Comparing the quantity and quality of glass, metals, and minerals present in waste incineration bottom ashes from a fluidized bed and a grate incinerator

Abstract

Bottom ash is the primary solid residue arising from municipal solid waste incineration. It consists of valuable materials such as minerals, metals and glass. Recovering these materials from bottom ash becomes evident when integrating Waste-to-Energy within the circular economy strategy. To assess the recycling potential from bottom ash, detailed knowledge of its characteristics and composition is required. The study at hand aims to compare the quantity and quality of recyclable materials present in bottom ash from a fluidized bed combustion plant and a grate incinerator, both located in the same city in Austria and receiving mainly municipal solid waste. The investigated properties of the bottom ash are grain-size distribution, contents of recyclable metals, glass, and minerals in different grain size fractions, and the total and leaching contents of substances in minerals. The study results reveal that most recyclables present are of better quality for the bottom ash arising at the fluidized bed combustion plant. Metals are less corroded, glass contains fewer impurities, minerals contain fewer heavy metals, and their leaching behavior is also favorable. Furthermore, recoverable materials, such as metals and glass are more isolated and not incorporated into agglomerates as observed in grate incineration bottom ash. Based on the input to the incinerators more aluminum and significantly more glass can potentially be recovered from bottom ash from fluidized bed combustion. On the downside, fluidized bed combustion produces about five times more fly ash per unit of waste incinerated, which is currently disposed of in landfills.

Keywords: Bottom ash; Circular economy; Fluidized bed combustion; Grate furnace; Municipal solid waste incineration; Recycling.