Environmental Engineering Reference
Certificate System 19 (RECS) which in contrast to the Swedish system does include municipal
waste. This shows that opinions as to how to classify waste in terms of whether it is a
renewable or not differ throughout Europe.
M ODELS AS D ECISION S UPPORT
Various models are often used as decision support tools, e.g. when municipalities make
infrastructural decisions, such as waste treatment capacity and energy utility plants. This
section describes some models based on system analysis. The models have been used to
assess waste management systems and waste incineration and the common theme is the
dilemma of the two purposes waste treatment and production of heat and sometimes
electricity, and how to handle this.
System analysis can be a mean to assess complex systems in order to e.g. determine how
available resources should be used to satisfy the aim of the system or to evaluate
environmental impacts of various measures. A model can be built that should include the
essential features of the system. By building a model, understanding and knowledge of the
system and the correlation between components in the system is gained.
Models and How to Handle the Double Function of Waste Incineration
The method used in earlier studies carried out by the author (Holmgren and Bartlett,
2004; Holmgren and Gebremedhin, 2004; Holmgren, 2006) is energy system modelling,
using the MODEST model (Henning 1998; 1999). MODEST is a linear programming model
which minimizes the cost of supplying heat and/or power demand during the analysed period.
The main purpose of the model is to find suitable investments, but it can also be used to
optimize the operation of existing plants. The results from these studies are mainly how waste
functions as a fuel in the district heating system, e.g. the impact on other fuels used, the cost
of supplying heat with different amounts of waste used as fuel, and the amount of electricity
produced in the DH networks. The effects of various policy instruments are also an
appropriate issue to assess. The influence of the waste management system in the model is
mainly via economic signals as regards the cost of waste as a fuel. Limits on amount of
available waste is also set. When analyzing the results, it is vital to be aware that also
considerations, more related to the waste management sector, should be included. A study has
also been made that has broadened the scope by comparing waste treatment options from an
energy efficiency viewpoint (Holmgren and Henning, 2004). Assuming that there is a district
heating system that can utilize the heat, which fractions of the waste are suitable to energy
recover and which to material recover? Another example of a study with the energy system in
focus is Sahlin et al (2004), which analyses the impact on Swedish district heating systems as
a whole, using a questionnaire and a simulating energy model named HEATSPOT.
Other methods have the waste management system in focus, as shown e.g. by Sundberg
et al (1994). The paper describes the model MIMES/WASTE, which seeks the most cost-
19 More information can be found at www.recs.org (November 2005).