The sugarcane bagasse is one of the most produced lignocellulosic materials in the world and represents the residue of cane stems after crushing and juice extrac­tion. It is a by-product of the sugar industry and is almost exclusively utilized in sugar mills as a fuel for steam generation. In the past few years, the research on the economic utilization of bagasse to produce electricity, paper and paper pulp, and fermentation products has intensified. For instance, the Colombian sugar sec­tor already produces paper from bagasse at an industrial level and commercializes 15 MW of electricity obtained from this material in the national interconnected electric network (Asocana, 2006). The technologies for production value-added products by fermentation employing bagasse are currently under development. In general, these technologies are oriented to the application of solid-state fermen­tation to produce animal feed, enzymes, amino acids, organic acids, and phar­maceuticals, among others (Pandey et al., 2000). The pretreated bagasse can be used as a substrate in submerged fermentations for production of xylitol, flavors, single-cell protein, cellulases, ligninases, and xylanases (Aguilar et al., 2002; Cardona and Sanchez, 2007; Pandey et al., 2000). In addition, sugarcane bagasse can be the feedstock for producing activated carbon with an exceptionally high adsorptive capacity (Cardona and Sanchez, 2007; Lutz et al., 1998).

The percentage of the main biopolymers in cane bagasse is quite similar to that of hardwood (see Table 3.11). In chemical terms, cane bagasse contains about 50% a-cellulose, 30% pentosans, and 2.4% ash. Due to its low ash content, the bagasse presents a better performance during fermentation than other residues, such as rice straw and wheat straw, which contain 17.5% and 11.0% ash, respec­tively. Moreover, the bagasse can be considered as a valuable means for accumu­lating solar energy due to its high yield (80 ton/ha) compared to wheat (1 ton/ha), grasses (2 ton/ha), and trees (20 ton/ha; Pandey et al., 2000). In general, great amounts of energy can be obtained from cane bagasse. By burning the bagasse in co-generation systems, the total amounts of process steam and electricity required to adequately cover the energy needs of sugar mills can be obtained, with an energy surplus that can be sold to the grid. Nevertheless, different energy and economic analyses indicate that more benefits can be achieved if the bagasse were used for ethanol production (Cardona and Sanchez, 2006; Moreira, 2000). To this regard, it is necessary to take into account that the electricity can be obtained from a great number of primary fuels, while the liquid fossil fuels for transporta­tion can be substituted only by a reduced amount of renewable fuels (bioethanol and biodiesel; Moreira, 2000).

The global production of cane bagasse can be estimated at 373 to 416 million tonne per year considering data of 2004 and yields from 280 kg bagasse per tonne of cane (Moreira, 2000) up to 312 kg/ton (Kim and Dale, 2004). The ethanol yields of bagasse depend on the conversion technology employed, which will be discussed in the following chapters. In a preliminary way, a yield of 140 L EtOH/ ton bagasse can be assumed based on the efficiency reported by different trials carried out in the National Renewable Energy Laboratory in the United States (Golden, CO), which has been used by Kim and Dale (2004). Considering the mentioned yield, the global potential for producing ethanol from cane bagasse reaches 58.2 million L/year, an amount greater than all the ethanol produced in the world in 2007.