FACTORS AFFECTING HEAVY METALS ENRICHMENT IN FLY ASH FROM SLUDGE INCINERATION BY A ROTATING DRUM FURNACE

Incineration tests were performed using sewage sludge as is or spiked with chlorinated organic compounds. Cd, Cr, Cu, Mn, Ni, Pb, and Zn behaviour was studied by assessing their partitioning among bottom, cyclone, and filter ash. Only Cd, Pb, and Zn undergo significant enrichment in the filter ash. Cd and Pb enrichment is enhanced by high chlorine concentrations in the feed-stream. With exception of zinc, the experimental results may be satisfactorily predicted by a thermodynamic model of the combustion chamber. The unpredicted volatilisation of Zn at low chlorine input is attributed to incomplete mixing conditions in the furnace (pyrolysis pockets).