Emissions of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from an Electric Arc Furnace , Secondary Aluminum Smelter , Crematory and Joss Paper Incinerators

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the stack flue gases, fly ashes and bottom ashes of various stationary sources were investigated. The mean total PCDD/F I-TEQ concentration of flue gas ranged from 0.00681 to 0.703 ng I-TEQ/Nm. However, the emission factor of PCDD/F from various incinerators was 0.00827 to 3.50 μg I-TEQ/ton, whereas it was 5.36 μg I-TEQ/body for a crematory (CM). In addition, the mean total PCDD/F I-TEQ content in fly ash from an electric arc furnace (EAF) and a secondary aluminium smelter (secondary ALS) were 74.0, and 49.9 ng I-TEQ/kg, respectively, whereas they are 21.3 and 0.494 ng I-TEQ/kg for bottom ash. Meanwhile, the removal efficiency of PCDD/F by bag filters from EAF was –44.4% which is attributed to the “memory effect”. The indicatory PCDD/Fs of EAF, and secondary ALS have the same congeners (1,2,3,7,8,9-HxCDF, 2,3,7,8-TeCDF, and 1,2,3,7,8-PeCDF). In addition, CM, joss paper-A (JP-A) and joss paper-B (JP-B) incinerators have similar indicatory PCDD/F (2,3,4,6,7,8-HxCDF, OCDF, 1,2,3,4,6,7,8-HpCDD, and OCDD). The high contribution of total PCDD/F is from fly ash (61.1-95.3%) for metallurgical facilities (EAF, secondary ALS), whereas 99.9% contribution of stack flue gas is from JP-A and JP-B. In conclusion, continually monitoring various PCDD/F emission sources is necessary to understand current PCDD/F emission (flue gas, fly/bottom ash) and the related removal efficiency of existing air pollution control devices. Information about both emission factors of PCDD/Fs and indicatory PCDD/F congeners are useful for the establishment of control strategies and for use as fingerprints with regard to the dominant congeners from different emission sources.


INTRODUCTION
Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) were first detected in the flue gas and fly ash from municipal solid waste incinerators in 1977 (Olie, 1977).Since then, PCDD/Fs have received considerable attention due to concerns about the related adverse health effects and emission problems (US EPA, 2000).Various forms combustions, such as incinerations, are believed to be the main sources of PCDD/F to the environment (Rappe, 1992;US EPA, 2000).Furthermore, these pollutants can be transported over long distances in the atmosphere, and be deposited on the surrounding environment (Tysklind et al., 1993;VanJaarsveld et al., 1993;Lee et al., 2009).
In Taiwan, the PCDD/F emission inventory has been reported that iron ore sintering, heat/power generation, electric arc furnaces, secondary aluminum smelter plants, crematories and ritual paper burning make contributions of 32%, 30%, 23%, 1.5%, 0.7% and 0.1% to the total emissions, respectively (Wang et al., 2003a;Lin et al., 2007).Regulations, control technology (devices), operating conditions and feeding materials can all affect PCDD/F emission and the related emission factors must be investigated yearly to develop appropriate control strategies (Wang et al., 2003b;Li et al., 2007a).Therefore, monitoring the PCDD/F emissions from various stationary sources is of great importance for environmental protection issue.For example, the removal efficiency of total PCDD/Fs and the international toxicity equivalence (I-TEQ) value were found to be 57% and 58%, respectively, after injecting powder activated carbon (PAC) in a hazardous waste incinerator (Karademir, et al., 2004).However, the PAC injection was followed by various types of air pollution control devices to enhance the removal efficiency of PCDD/Fs, approaching the range of 92%-99% in a municipal waste incinerator (Tejima, et al., 1996;Abad et al., 2003).A combination of air pollution control devices, including a dry scrubber, activated carbon injection and bag filters have been frequently used, achieving overall removal efficiencies of up to 99% (Li et al., 2008;Wang et al., 2009).
This study investigates the characterization of PCDD/F emission from an electric arc furnace (EAF), a secondary aluminum smelter (secondary ALS), a crematory (CM) and two joss paper incinerators (JP-A, JP-B) in southern Taiwan.Meanwhile, the fly ash and bottom ash were collected to measure the PCDD/F content.In addition, the removal efficiencies of PCDD/F by bag filters were evaluated.Finally, the emission factors of PCDD/Fs from five emission sources were reported and the indicatory PCDD/F congeners were established.

Sampling of PCDD/Fs
The stack flue gas samples were collected from an electric arc furnace (EAF), a secondary aluminium smelter (secondary ALS), a crematory (CM), and two joss paper incinerators (JP-A, JP-B).The sampling procedures followed those of the US EPA Modified Method 23 (US EPA, 1996).Prior to sampling, XAD-2 resin was spiked with PCDD/F surrogate standards prelabeled with isotopes.The fly ash samples were collected by the bag filters and bottom ash samples were collected directly from each furnace.The ash samples were well-mixed and diagonally sectioned for PCDD/F analyses.

Analysis of PCDD/Fs
The analyses of the stack flue gas samples were performed according to the US EPA Modified Method 23, while the fly/bottom ash samples were analysed with the US EPA Method 1613B (US EPA, 1994;1996).In brief, samples were extracted with toluene for 24 hr and this was then followed by a series of sample cleanup procedures, including a multilayer silica gel column, alumina column and activated carbon column.The extract was transferred to a vial, and finally further concentrated by a N 2 gas stream.
The high-resolution gas chromatographs/high-resolution mass spectrometers (HRGC/HRMS) were used for PCDD/F analysis.The HRGC (Hewlett-Packard 6970 Series gas, CA) was equipped with a DB-5 fused silica capillary column (L = 60 m, ID = 0.25 mm, film thickness = 0.25 μm) (J&W Scientific, CA) with a splitless injection, while the HRMS (Micromass Autospec Ultima, Manchester, UK) had a positive electron impact (EI+) source.The analyzer mode of the selected ion monitoring was used with the resolving power at 100,000.The electron energy and source temperature were specified at 35 eV and 250°C, respectively.The oven temperature program was set as followings: initially at 150°C (held for 1 min), then increased by 30 °C/min to 220°C (held for 12 min), and finally increased by 1.5 °C/min to 310°C (held for 20 min).Helium was used as the carrier gas.The recoveries of PCDD/F internal standards ranged from 65-102% which met the criteria within 25-130%.

Indicatory PCDD/Fs
The indicatory PCDD/F is used to figure out the major PCDD/F congener for different PCDD/F emission sources.The indicatory PCDD/Fs analysis is undertaken using the following equation (Yang et al., 1998;Lee et al., 2004;Lin et al., 2006;Lin et al., 2007): where the numerator is the mass fraction of the i th congener of emission source j, and the denominator is the minimum value of the mass fraction of the i th congener among all emission sources.A higher value of Ratio ji means that the i th congener of emission source j is the one that has a greater contribution than the other emission sources.In this way, the highest three ratio values of PCDD/Fs for each source were recognized as the indicatory PCDD/Fs.

PCDD/F Concentrations in the Stack Flue Gas
The mean PCDD/F concentrations in the stack flue gases of various sources are listed in Table 1.The mean total PCDD/F concentration ranged from 0.315 to 18.7 ng/Nm 3 , while the corresponding total I-TEQ value ranged from 0.00681 to 0.703 ng I-TEQ/ Nm 3 .These results are close to those of previous studies, such as, 0.28 ng I-TEQ/Nm 3 for EAF, 3.3-22.7 ng I-TEQ/Nm 3 for ALS and 0.166-4.13ng I-TEQ/Nm 3 for JP (Chen et al., 2004;Lee et al., 2005;Li et al., 2007a;Hu et al., 2009).
The results of the experiment showed that the total PCDD/F I-TEQ concentrations from secondary ALS, CM and JP-A were higher than the PCDD/F emissions standard for a stationary source (0.1 ng I-TEQ/Nm 3 ) (EPA Taiwan, 2009).Therefore, using some air pollution control methods, such as activated carbon injection and bag filter, are necessary to reduce PCDD/F emissions from the above emission sources.

Emission Factors of Various PCDD/F Sources
The emission factors can be used to establish the PCDD/Fs inventory and to develop an integrated the PCDD/F control strategy.Table 2 lists the measured mean emission factors of PCDD/Fs from the five emission sources.The input rate of feeding materials from EAF, secondary ALS, JP-A, JP-B and CM are 72.0 ton/hr, 1.2 ton/hr, 4.0 kg/hr, 2.4 kg/hr, and 0.5 body/hr, respectively.The emission factor of PCDD/F from EAF, secondary ALS, JP-A and JP-B are 0.416, 3.50, 0.166 and 0.00827 μg I-TEQ/ton, respectively.These results are consistent with those obtained in previous studies, which were 1.8-2.4μg I-TEQ/ton for EAF, 2.66-50.1 μg I-TEQ/ton for ALS and 0.0203-0.176μg I-TEQ/ton for JP (Chen et al., 2004;Lee et al., 2005;Lin et al., 2007;Li et al., 2007a;Hu et al., 2009).For CM, the emission factor is 5.36 μg I-TEQ/body, which is also close to the results in an earlier study (6.11-13.6 μg I-TEQ/body) (Wang et al., 2003c).

PCDD/F Contents in Fly Ash and Bottom Ash
The mean PCDD/F contents in fly ash and bottom ash are listed in Table 3.The mean total PCDD/F content in fly ash from EAF and secondary ALS were 1039, and 639 ng/kg, respectively, while the corresponding I-TEQ values were 74.0, 49.9 ng I-TEQ/kg.As for bottom ash, the total PCDD/F content from EAF, secondary ALS, JP-A and JP-B were 528, 8.87, 8.36 and 5.98 ng/kg, respectively, and the corresponding I-TEQ values were 21.3, 0.494, 0.457 and 0.148 ng I-TEQ/kg.The highest total PCDD/F I-TEQ value (74.0 ng I-TEQ/kg) in fly ash from EAF was lower than that (194 ng I-TEQ/kg) from a municipal solid waste incinerator (Giugliano et al., 2002).Since the total flue gas PCDD/F concentration is low, the fly ash contents are also expected to be low.

PCDD/F Removal Efficiency by Bag Filter
The gas samples were taken at the same time before and after the bag filters to evaluate the efficiencies of the filters in EAF.The mean PCDD/F emission rate before and after the bag filter were 277 and 400 μg/hr, respectively, while   the corresponding I-TEQ values were 21.7 and 42.1 μg I-TEQ/hr.The results show that, there was a reduction of -44.4 and -94.0% for total PCDD/Fs and total PCDD/Fs TEQ, respectively.This phenomenon was recognized as being due a "memory effect", in which the wet scrubber made up of plastic material enhanced the PCDD/F adsorption and subsequent desorption (Kim et al., 2001;Löthgren and Bavel, 2005).Therefore, the bag filters must be replaced regularly in order to reduce PCDD/F emissions.

The Fate of PCDD/Fs
The contribution fractions of total PCDD/F in fly ash, bottom ash and stack flue gas from EAF were approximately 61.1%, 38.9% and 0.00587%, respectively, whereas they were 95.3%, 3.31% and 1.37% from secondary ALS.These results show that fly ash from metallurgical facilities (EAF, secondary ALS) contributed a high total PCDD/F mass that is consistent with the results in a previous study (Li et al., 2007b).However, JP-A and JP-B contribute over 99.9% of total PCDD/F from stack flue gas and only 0.00947% is from bottom ash.Therefore, the high contribution of total PCDD/F in fly ash from the metallurgical facilities (EAF, secondary ALS) should be carefully treated, while JP-A and JP-B need to be equipped with some air pollution control devices (bag filters) to reduce PCDD/F emission.

CONCLUSIONS
The mean total PCDD/F I-TEQ concentration of five different sources ranged from 0.00681 to 0.703 ng I-TEQ/Nm 3 , while the emission factor of PCDD/Fs ranged from 0.00827 to 3.50 μg I-TEQ/ton (5.36 μg I-TEQ/body for CM).Furthermore, in the indicatory PCDD/Fs analysis, the EAF, and secondary ALS have the same congeners, while CM, JP-A and JP-B have similar indicatory PCDD/Fs.In addition, the highest contribution of total PCDD/Fs is from fly ash (61.1-95.3%)for metallurgical facilities (EAF, secondary ALS), while 99.9% of the stack flue gas is from JP.Hence, fly ash from the metallurgical facilities should be carefully treated and JP incinerators need to be equipped with some air pollution control devices (such as bag filters) to reduce PCDD/F emission.Moreover, the removal efficiency of PCDD/F by bag filters was -44.4%, and this result was due to the PCDD/F memory effect with these filters.Therefore, bag filters must be replaced regularly in order to reduce PCDD/F emissions.

Table 1 .
PCDD/F concentration in the stack flue gas from various sources.

Table 2 .
PCDD/F emission factor from various sources.

Table 3 .
PCDD/F content in fly ash and bottom ash from various sources.