SECONDARY FORMATION OF PCDD F DURING THE THERMAL STABILIZATION OF SEWAGE-SLUDGE/

In the City of Nuremberg, from 1972 to 1992 the sewage sludge used to be thermally stabilized in a modified Porteous process. In recent year s the impact of this process on the concentration of various persisten t contaminants in the sludge has been studied. In the process part the organic material in the sludge is decomposed and to the same extent a n increase of the concentration of persistent components is found in t he processed sewage sludge. The enrichment factors for heavy metals an d PCB show a modest variation between 1.15 and 1.63 with a mean value around 1.3. In contrast to these data, for PCDD/F enrichment factors u p to 8 are found with a strong variation between the congeners, and th e highest enrichment factors to be found for tetra-and pentachlorinate d dioxins. The thermal stabilization of sewage sludge seems to be a so urce of PCDD/F due to their secondary formation in the process.