Process-based analysis of waste management systems: A case study
Introduction
As for many large European cities, the urban area of Paris is faced with the problem of an ever-increasing and not yet stabilizing production of household waste (the increase between 1995 and 2007 was on the order of 20%). The SYCTOM (inter-communal organisation for the treatment of municipal solid waste) of the Paris agglomeration is in charge of treating waste while complying with target objectives set by European policies in terms of recycling of waste (EN, 2006, OJC, 2004), treatment emission limits (OJC, 2000), energy recovery from waste (CEC, 2003) or limitation of the landfilling of waste (in particular organic matter; OJC, 1999). The SYCTOM is therefore particularly interested in identifying environmentally sound and economically advantageous ways of managing its waste while complying with European objectives.
Methodologies for analyzing waste management systems or strategies include material flow analysis (MFA) (Brunner and Rechberger, 2003), cost-benefit analysis (CBA) (Farrow and Toman, 1999) and life cycle analysis (LCA) (Hunt, 1995). The LCA approach is recommended in several recent pieces of European legislation on waste (and in the future Waste Framework Directive) and several software tools have been developed as for example the WISARD software (see Clift et al., 2000), the SIMA PRO tool developed by Pre consultants and more recently the EASEWASTE tool (Kirkeby et al., 2006a, Kirkeby et al., 2006b) which represent an effort to design a flexible tool for comparing different waste management strategies. Life cycle analyses are generally based on an inventory of all flows of resources, energy, and emissions that compose each element of individual operations encountered in the system, including not only the operation of waste management processes but also for example the contributions of the primary processes related to the production of cement or metals present in the buildings or vehicles used for waste treatment. Methods based on LCA have sometimes been criticized for not being sufficiently transparent, as they may rely on default parameters that are not readily accessible to the user, or for being sometimes so wide in scope that they may be difficult to apply to specific waste management systems. Winkler (2004) compared six different LCA models applied to waste management and found large differences between model results, which in some cases led to contradictory conclusions regarding the respective environmental performances of the waste management processes. Winkler attributed these differences to the difficulties in modelling the extreme complexity of modern waste management systems and the inadequacy of the static linear modelling approach adopted by models tested in his analysis.
The approach presented in this paper (called AWAST), which is complementary to life cycle analysis, has an objective of flexibility and adaptability to complex real-world situations of waste management. The main idea behind AWAST is that in real-world situations, similar processes may not have similar performances, depending on the quality of the feed material, the characteristics of the treatment units and other specific parameters that are typically omitted in global inventory approaches. Rather than to rely on averages, for example national statistics of waste production per capita or generic characteristics of waste treatment technologies, decisions need to rely on analyses that account for the specific characteristics of a given waste management system in terms of waste streams and treatment processes.
In 2003, the SYCTOM initiated a project aimed at examining various options for improving waste management in the south-eastern area of Paris (the Ivry waste collection basin). The objective of the project presented in this paper was to analyze the overall management of waste in the south-east of Paris, taking into account all waste fluxes from input (collection) to output (secondary materials, landfill, etc.). The project was divided into three phases. During the first phase, data was collected and a simulator was developed that reproduced the situation of waste management in this area at the start of the project (reference year: 2003). This simulator provided the main indicators regarding material balances, energy consumption and production, environmental emissions and costs. Once this calibration was completed, the SYCTOM defined, during the second phase, waste management scenarios that combined four different strategic options with respect to waste collection in the Ivry basin. Each scenario was simulated up to the year 2015 and performance indicators were calculated. During the third phase, the results from the different scenarios were compared using a multiple-criteria approach, to help the SYCTOM make choices with respect to waste management options. This paper presents an outline of the methodology that was used, discusses the main results and suggests possible directions for future research.
Section snippets
Overview of the simulator
The AWAST simulator is an application, dedicated to waste management, of the process simulator USIM PAC (Brochot et al., 2002). The AWAST simulator was developed within a project of the 5th FRDP (Framework Research and Development Programme) in collaboration with eleven European partners. Its objective is to provide stakeholders involved in MSW management with a simulation software tool based on a description of processes involved and that accounts for environmental emissions, energy fluxes,
Simulation of the 2003 situation
The SYCTOM’s waste collection basin covers an area of approximately 5910 km2 and includes the city of Paris as well as 88 municipalities located around Paris. The collection basin is subdivided into four sub-basins: Issy, Ivry, Romainville and Saint-Ouen. These sub-basins receive the waste from Paris and surrounding municipalities and are equipped with several waste treatment systems. Waste collected within a given sub-basin is generally treated by equipment that belongs to this sub-basin, but
Discussion and conclusions
The performance and impact indicators calculated in the previous section may be used to compare the pros and cons of the different scenarios. It is also possible to introduce weights for the different indicators, in a multiple-criteria analysis framework. If the indicators are considered without any particular weights, then sub-scenario 2 (sorting of MSW followed by methanisation of residual waste and incineration of RDF) may appear to be more favourable than the others as it leads to a better
Acknowledgements
The development of the AWAST simulator was supported by the European Research 5th Framework Program. We are also grateful to the anonymous reviewers for their helpful comments.
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