type of treatment options that already exist in Gothenburg
today. The conclusion holds even when comparing new
investments in new or existing technologies.
II. Having said so, we can consider that the only new technology
found to be economically competitive to existing treatment
options are anaerobic digestion of food waste. The conclusion
holds for a situation when the treatment capacity has to
increase in order to meet the demand in the region. This is not
the situation of today, but it is most likely that the situation
will arise in the future because of increased demand for waste
treatment or because the existing treatment facilities become
too old.
III. Increasing the share of electricity generated from waste
incineration is a clear advantage in order to realize a decrease
of emissions of climate gases. This is partly because the fact
that the electricity produced from the incinerator keep out
other electricity production with higher emissions of climate
gases. A second positive factor is that a higher share of electricity
production results in a minor share of district heat
production, which in turn results in increased production in
other combined heat and power plants in the district heating
system. Thereby even more electricity is being produced
within the system, keeping out other electricity production
with higher emissions of climate gases.
IV. Another good way to reduce climate gases is to produce
biogas from waste and use it within the transport sector. The
reason for this is partly that the biogas is used as a substitute
for fossil fuels, but it is also because of the fact that the need
for waste is decreased. As described above, this leads to
increased use of other combined heat and power plants
within the district heating system, resulting in more electricity
produced from the system.
V. Results from the project show that today’s composting of food
waste and anaerobic digested sludge from wastewater treatment
result in emissions of acidifying substances. A better
option for treatment of food waste is anaerobic digestion
followed by spreading of the digestate on agricultural land as
fertilizer. The sludge should also be utilised as fertilizer, or
alternatively used as fuel in waste incineration.
VI. In a comparison between source separation and central
sorting of food waste, the latter turns out to be a better choice
regarding economic aspects. The main reason for this is that
the capital costs related to central sorting are lower compared
to the costs for a system with source separation of the food
waste. Regarding the environmental aspects, the two systems
are almost equal. Uncertainties within the results primarily
concern the performance of a central sorting system. Even
though it’s not evident, the assumption made is that the
sorted fractions from the central sorting facility hold an equal
quality with the one from a source separation system.
VII. When comparing waste incineration with gasification of
waste the latter turns out to be in favour regarding emissions
of climate gases. On the other hand, waste incineration is by
far the best choice when regarding economy. The reason for
the good result for gasification of waste when comparing
emissions of climate gases is first of all that the district heat
output from gasification is much lower than the output from
waste incineration. As described earlier, this results in
increased electricity production within the district heating
system, keeping out other electricity production with higher
emissions of climate gases. Secondly, gasification of waste by
itself has a higher output of electricity compared to waste
incineration.
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 equa