Metals Accumulation During Thermal Processing of Sewage Sludge - Characterization of Fly Ash and Air Pollution Control (APC) Residues

Sewage sludge thermal utilization leads to production of fly ash and APC residues which may contain elevated amounts of some metallic or toxic elements (Fe, Zn, Pb, Sn, Au, Hg, Cd, As). Distribution of these elements in studied fly ash and APC residues was unequal and dependent on their melting temperature. Metals in fly ash are present as Fe-rich grains and rims around Si-glass whereas in APC metallic components are mostly represented by Sn-rich inclusions dispersed in matrix, Ca-phosphates or as separate micro-grains. Elements concentrations were elevated but overall content was low thus disqualifying the material in terms of recovery.