2.3. Sorting efficiencies
The total impact from the system was calculated based on the
quantities of each recycled fraction and the quantity and waste
composition of the incinerated waste. The quantities of waste
recycled and incinerated can either be calculated using estimated
source-separation efficiencies or taken from measured quantities
of these fractions. Both cases were modelled in this study (Fig. 2).
In the first case (Case 1) we kept the sorting efficiencies constant
and at a level based on the typical sorting efficiencies found
in many Norwegian cities. A change in waste composition combined
with constant sorting efficiency resulted in changes in both
the quantities of recyclables and the quantity and composition of
waste incinerated. This calculation method relates to uncertainty
in waste composition when performing LCAs on new systems or
when introducing changes to existing systems, such as increased
sorting efficiencies or the introduction of food waste sorting. The
sorting efficiencies were set to 75% for paper and cardboard, 25%
for plastic, 60% for glass and 65% for metals. In addition we assumed
that 10% of the non-recyclable paper and cardboard was
sorted as paper and that 10% of the non-recyclable plastic was
sorted as plastic. These sorted non-recyclable fractions were separated
at the MRFs and sent for incineration.
In the second case (Case 2) the quantities recycled and incinerated
were kept constant. A variation in waste composition will in
this case change the sorting efficiencies used in the calculations.
This method is used for accounting LCA in existing systems when
the waste composition and quantities of waste are known. Case 2