after acid/enzyme hydrolyses. The chief advantages of this continuous process are that hydrolysates are practically free of enzymes and yeast inhibitors. These feedstocks can produce up to 310 L anhydrous bioethanol dry t −1 and have a great potential for widespread use.