Dechlorination and destruction of PCDDs/PCDFs in fly ashes from municipal solid waste incinerators by low temperature thermal treatment

Dechlorination and destruction characteristics of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs) in fly ashes from commercial-scale municipal solid waste incinerators by low temperature thermal treatment using a laboratory-scale heating system were investigated. Experiments were carried out in reducing atmosphere at temperatures of 300 degrees C, 450 degrees C and 600 degrees C respectively, for the treatment time of 1h and 3h. Concentrations of PCDDs/PCDFs in raw fly ashes ranged from 35.5 to 107.3 microg kg(-1) (1.5-3.4 microg TEQ kg(-1)) and treated fly ashes ranged from 0.34 to 45.3 microg kg(-1) (0.012-1.63 microg TEQ kg(-1)). Concentrations of PCDDs/PCDFs in fly ashes treated at the different temperatures and times were observed to decrease with increase of treatment temperature and time by dechlorination or destruction. The distribution of octa- and hepta-chlorinated congeners were decreased and tetra-, penta- and hexa-chlorinated congeners were increased at 300 degrees C and 450 degrees C, but the distribution of octa- and hepta-chlorinated congeners were increased and tetra-, penta- and hexa-chlorinated congeners were again decreased at 600 degrees C. Total destruction efficiencies of PCDDs/PCDFs in fly ashes showed above 95% at the treatment temperature of 450 degrees C for 3h. However, removal efficiency of each congener in fly ashes varied, especially, 2,3,7,8-TeCDD and 1,2,3,7,8-PeCDD in fly ash A increased. And the dechlorination and destruction characteristics of PCDDs/PCDFs in fly ash A and B was different due to difference in contents of Ca-compounds and metal oxides such as CuO and PbO in fly ashes.