| Summary: | 博士 === 國立成功大學 === 環境醫學研究所 === 100 === Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) have been widely considered as an important hazard to environment and human. Understanding of the fate of PCDD/Fs from source to receiver would be helpful for emission control and environmental impact reduction of PCDD/Fs. This study focuses on (1) the formation of PCDD/Fs in industrial process, (2) controlling PCDD/Fs emission from the potential sources through air pollution control devices (APCD), and (3) the environmental transportation of PCDD/Fs.
In recent year, owing to the strict emission regulation, PCDD/Fs emissions from waste incinerators has decreased. In this stage, the focus has shifted to iron ore sinter plant for PCDD/Fs emission. Theoretically, in process suppression of PCDD/Fs generation is the best way to reduce PCDD/Fs emission. However, the PCDD/Fs formation pathway in sintering process is still unconcluded and limits the development of suppression of PCDD/Fs generation in sintering process. Therefore, the first research subject is to study the formation of PCDD/Fs during sinter process was studied. Since the sinter raw mix, (such as iron ores, coke breeze, flux and return fine), which with chlorine, metals and other organic matters have favored de novo synthesis. Moreover, the temperature profile of sinter bed revealed that the temperature of flue gas in the windbox of the later phase of sintering process could reach 400 to 500 C, indicating that the atmosphere of the windbox could be favorable for the de novo synthesis. However, the evidences for the possible de novo synthesis of PCDD/Fs in the windbox are still limited. We took the windbox dust from a commercial sinter plant for direct measurement of ionic and chemical functional group constituents for predicting possible de novo synthesis pathways of dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). We discovered that the abundance in both KCl and NaCl may provide a favorable environment for de novo synthesis of PCDD/Fs in the WB. Al, Fe, K, Ca, and Pb were the top five contents in WB16 dusts, but the co-existence of the above five metal contents need further investigation on their roles in PCDD/F formation processes in the future. Although a low concentration of Cu was detected, it might be of importance to PCDD/Fs formation inside the WB. A total of 29 chemical compounds were identified. Among them, several oxygenated organic compound might be associated with PCDD/F formations at the beginning stage, but the roles of aromatic oxygenates on the formation of PCDD/Fs required further investigation. Finally, possible de novo synthesis pathways of PCDD/Fs were proposed based on the above findings. However, the above pathways are required further laboratory studies for validation before possible formation suppression approaches can be determined.
Besides direct suppression of PCDD/Fs generation, the end-of-pipe treatment (air pollution control devices, APCDs) is widely used as a major ways to reduce PCDD/Fs emission nowadays. However, using the data obtained by current flue gas sampling methods to evaluate the PCDD/Fs removal efficiencies of installed APCDs remains potential error. The misestimating of removal efficiencies might cause the unexpected emission of PCDD/Fs into the environment. Therefore, the second part of this study was aimed at developing an approach for correcting the gas and particle partitioning of PCDD/F congeners for samples collected from the flue gas of an iron ore sinter plant. An iron ore sinter plant equipped with an electrostatic precipitator (EP) and a selective catalytic reduction (SCR) was selected. Flue gas samples were collected at EP inlet (EPi), EP outlet (EPo) and SCR outlet (SCRo). Both particle- and gas-phase PCDD/Fs were analyzed for each collected sample. PCDD/F contents in EP ashs (EPash) were also analyzed and used to correct the gas and particle partitioning of PCDD/F congeners of the collected flue gas samples. Results show that PCDD/Fs in the flue gas were dominated by the gas-phase. Before correction, the removal efficiencies for the gas- and particle-phase PCDD/Fs for EP were -58.1% and 64.3%, respectively, and SCR were 39.4% and 83.9%, respectively. The above results were conflict with the expected results for both EP and SCR indicating the need for correcting the gas and particle partitioning of PCDD/F congeners for all collected flue gas samples. After correction, the removal efficiencies become more reasonable for EP (=4.22% and 97.7%, respectively), and SCR (=54.7% and 62.0%, respectively). The above results confirm the feasibility of correcting approach developed by this study.
Once PCDD/Fs as well as dioxin-like compounds have entered the atmosphere from the sources, they move from atmosphere to other environmental compartment and eventually entered the food chain. Therefore, understanding their fate in the terrestrial environment also became an important issue. In the third part of this study, the PCDD/Fs as well as dioxin-like compounds concentrations in the ambient air and their impact on vegetation and soil are investigated. Ambient air, vegetation, and soil samples were collected from the vicinity of an industrial complex. For each collected sample, the polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/F), coplanar polychlorinated biphenyls (coplanar PCB), brominated dibenzo-p-dioxins/ dibenzofurans (PBDD/F), and polybrominated diphenyl ethers (PBDE) concentrations are analyzed. Principal component analysis (PCA) is adopted to explore the relationships between the concentration of each POP type in the ambient air and those in soil and vegetation. Results showed that atmospheric PCDD/Fs, PBDD/Fs, and PBDEs are dominated by the particle phase. PCDD/Fs in vegetation and soil are contributed by gas-phase and particle-phase PCDD/Fs, respectively. For coplanar PCBs, only the gas-phase coplanar PCBs contribute to the content in vegetation and soil. For PBDD/Fs, both vegetation and soil are contributed by particle-phase PBDD/Fs. PBDEs in vegetation are contributed by both gas- and particle-phase PBDEs, while soil PBDEs are by particle-phase only. The above results are confirmed by comparing with those obtained from theoretical calculations and previous studies.
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