Page 70 - Materials Chemistry, Second Edition

2.5 Life cycle assessment and waste management 57
Avoided virgin PET
2
kgs of CO 2 per kg PET presented at kerbside 1.5

1
0.5

0

-0.5 Recycling Other reprocessing All other
collection and Caustic soda operations recycling
-1 transport use in reprocessing processes

Figure 6.5 Greenhouse gas savings and impacts from polyethylene terephthalate (PET) recycling
in terms of kilograms of carbon dioxide per kilogram of PET presented at kerbside.

The impacts omitted, due to limited available data or where the LCA methodology at the
time was unable to handle such data, were:
s human and eco-toxicity impacts from virgin material production, recyclables and waste
collection, reprocessing of materials and landfill leachate
s land use and soil impacts, particularly from forestry operations in virgin paper fibre
production and agricultural operations in wheat production
s local amenity impacts from landfill
s resource consumption and/or depletion
s consumer behavioural data.

Modelling the degradation of the organic fraction took into account that carbon dioxide
and methane are the by-products of degradation, with some of the methane captured for
flaring or electricity generation while the remainder is lost to the atmosphere. The carbon
fractions that do not degrade are sequestered and become a carbon sink (Fig. 6.6). At the time
of the study, from the late 1990s to early 2000, different assumptions and approaches were used
to determine the degradation rates of organic fractions in landfill. Due to great uncertainty
concerning these rates and ultimate levels of degradation, three different landfill degradation
scenarios were modelled:
s full degradation, in which all organic components are completely degraded
s carbon sequestration (CS US EPA data), in which 34% of newspapers and 23% of paper
and cardboard is assumed not to break down. This was used as the baseline assumption,
based on ICF (1997) and US EPA (1998)
s lignin content (CS lignin content calculations), in which 78% of newspapers and 53%
of paper and cardboard is assumed not to break down, based on Tchbanoglous et al.
(1993).
Depending on the degradation scenario selected, the results differ significantly for the
organic fractions of old newspapers, paper and cardboard, and LPB (Fig. 6.7).
Several sensitivity analyses were undertaken:
s landfill gas capture
s reprocessing yield

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