For the calculation of the GHG emission factors presented in the
sections above, numerous assumptions had to be made. Each of
these assumptions might have introduced a margin of error. From
the emission factors calculated for recycling, the one factor derived
from the least number of assumptions and the most measured
parameters is the emission factor for glass. The ones with the most
assumptions used are the GHG emission factors for the different
plastic types. In particular, the use of European data on plastic production
when calculating GHG from substitution of raw plastics is
an underestimation of the likely South African emissions, which
means in reality GHG savings are higher. This is because the South
African electricity mix is different from the European one and has a
higher GHG burden. Electricity is used in the production of all
types of plastics.
Representativeness of compost calculations is another limitation
which has to be noted. Composting studies rely on specific
parameters derived from individual studies which then are generalised
for a waste management system of a country and region.
This is the case also for the South African situation, in which composting
has been studied for garden waste from the eThekwini
Municipality, which is situated in a subtropical location. The vegetation
and the other parameters (most importantly temperature
and moisture) might not be representative for other parts of the
country, which have arid conditions. However, until more detailed
composting studies are done, covering more climatic areas in the
country, the factors calculated in this paper are considered more
representative than the theoretical, international ones published
in the literature.
The emission factors developed in this study are targeted towards
waste managers and professionals involved with decision
making affecting the municipal waste management system in local
municipalities. The use of these factors will enable scenario modelling
and local choices for best practices with regard to reducing
GHG emissions from municipal waste management. Therefore, in
a next step a simple tool should be developed and distributed to
local authorities. It should facilitate the use of these factors for
GHG calculations and accounting at this level, since it is the most
important level for operational decision making, with significant
outcomes in terms of GHG savings from waste management in
South Africa. In addition, an educational tool for households,
schools and other general institutions should also be developed
based on these emission factors.