Waste management models
A large variety of models used for analysing various aspects of waste management are described in the literature. The objective of a model is important since it largely determines the system boundaries and levels of detail to be used. Several review articles have been written on waste management models e.g. Chang et al. (1996) and MacDonald (1996a). An international workshop was also recently held on the subject, entitled 'Systems Engineering Models for Waste Management', in which several models and case studies were presented (Sundberg et al., 1998).
However, most of the models found in the literature deal with economic considerations, although during recent years several models focusing on environmental impact have also appeared. Examples of economic models which also consider environmental aspects are the SWIM model (Wang et al., 1996), the MIMES/WASTE model (Sundberg, 1993) and a model presented by Chang et al. (1996). Models dealing with both economic and environmental aspects by using multi-criteria evaluation methods are presented by Mainmone (1985), Caruso et al. (1993) and Hokkanen et al. (1995). Furthermore Rubenstein (1997) and MacDonald (1996b) presented models dealing with both these aspects but focusing on the planning process. A few simulation models focusing on environmental impacts and which use life cycle analysis methodology are also available (Gupta and Shepherd, 1992 and White et al., 1995). A comprehensive life-cycle study of municipal solid waste management, including construction of a linear programme model, is also currently being carried out by the U.S. Environmental Protection Agency (Barlaz et al., 1997).
In this paper the features of a model named ORWARE (Organic Waste Research model) are presented and the experiences gained from a number of case studies are discussed. The model was developed to simulate the environmental impacts of biodegradable solid and liquid waste fractions. The aim was to allow comparison of systems for handling mixed waste fractions with systems based on source separation and the recirculation of nutrients. Addi tional objectives were to identify activities associated with organic waste management systems which have large environmental impacts. The importance of using system boundaries that consider the differences in energy and nutrients utilised from the waste when comparing waste management alternatives is specially emphasised in this paper. Furthermore, the influence of systems design is highlighted by comparing case studies where different design of anaerobic digestion systems have been simulated.
The development of the ORWARE model was carried out as a collaboration project in which the Swedish Institute of Agricultural Engineering, the Swedish University of Agricultural Sciences, the Royal Institute of Technology and the Swedish Environmental Research Institute were all participants. The Waste Research Council at the Swedish Environmental Protection Agency funded the work.