QUANTITATIVE COMPARISON OF DENOVO AND PRECURSOR FORMATION OF POLYCHLORINATED DIBENZO-P-DIOXINS UNDER SIMULATED MUNICIPAL SOLID-WASTE INCINERATOR POSTCOMBUSTION CONDITIONS

Model studies were performed to determine quantitatively the predominance of two proposed pathways of polychlorinated dibenzo-p-dioxin (PCDD) formation during municipal refuse incineration: surface-catalyzed reactions of precursors occurring on fly ash and de novo synthesis of PCDD and related compounds from reactions of particulate carbon. The relative yields of PCDD formed from the model precursor compound pentachlorophenol (PCP) were 72-99000 times higher than PCDD formed from the reactions of activated charcoal, air, inorganic chloride, and Cu(II) as catalyst under identical reaction conditions. Yields and homologue distributions of PCDD were strongly influenced by heating time, air flow rate, and temperature, with marked differences observed between the two pathways. Activated charcoal also catalyzed the formation of PCDD from PCP in the absence of Cu(II) and promoted the dechlorination of PCDD. We speculate that Cu(II) and carbon represent two different types of active catalytic species which could be present on the surface of municipal incinerator fly ash.