Life Cycle Assessments of Energy From Solid Waste (PDF)

landfill may then be considered as a so called carbon sink. This is here performed by
inventorying the biological carbon remaining in the landfill after the surveyable time period
has passed as negative emissions of CO 2 . However, this is only applicable if the time frame is
limited.
3.6 Scenario Plastic Palisade
When recycling thermo plastics the material is re-melted and the re-granulate may be used for
production of new plastic products, usually carrier bags, refuse sacks and packaging not to be
used for food stuff, etc. (Naturvårdsverket 1997, p 36). Collected plastics that are mixed
and/or very dirty may be recycled without extensive sorting and washing previous to the
process. Plastics recycled may also be used for producing ”profiles” ending up as noise
barriers, composting containers or poles often replacing impregnated wood. In this scenario
palisades made from recycled mixed plastics are studied and assumed to replace palisades
from impregnated wood.
3.7 Qualitative discussions
The impacts of a couple of aspects have been qualitatively discussed. These are the assumed
degree of efficiency at incineration plants and the characterisation of metals and heavy metals
as grouped emissions. The first aspect is an example of how technology assumptions may be
of importance. The other one shows upon the dilemma of undetailed inventories, where
emissions or resources may be aggregated leading to extra difficulties in assessing the
resource use and environmental impacts.
3.8 Additional time perspectives on global warming
The gases contributing to global warming have different life times in the atmosphere. Global
warming potentials (GWP) used in the characterisation of global warming may therefore be
calculated for different time frames. The International Panel on Climate Change provides
global warming potentials for 20, 100 and 500 years (Houghton et al. 1996). In the base
scenario we use those for the time frame 100 years. In one scenario the calculations in the
base scenario are compared with calculations using the time frames 20 and 500 years. This is
expected to mainly affect landfilling where substantial emissions of methane occur. The GWP
for methane varies from 56 CO 2 -equivalents over a 20 year perspective, to 21 in a 100 year
perspective and 6.5 in a 500 year perspective. The results may however also be influenced by
the GWP of nitrous oxide, which is 280 CO 2 -equivalents in the 20 year perspective, 310 in the
100 year perspective and 170 in the 500 year perspective. The GWPs for the different time
frames can be found in Appendix 2.
3.9 Summary of the scenarios
Some of the features of the different scenarios are summarised below.
3.9.1 Base Scenario
The transport distances are in the base scenario short and there are no transports by private
cars. The avoided heat is from forest residues. The ashes from incineration of forest residues
are spread in the forest. The ”saved” forest from recycling of paper is left in the forest. The
time period considered for landfills are long corresponding to the ”hypothetical infinite time
period”. Recycled materials are assumed to replace virgin materials of the same kind.
Electricity is produced from a modern coal condensing power plant.
37