Fractions of heavy metals in residue after incineration of sewage sludge

Comparative evaluation of metal occurrence was conducted for sludge originating from three wastewater treatment plants, which differ in wastewater treatment methods, processing and drying of sludge. It was demonstrated that metals (Zn, Cu, Ni, Pb, Cd, Cr) in sludge are mainly bound to organic-sulfide fraction. Zinc was also present in significant amounts in hydrated iron and manganese oxide fraction, nickel and cadmium in exchangeable-carbonate fraction, whereas lead in residue fraction. In ash obtained after calcination at 600 °C occurred mainly metal enriched nearly insoluble compound fraction (residual fraction). Metal accumulation in such non-mobile fraction is advantageous with respect to soil-water environment protection.