Environ. Sci. Technol. 2001, 35, 3601-3607
Dioxin-like PCBs Released from Waste Incineration and Their Deposition Flux S H I N - I C H I S A K A I , * ,† KENICHI HAYAKAWA,‡ HIROSHI TAKATSUKI,‡ AND ISAMU KAWAKAMI§ National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-0053, Japan, Environment Preservation Center, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan, and Sumitomo Heavy Industries Ltd., 5-9-11 Kitashinagawa, Shinagawaku, Tokyo 141-8686, Japan
To investigate the formation and decomposition behaviors of dioxin-like PCBs during incineration of municipal solid wastes in a recently constructed facility, the concentrations of dioxin-like PCBs were measured in municipal solid waste before incineration and in the incinerator emission gas and residues. Using these values, release/ inflow ratios of dioxin-like PCB congeners (ratio of the amount released from the incinerator to the amount flowing into the incinerator through waste) were calculated. For PCB congeners 126, 169, and 189, these ratios were greater than 1. In contrast, ratios of the other dioxin-like congeners were much less than 1. To take into account atmospheric sources, the amounts of dioxin-like PCBs released via emissions from municipal solid waste incineration were compared with atmospheric depositions in the Kyoto City area. Most of the PCDD/F congeners and homologue groups were deposited in amounts similar to those found in emissions from the waste incinerator. Deposition of dioxinlike PCB congeners 81, 126, 169, and 189 were also found in amounts similar to those released via the waste incinerator emissions. However, depositions of congeners 105, 114, and 118 greatly exceeded the amounts released via waste incinerator emissions. In reviewing the congener profiles of industrial PCB products and emission gas, the following general trends were observed: (i) For congeners whose contents are high in industrial PCB products (e.g., 105 and 118), the amounts deposited were much higher than the amounts released with waste incineration emission gas. (ii) For congeners whose percentages were high in the waste incineration emission gas (e.g., 126 and 189), the amounts deposited were similar to the amounts released in the waste emission gas.
Introduction Polychlorinated biphenyls (PCBs) are considered environmental pollutants because of their toxicity, their ability to accumulate in living organisms, and their persistence in the * Corresponding author phone: +81-298-50-2806; fax: +81-29850-2808; e-mail:
[email protected]. † National Institute for Environmental Studies. ‡ Kyoto University. § Sumitomo Heavy Industries Ltd. 10.1021/es001945j CCC: $20.00 Published on Web 08/10/2001
2001 American Chemical Society
environment. Environmental pollution by PCBs has been widely observed since Jensen (1, 2) detected PCBs in eagles and herrings in Sweden in 1966. Since then, PCBs have been detected in various environmental media and regions (3-5). Non- and mono-ortho-substituted PCB congeners have a high toxicity, similar to that of polychlorinated dibenzop-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Therefore, these dioxin-like PCBs are referred to as dioxinrelated compounds and are evaluated equally with PCDD/ Fs in toxicity (6, 7). Well-known sources of dioxin-like PCBs include those released by the use or disposal of industrial PCB products or formed as byproducts during municipal solid waste (MSW) incineration (8-10). It is also well-known that PCBs are thermally decomposable. In Japan, 5300 t of waste liquid PCBs, namely, Kanechlors, was thermally destroyed at the Takasago plant of Kaneka Co. Ltd. in 1988 (11). In European countries and the United States, waste PCBs are regularly incinerated at high temperatures. MSW incineration processes have the potential to both produce and destroy PCBs. Previously, we reported the results of substance flow analyses in a MSW incineration facility in Kyoto City (12, 13). In those reports, we viewed the existing MSW incinerator (PCDD/F levels in stack emission gas: 2.0 ng TEQ/Nm3) as a system and examined the inflow amounts of dioxin-like PCBs and PCDD/Fs in solid municipal waste and the amounts released via emission gas and incineration residues. In this study, we performed a substance flow analysis for dioxin-like PCBs in a recently constructed facility and compared the results with those from the existing facility. To take into account sources of dioxin-like PCBs in the atmosphere, we measured the bulk deposition of dioxin-like PCBs and compared it to amounts released by MSW incineration in the Kyoto City area.
Experimental Methods Recently Constructed Facility. The recently constructed MSW incineration facility examined in this study has stokertype furnaces with an incineration capacity of 480 t/d (160 t/d × 3 furnaces, continuous operation). The average temperature of the secondary combustion chambers is 880 °C. Waste heat is recovered by a waste heat boiler used to generate power. Purification of waste gas is performed by a bag filter with a dry slaked lime spray at approximately 150 °C. The waste gas temperature is then raised to 210 °C. The emission gas moves through catalytic denitrification equipment and is released into the air. The unit amount of emission gas is 5200 Nm3/waste-ton. Fly and bottom ashes are 22 and 56 kg/waste-ton, respectively. Existing Facility. Details of the existing facility have already been reported (12, 13). This facility began operation in 1968. It has two continuous incinerators with a maximum capacity of 200 t/d. The furnace is a stoker type, with waste gas purification by a dry system (lime addition) and an electrostatic precipitator installed as a dust collector. Sampling. We took emission gas samples at three points: boiler outlet, bag filter (BF) outlet, and stack. We prepared samples of MSW as follows: a few hundred kilograms of waste was mixed well and repeatedly reduced by quartering; the reduced samples were then sorted into subsamples according to physical composition (e.g., papers, plastics, metals). Sorted subsamples were cut into small pieces and then remixed together so that the proportion of each subsample was the same as that in the original waste. In this way, we prepared three waste samples. VOL. 35, NO. 18, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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We took bulk deposition samples at the Kyoto University campus in March 1999, August 1999, and January 2000. A cylindrical stainless steel vessel (45 cm i.d., 45 cm height) was placed on the roof of a building for 2 weeks. Before placement, 500 mL of diethylene glycol was added to maintain a liquid surface on the bottom of the vessel. Analysis. Sample extraction and cleanup methods were based on the Standard Manual on Dioxins Analysis in Waste Management (14) and the JIS K0311 method (15). We extracted the emission gas samples (drain, XAD resin, and dust filter) and ashes with toluene. Prior to the toluene extraction, the dust filter and ashes were digested with HCl. MSW samples were air-dried and extracted with toluene. Bulk deposition samples were filtered, and the filter residues were extracted with toluene. The filtrate was extracted with dichloromethane by liquid-liquid extraction and was mixed with the extract of the filter residue. 13C-labeled internal standards were added to the samples and cleaned up in a multilayer silica gel column. For waste samples only, a DMSO partition procedure (16) was performed prior to placement in the multilayer silica gel column. For PCB analysis, silica gel column effluents were concentrated and analyzed. For PCDD/Fs, additional fractionation with a basic alumina column was conducted, and the second fraction (50% dichloromethane-hexane) was concentrated and analyzed. Quantification was performed with high-resolution gas chromatography equipped with a high-resolution mass spectrometer. Recoveries ranged from 50% to 110% for PCDD/Fs and from 40% to 110% for PCBs.
Results and Discussion Concentrations in MSW, Emission Gas, and Residues. Concentrations of dioxin-like PCBs and PCDD/Fs in MSW are shown in Table 1. These values are slightly higher than those previously reported (0.13-0.29 pg TEQ/g wet for dioxinlike PCBs and 0.82 pg TEQ/g wet for PCDD/Fs) (12, 13). PCDD/F concentrations in German MSW samples, which were taken in 1980 by Wilken et al. (17), were 50.2 pg TEQ/g wet. Fricke et al. (18) reported that concentrations of PCDD/ Fs and PCBs in compost on a dry basis were 12.1 pg TEQ (BGA)/g and 25.4 ng/g, respectively. Concentrations of dioxin-like PCBs, total PCB homologues, and PCDD/Fs in emission gases sampled at various points in each residue and in the bulk depositions are shown in Table 2. Levels of most dioxin-like PCB congeners were lower at the BF outlet and the stack than at the boiler outlet. However, levels of 77 and 105 at the stack were the same as those at the boiler outlet. Levels of M1CBs to P5CBs at the stack were also the same as those at the boiler outlet. These results suggested that levels of 77, 105, and 2- to 4-chlorinated PCB homologues were influenced by air after outlet from the BF as these congeners and homologues are generally detected in the air. Substance Flow Analysis of Dioxin-like PCBs, Total PCB Homologue Groups, and PCDD/Fs in MSW Incineration Facilities. We calculated the amounts of each congener and homologue that flowed into the incinerators with the MSW and the amounts released from the incinerator as emission gas and fly and bottom ashes. Inflow amount with incineration of 1 t of MSW (µg/waste-ton) was defined based on the average of the three measured concentrations in the MSW samples. We calculated the amount released during the incineration of 1 t of MSW by using the value measured at the BF outlet as the concentration in the emission gas. Values below the quantification limit were regarded as the half of the quantification limit. To investigate whether dioxin-like PCBs, total PCB homologue groups, and PCDD/Fs tend to be formed or decomposed in the MSW incineration facilities, the release/ inflow ratio (defined as the value of the amount released in 3602
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TABLE 1. Dioxin-like PCBs, Sum of PCB Homologue Groups, and PCDD/Fs in MSW
3,3′,4,4′-TeCB (77) 3,4,4′,5-TeCB (81) 3,3′,4,4′5-PeCB (126) 3,3′,4,4′,5,5′-HxCB (169) 2,3,3′,4,4′-PeCB (105) 2,3,4,4′,5-PeCB (114) 2,3′,4,4′,5-PeCB (118) 2′,3,4,4′,5-PeCB (123) 2,3,3′,4,4′,5-HxCB (156) 2,3,3′,4,4′,5′-HxCB (157) 2,3′,4,4′,5,5′-HxCB (167) 2,3,3′,4,4′,5,5′-HpCB (189) 2,2′,3,3′,4,4′,5-HpCB (170) 2,2′,3,4,4′,5,5′-HpCB (180) TEQa,b Σdioxin-like PCBsc
waste sample 1 (ng/g wet)
waste sample 2 (ng/g wet)
waste sample 3 (ng/g wet)
0.048 0.0053 0.0047 0.0024 0.11 0.033 0.24 0.0067 0.031 0.0095 0.013 0.0029 0.043 0.11 0.00057 0.66
0.048 0.0038 0.0042
