Emission Characteristics and Formation Pathways of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from a Typical Pesticide Plant

The emission characteristics and the formation pathways of the polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from a pesticide plant were well investigated. In the present study, the international toxic equivalent quantity (I-TEQ) value of the PCDD/Fs (0.087 ng I-TEQ Nm(-3)) in the flue gas at the outlet of stack can meet the emission limit (0.1 ng I-TEQ Nm(-3)). The I-TEQ value of the PCDD/Fs (3.25 pg I-TEQ g(-1)) in the fly ash is much lower than the permitted standard for disposal in sanitary landfill sites (3.0 ng of I-TEQ g(-1)). In addition, 1,2,3,4,6,7,8-HpCDD, OCDD and 1,2,3,4,6,7,8-HpCDF are the three main congeners in the PCDD/Fs for the outlet of both the secondary combustion chamber and the stack. 1,2,3,7,8-PeCDD, 1,2,3,6,7,8-HxCDD, 1,2,3,4,6,7,8-HpCDD and OCDD are the most dominant congeners for the PCDD/Fs from inlet of bag filter. PCDD/Fs may be formed through high temperature homogeneous synthesis and heterogeneous precursor synthesis in the flue gas. In addition, PCDD/Fs might be formed in bag filter via de novo synthesis. The main formation areas of PCDD/Fs are waste heat boiler and quenching/deacidification tower in this pesticide plant. The TEQ estimated emissions of PCDD/Fs reaches 9.3 g year(-1). These findings are helpful for further controlling the formation and emission of PCDD/Fs in pesticide plants, yet more studies are still required.