Page 137 - Materials Chemistry, Second Edition

122 A. Bjørn et al.

product flows, such as recycled materials or electricity. We refer to Chap. 35 on
application of LCA to solid waste management systems for more details on how
these special cases of multifunctionality are solved in LCA practice.

Subdivision
When possible, subdivision should always be the solution to multifunctionality.
Unit processes can be defined at many levels of detail and for the use in LCA there
is no point in detailing them beyond what is needed for the modelling purpose in
the LCA. This may mean that by increasing the detail applied in the modelling, the
multifunctionality may be revealed as artificial. For example, a process that
encompasses an entire factory producing two different products may have been
identified from the procedure detailed in Sect. 9.2.1. If this factory is in fact using
different and independent machines and work stations for manufacturing the two
products, the initial process can, by introducing additional detail in the modelling of
the process, be subdivided into two or more processes that each contribute to the
production of only one of the products, see Fig. 9.2. Note that it is often not
possible to fully physically divide a process according to the co-products. In the
factory example room lighting, room heating and administration (all level 3 pro-
cesses, according to Sect. 9.2.1) may not be possible to divide between the
co-products. In such cases, subdivision needs to be supplemented with or replaced
by another solution to multifunctionality. Note also, that in practice data availability
often determines whether subdivision is possible. In the factory example, it may be
that data only exist for the electricity consumption of the entire factory, i.e. the
consumption of each machine is unknown and in this case, subdivision would be
practically impossible. In addition, there are many situations where the creation of
the co-products is integrated into the process in a way that impedes the multi-
functionality to be addressed by subdivision. This is the case for many biological
and chemical processes.

Emissions to air, Emissions to air,
water and soil water and soil

Materials Materials

Product 1 Product 1
Unit process
Product 2 Product 2

Fig. 9.2 Solving the multifunctionality problem by increasing the modelling resolution and
sub-dividing the process into minor units which can unambiguously be assigned to either of the
functional outputs