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significant) range in GHG results for biofuels when different coproduct allocation
methods are used. The expansion of system for use of coproducts within the
system is recommended for biofuel production system. If allocation cannot be
avoided, then allocation could be done on the basis of carbon content of all
products as the target of biofuel production is to minimize the GHG emission and
the mass/volume of products is not a precise measure of energy/emission and
economic value is fluctuating with the market.

4.6 Inventory Analysis

A LCI is a process of quantifying energy and raw material requirements, envi-
ronmental pollution for the entire life cycle of a product, process, or activity (SAIC
2006). The inventory analysis requires data on the physical inputs and outputs of
the processes of the product system, regarding product flows as well as elementary
flows (Singh and Olsen 2011). The main issue of inventory analysis includes data
collection and estimations, validation of data and relating data to the specific
processes within the system boundaries. After the initial data collection, of which
the source should be clearly declared, the system boundaries can be refined as a
result of decisions on exclusion of subsystems, exclusion of material flows or
inclusion of new unit processes. The validation of data as a mean of data quality
improvement or the need for supplementary data would improve the outcome of
the analysis (Jensen et al. 1997). The inventory analysis requires very extensive
data. The outcome of the study totally depends on the availability and quality of
the datasets. So that, there is a great need to collection of standardized data,
especially for background processes (Singh and Olsen 2011).

4.7 Impact Assessment

Impact assessment establishes a relationship between the product or process and its
potential impacts on human health, environment, and sources depletion (SAIC
2006). ISO developed a standard for conducting an impact assessment entitled ISO
14042, LCIA (ISO 1998). Life cycle impact assessment (LCIA) is structured in
classification, characterization, normalization, and weighting. The first three steps
are mandatory steps for the determination of impact categories, which corresponds
to an important environmental problem (e.g., eutrophication, depletion of non-
renewable energy resources, and ozone depletion) (Singh and Olsen 2011). There
is no standardized list of impact categories (IFEU 2000). Guinée et al. (2002) has
tabulated most of the impact categories in the ‘‘Handbook of LCA.’’ The main
problems faced during LCIA result from the need to connect the right burdens with
the right impacts at the correct time and place (Reap et al. 2008b), in this regard,
impact category selection is the most important step which can influence results
significantly.