Bioethanol can be produced from raw materials that contain high amounts of sugars, or compounds that can be converted into sugars, such as starch, cellulose or hemicellulose. The fuel ethanol commercially available today, also called 1^st generation bioethanol, is mainly from sugar- and starch-containing substrates (e.g. sugarcane, corn or wheat). However, as the demand for bioethanol is increasing, lignocellulosic raw materials, such as agricultural residues or forest leftovers, must also be considered (2^nd generation bioethanol).
Sugarcane bagasse is an abundant and readily available agricultural byproduct, which has good potential for bioethanol production. However, it contains not only around 40% cellulose but also 25% hemicellulose, of which the main component, approximately 85%, is xylose. Since xylose is a pentose, it is not fermented by wild-type S. cerevisiae. In order to co-ferment pentoses with hexoses, modified organisms have to be used.
In this study, production of ethanol in simultaneous saccharification and fermentation of steam-pretreated bagasse was investigated in process development unit scale, using S. cerevisiae TMB3400, a genetically modified xylose-fermenting yeast. The bagasse was subjected to steam pretreatment with addition of either SO₂, CO₂ or H₃PO₄ as catalysts, to produce a slurry of partly-hydrolyzed material. In order to adapt the yeast to the toxic environment, TMB3400 was cultivated on the liquid fraction of the pretreated bagasse, supplemented with molasses. Results from the study will be presented.