LEVELS AND CONGENER PATTERNS OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS IN SOLID RESIDUES FROM WOOD-FIRED BOILERS. INFLUENCE OF COMBUSTION CONDITIONS AND FUEL TYPE

摘要

The levels of polychlorinated dibenzo-p-dioxins and dibenzofurans have been determined in bottom ash and fly ash samples from different wood combustion systems for heat production (effect between 6-850 kW). Both untreated wood and waste wood were burned. The concentrations expressed as 2,3,7,8-tetrachloro dibenzo-p-dioxin equivalents (2,3,7,8-TE, international model) in bottom ash were in the order of 1 pg/g when natural wood was incinerated. However, in filter ash the levels were about 2 orders of magnitude higher. Burning of waste wood resulted in concentrations in the range of 1-10 ng/g 2,3,7,8-TE. The reason for the high filter ash burden seems to be secondary formation on the ceramic filter surface at temperatures around 350℃. Incineration of the combustible fraction of household waste in a small stove increased 2,3,7,8-TE levels in the bottom ash by three orders of magnitude compared to charcoal (0,5 pg/g). The PCDD/PCDF congener patterns found were influenced by both the type of wood burned and the construction of the combustion system.