Emissions of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans from the Incinerations of Both Medical and Municipal Solid Wastes

1 Department of Chemical Engineering, Cheng-Shiu University. 840, Chengching Rd., Kaohsiung 833, Taiwan, ROC 2 Department of Environmental Engineering, National Cheng Kung University. 1, University Rd., Tainan 70101, Taiwan, ROC 3 Graduate Institute of Environmental and Occupational Health, Medical College, National Cheng Kung University. 138, Sheng-Li Rd., Tainan 70428, Taiwan, ROC 4 Southern Incinerator Plant, Department of Environmental Protection, Kaohsiung Municipal Government, 6, Bei-Lyn Rd., Kaohsiung 812,Taiwan, ROC


Introduction
After polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were discovered in the flue gases and fly ash of *Corresponding author: Tel: +886-7-7310606 ext. 225 Fax: +886-7-7338946 E-mail address: wison@cc.csit.edu.twmunicipal solid waste incinerators (MSWIs) in 1977 (Olie et al., 1977), PCDD/Fs have become a serious issue in many countries, because of their toxicological effects and associated adverse health and 1995, respectively.In the United Kingdom, the total estimated emissions of PCDD/Fs into the atmosphere ranged from 560 to 1100 g I-TEQ year -1 ; MSWIs dominated, contributing 460-580 g I-TEQ year -1 , an average of 63% to the total emissions.MWIs contributed 18-88 g I-TEQ year -1 in the UK (Eduljee et al., 1996).Despite source reduction measures (emissions fell to 220-660 g I-TEQ year -1 in 1999), MSWIs remain a significant source of PCDD/Fs to the atmosphere, contributing 460-580 g I-TEQ year -1 , an average between 30-50% of the total PCDD/Fs I-TEQ emissions (Alcock et al., 1999).Although emissions from MWIs are less than those from MSWIs, on-site MWIs cause special attention, mainly because of the typical hospital's proximity to a city (Lee et al., 1996).

Sampling
Three PCDD/F samples were collected from the

Congener Profiles
The congener profiles of the 2,3,7,8-substituted PCDD/Fs were selected as the signatures of the MWIs and MSWIs.Figure 1 shows the congener profiles of the "dirty" seventeen PCDD/Fs (mean±SD) detected from the stack flue gases of MWIs and MSWIs.Each selected congener was normalized by reference to the total weight of all 2,3,7,8-congeners.The variable "m" represents the number of incinerators while the variable "n" represents the number of total stack flue gas  EPA, 1998).ton-waste -1 ~ 40.7 µg I-TEQ ton-waste -1 , RSD: , respectively (Eduljee et al., 1996).These values were higher than those obtained here.

Annual Emissions of PCDD/Fs from MWIs and MSWIs
The annual emissions of PCDD/Fs are estimated by the following formula (US EPA, 1998).
where: E total = annual emissions from all facilities (g I-TEQ year -1 ); ∑E tested,i = annual emissions from all tested facilities in class i; ∑E untested,i = annual emissions from all untested facilities in class i; EF i = mean emission factor of tested facilities in class i; A i = activity measure for untested facilities in class i.
According to statistical data (Taiwan EPA, 2003) and operational records of each tested facility, in Taiwan, annual emissions of PCDD/Fs from MWIs and MSWIs are calculated as 0.371 g I-TEQ year -1 and 0.737 g I-TEQ year -1 , respectively.The confidence of these reported values are medium or high, especially for MSWIs because their tested percentage is very high.
Although the contribution of PCDD/Fs from MWIs to the atmosphere was 50.3% of that from MSWIs, it should be noted that most MWIs are equipped with a low stack and are situated in the proximity of the residential area and PCDD/F emissions from MWIs could significantly affect its surrounding environment.

Conclusions
The implications.US EPA's Office of Research and Development (ORD) had developed the "Database of Sources of Environmental Releases of Dioxin like Compounds in the United States" (US EPA, 2001) to be a repository of PCDD/Fs emissions data from all known sources.It reveals that MSWIs released 64% and 38% of the total PCDD/F emission into the air in 1987 and 1995, respectively; medical waste incinerators (MWIs) released 20% and 16% of the total PCDD/F emission into the air in 1987 PCDD/F emissions from most combustion processes are detected as a mixture of 75 PCDD and 135 PCDF congeners.The mixture can be translated into profiles, which represent the distribution of individual PCDD/Fs.These profiles may give a signature or fingerprint of the types of PCDD/Fs associated with particular incinerators and air pollution control devices (APCDs).The fingerprinting of PCDD/Fs has been interestingly applied in identification of sources, atmospheric transport and transformation studies and formation mechanism elucidation(Buekens et al., 2000).

Figure 1 .
Figure 1.Congener profiles of seventeen 2,3,7,8 chlorinated substituted PCDD/Fs in the stack flue gas of MWIs and MSWIs 75.1%), while that of the ten MSWIs is 0.0939 µg I-TEQ ton-waste -1 (Range: 0.0475 µg I-TEQ ton-waste -1 ~ 0.187 µg I-TEQ ton-waste -1 , RSD: 46.4%).These emission factors were based on total weights of waste, excluding fuel.The mean PCDD/F emission factors (20.1 µg I-TEQ ton-waste -1 ) of the MWIs was about 210 times of magnitude higher than that of MSWIs, which was 0.0939 µg I-TEQ ton-waste -1 .It is resulted from that MWIs are typically small-scale incinerators, with low combustion efficiency, and without advanced APCDs; most importantly, PVC is a major constituent in the feed waste stream for incineration.The emission factors of MWIs and MSWIs (new plants) in the United Kingdom were 20-200 and 0.8 µg I-TEQ ton-waste -1 mean PCDD/F concentrations in the stack flue gases of these four MWIs and ten MSWIs is 0.521 ng I-TEQ Nm -3 and 0.0533 ng I-TEQ Nm -3 , respectively.In the stack flue gases of MWIs, HpCDF and OCDF were the major congeners, while in MSWIs, OCDD and 1,2,3,4,6,7,8-HpCDD were the major ones.The mean PCDD/F emission factors (20.1 µg I-TEQ ton-waste -1 ) of the MWIs was about 210 times of magnitude higher than that of MSWIs, which was 0.0939 µg I-TEQ ton-waste -1 .It is resulted from that MWIs are typically small-scale incinerators, with low combustion efficiency, and without advanced APCDs; most importantly, PVC is a major constituent in the feed waste stream for incineration.In Taiwan, the annual emissions of PCDD/Fs from MWIs and MSWIs are 0.371 g I-TEQ year -1 and 0.737 g I-TEQ year -1 , respectively.Although the contribution of PCDD/Fs from MWIs to the atmosphere was 50.3% of that from MSWIs, it should be noted that most MWIs are equipped with a low stack and are situated in the proximity of the residential area and PCDD/F emissions from MWIs could significantly affect its surrounding environment.

Table 2 .
Mean PCDD/F concentration in the stack flue gases of MWIs and MSWIs Table 1 presents basic information concerning the four MWIs (H1 ~ H4) and ten MSWIs (M1 ~ M10) investigated here, including each capacity and APCDs in sequence.The operation type of all MWIs is intermittent while that of MSWIs is continuous.

Table 3 .
Mean PCDD/F emission factors and

Table 3
and table 4 list the mean PCDD/F emission factors from the stack flue gases of MWIs and MSWIs, respectively.The mean PCDD/F emission factors of the four MWIs is 20.1 µg I-TEQ ton-waste -1 (Range: 1.34 µg I-TEQ

Table 4 .
Mean PCDD/F emission factors and their RSD of these ten MSWIs