Emissions of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from Various Stationary Sources

This work investigated the characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in stack-flue gases from six stationary emission sources in five types of incinerators: industrial waste incinerator (IWI), small-scale municipal solid waste incinerator (MSWI), medical waste incinerator (MWI), cement kilns (CK), and crematories (CR). These characteristics were further investigated using factor analysis and cluster analysis. Experimental results reveal that PCDDs dominate MSWI and CR, and PCDFs dominate IWIa, IWIb, CK and MWIs. The factor analysis results showed that CR and MSWI have similar fingerprints, as do IWIb and MWI3. The cluster analysis showed that if a vertical line is cut at a rescaled distance of four, then the PCDD/F congener profiles fall into four groups. The indicators of PCDD/Fs are OCDD, 1,2,3,4,6,7,8-HpCDF, 2,3,4,7,8-PeCDF, and 1,2,3,4,6,7,8-HpCDD. The emission factors of PCDD/Fs herein were from 0.0433 (CK) to 18.7 (MSWI) μg I-TEQ/ton-feedstock.

Cement kilns use coal as burner fuel; the other sources use diesel.The feedstock of CK is mostly cement as a raw material and a few waste tires, IWIa is fed with general waste from nuclear power plants, and IWIb is fed mostly with waste-oil sludge.For pollution control, MSWI uses a semi-dry washing tower and a baghouse, MWI uses a Venturi scrubber and a quench tower, CK uses an electrostatic precipitation (ESP), IWIa uses a baghouse, and IWIb uses a cyclone and an ESP.This paper reports on measurements of PCDD/Fs from the stacks of six incinerators.Emission characteristics of PCDD/Fs from these incinerators are presented, including concentrations, fingerprints and emission factors.Also, similar and dissimilar features between them are further studied using factor analysis and cluster analysis.The data derived from this study can provide guidance to improve operating conditions of the incinerators and to assess the potential health risk to the neighboring community.

PCDD/FS Sampling
PCDD/Fs in stack-flue gases were collected using the Taiwan EPA method NIEA A807.73C, which is based on the US EPA Method 23A.Prior to sampling, XAD-2 resin was spiked with isotopically labelled PCDD/F surrogate standards.Each stack gas sampling took 3 h.One trip blank and one field blank were also obtained during field sampling to ensure that the collected samples were not contaminated.

PCDD/FS Analysis
PCDD/Fs were analyzed for stack-flue gases, according to U.S. EPA modified Method 23, using high-resolution gas chromatographs/high-resolution mass spectrometers (HRGC/HRMS).The analysis was conducted at the Super Micro Mass Research and Technology Center at Cheng Shiu University in Taiwan.The HRGC (Hewlett-Packard 6970) was comprised of a DB-5 MS fused silica capillary column (0.25 mm 60 m, 0.25 m) (J&W Scientific) with splitless injection.Helium was used as the carrier gas.The HRMS (Micormass Autospec Ultima, Manchester, UK) had a positive electron impact (EI+) source.The selected ion-monitoring mode (Park et al., 2004) had a resolving power of 100,000.The specified electron energy and source temperature were 35 eV and 250 C, respectively.

PCDD/F Concentrations in Stacks
Table 1 shows that the total PCDD/F concentrations in the stack gases of IWIa, IWIb, MSWI, MWI, CK, and CR were 0.604, 1.397, 30.1, 1.14, 0.350, and 29.8 ng/Nm 3 , respectively, and the order was MSWI > CR > IWIb > MWI > IWIa > CK, indicating that PCDD/F concentrations in the stacks of MSWI and CR greatly exceeded those of other incinerators.The efficiency of a baghouse in removing PCDD/Fs was around 37.6% (Lee et al., 2004); so, highly concentrated PCDD/Fs could be formed from MSWI during combustion.CR should include pollution control equipment to reduce the concentration of PCDD/Fs in the stack-flue gases.The PCDD to PCDF ratios were 0.464, 0.415, 0.903, 0.423, 0.292, and 0.869, respectively.The PCDD/Fs ratios in the stacks followed the order CR > MSWI > IWIa > MWI > IWIb > CK, indicating that PCDDs dominated CR and MSWI and PCDFs dominated the other burners.The total PCDD/Fs I-TEQs were 0.030, 0.137, 3.35, 0.168, 0.062, and 3.00 ng I-TEQ/Nm 3 , respectively.The order of total PCDD/F I-TEQ was MSWI > CR > MWI > IWIb > CK> IWIa, similar to that of the total PCDD/F concentration in stacks.
In summary, when considering PCDD/F concentrations, PCDD/F ratio and PCDD/F I-TEQ, MSWI and CR are two leading PCDD/F contributors among the six incinerators.

Cluster Analysis
Cluster analysis, using nearest-neighbour method, was employed to divide the congener profiles from different stack-flue gases into several groups (Johnson and Wichern, 2002).The dendrogram in Fig. 3 from cluster analysis shows that if a vertical line is cut at a rescaled distance of four, then the PCDD/F congener profiles fall into four groups, namely: GROUP1, GROUP2, GROUP3, and GROUP4.GROUP1 comprises CK2 and CK3, and GROUP2 comprises MWI1 and MWI2.GROUP 3 comprises MSWI (MSWI1-MSWI3) and CR (CR1-CR3) which is consistent with the results of similar fingerprints in these two processes discussed earlier.GROUP4 is comprised of IWIb (IWIb1-IWIb3) and MWI3.IWIa (IWIa1-IWIa3) and CK1 do not belong to any group.Generally, cluster analysis results (Fig. 3) agree fairly well with factor analysis results shown in Fig. 2.

Emission Factors of PCDD/FS
Table 4 shows that the emission factors of PCDD/Fs herein were from 0.0433 (CK) to 18.7 g I-TEQ/ton-feedstock (MSWI), whereas previous studies yielded 0.52 to 200 g I-TEQ/ tonfeedstock (Wang et al., 2003a and2003b).The PCDD/F emission factors of CR were 41.1 g I-TEQ/ body herein, a value which is around three times greater than the value reported by Wang et al. (2003a).The PCDD/F emission factors of MSWI and MWI ranked second and third herein.
It is known that precursors are responsible for the formation of PCDD/Fs.Therefore, the control of feedstock components and the complete combustion of wastes are important in reducing the emission of PCDD/Fs from the stack-flue gas.
(2) The factor analysis results showed that CR and MSWI have similar fingerprints; similarly between IWIb and MWI3.The cluster analysis showed that if a vertical line is cut at a rescaled distance of four, then the PCDD/F congener profiles fall into four groups.These two analyses generally yielded consistent results.
Since precursors are responsible for the formation of PCDD/Fs, additional studies should be conducted to provide further understanding on their formation mechanisms during combustionrelated processes.

Fig. 2
Fig.2shows the component plot, with Factor1 as the horizontal axis and Factor2 as the vertical axis.In the plot, the closeness of the emission sources to each other implies the similarity in their congener profiles.The plot shows that CR and MSWI have similar fingerprints; similarly for IWIb and MWI3.

Table 1 .
The PCDD/F concentrations in the stack-flue gases of six emission sources.

Table 2 .
Factor analysis of PCDD/Fs in six stack-flue gases.

Table 3 .
The highest three indicatory PCDD/Fs of various PCDD/F emission sources.

Table 4 .
PCDD/F emission factors of various emission sources.