Page 136 - Materials Chemistry, Second Edition

9 Life Cycle Inventory Analysis 121

Processes downstream, i.e. in the use and waste management stages, should be
identified in a similar fashion. The procedure is, in principle, repeated until the
foreground system is completed and can be linked to LCI database processes of the
background system, as described later in this chapter. When carrying out this
procedure, the LCA practitioner should identify all multifunctional processes,
because they have to be handled next.
Note that the step of identifying processes for the LCI model and the step of
planning and collection of data are somewhat interrelated. For example, data col-
lected for a given process may lead to the realisation that one or more upstream
processes are different than the ones previously (assumed) identified. During data
collection the LCA practitioner may, for example, realise that a plastic component
is actually produced from biomaterials rather than petrochemicals, as was initially
assumed. The identified processes in this first inventory step should therefore be
considered preliminary.
In practice, many processes belonging to level 3 and 4 will end up being entirely
omitted from an LCI model, because their individual contribution to the indicator
score is expected to be insignificant and because data can be hard to find, at least
when using the ‘bottom-up’ (=process-based) approach to constructing inventories.
In such cases, the environmental impacts of product systems are systematically
underestimated by various degrees. It is an important task of the inventory analysis
and consecutive impact assessment to ensure that this underestimation does not
violate the completeness requirements for the study. Chapter 14 shows how
IO-LCA can complement process-based LCA to better cover the impacts from level
3 and 4 processes.

9.2.2 Handling of Multifunctional Processes

Section 8.5.2 presented the ISO hierarchy for solving multifunctionality, i.e. pro-
cesses in the product system that deliver several outputs or services of which not all
are used by the reference flow of the study. According to this hierarchy, the pre-
ferred solution is subdivision of the concerned process, and if this is not possible,
system expansion and, as a last resort, allocation. Below, examples are given for
how to carry out each solution in practice. This guidance is primarily relevant for
the foreground system because multifunctionality has typically already been han-
dled for the processes in the LCI databases that are used to construct the back-
ground system. Some LCI databases exist in different versions, according to how
multifunctionality has been solved (see Sect. 9.3 below). For the background
system this reduces the job of the LCA practitioner to just source processes from the
appropriate version of the LCI databases. Yet, even in the background system, the
LCA practitioner may sometimes have to solve multifunctionality manually when
no appropriate solutions exist in the used LCI databases. We note that many waste
treatment processes are multifunctional because they both offer the function of
managing (often heterogeneous) waste streams and the function of providing