Microsoft Word - Environmental benefits of recycling 2010 update.doc

A 100-year period is chosen in most LCAs but there is a debate around this issue among LCA experts. It can
for instance be noted that SETAC recommends infinite emissions consideration (Thomas & McDougall, 2005).
This choice of the time period mainly affects the climate change potential since emissions of GHG
are directly affected by this parameter. This issue is critical, especially for plastics, since as they are made of
fossil carbon their degradation is very slow, so that emissions take place over a time horizon that largely exceeds
100 years. Among the studies assessed, study no 3 assumes an infinite time period while the other studies stick
to the usual 100-year time span.

To illustrate the importance of this parameter, a sensitivity analysis is conducted in study no 3 (Finnveden, 2000).
The results are compared for an infinite time period versus a 100-year time horizon. Under the 100-year
assumption, it is considered that only 3% of the carbon contained in plastics is released while full degradation is
assumed in the case of an infinite time horizon. The results obtained show that this change induces a new
ranking between the various alternatives because, unlike in the base case, landfill becomes a more
favourable option than incineration for a 100-year time period as illustrated below.

Table 39 Analysis of the influence of the time perspective on the performances of landfill in Finnveden et al., 2000

Time perspective

Infinite

100  years

Ranking between alternatives for the

potential impact on climate change

recycling < incineration<landfill

recycling < landfill < incineration

This conclusion points out that this parameter should be given special attention and it is thus interesting to check
how this parameter can explain the differences between the various cases analysed in this study. It should first
be noted that cases from study no 3 are the only cases for which landfill is the worst alternative regarding the
climate change potential as illustrated on Figure 21. For all the other cases, landfill appears to be preferable to
incineration for this indicator. This observation therefore tends to confirm that the time perspective is a key
assumption that significantly affects the assessment of the environmental performance of landfill. It can also be
noted that in studies 1, 2 and 6 the results from the comparison between incineration and landfill are very
homogenous, as landfill performs from 90 to 100% better in the nine cases concerned.

24 3

1

5

‐175%

‐150%

‐125%

‐100%

‐75%

‐50%

‐25%

0%

25%

50%

75%

100%

125%

150%

175%

Relative difference for the climate change potential

between incineration with energy recovery

and landfill according to the study

>150%

<‐ 1

50

%

<‐150%

incineration with

energy recovery

preferred to landfill

landfill preferred to

incineration with

energy recovery

Infinite time

period

Study n°1 Study n°2 Study n°4 Study n°6 Study n°3

100 ‐year time

period

Figure 21 Influence of the time perspective on the relative comparison between incineration and landfill for climate change