5. ConclusionThe uncertainty in was

5. Conclusion
The uncertainty in waste management LCA arising from uncertainty
in waste composition has been less extensively studied than
uncertainty stemming from the choice of system boundaries, technology
and energy replacement. In this paper we have systematically
modified the average waste composition estimated from the
waste composition of five Norwegian cities. We found that a
±15% change in selected fractions resulted in a greater than 10%
change in global warming, nutrient enrichment and human toxicity
via water impact categories. Hence, such LCA impacts are highly
sensitive to uncertainties in waste composition. If the quantities of
source-separated material are known the uncertainty is low for
most categories, but still 10% for global warming. A percentage
change in the large fractions – paper, plastic and food waste – is
of most importance, together with changes in the metal content.
When comparing scenarios, the results are more robust. The analysis
of the five cities showed wide variation in waste composition
in the municipalities, and using a waste composition from another
city or an estimated average can influence the result of a study.
Having good data on the quantity of waste recycled, and the quality
of this waste is of importance for the reliability of the results.