Influence of assumptions about selection and recycling efficiencies on the LCA of integrated waste management systems |
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Authors: | Lucia Rigamonti Mario Grosso Maria Caterina Sunseri |
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Institution: | (1) Politecnico di Milano, DIIAR Sezione ambientale, Piazza Leonardo da Vinci, 32-20133 Milan, Italy |
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Abstract: | Background, aim, and scope Life cycle assessment (LCA) applied to alternative waste management strategies is becoming a commonly utilised tool for decision
makers. This LCA study analyses together material and energy recovery within integrated municipal solid waste (MSW) management
systems, i.e. the recovery of materials separated with the source-separated collection of MSW and the energy recovery from
the residual waste. The final aim is to assess the energetic and environmental performance of the entire MSW management system
and, in particular, to evaluate the influence of different assumptions about recycling on the LCA results.
Materials and methods The analysis uses the method of LCA and, thus, takes into account that any recycling activity influences the environment not
only by consuming resources and releasing emissions and waste streams but also by replacing conventional products from primary
production. Different assumptions about the selection efficiencies of the collected materials and about the quantity of virgin
material substituted by the reprocessed material were made. Moreover, the analysis considers that the energy recovered from
the residual waste displaces the same quantity of energy produced in conventional power plants and boilers fuelled with fossil
fuels.
Results The analysis shows, in the expanded model of the material and energy recovering chain, that the environmental gains are higher
than the environmental impacts. However, when we reduce the selection efficiencies by 15%, the impact indicators worsen by
a percentage included between 10% and 26%. This phenomenon is even more evident when we consider a substitution ratio of 1:<1
for paper and plastic: The worsening is around 15–20% for all the impact indicators except for the global warming for which
the worsening is up to 45%.
Discussion Hypotheses about the selection efficiencies of the source-separated collected materials and about the substitution ratio have
a great influence on the LCA results. Consequently, policy makers have to be aware of the fact that the impacts of an integrated
MSW management system are highly dependent on the assumptions made in the modelling of the material recovery, as well as in
the modelling of the energy recovery.
Conclusions LCA allows to evaluate the impacts of integrated systems and how these impacts change when the assumptions made during the
modelling of the different single parts of the system are modified. Due to the significant impacts that hypotheses about material
recovery have in the results, they should be expressed in a very transparent way in the report of LCA studies, together with
the assumptions made about energy recovery.
Recommendations and perspectives The results suggest that the hypotheses about the value of the substitution ratio are very important, and the case of wood
should therefore be better analysed and a substitution ratio of 1:<1 should be used, as for paper and plastic. It seems that
the assumptions made about which material is replaced by the recycled one are very important too, and in this sense, more
research is needed about what the recycled plastic may effectively substitute, in particular the polyolefin mix. |
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Keywords: | Integrated waste management systems Life cycle assessment Recycling Selection efficiencies Substitution ratio |
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