Modelling material cascades — frameworks for the environmental assessment of recycling systems

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Abstract

The authors develop a methodological framework for the environmental assessment of materials recycling systems. Typically such systems exhibit both dynamic and non-linear behaviour. By contrast, many existing environmental assessment techniques (such as Life Cycle Assessment and Materials Flow Analysis) employ a static linear model of the underlying system. This paper first reviews some of the attempts to develop dynamic non-linear models for materials systems. It then discusses the structural peculiarities of recycling systems drawing attention in particular to the presence of dynamic features (such as time lags between production and disposal) and non-linearities (such as the dependency of scrap collection energies on the flow of material through the recycling loop). The principal analytic task of this paper is to construct an illustrative case study, in which different modelling techniques are used to assess the energy requirements of a hypothetical recycling system possessing both dynamic and non-linear features. The difference in system energy intensity derived using the different types of model are analysed. Finally, the paper discusses the policy implications of these results.

Introduction

This paper develops a methodological framework for environmental assessment of material ‘cascades’ — complex systems of material use in which materials and products are re-used or recycled a number of times before being discarded (Clift and Longley, 1995, Jackson, 1996).

Existing environmental assessment tools such as Energy Analysis and Life Cycle Assessment (LCA) have sometimes been applied to simple recycling systems, but application to multiple loop recycling processes is in its very early stages. Moreover, LCA and the related methodology of Materials Flow Analysis (MFA) essentially rely on static linear models of the underlying system. In the real world, the underlying systems exhibit dynamic and non-linear characteristics. Dynamic effects arise as a result of time-lags within the system — such as those implied by changes in product or material lifetimes. Non-linear effects can arise in a number of different ways. Typically, in material systems of the kind discussed here, they arise because the environmental impacts of particular life cycle stages are not uniform with respect to material flow through the system.

This paper first reviews some earlier attempts to model these kinds of systems. It then provides a formal discussion of the dynamic and non-linear elements of material cascades, and of the models suitable for modelling such systems. The core analytic task of this paper is to present an illustrative case study, in which different kinds of modelling techniques have been used to assess the energy requirements of a hypothetical recycling system. The results from this case study illustrate clearly that for systems which exhibit dynamic and non-linear behaviour, different modelling techniques may produce rather different conclusions about the energy requirements (and hence the environmental performance) of the system. The policy implications of this result are discussed.

Section snippets

An overview of modelling approaches

The literature on environmental modelling of complex material systems is expanding rapidly. In this section a limited overview of the field is provided. Both LCA and MFA approaches may be applied to environmental analysis of material cascades. The purpose and decision focus of each approach is different, and the unit of assessment differs also. An LCA approach is used to determine the life cycle environmental impacts associated with a given service provided by a product system (ISO, 1997). A

Characteristics of material cascades

The kinds of systems with which this paper is concerned typically involve the extraction of primary resources for the manufacture of a high-quality material or product, the distribution of the product for consumption or use, the degradation of the product through use, collection at the end of its initial life, and then various cycles of re-use, reconditioning, or the recycling of its component materials before final disposal. Fig. 1 shows a simple example of such a system involving only one

An illustrative case study

In this section the application of the four different modelling types defined in the previous section to an illustrative materials flow case study is demonstrated. Specifically the energy requirements associated with a hypothetical material recycling system over a notional time period 1995–2025 were investigated.

Summary and conclusions

The analysis presented in this paper has attempted to illustrate how dynamic, non-linear modelling can be used to model the complexities of material cascades — systems involving materials use, re-use and recycling loops. It has been argued that such methods may, in certain circumstances, provide a more accurate representation of the underlying system than traditional static, linear techniques such as those mainly adopted in current LCA or MFA studies. In particular, a hypothetical case study

Acknowledgements

The authors are grateful for financial support during the duration of this study from the UK Engineering and Physical Sciences Research Council (EPSRC), and the UK Royal Academy of Engineering. We are also grateful for critical inputs from participants at the SETAC-Europe Annual Meeting held in Bordeaux in April 1998 and the International Resource Accounting and Modelling Workshop held in Groningen in September 1998, at which earlier versions of this paper were presented.

References (39)

  • C. Cleveland et al.

    Interconnections between the depletion of minerals and fuels: the case of copper production in the United States

    Energy Sources

    (1996)
  • Clift R, Frischknecht R, Huppes G, Tillman A-M, Weidema B. Towards a coherent approach to life-cycle inventory...
  • R. Clift et al.

    An introduction to clean technology

  • U. Diwekar et al.

    Industrial ecology and process optimization

    Journal of Industrial Ecology

    (1998)
  • ETH. Ecoinventare von Energiesystem [Eco-Inventory of Energy Systems] 3rd Edition. ETH Group, Swiss Federal Institute...
  • Euromonitor. Market Research Great Britain 1992. In: Cooper T 1994, editor. Beyond Recycling: The Longer Life Option....
  • Frischknecht R. Life Cycle Inventory Analysis for Decision-Making. PhD Thesis. Swiss Federal Institute of Technology,...
  • C. Hall et al.

    Energy and Resource Quality: the Ecology of the Economic Process

    (1992)
  • B. Hannon et al.

    Steel recycling and energy recycling

    Science

    (1982)
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