A-role of alkaline elements in formation of PCDDs, PCDFs, and coplanar PCBs during combustion of various paper...

Combustion of industrial and domestic wastes produces significant amounts of dioxins (PCDDs, PCDFs, and coplanar PCBs). These wastes contain numerous kinds of materials, including inorganic elements, which may play an important role in dioxin formation upon combustion. Six paper samples--impregnated with NaHCO3, NaCl + fly ash, polyvinyl chloride (PVC), and PVC + NaHCO3--were combusted in a well-controlled incinerator at 512-760 degrees C and exhaust gases were analyzed for dioxins (PCDDs, PCDFs, and coplanar PCBs). Addition of fly ash, which contained high levels of Ca and Cl, to NaCl impregnated-newspaper increased total dioxin formation from 80.8 ngg(-1) to 139 ngg(-1) during combustion. Addition of NaHCO3 to PVC-impregnated newspaper increased total dioxin formation from 220 ngg(-1) to 288 ngg(-1). Formation of PCDDs from NaHCO3/PVC-impregnated newspaper were significantly less than that from newspaper impregnated with PVC alone. On the other hand, more PCDFs formed from NaHCO3/PVC-impregnated newspaper than from newspaper impregnated with PVC alone. Addition of NaHCO3 to a PVC-impregnated newspaper changed the production pattern of dioxins. PVC- impregnated newspaper produced the greatest amount of coplanar PCBs (12.3 ngg(-1)), which may be accounted for by the relatively high level of TEQ value (3.31 ng-TEQg(-1)) of this sample. Generally, addition of fly ash and alkali metals, such as Na, to paper samples increased the total dioxin formation in exhaust gases during combustion. The results suggest that alkali metals increase Cl concentrations at a reaction site by trapping chloride ions and/or chloride radicals and consequently increasing dioxin formation.