SUbstance flow analysis of the recycling of small waste electrical ...

3. Method 57
3.3.2. Data on material and substance flows
Reuter et al. (2005) observed that the data to conduct SFA are sometimes hardly available,
and must be obtained from very heterogeneous sources. Two approaches are possible to
quantify the flows entering and leaving a system: either all the input and output flows are
quantified independently from each others, or transfer coefficients are determined to quantify
how the input of the subsystem is distributed over the outputs. On a case-by-case basis
depending on the processes and on the available data, both approaches were combined or
an approach was preferred to the other one.
Five subsystems, in which flows of sWEEE and of precious metals occur, can be
distinguished (Table 8):
Generation
Collection
Reuse
Formal treatment
Informal treatment
If previous research works already gathered and published data on the material flows or on
the transfer coefficients in one or various subsystems, these results were taken into
consideration. Some experimental investigations were carried out to quantify material flows
for which no data is available in the literature. The information that was still missing was then
gathered through observations, interviews and estimates. The quality of all these data was
assessed by quantifying uncertainties (see 3.3.3).
3.3.2.1. Literature review
An extensive review of the available data on the flows of sWEEE in Germany and in the USA
was carried out. The data made available by other studies were integrated in this research as
far as possible, considering the following challenges related to the data consistency:
The definition of equipment groups and of sWEEE: if the material flows are defined in
another way than in this investigation, the data had to be “adapted” to provide data
on flows of sWEEE as defined in this thesis;
The considered processes, which are not always defined as in Table 9;
The geographical system boundaries, because some investigations focussed on
other regions (for example only one state in Germany or in the USA);
The temporal system boundaries, because previous studies usually mapped the
flows of sWEEE in years previous to 2007.
Some pragmatic assumptions or adaptations were needed to apply the data to conduct the
SFA. Chapter 4 explains on a case-by-case basis the assumptions that were made to
integrate the data from the literature into this investigation.