the agricultural sector (nutrients from anaerobic digestion of waste
and sludge are used instead of mineral fertiliser) etc. In this study;
two different types of scenarios that reflect the situation of year
2030 have been set up: local scenarios and external scenarios [6]. In
a local scenario we define the waste treatment processes that are
assumed to be in operation in Gothenburg’s waste treatment
system in year 2030 (e.g. waste incineration, anaerobic treatment).
Furthermore, an external scenario reflects the situation in the
surrounding systems (e.g. price of electricity, fuels and CO2-
allowances). The local scenarios thereby describe developments
that the actors in Gothenburg can influence, while the external
scenarios describe developments that the actors have to adapt to.
The main principles of the local scenarios that have been set up are
as follows:
- Business-as-usual: This local scenario is characterized of
a traditional development of the waste treatment system in
Gothenburg, i.e. a significant share of waste incineration. The
capacities in existing facilities are adapt to the amount of waste
that are assumed to arise in year 2030. Today’s central composting
is still used for treatment of biological degradable
waste from households. Sludge from the wastewater treatment
plant is first treated in an anaerobic treatment facility, thereafter
composted and finally sold as a soil product.
- Maximized return of nutrients: In this local scenario more of
the arising waste is treated in biological treatment facilities,
compared to “Business-as-usual”. The capacity of the source
separation system in Gothenburg is expanded and an anaerobic
treatment facility is built that replaces the central composting.
The capacity of the anaerobic treatment facility is set to
60 000 tonnes/year. The capacity of waste incineration is
thereby decreased in comparison to the case in the local
scenario “Business-as-usual”. Sludge from the wastewater
treatment plant is treated in an anaerobic treatment facility
and thereafter used as fertilizer in the agricultural sector.
- Maximized electricity production: the source separation
system is expanded and an anaerobic treatment facility is being
built, similarly to the local scenario “Maximized return of
nutrients”. Furthermore a part of the combustible waste is
going through a mechanical treatment process to create
a refuse derived fuel. This fuel is used in a new waste incineration
facility with a slightly higher electrical efficiency than the
existing ones. Sludge from the wastewater treatment plant is
treated in an anaerobic treatment facility. Thereafter the sludge
is dehydrated and turned into pellets that are used as fuel in
the new waste incineration facility.
Within the project a number of external scenarios capturing
several parameters that describe the state in the economy, the
energy system, the waste system (such as waste amounts etc.) etc.
were discussed. Eventually three of these were selected for a more
careful analysis.
- Reference: is a scenario that reflects a conservative development
in the surrounding environment. The background system
is changed, but mainly the same impact and policy as of today
prevails. The reference scenario is not to be interpreted as the
most likely scenario. There is no valuation of which of the three
external scenarios is the most likely one. All three projects
constitute a “window of development” which is assessed as
possible and realistic.
- Material lean growth: is a scenario that reflects a development
where the society in general puts a lot effort in reducing
environmental impact on a long-term and evident environmental
improvements are achieved compared to the system of