Developing material recovery projects: Lessons learned from processing municipal solid waste incineration residues

Abstract

This research explores the material recovery from bottom-ash, which is a residue from municipal solid waste incineration. The investigations aimed to characterize, evaluate, categorize and classify the development status of the recovery projects in the Canton of Zürich, including two technology pathways, i.e. dry and wet bottom-ash recovery. The temporal scale commenced with the exploration phase in 2003 and concluded with two technological pathways, both operating commercial projects in 2017. A retrospective view allowed the identification of enablers and barriers that affected the development status of the recovery projects. Further the recovery perspective allowed the results to be communicated to the United Nations Framework Classification for Resources (UNFC). The investigation showed two main trends. Firstly, the development status of the recovery projects from exploration to commercial project phase was mainly driven by the knowledge increase regarding sampling and metal characterization in bottom-ash, the readiness and effectiveness of the recovery technologies and the changes of the legal and financial environment. Secondly, the amount of recovered material (dry matter content) increased from about 6900 tons in 2003 to 16,500 tons in 2017, which is congruent with an increase in the recovery rate from 5 to 14 percent per weight. In particular, the amount of elements recoverable with an economic and environmental benefit, such as copper, gold and silver, increased. Correspondingly, the residual particular metal content in the disposable bottom-ash (fraction 2–16 mm) decreased to < 1 percent per weight dry matter and therefore reduced the risk for environmental at the sanitary landfills. The findings provide ‘lessons learned’ for companies, authorities and investors who intend to develop material recovery projects. Even though the recovery potentials depend on site-specific conditions, the UNFC allows comparing individual recovery projects under different boundary conditions.