Page 52 - Materials Chemistry, Second Edition

36 2 Goal and Scope Definition

• On the side of impact assessment, the so-called Eigenzeiten 23) and ‘rhythms’ of
24)
ecosystems, which are affected by product systems, are to be considered. Today,
it is not yet clear how time can be better integrated into LCA without making the
method too complicated.

Some impact categories require the specification of a time horizon for the
selection of suitable characterisation factors (see Chapter 4): With the greenhouse
effect, for example, usually a time horizon of 100 a is assumed. Longer time horizons
are very uncertain because of our total ignorance of the far future, but are, however,
often demanded for reasons of justice towards coming generations. 25) There is a
close link to the question whether negative effects on the environment – in analogy
to financial computations – may be discounted. 26)
Statements to the time horizon must be provided at the beginning of the study;
if necessary, modifications can be made during the progress of the study.

Exercise: System Analysis

Provide a first system flow chart for the product system ‘Strawberry Yogurt in a
polypropylene (PP)-cup with aluminium cover – 150 g’. In the initial phase of an
LCA, it is always useful to have the product in reality and to weigh individual
components, if necessary.

• Set up a list of the materials contained in the product.
• Make a first assessment of materials that may not be examined by their entire
life cycle using the cut-off criterion ‘mass’.
• Draw the flow chart and indicate the technical system boundary in your sketch.
• Make sure that in your flow chart the boxes (unit processes) indicate processes
and not substances or materials.
• Name in further sketches all inputs and outputs qualitatively for each process
you considered. Since no detailed research has yet taken place, the degree of
detail in this step is dependent on your background knowledge of the processes
you defined.
• Consider usual recycling pathways (open loop and closed loop) in your flow
chart.
• Explain the meaning of ‘co-products’ using the example of the unit process ‘milk
production’.
• Define the geographical and temporal system boundaries.

23) ‘Eigenzeit’ is difficult to translate; it means a time specific or intrinsic for the system under
consideration.
24) Held and Geißler (1993, 1995) and Held and Kl¨ opffer (2000).
25) World Commission on Environment and Development (1987).
26) Hellweg, Hofstetter and Hungerb¨ uhler (2003).