Purpose This paper aims to provide an alternative method for calculating the environmental credits associated with material recycling in life cycle assessment (LCA) of waste management systems. The method proposed here is more consistent with the general attributional approach in LCA than the hitherto common practice of simply assuming a 1:1 substitution of primary material production.
Methods The formula proposed for estimating the environmental credit is applicable for the recovered materials that are reintroduced into the market (outputs of the recycling facilities), after all process losses in the various stages of the waste management system have been accounted for. It considers the displacement of materials by using the mix of virgin and recycled materials for each individual material that is used in the market for the production of goods. Moreover, it also considers the changes in the inherent properties of the materials undergoing a recycling process (‘down-cycling’), by introducing a quality (Q) factor, affecting the proportion of virgin material that is accounted for.
Results and discussion Example applications of the proposed formula to a number of different materials (aluminium, steel, paper and cardboard and plastics) illustrate the range of possible results obtained.. The environmental credit calculated using the proposed formula can be interpreted as an indication of the remaining margin for improvement, since it depends on the existing mix of virgin and recycled materials already on the market, and on the potential of the recycled material to actually replace the primary one on a functional basis. We also discuss the possible use of a material’s Q factor to estimate the maximum allowable % of recycled material in a product consistent with the quality demands of selected applications.
Conclusions and recommendations We have introduced here a consistent and unified formula for the evaluation of the credits associated with material recovery of all waste materials in waste management systems (paper, glass, plastics, metals, etc.). Such a formula requires the knowledge of the current average market consumption mixes of primary and secondary materials (or the application-specific average mixes when the final application of the recovered materials is known), and of suitable Q factors for the material(s) that are recycled. As the latter are often not readily available, more research is called for to arrive at a ready-to-use Q factors database.
Gala, ARaugei, Marco
Faculty of Technology, Design and Environment\Department of Mechanical Engineering and Mathematical Sciences
Year of publication: 2015Date of RADAR deposit: 2016-02-17
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