Exergy analysis of aluminum recovery from municipal solid waste incineration

Two main challenges, associated with the recovery of aluminum from state-of-the-art municipal solid waste (MSW) incineration plants, are yield as well as quality losses of metallic aluminum due to particle surface oxidation and presence of impurities. Yet, in the framework of life cycle assessment (LCA) a direct measure for expressing the quality of primary and secondary resources is missing. In view of a possible solution, exergy has been proposed as a concept to evaluate the quality of resources. In this paper, LCA and exergy analyses for two waste treatment approaches are conducted in parallel to each other, with a goal to evaluate the added value of exergy for LCA studies in the resource recovery context. The functional unit is the treatment of 1 ton MSW. Two alternative approaches for recovering aluminum from MSW directed to a waste-to-energy plant are considered. A) MSW is treated in a two-step system consisting of a waste-to-energy process and a consequent bottom ash treatment. B) An aluminum-pre-sorting step takes place prior to the thermal treatment. In case of B, an additional exergy is spent on pre-sorting, but, in return, a metal of higher quality is obtained. The discussion of exergy analysis in the LCA framework represents an important contribution to address resource quality in environmental assessment of thermal waste treatment.