Page 45 - Materials Chemistry, Second Edition

Key Issues in Conducting Life Cycle Assessment 31

should be mutually independent in order to avoid double counting of environ-
mental burden. Life cycle impact assessment (LCIA) consists of seven activities,
i.e., selection of impact category, classification, characterization, normalization,
grouping, weighting, and data quality analysis. According to the ISO standard for
LCA (ISO 2006), the first three are mandatory, while the rest are optional. Two
aspects of LCIA that need further elaboration with regard to bioenergy systems are
impact categories and regionalized impact assessment.

4.1 Impact Categories

It is important to properly select the set of relevant impact categories in the
bioenergy systems under study. Areas of protection in environmental impact
assessment include ecosystem health, human health, resource availability, and
man-created environment. Assessment of bioenergy production from specific
biomass is suggested to be based on a complete set of impact categories, including
climate change, ozone depletion, human and ecotoxicity, photo-oxidant formation,
acidification, eutrophication, land-use impacts, and depletion of abiotic resources.
But McKone et al. (2011) suggested a balance between being comprehensive and
being parsimonious. Failure to address a key impact can lead to incomplete or
unreliable information, creating biased decisions. Clearly, the set of chosen impact
categories need to be fixed accordingly in the formulation of goal and scopes of the
study, but a default minimum would restrict the risk of biased decisions.
Early LCA studies were often limited to net energy output and global warming.
The net energy output is an important parameter because, in many cases, the
process of producing fuels from the feedstock is energy intensive and, therefore,
limits the overall benefit. This parameter (net energy output), however, only
determines the technical feasibility of the bioenergy systems rather than being an
impact itself. For global warming, the result of the LCI is a list of GHG emissions
of all processes in the chain, which are then added up and translated into CO 2
equivalents (so-called carbon footprints). According to the recent review by
Cherubini and Strømman (2011), approximately 90 % of bioenergy LCAs include
global warming in their evaluation while primary energy demand rates second
(71 %). Other impact categories, mainly acidification and eutrophication, are
estimated by 20–40 % of the studies. Only 9 % included the land-use category in
their impact assessment. The reason for including global warming in most of the
studies is because climate policy dominates the scene, while other impacts are not
considered as important. In addition, some of them are site specific, which may
limit the generalization of the result. Also, there is significantly less agreement in
the quantification methods of some impact categories. Particularly notorious are
the impacts related to land use, water use, biodiversity, and genetically modified
organisms (Heijungs and Wiloso 2012). With the increasing pressure of a growing
population, water use is now also considered as increasingly relevant. Water
footprints specify water requirements on a cradle-to-gate basis, and their studies in