Characterization of incineration residues from wastewater treatment plant in Polish city: a future waste based source of valuable elements?

To support the rational management of raw materials in the European Union more attention is being paid to the resource potential of waste materials, which are increasing in volume due to industrial development and the world population growth. One of the methods to reduce the amount of produced and landfilled waste is incineration. As a result of sewage sludge incineration, fly ash (ISSA—incinerated sewage sludge ash) and APC (air pollution control) residues are produced. The goal of this study was to characterize incineration residues from waste water treatment plant in Polish city with ca. one million inhabitants using mineralogical, chemical methods, and to estimate the recovery potential of valuable components. Both incineration products accumulate elements which are of valuable concentrations, such as P (17 wt% of P2O5 on average in the ISSA), as well as significant amounts of metals such as Zn, Pb, Cu, Ni, and Cr. Small particle sizes < 125 µm in both materials favor the accumulation of elements of higher volatility during incineration, but they are usually dispersed within a matrix, main minerals or amorphous substance, or are present in the form of micro inclusions or grains < 10 µm, which thus excludes their easy recovery.