VIII. In the analysis we’ve blocked the possibility of importing
waste to the system in study. This restriction has been
evaluated in a sensitive analysis, which shows that import of
waste for treatment in waste incineration within the system
give positive effects on the emissions of climate gases. The
main reason for this is that the import of waste results in
a decrease of the amount of waste going to landfills outside
the system. Since landfilling of organic waste result in high
emissions of climate gases it is highly desired to decrease this
activity.
IX. Composting of food waste and anaerobic digested sludge
from wastewater treatment also result in emissions of
substances that leads to eutrophication. However, spreading
digested sludge and digestate from anaerobic digestion of
food waste on agricultural land will also lead to eutrophication.
From this perspective, it is better to use the digestate as
fuel in waste incineration.
X. In a sensitive analysis regarding handling of anaerobic
digested sludge the result shows that the best treatment
method from an economic point of view is to spread the
sludge on agricultural land. As discussed above (in conclusion
IX), when considering eutrophication it is better to use
the sludge as fuel in waste incineration. The different
treatment options studied for sludge give equal results
concerning acidification and emissions of climate gases.
In general it can be concluded that the results are almost equal
irrespective of which external scenario is being studied. This means
that the results hold even though changes occur in the surrounding
systems. The external scenarios differ significantly and create varied
prerequisites for the waste treatment system; nevertheless the
results show that the same treatment methods should be chosen.
Having said so, we also have to be aware of the uncertainties
that exist in the analysis. For example we’ve not studied how the
economic results would react from a change in competitiveness for
the waste treatment facilities. It is also important to notice that this,
first of all, is a scientific project which points out interesting future
waste treatment technologies. This means that the result should
not be seen as a comprehensive material for an investment decision.
Furthermore, the analysis is based on today’s tax system,
which of course is a simplified description of the situation of year
2030. It should also be noticed that it’s difficult to find valuated data
for new technologies. The data can both be overestimated, caused
by to ambitious thoughts regarding the technology, and underestimated
as further developments of the technology can result in
decreased costs and increased performance.
Regarding the results for climate change the assumptions for the
development of the electricity production system play a significant
role. If the electricity production in northern Europe will transform
into a system with less emissions of carbon dioxide the value of
electricity production in Gothenburg will decrease, and vice versa.
Furthermore the results for acidification and eutrophication are
difficult to interpret as these environmental problems are regional
and not global. Therefore the question of where the emissions are
made becomes essential. This fact has not been taken into consideration
in the main results, however an alternative analysis has
been made that describes this factor in more detail.
We will emphasise that many but not all aspects have been
analysed for the waste treatment and district heating system. For
example we have not included toxic effects or the consumer
perspective. Furthermore, we have not included effects from the
fact that some natural resources used within the system may be
limited on a global scale; this is for example the case for phosphorous
and biofuels