Page 29 - Materials Chemistry, Second Edition

Key Issues in Conducting Life Cycle Assessment 15

methane), fermentation (fuel: bioethanol), trans-esterification (fuel: bioediesel),
and photosynthesis (fuel: hydrogen) (IEA-Bioenergy 2009). These various con-
version technologies will dictate overall environmental performances. For exam-
ple, ethanol production through biochemical or thermochemical conversions is
expected to result in different levels of decreasing GHG emissions. However, these
conversion-related differences are likely to be small in relation to those associated
with feedstock production (Williams et al. 2009). In addition, emissions of
methane or nitrous oxide from agricultural field and indirect land-use change may
contribute to a more complicated overall picture (Cherubini and Strømman 2011).
Side and rebound effects, as well as market mechanisms, of large-scale production
of biofuels also affect food markets, resource scarcity, and environmental quality,
while these factors are often left out in a sustainability assessment (Guinée et al.
2011; van der Voet et al. 2010). Moreover, bioenergy systems may involve a unit
process with input–output flows, which often make it difficult to differentiate
between economic (products) and elementary (resource use or emissions) flows.
Recently, there have been tremendous numbers of LCA studies describing
bioenergy in order to support policy making. The growing debate on bioenergy
and other bio-based products contributed to the acceleration of the development of
LCA methodology. However, it is difficult to draw general conclusions from the
set of studies due to large variations in outcomes. Sources of these variations
include real-world differences, data uncertainties, incompleteness of included
impacts, and methodological choices (van der Voet et al. 2010). More specifically,
the methodological choices are related to the selection of a functional unit, system
boundary, land-use aspects, biogenic carbon, treatment of multi-functional pro-
cesses, data variability, and regionalized impact assessment (Cherubini and
Strømman 2011; van der Voet et al. 2010; Guinée et al. 2009; Finnveden et al.
2009). This indicates that bioenergy poses more methodological challenges than
other renewable energy. Moreover, these issues are insufficiently comprehensively
addressed by current LCA studies.
This chapter is aimed at providing a systematic overview on the above-men-
tioned key issues in conducting LCA of bioenergy. Detailed comparison of
methodological choices among different LCAs of bioenergy systems can be found
in recent surveys such as those of Cherubini and Strømman (2011), van der Voet
et al. (2010), Wiloso et al. (2012), and Singh et al. (2010). The structure of this
chapter will follow the first three phases of the LCA framework (ISO 2006),
including goal and scope definition, inventory analysis, and impact assessment as
follows:

• Goal and scope definition:
– Attributional and consequential LCA
– Functional unit

• Inventory analysis:
– System boundary
– Land use and land-use change