The methodology of life cycle assessment (LCA) is a systematic analysis tool considering the environmental impacts of products, processes, or services, and provides a reference structure for the development and application of screen­ing indices and environmental performance indicators, especially during the extension of the system boundaries to the other steps of a life cycle of a product. Therefore, LCA is a technique for assessing the environmental performance of a product, process, or activity from “cradle to grave,” i. e., from extraction of raw materials to final disposal (Azapagic, 1999).

Life cycle assessment is defined as a process to evaluate the environmental burdens associated with a product, process, or activity by identifying and quanti­fying energy and materials used and wastes released to the environment; to assess the impact of those energy and material uses and releases to the environment;

and to identify and evaluate opportunities to effect environmental improvements (Azapagic, 1999). A fundamental feature of LCA compared to other methodolo­gies for environmental evaluation is the analysis of a system (for instance, a pro­cess for production of a particular chemical) during its whole life cycle from the extraction and processing of the feedstocks to the disposal of the target product, co-products, and by-products considering their effect over the whole environment (over the global warming, ozone layer depletion, etc.) and including manufactur­ing, transport, use, reuse, maintenance, and recycling of the different materials involved. In contrast, most methods for environmental assessment are focused only on the immediate effects of the system on the surroundings, such as the effects of the emissions and burdens from the processing plant. In this sense, there exists the possibility that certain measures adopted to reduce these emis­sions and burdens in a given process lead to the increase of other emissions or burdens in other steps of the life cycle of this process, e. g., during the feedstock extraction. Despite these conceptual advantages, the application of LCA during the conceptual design step is quite difficult due to the limitation in the available information as mentioned above.

Applying the LCA methodology, the environmental benefits of using the excess of cane bagasse, which remains after employing the bagasse as an energy source in sugar mills, as a feedstock for fuel ethanol production instead of burning it in open fields were demonstrated (Kadam, 2002). Thus, some achievements can be attained such as the emissions reduction, less fossil fuels consumption, diminu­tion in the rate of natural resources depletion, reduction of human toxicity, and less contribution to greenhouse gas effect. Hu et al. (2004b) performed LCA for cars fueled by blends using ethanol from cassava obtaining better results than for conventional cars in China. Kim and Dale (2002) proposed an allocation proce­dure based on the system expansion approach for the net energy analysis of corn ethanol. The allocation procedure is a key factor in LCA when the multi-input/ output process is analyzed as in the case of ethanol production employing wet and dry milling. These same authors also determined the nonrenewable energy con­sumption and greenhouse gas emissions for corn ethanol production in selected counties in the United States, showing positive net energy values and the pos­sibility for reducing greenhouse gas emissions (Kim and Dale, 2005a). Bullock (2002) cites the LCA studies based on data from Australian ethanol plants for gasoline blends with 10% ethanol content. These studies indicate that there is no greenhouse abatement when molasses, wheat starch waste, or wheat are used as feedstocks. In contrast, the hypothetical process from wood waste can lead to CO2 abatement. Gasoline blends with 85% ethanol content present significant environ­mental benefits represented mainly by the greenhouse gas abatement.

Several recent studies applying the LCA methodology have been published demonstrating some advantages of fuel ethanol production even in the polemic case of corn ethanol. For example, using ethanol derived from corn dry milled as liquid fuel (E10 fuel) would reduce nonrenewable energy and greenhouse gas emissions, but would increase acidification, eutrophication, and photochemical smog, compared to using gasoline as liquid fuel (Kim and Dale, 2005a). Other studies using the cereal straw or corn stover as feedstocks for biomass ethanol have also indicated the environmental benefits, but show problems related to soil acidification and eutrophication (Gabrielle and Gagnaire, 2008; Kim and Dale, 2005b).

In a similar way, the LCA performed in France by comparing the ethyl tert — butyl ether (ETBE) obtained from beet ethanol (a partial renewable product) to the methyl tert-butyl ether (MTBE) from fossil origin showed that the energy yield of ethanol (1.18) and ETBE (0.93) are higher than the yields of gasoline (0.74 to 0.80) and MTBE (0.73). Moreover, the ETBE has a lower contribution to the greenhouse gas effect due to its renewable character, and its use as a gasoline oxygenate provokes fewer emissions of nonburnt hydrocarbons than in the case of MTBE. Nevertheless, the ethanol cost for ETBE production in France has been higher than the cost of gasoline and methanol (a feedstock for MTBE production; Poitrat, 1999).