Page 134 - Materials Chemistry, Second Edition

L1644_C03.fm Page 108 Tuesday, October 21, 2003 3:11 PM

A quantitative multicriteria assessment is based on weighting factors established
by the explicit weighting of the impact potentials.
In the event, an important point about LCA application must be remarked no
matter which interpretation method is selected. This methodology is a powerful
instrument of support regarding the evaluation of environmental and human health
impacts; however, in many cases its results can be useful without an appreciation
of the reliability and validity of the information. In this framework, a quantitative
sensitivity analysis must be performed to assess the effect of the key assumptions
on the final results, to check the data whose quality is suspected or unknown, to
show if the study results are highly dependent on particular sets of inputs, and to
evaluate life-cycle effects of changes being considered (Consoli et al., 1993).
Conclusions should only be drawn on study results with consideration of the
data variability and resulting variability of the findings. Chapter 5 will discuss this
subject more thoroughly and present alternative methods to carry out a qualitative
sensitivity analysis.

3.10 EXAMPLE: COMPARISON OF PET AND GLASS FOR
MINERAL WATER BOTTLES
This example addresses the question of what is better from an environmental point
of view: consuming mineral water in nonreturnable small plastic bottles made of
PET or in returnable glass bottles. For the sake of simplicity, as parameter for the
comparison, only the greenhouse effect (GWP) is to be considered. The basis of the
calculation is 1 L of mineral water consumed in small bottles. Calculations must be
made taking into account the life-cycle of the two types of bottles and the environ-
mental load of water and bottle transportation. The following assumptions are con-
sidered:

• In the case of the plastic bottles, the impact related to bottle manufacturing
is not taken into account. The same holds for transportation because the
bottles are manufactured in the bottling plant. Empty glass bottles are
delivered from the glass factory in 16-t trucks.
• The bottled water is delivered from the bottling plant to the wholesaler
in 16-t trucks and from the wholesaler to the retail trader by van. The
glass bottles are returned by van to the wholesaler and from the wholesaler
to the bottle manufacturer in 16-t trucks.
• The impact of cleaning the bottles is not considered.

For the calculations the following data must be used:
PET Glass
Bottle weight (g) 20 237
Bottle capacity (L) 0.33 0.25
Number of uses 1 20
Distance from bottling plant to wholesaler (km) 50 50
Distance from wholesaler to retail trader (km) 20 20
Distance from bottle manufacturer to bottling plant (km) — 100

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