FORMATION OF OCTA-CHLORODIBENZO-P-DIOXIN AND HEPTACHLORODIBENZO-P-DIOXIN DURING SEMI ANAEROBIC-DIGESTION OF SEWAGE-SLUDGE

Octa- and heptachlorodibenzo-p-dioxins (OCDD and HpCDD) were formed du ring semi anaerobic digestion of sewage sludge at low temperature (20 degrees C). A twofold increase of OCDD and HpCDD was found after a dig estion period of 192 days even if concentrations were corrected by cor responding accumulation factors caused by the degradation of biomass. Other polychlorinated dibenzo-p-dioxins and furans (PCDD/F) and polych lorinated biphenyls (PCB) were not increased. Under strictly anaerobic and aerobic conditions, however, no OCDD and HpCDD were formed. Semi anaerobic formation of OCDD and HpCDD may explain the prevalence of hi gher chlorinated PCDD in the homologues pattern typical for sewage slu dge. (C)1998 Elsevier Science Ltd. All rights reserved.