Mono- to Octa-chlorinated PCDD/Fs in stack gas from typical waste incinerators and their implications on emission

Mono- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans (mono- to octa-CDD/Fs) were determined in 14 stack gas samples from two municipal solid waste incinerators and two medical waste incinerators. The total PCDD/F concentrations were 5.1-390 ng/Nm(3), and the mono- to trichlorinated homologues contributed 53.2-94.5% of the total concentrations. The homologue profiles were dominated by the MoCDF, ranged from 1.51 to 113.1 ng/Nm(3), and the proportion that each PCDF homologue group contributed to the total concentration decreased with increasing chlorination level. The toxic equivalent concentrations (I-TEQs) were 0.01-2.81 ng I-TEQ/Nm(3), with 2,3,4,7,8-PeCDF being the biggest contributor, at 30.6-60.0%. Correlations were found among the PCDD/PCDF ratios (D/F ratios), the degree of chlorination, and the TEQ. Stack gases with low I-TEQs had higher proportions of the less chlorinated homologues and lower D/F ratios, which could be attributed to the removal of the more chlorinated isomers by the air pollution control systems used by the incinerators. 2,8-DiCDF, 2,4,8-TrCDF, DiCDF, and TrCDF can be used as TEQ indicators for monitoring PCDD/Fs. 2,8-DiCDF and 2,4,8-TrCDF correlated well with the TEQ because they strongly correlated with 2,3,4,7,8-PeCDF, implying possible correlations in their formation mechanisms.