Integration of life cycle assessment with monetary valuation for resource classification: The case of municipal solid waste incineration fly ash

Recently, recycling of municipal solid waste incineration (MSWI) fly ash has gained increasing interest, although it is still unclear if recycling is preferable over disposal from an economic and environmental point of view. The objective of the present study is to assess the resource potential of MSWI fly ash for the production of three different commodities (cement, metals, de-icing salts) from a private investor's micro and a public entity's macro perspective. Therefore, the environmental impacts and economics were determined by life cycle assessment (LCA) and discounted cash flow (DCF) analysis, respectively. Monetary valuation was applied to the LCA results in order to determine the external costs, which were subsequently added to the DCF analysis results from the macro perspective (i.e. internal costs) to determine the socio-economic viability (i.e. total costs) of MSWI fly ash recycling. The resource classification scheme UNFC was used to classify MSWI fly ash for utilisation in cement production, metal and salt recovery based on the combined result from LCA and DCF analysis. The consideration of project feasibility and geological knowledge leads to the classification as commercial project (111) for cement production (micro and macro view) and for metal recovery (macro view). Metal recovery is classified as other combination (211) from a micro view due to a negative median net present value and salt recovery is classified as non-commercial project (321) from a micro and macro view. It was demonstrated that monetary valuation of LCA results is a useful tool for including external costs into resource classification.