Life Cycle Assessments of Energy From Solid Waste (PDF)

2.1.5 Interpretation
In the interpretation phase of LCA the findings from the inventory analysis and the impact
assessment are combined together in order to reach conclusions and recommendations,
consistent with the goal and scope of the study (ISO 1997). This phase may also involve the
reviewing and revising of the goal and scope, as well as the nature and quality of the data
collected.
2.2 LCA Methodology and Integrated Solid Waste Management
The general LCA methodology has been described above. Essentially the same methodology
can be applied when applied to waste management systems although different aspects of the
methodology may come into focus. It is also important to notice that although improvements
have been made to LCA methodology, there are still a number of unresolved issues, which
need further attention (Udo de Haes and Wrisberg 1997). Here, some methodological aspects
of relevance for LCAs on waste management systems will be discussed. It is suggested that
many of these aspects are of relevance also for other types of systems engineering models of
waste management systems (Finnveden 1999c). This section is largely based on previous
methodological publications (Finnveden 1999c, Clift et al. 2000, Ekvall and Finnveden
2000b, Finnveden 2000b). Aspects that will be discussed include: Upstream and downstream
system boundaries, Open-loop recycling allocation, Multi-input allocation, Time especially in
relation to landfills, Landfills as a carbon sink, and Life cycle impact assessment.
2.2.1 Upstream and downstream system boundaries
A key aspect of LCA is that the system should be modelled in such a manner so that inputs to
and outputs from the system are followed from the “cradle to the grave”, which means that the
inputs should be flows that are drawn from the environment without human transformation,
and outputs should be flows that are discarded to the environment without subsequent human
transformations (ISO 1997). In LCAs of waste management systems, this is typically not
done. Instead, the inputs are often solid waste as they appear, e.g. from households. This is,
however, still compatible with the LCA definition, if the same inflow appears in all systems
which are to be compared. This is because those parts of the systems, which are identical in
all systems that are compared, can be disregarded. The upstream system boundary may,
however, have to be changed, if one of the systems to be compared produce more or less
waste than the others. In this situation the system inputs are no longer identical, and in
principle the system boundary should be moved and upstream activities be included, at least
those parts which differ between different systems. This may in practise prove to be very
difficult and therefore not done. In that case it should, however, be carefully noted that the
impacts of the system which produces less waste is overestimated compared to the others.
A similar situation may occur for the downstream system boundary when materials or energy
are recycled into new products. In LCAs of waste management systems, products from
recycling are normally not followed to the “grave” and neither are the products, which are
replaced by the products from recycling. Again this is compatible with the LCA definition, if
the products are “identical” in all systems which are compared. In these cases the products
can be disregarded. “Identical” does not mean that they have to be exactly identical in all
aspects. It is enough if they are providing a comparable function to the user, and if they have
the same environmental impacts. If the products are not providing comparable functions, they
cannot replace each other. If the products do not have the same environmental impacts, at
least the difference should be included in the LCA.
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