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Background |
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The era of cheap non-renewable fossil fuels has almost ended. To maintain current living standards, it is necessary to find alternative fuels. Cellulose, a major component of all plant matter, may prove to be a renewable fuel (Reference 2). Cellulosic materials are the most abundantly produced biopolymers on earth. Cellulose is one of the main components of plants and is equivalent to approximately 33 percent of all plant dry matter. Composed of the simple sugar glucose, cellulose may be used as a feedstock for ethanol production (Reference 2). Cellulase is a class of enzymes that breaks down cellulose into glucose. Endo-cellulase breaks internal bonds to disrupt the crystalline structure of cellulose and expose individual cellulose polysaccharide chains. Exo-cellulase cleaves 2-4 units from the ends of the exposed chains produced by endocellulase, resulting in tetrasaccharides, cellobiose, and glucose. Cellobiase or beta-glucosidase hydrolyses cellobiose into glucose. (Reference 1)
Ethanol is one of the most important renewable fuels in the world. Its use reduces the amount of green-house gases generated by the utilization of fossil fuels. The majority of commercial ethanol is produced through the fermentation of glucose, which comes either from hydrolyzing grain starches or from industry crops such as sugarcane. The use of farmland to produce fuel partially caused a shortage of food, posing an ethical question of whether crops should be used for food or fuel. The main challenge of ethanol production is to produce ethanol competitively with fossil fuels. Non-food matters, such as cellulose, may provide the key to solving the fuel shortage without raising the ethical question of food or fuel (Reference 4). One of the non-food matters usable for the production of ethanol is the biowaste originating from households and industries. Among them, wastepaper constitutes approximately half of all municipal solid waste, making it a potential source of bioenergy. The cellulose section of wastepaper can be bio-converted to glucose by cellulase (Reference 5). The fermentation process of efficiently producing ethanol via grains or sugarcanes is quite mature while the process of using cellulose as the starting material is still in the experimental stage. The main obstacle for cellulose fermentation is finding a high efficiency cellulase system that can break down cellulose into fermentable sugars as fast as commercial amylases can convert grain starch into glucose. |
