Page 35 - Materials Chemistry, Second Edition

Key Issues in Conducting Life Cycle Assessment 21

used, directly and indirectly, as a result of the consequential effects of introducing
biofuels to the global economy. In this regard, the rule is to include only relevant
affected processes, defined as those that respond to changes in demand or supply
driven by the decision at hand (Zamagni et al. 2012). In doing so, the resulting
functional unit of the whole system may consist of multiple functions, including
the main system and those processes added into the system boundary. However,
when a comparative analysis must be conducted, it may be difficult to guarantee
the functional equivalency between the systems compared since the processes
included could serve different functions. Such a resulting multi-functional system
raises some concerns about whether it can still be considered a functional unit
(Zamagni et al. 2012). In this case, differences in system boundaries are rather
crucial. Therefore, they must be specified, unambiguous, consistent, and in-line
with the actual goal and scope of the study (van der Voet et al. 2010). This may be
the most difficult problem to address.
The cradle-to-gate approach is sufficient for comparing various production
technologies to make the same biofuel from different feedstocks, while the cradle-
to-grave is the best approach for comparing, for example, the utilization of certain
biofuels with fossil fuels (Singh et al. 2010). Cradle-to-gate studies are performed
by excluding the use and waste treatment stages, but it is, of course, admissible
only when there is no difference between these stages. To illustrate this, a com-
parison between a plastic cup and a paper cup for drinking tea can be used. In this
case, the upstream stages (the growing of tea plants, the processing of tea leaves,
and the boiling of water) are likely the same, but the waste treatment of plastic
cups is obviously different from that of paper cups (Heijungs and Wiloso 2012).
The same system boundary with a difference in functions will have a different
basis of comparison. For example, electricity generated from municipal solid
waste is not very efficient and usually shows no improvement over a fossil fuel
alternative. However, when a waste management aspect is included in the
electricity generation, this extended new waste-to-energy system boundary will
likely favor over the waste management alone (without electricity generation) or
over a fossil fuel system (van der Voet et al. 2010).

3.2 Land Use and Land-Use Change

Although the majority of global GHG emissions have been blamed on the use of
fossil fuels, there has recently been growing recognition that land use also
significantly contributes to the emissions. The increased understanding of the
effects of land-use change needs further consideration in bioenergy systems. In this
regard, a UNEP-SETAC guideline on land-use impacts (soil quality, biodiversity,
and ecosystem services) has been proposed (Koellner et al. 2012), but there is
currently no widely acceptable way to incorporate land-use impacts in an LCA
study. The main reason may be that this aspect is very difficult to quantify.