Kai Hsien Chi

Innovative PCDD/F-containing gas stream generating system applied in catalytic decomposition of gaseous dioxins over V2O5-WO3/TiO2-based catalysts.

Development of effective PCDD/F (polychlorinated dibenzo-p-dioxin and dibenzofuran) control technologies is essential for environmental engineers and researchers. In this study, a PCDD/F-containing gas stream generating system was developed to investigate the efficiency and effectiveness of innovative PCDD/F control technologies. The system designed and constructed can stably generate the gas stream with the PCDD/F concentration ranging from 1.0 to 100ng TEQ Nm(-3) while reproducibility test indicates that the PCDD/F recovery efficiencies are between 93% and 112%. This new PCDD/F-containing gas stream generating device is first applied in the investigation of the catalytic PCDD/F control technology. The catalytic decomposition of PCDD/Fs was evaluated with two types of commercial V(2)O(5)-WO(3)/TiO(2)-based catalysts (catalyst A and catalyst B) at controlled temperature, water vapor content, and space velocity. 84% and 91% PCDD/F destruction efficiencies are achieved with catalysts A and B, respectively, at 280 degrees C with the space velocity of 5000h(-1). The results also indicate that the presence of water vapor inhibits PCDD/F decomposition due to its competition with PCDD/F molecules for adsorption on the active vanadia sites for both catalysts. In addition, this study combined integral reaction and Mars-Van Krevelen model to calculate the activation energies of OCDD and OCDF decomposition. The activation energies of OCDD and OCDF decomposition via catalysis are calculated as 24.8kJmol(-1) and 25.2kJmol(-1), respectively.

Increases in ambient PCDD/F and PCB concentrations in Northern Taiwan during an Asian dust storm episode

In spring 2006, an Asian dust storm (ADS) that originated in the deserts of Mongolia and China eventually reached populated areas of East Asia, including Taiwan. The concentrations of total suspended particles (TSP), vapor/solid-phase dioxin-like compounds and metal content in atmospheric aerosols were monitored at two sampling sites in northern Taiwan during the ADS episode: one along the northern coast (Site A), and the other in Taipei city (Site B). The ADS swept across northern Taiwan from 13 March to 19 March, 2006. Data indicate that the atmospheric dibenzo-p-dioxin and dibenzofuran (PCDD/F, 32.2 to 52.5 fg-I-TEQ/m(3)) and polychlorinated biphenyl (PCB, 2.23 to 4.49 fg-TEQ(WHO)/m(3)) concentrations measured at the two sampling sites prior to the ADS episode were considerably lower than those measured in other Asian countries. However, measurements made at both sites on 13 and 18 March 2006 indicate that the atmospheric PCDD/F and PCB concentrations increased 2.5 and 3.2 times at Site A, and 2.1 and 1.9 times at Site B, respectively, during the ADS episode. The concentrations of aluminum (Al), potassium (K) and Titanium (Ti) in atmospheric aerosols were also found to increase about 2 to 5 times during this period. As no specific dioxin emission sources exist within nearly 20 km of Site A, the increase in PCDD/F and PCB concentrations observed there is likely to be related to the ADS from mainland China. Additionally, the amount of PCDD/Fs bound to suspended particles increased from 257-259 to 339-512 pg-I-TEQ/g-TSP during the ADS episode. The distribution of OCDD congener observed in Taipei city increased dramatically during the ADS episode, however, the distribution of PCB congener did not vary significantly.

Sampling and analysis of ambient dioxins in northern Taiwan.

In this study, ambient air samples were taken concurrently in the vicinity area of a large-scale municipal waste incinerator (MWI) and the background area for measuring polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) concentrations from November 1999 through July 2000 in northern Taiwan. The results obtained from eighteen ambient air samples indicate that the mean PCDD/F concentration of seventeen 2,3,7,8-substituted congeners in wintertime (188-348 fg-I-TEQ/m(3)) is significantly higher than that measured in summertime (56-166 fg-I-TEQ/m(3)). In addition, the seasonal PCDD/F concentrations are compared with the ambient air quality data including CO, NO(2), PM(10) and TSP sampled from Taipei area to gain better insights. It indicates that the variation of ambient air PCDD/F concentrations is closely correlated with that of PM(10) concentrations. Besides, the results indicate that the I-TEQ concentration of ambient air in sampling site B (directly downwind of the MWI) is of the highest while the sampling site A (upwind of MWI) is of the lowest among all sampling sites. This implies that existing MWI can be a significant emitter of PCDD/Fs in this area. Furthermore, the patterns of the PCDD/F congener distribution at all sampling sites (including the background site in Taoyuan) are quite similar. OCDD concentration is of the highest among seventeen PCDD/F congeners investigated and accounts for about 35% of the total concentration. As for the I-TEQ concentrations, 2,3,4,7,8-PeCDF is the most significant contributor, generally being responsible for 30-45% of the total I-TEQ values depending on the sampling sites and seasons.

Reduction of dioxin emission by a multi-layer reactor with bead-shaped activated carbon in simulated gas stream and real flue gas of a sinter plant.

A laboratory-scale multi-layer system was developed for the adsorption of PCDD/Fs from gas streams at various operating conditions, including gas flow rate, operating temperature and water vapor content. Excellent PCDD/F removal efficiency (>99.99%) was achieved with the multi-layer design with bead-shaped activated carbons (BACs). The PCDD/F removal efficiency achieved with the first layer adsorption bed decreased as the gas flow rate was increased due to the decrease of the gas retention time. The PCDD/F concentrations measured at the outlet of the third layer adsorption bed were all lower than 0.1 ng I-TEQ Nm⁻³. The PCDD/Fs desorbed from BAC were mainly lowly chlorinated congeners and the PCDD/F outlet concentrations increased as the operating temperature was increased. In addition, the results of pilot-scale experiment (real flue gases of an iron ore sintering plant) indicated that as the gas flow rate was controlled at 15 slpm, the removal efficiencies of PCDD/F congeners achieved with the multi-layer reactor with BAC were better than that in higher gas flow rate condition (20 slpm). Overall, the lab-scale and pilot-scale experiments indicated that PCDD/F removal achieved by multi-layer reactor with BAC strongly depended on the flow rate of the gas stream to be treated.

Distribution, Fate, Inhalation Exposure and Lung Cancer Risk of Atmospheric Polycyclic Aromatic Hydrocarbons in Some Asian Countries

A large-scale monitoring program, the Asia Soil and Air Monitoring Program (Asia-SAMP), was conducted in five Asian countries, including China, Japan, South Korea, Vietnam, and India. Air samples were collected using passive air samplers with polyurethane foam disks over four consecutive 3-month periods from September 2012 to August 2013 to measure the seasonal concentrations of 47 polycyclic aromatic hydrocarbons (PAHs), including 21 parent and 26 alkylated PAHs, at 176 sites (11 background, 83 rural, and 82 urban). The annual concentrations of total 47 PAHs (∑47PAHs) at all sites ranged from 6.29 to 688 ng/m(3) with median of 82.2 ng/m(3). Air concentrations of PAHs in China, Vietnam, and India were greater than those in Japan and South Korea. As expected, the air concentrations (ng/m(3)) were highest at urban sites (143 ± 117) followed by rural (126 ± 147) and background sites (22.4 ± 11.4). Significant positive correlations were found between PAH concentrations and atmosphere aerosol optical depth. The average benzo(a)pyrene equivalent concentration (BaPeq) was 5.61 ng/m(3). It was estimated that the annual BaPeq concentrations at 78.8% of the sampling sites exceeded the WHO guideline level. The mean population attributable fraction (PAF) for lung cancer due to inhalation exposure to outdoor PAHs was on the order 8.8‰ (0.056-52‰) for China, 0.38‰ (0.007-3.2‰) for Japan, 0.85‰ (0.042-4.5‰) for South Korea, 7.5‰ (0.26-27‰) for Vietnam, and 3.2‰ (0.047-20‰) for India. We estimated a number of lifetime excess lung cancer cases caused by exposure to PAHs, which the concentrations ranging from 27.8 to 2200, 1.36 to 108, 2.45 to 194, 21.8 to 1730, and 9.10 to 720 per million people for China, Japan, South Korea, Vietnam, and India, respectively. Overall, the lung cancer risk in China and Vietnam were higher than that in Japan, South Korea, and India.

PCDD/F Measurement at a High-Altitude Station in Central Taiwan: Evaluation of Long-Range Transport of PCDD/Fs during the Southeast Asia Biomass Burning Event

Recent biomass burning in Southeast Asia has raised global concerns over its adverse effects on visibility, human health, and global climate. The concentrations of total suspended particles (TSPs) and other vapor-phase pollutants (CO and ozone) were monitored at Lulin, an atmospheric background station in central Taiwan in 2008. To evaluate the long-range transport of persistent organic pollutants (POPs) during the Southeast Asia biomass burning event, the atmospheric polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were also measured at Lulin station. The atmospheric PCDD/F and TSP concentrations measured at Lulin station ranged from 0.71-3.41 fg I-TEQ/m(3) and 5.32-55.6 microg/m(3), respectively, during the regular sampling periods. However, significantly higher concentrations of PCDD/Fs, TSPs, CO, and ozone were measured during the spring season. These high concentrations could be the result of long-range transport of the products of Southeast Asia biomass burning. During the Southeast Asia biomass burning event (March 18-24, 2008), an intensive observation program was also carried out at the same station. The results of this observation program indicated that the atmospheric PCDD/F concentration increased dramatically from 2.33 to 390 fg I-TEQ/m(3) (March 19, 2008). The trace gas (CO) of biomass burning also significantly increased to 232 ppb during the same period, while the particle-bound PCDD/Fs in the TSP increased from 28.7 to 109 pg I-TEQ/g-TSP at Lulin station during the burning event. We conclude that there was a significant increase in the PCDD/F concentration in ambient air at a high-altitude background station in central Taiwan during the Southeast Asia biomass burning event.

Degradation of gaseous dioxin-like compounds with dielectric barrier discharges

Developing effective technologies to reduce dioxin emissions has become an important issue in the research and industrial fields. In this study, a dioxin-containing gas stream generating system was applied to evaluate the effectiveness of dielectric barrier discharge (DBD) plasma technology for the destruction of dioxin-like compounds. The results indicate that the destruction efficiencies of dioxin-like compounds achieved with DBD plasma strongly depend on the composition of the simulated gas stream. As the DBD plasma is operated with the simulated gas stream containing 20% water vapor, around 74% PCDDs and 89% PCDFs can be destroyed by DBD plasma. UV, electrons, and OH radicals are generated via the DBD plasma process and react with the dioxin-like compounds in the gas stream. Dechlorination via UV and electrons and decomposition via OH radicals occur at the same time and significantly increase the destruction efficiency of PCDD/Fs in the presence of oxygen and water vapor. Additionally, the total toxicity destruction of dioxin-like compounds with the input energy of 1 kJ increases from 1.47 to 3.06 ng-TEQ(WHO) as the water vapor is incorporated into the gas stream.

Atmospheric deposition of PCDD/Fs measured via automated and traditional samplers in Northern Taiwan.

Most polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the atmosphere are bound to particles which are suspended in the atmosphere, and eventually settle on soil, vegetation, water bodies or other receptors in the environment. Monitoring atmospheric deposition fluxes (dry/wet) is important in tracing the environmental fate and behavior of PCDD/Fs. PCDD/F depositions were collected via an automated PCDD/F ambient sampler and traditional cylindrical vessels, respectively, from April 2007 to February 2008. The automated PCDD/F ambient sampler used in this study can prevent both re-suspension and photo degradation of the PCDD/Fs collected and effectively separates the PCDD/F samples into dry and wet contributions. The results indicated that the ambient PCDD/F concentrations collected using the PS-1 sampler ranged from 0.02 pg I-TEQ/m(3) to 0.16 pg I-TEQ/m(3) in Northern Taiwan. The results also indicated that the PCDD/F deposition flux collected using the automated PCDD/F sampler (17.5 pg I-TEQ/m(2) d to 25.8 pg I-TEQ/m(2) d) was significantly higher than that sampled with the cylindrical vessels (2.0 pg I-TEQ/m(2) d to 9.9 pg I-TEQ/m(2) d). The difference was attributed to the fact that part of the PCDD/F depositions collected using the traditional cylindrical vessels had undergone photo degradation and evaporation. In addition, the wet deposition flux of PCDD/Fs (39.4 pg I-TEQ/m(2) rainy day to 228 pg I-TEQ/m(2) rainy day) observed in this study was significantly higher than the dry deposition flux (12.3 pg I-TEQ/m(2) sunny day to 16.7 pg I-TEQ/m(2) sunny day). These results demonstrated that wet deposition is the major PCDD/F removal mechanism in the atmosphere.

Historical trends of dioxin-like compounds and heavy metals in sediments buried in a reservoir in central Taiwan.

Polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), polychlorinated biphenyl (PCB) and heavy metal concentrations were analyzed at 1-2 cm intervals in a sediment core collected from a reservoir to evaluate anthropogenic pollution history in central Taiwan. The age of the sediment core was estimated from the sedimentation rate (0.44-0.52 cm year(-1), calculated by (210)Pb and (137)Cs analysis). The highest PCDD/F (4.10 ng TEQ(WHO)kg(-1)d.w.) and PCB (0.345ngTEQ(WHO)kg(-1)d.w.) concentrations occurred around 1985 (i.e. at a downcore depth of 10-12 cm). Our results also demonstrated that PCDD/F and PCB concentrations in the reservoir sediment core started to decrease at a depth of 8-10 cm (estimated year: 1989). This may be attributed to the fact that the Taiwan Environmental Protection Administration (EPA) proposed the regulation of pentachlorophenol (PCP) production and PCB manufacture in 1983 and 1988, respectively. In addition, a linear increasing trend in metal content with time (towards the core top) was observed for several metals (Zn, Cr, Cu, Cd and Pb). Results of the enrichments rates of anthropogenic metals indicated that the metal/alumina (M/Al) ratios of Zn, Cd and Pb in sediment cores exceeded those in crust compositions by 47%, 59% and 78%, respectively. The results revealed that considerable amounts of heavy metals were carried into the reservoir following significant immigration during the Chinese civil war (1950).

Deposition fluxes of PCDD/Fs in a reservoir system in northern Taiwan.

In this study, polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) concentrations and depositions in ambient air, water column and sediment were measured at a coupled reservoir-watershed system in northern Taiwan. The atmospheric PCDD/F concentration measured in the vicinity of the reservoir ranged from 4.9 to 39 fg I-TEQ m(-3) and the Asian dust storm in February accounted for the peak value, which corresponded to a total suspended particle concentration of 128 μg m(-3). The atmospheric PCDD/F deposition ranged from 1.4 to 19 pg I-TEQ m(-2)d(-1), with higher deposition occurring during winter and spring (long-range transport events). During summer, when atmospheric deposition is lower, consecutive tropical cyclones (typhoons) bring heavy rainfall that enhances soil erosion and creates turbidity-driven intermediate flow. This results in significantly higher PCDD/F deposition in water column of the reservoir at 70 m water depth (179 pg I-TEQ m(-2)d(-1)) than at 20 m (21 pg I-TEQ m(-2)d(-1)) during typhoon event. The accumulation rate of PCDD/Fs (9.1 ng I-TEQm(-2)y(-1)) in the reservoir sediments (depth: 0-2 cm) was consistent with PCDD/F deposition obtained from water column (6.1 and 8.3 ng I-TEQ m(-2)y(-1)); however, it is significantly higher when compared to the atmospheric deposition (2.0 ng I-TEQ m(-2)y(-1)). Based on the mass balance between the measurements of atmospheric deposition and sinking particles in water column, around 54-74% of PCDD/F inputs into the reservoir were contributed by the catchment erosion during normal period. However, the PCDD/F input contributed by the enhanced catchment erosion significantly increased to 90% during intensive typhoon events.