how many times can you spot the letter u in:
the looming energy challenges around the world will have to be tackled with a portfolio of different raw materials and technologies. biomass is a widely available renewable carbon source and includes organic wastes and energy crops, which can be used for the production of biofuels to contribute to the reinvigoration of the biomass industry, among others. energy crops have to be produced in a cheap and environmentally benign way in order to be utilized for the sustainable production of biofuels. energy crops include mainly three categories, namely oil-rich crops, sugar crops, which contain sugars directly available for biofuel production, and lignocellulosic crops, which contain tightly bound cellulose, hemicellulose and lignin. in this chapter focus is given on fermentative biofuel production from sugar-rich and lignocellulosic biomass. ethanol production from energy crops has been studied in the literature since the 1980s, but in the last decade significant research efforts have been addressed towards biological hydrogen production. therefore, ethanol and hydrogen are considered two representative options for short- and long-term biofuel production, respectively. in particular, biofuel production from lignocellulosic crops or agricultural residues is more intensively discussed, given the higher degree of complexity of the utilization of these raw materials for biofuel production. various pretreatment methods can be applied to enhance the accessibility of lignocellulosic carbohydrates for enzymatic hydrolysis and the production of fermentable substrates. the efficiency of ethanol/hydrogen production from these substrates is dependent on their quality, which largely depends, in turn, on the amount of degradation products which act as inhibitors in the fermentations. therefore, significant discussion is dedicated to the key aspects of the role of pretreatment of biomass on the efficiency of biofuel production. the development of dedicated pretreatment techniques which are tuned to special characteristics of different energy crops is discussed. sweet sorghum and sugar beet are regarded as two energy crops that can be instrumental in the promising field of biofuels. sweet sorghum is interesting because it constitutes a highly productive sugar crop which, after sucrose extraction, provides a yet not well studied lignocellulosic residue, sweet sorghum bagasse. sweet sorghum bagasse is currently unexploited, poses a disposal problem and its usage as fodder for animals is not a sufficiently viable solution. similarly, sugar beet constitutes a traditional sugar crop, which can provide the biofuel industry with innovative raw materials with no competition with food production. from the viewpoint of sustainability, it is necessary to simultaneously assess the impact of the aforementioned biomass and biofuels on the environment and the economic growth. in principle, the use of organic wastes can be a win-win solution; however, biomass crops can present peculiar advantages for their potential in protecting/reclaiming vulnerable and marginal soils, sequestering co2, bio-depurating wastewater and enhancing biodiversity and wildlife.
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The text includes ninety-seven "u"s in total.
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