Sources of dioxins in the United Kingdom: the steel industry and other sources

Several countries have compiled national inventories of dioxin (polychlorinated dibenzo-p-dioxin [PCDD] and polychlorinated dibenzofuran [PCDF]) releases that detail annual mass emission estimates for regulated sources. High temperature processes, such as commercial waste incineration and iron ore sintering used in the production of iron and steel, have been identified as point sources of dioxins. Other important releases of dioxins are from various diffuse sources such as bonfire burning and domestic heating. The PCDD/F inventory for emissions to air in the UK has decreased significantly from 1995 to 1998 because of reduced emissions from waste incinerators which now generally operate at waste gas stack emissions of 1 ng I-TEQ/Nm3 or below. The iron ore sintering process is the only noteworthy source of PCDD/Fs at integrated iron and steelworks operated by Corus (formerly British Steel plc) in the UK. The mean waste gas stack PCDD/F concentration for this process is 1,2 ng I-TEQ/Nm3 based on 94 measurements and it has been estimated that this results in an annual mass release of approximately 38 g I-TEQ per annum. Diffuse sources now form a major contribution to the UK inventory as PCDD/Fs from regulated sources have decreased, for example, the annual celebration of Bonfire Night on 5th November in the UK causes an estimated release of 30 g I-TEQ, similar to that emitted by five sinter plants in the UK.     

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from various industrial sources

This study characterized the emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from the stack flue gases of 17 industrial sources, which were classified into 10 categories. The results show that the mean PCDD/PCDF concentration of secondary zinc smelter (Zn-S) and secondary copper smelter (Cu-S) is 2.44 ng international toxic equivalent (I-TEQ)/Nm3 (N represents normal conditions at 0 degrees C, 760 mmHg), which was found to be significantly greater than that of industrial waste incinerators (mean concentration = 0.15 ng I-TEQ/Nm3). These results imply that the controlling of secondary metallurgical melting processes is more important than industrial waste incineration for the reduction of PCDD/PCDF emissions. The mean emission factors of cement production, Zn-S and Cu-S, are 0.052, 1.99, and 1.73 microg I-TEQ/t product, respectively. For industrial waste incineration, the mean emission factors of waste rubber, waste liquor, waste sludge, industrial waste solid (IWI)-1, IWI-2, IWI-3, and IWI-4 are 0.752, 0.435, 0.760, 6.64, 1.67, 2.38, and 0.094 microg I-TEQ/t feed, respectively. Most of the PCDD/PCDF emission factors established in this study are less than those reported in previous studies, which could be because of the more stringent regulations for PCDD/PCDF emissions in recent years.     

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from stack gases of electric arc furnaces and secondary aluminum smelters

This study investigates the emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from four electric arc furnaces (EAFs) and eight secondary aluminum smelters (secondary ALSs) in Taiwan. The mean PCDD/F International-Toxicity Equivalents (I-TEQ) concentrations in the stack gases of these EAFs and secondary ALSs are 0.28 ng I-TEQ/Nm3 (relative standard deviation [RSD]= 100%) and 3.3 ng I-TEQ/Nm3 (RSD = 260%), respectively. The high RSDs, especially for those obtained from secondary ALSs, could be caused by the intrinsic differences in their involved feeding materials, furnace operating conditions, and air pollution control devices. The mean I-TEQ emission factor of PCDD/Fs for EAFs (1.8 microg I-TEQ/tonne-feedstock) is lower than that for secondary ALSs (37 microg I-TEQ/tonne-feedstock). This result might be because the involved furnace temperatures for secondary ALSs (650-750 degrees C) are lower than those for EAFs (1600-1700 degrees C), resulting in the deterioration of the combustion condition, leading to the formation of PCDD/Fs during the industrial process. This study found that the total PCDD/F emissions from EAFs (20 g I-TEQ/yr) and secondary ALSs (18 g I-TEQ/yr) are approximately 27, 53, and approximately 24, 49 times higher than those from municipal solid waste incinerators (MSWIs; 0.74 g I-TEQ/yr) and medical waste incinerators (MWIs; 0.37 g I-TEQ/yr), respectively; while those are 44 and 40% of total PCDD/F emission from sinter plants (45 g I-TEQ/ yr), respectively. Considering a more stringent emission limit has been applied to waste incinerators (0.1 ng I-TEQ/Nm3) in Taiwan lately, the results suggest that the control of the emissions from metallurgical processes has become the most important issue for reducing the total PCDD/F emission from industrial sectors to the ambient environment.     

Polychlorinated dibenzo-p-dioxins, dibenzofurans and 'dioxin-like' PCBs in flue gas emissions from municipal waste management plants

The aim of this work is to give representative data on polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyl (PCBs) from stack gas emissions of an urban solid waste management plant which has to comply with the limit of 0.1 ng I-TEQ/Nm3. In particular, the study is focused on 29 target compounds, the seventeen 2,3,7,8-PCDDs/Fs, four non-ortho PCBs and eight mono-ortho PCBs which configure so-called 'dioxin-like' PCBs (DL-PCBs). To this end, emission measurements were performed during one year over the three operating combustion lines in a selected waste management plant. In general, accurate methodology allowed characterizing all target compounds in almost all the samples analyzed. In addition, a typical pattern for DL-PCBs is reported. The pattern presented PCB #118 to be the highest, nevertheless the figures demonstrated DL-PCBs contribution to the total TEQ around 3% being PCB #126 the most important congener due to its TEF of 0.1. Finally, remarkable differences were achieved in comparison with both environmental and biological samples such as soils, sediments, human milk or fish since these matrices may present DL-PCB contribution to the total TEQ up to 77%.     

Dioxin mass balance in a municipal waste incinerator

A dioxin mass balance in an Spanish municipal waste incinerator (MWI) is presented. Input and output inventories from two sampling collection episodes including the analysis of PCDD/PCDF in urban solid waste (USW), stack gas emissions, fly ash and slag are reported. In one collection the levels of USW were around 8 pg I-TEQ/g and non-thermal destruction was observed overall. In the other collection the levels of USW were higher (around 64 pg I-TEQ/g) and the dioxin balance revealed a thermal destruction. Analysis of the different waste materials (textile, organic, plastic, wood and paper) was performed separately and the textile samples presented the highest levels.     

Long-term monitoring and modeling of polychlorinated dibenzo-p-dioxins and dibenzofurans from municipal solid waste incinerators and surrounding area in northern Taiwan

Municipal solid waste incinerators (MSWIs) have long been the major contributors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) to ambient air in Taiwan. After stringent MSWI emission standards were introduced in 2001, the long-term continuous monitoring of flue gas and ambient air quality became necessary to ensure the effectiveness of the related control strategies. Three MSWIs and the surrounding ambient air were investigated in the current study for PCDD/F characteristics during 2006 to 2011. The average concentrations in the flue gas ranged from 0.008?~?0.0488 ng I-TEQ/Nm³, which is much less than the emission standard in Taiwan (0.1 ng I-TEQ/Nm³) (I-TEQ is the abbreviation of International Toxic Equivalent). This led to extremely low levels in the ambient air, 0.0255 pg I-TEQ/Nm³, much less than the levels seen in most urban areas around the world. Additionally, the results obtained using the Industrial Source Complex Short-Term Dispersion Model (ISCST3) indicate that the PCDD/F contributions from the three MSWIs to the ambient air were only in the range from 0.164?~?0.723 %. Principal component analysis (PCA) showed that the PCDD/Fs in the air samples had very similar characteristics to those from mobile sources. The results thus show that stringent regulations have been an effective control strategy, especially for urban areas, such as Taipei City.     

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from stack flue gases of sinter plants

This study investigated four sinter plants, classified into two categories--with selective catalytic reduction (SCR) (S1, S2 and S3) and without SCR (S4) as its air pollution control device. Polychlorinated dibenzofurans (PCDFs) are dominant in the stack flue gases of sinter plants with and without SCR. The polychlorinated dibenzofurans/polychlorinated dibenzo-p-dioxins (PCDFs/PCDDs) ratio exceeds 1 extremely. The degree of chlorination of the sinter plant without SCR is towards hepta and hexa congeners while that of the sinter plant with SCR is towards penta and hexa congeners. PCDD/Fs are indeed decomposed (75.5% and 69% on ng and ng TEQ bases, respectively) and not only reduced in degree of chlorination. The overall concentration in the stack flue gas of sinter plants with SCR (7.97-14.1 ng/Nm(3); 0.995-2.06 ng TEQ/Nm(3)) is lower than that of the sinter plant without SCR (28.9 ng/Nm(3); 3.10 ng TEQ/Nm(3)). In Taiwan, based on the emission factors of 0.970 microg TEQ/ton-feedstock (sinter plants with SCR) and 3.13 microg TEQ/ton-feedstock (sinter plant without SCR), the annual PCDD/F emission of 44.7 g TEQ/year from sinter plants is 60 and 121 times higher than those from municipal solid waste incinerators (0.750 g TEQ/year) and MWIs (0.369 g TEQ/year). These results show that sinter plants have become the dominating PCDD/F emission source since tighter emission limits have been applied to incinerators.     

Evaluation of the emission characteristics of PCDD/Fs from electric arc furnaces

Distribution of PCDD/F (polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran) congeners at two electric arc furnaces (EAFs) in Taiwan is evaluated via intensive stack sampling and analysis. Two kinds of exhaust system in EAFs including stack system and shutter system are selected for measuring dioxin emissions. In addition, dioxin emissions during oxidation and reduction stages at EAF-A were characterized. Results indicate that the PCDD/F concentration of stack gas in EAF-A was 4.39 ng/N m³ while total Toxic Equivalent Quantity (TEQ) concentration was 0.35 ng I-TEQ/N m³. The PCDD/F concentration of stack gas in EAF-B was 2.20 ng/N m³ and the TEQ concentration was 0.14 ng I-TEQ/N m³. 1,2,3,4,6,7,8-H_pCDF, OCDD and OCDF are the major contributors of the dioxin concentrations for two EAFs investigated and the percentage of PCDD/F in particulate phase increases as the chlorination level of the PCDD/F congener increases. The results obtained on gas/particulate partitioning of PCDD/Fs in flue gases prior to the APCD in EAFs indicate that more than 90% exists in particulate phase. In EAF-A, the PCDD/F concentration during oxidation stage is slightly higher than that measured during reduction stage, including the sampling points of CO converter outlet, prior to bag filter and stack. Majority of PCDD/Fs emitted from steel-making processes exists in particulate-phase (about 60–70%) at both EAFs investigated.     

Behavior of PCNs, PCDDs, PCDFs, and dioxin-like PCBs in the thermal destruction of wastes containing PCNs

In the first known study to characterize the emissions of polychlorinated naphthalenes (PCNs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (dl-PCBs) from the thermal treatment of wastes containing PCNs, the formation and decomposition behavior of these pollutants was investigated both at laboratory scale and at plant scale. Exhaust gas measurements from laboratory-scale combustion of rubber belts containing PCNs (FB belts) were used as the basis for calculations predicting that the incremental dioxin toxic equivalency (TEQ) emissions from municipal solid waste (MSW) incinerators would be less than 0.1 ng/m3 N. In order to directly examine co-incineration of FB belts with MSW and to address potential differences between the laboratory experiment and full-scale MSW incinerators, experiments were conducted using a larger scale thermal treatment test facility with sampling and analysis at several points in the thermal treatment process. Congener specific analysis of PCNs clearly showed that both destruction and synthesis simultaneously occurred during combustion in the kiln. Most of the PCNs were destroyed by secondary combustion, and almost all PCNs were removed after flue gas treatment. Almost all PCDDs/DFs were synthesized as by-products of kiln combustion, most of them were destroyed by the secondary combustion, and almost all dioxins (PCDDs/DFs and dl-PCBs) were removed after flue gas treatment. The TEQ emission levels were less than 0.1 ng/m3 N for all plant-scale tests, and differences in TEQ emission levels were very small. Adding wastes containing PCNs to MSW will not influence thermal treatment emissions to the environment from modern solid waste incinerators.     

流化床垃圾焚烧炉产生的有毒二噁英同类物分布研究

测定了流化床垃圾焚烧炉焚烧产生的飞灰、烟尘和烟气中的2，3，7，8位氯取代二噁英同类物的含量及其毒性当量。结果表明，产生的二噁英主要存在于飞灰中，烟气中的含量很少。飞灰中二噁英总浓度和毒性当量分别为8.44ng／g和0．80ng／g，经过布袋除尘器后的烟尘和烟气中二噁英的浓度之和与毒性当量之和分别为0．34ng／m^3和0．02ng／m^3，而布袋除尘器前的烟尘和烟气中二噁英的浓度之和与毒性当量之和分别为40．78ng／m^3和3．0ng／m^3。飞灰和烟尘中2，3，7，8位氯取代二噁英同类物的分布相似，但是与烟气中2，3，7，8位氯取代二噁英同类物的分布差别较大。通过了解有毒二噁英同类物的分布，可以进一步优化流化床垃圾焚烧炉的焚烧条件，降低二噁英的排放量，减少垃圾焚烧对环境的污染。     

Emissions of Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans from Various Industrial Sources

Abstract

This study characterized the emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from the stack flue gases of 17 industrial sources, which were classified into 10 categories. The results show that the mean PCDD/PCDF concentration of secondary zinc smelter (Zn-S) and secondary copper smelter (Cu-S) is 2.44 ng international toxic equivalent (I-TEQ)/Nm³ (N represents normal conditions at 0 °C, 760 mmHg), which was found to be significantly greater than that of industrial waste incinerators (mean concentration = 0.15 ng I-TEQ/Nm³). These results imply that the controlling of secondary metallurgical melting processes is more important than industrial waste incineration for the reduction of PCDD/PCDF emissions. The mean emission factors of cement production, Zn-S and Cu-S, are 0.052, 1.99, and 1.73 μg I-TEQ/t product, respectively. For industrial waste incineration, the mean emission factors of waste rubber, waste liquor, waste sludge, industrial waste solid (IWI)-1, IWI-2, IWI-3, and IWI-4 are 0.752, 0.435, 0.760, 6.64, 1.67, 2.38, and 0.094 μg I-TEQ/t feed, respectively. Most of the PCDD/PCDF emission factors established in this study are less than those reported in previous studies, which could be because of the more stringent regulations for PCDD/PCDF emissions in recent years.     

Cluster Analysis for Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans Concentrations in Southern Taiwan

Abstract

This study investigates the characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the ambient air of two municipal solid waste incinerators (MSWIs: GS and RW) and a coal-fired power plant (PW) in the Kaohsiung County (KC) area in Taiwan. The results show that the toxic equivalency (TEQ) concentration in the flue gas of GS and RW averaged 0.090 and 0.044 ng international toxic equivalents (I-TEQ)/N·m³, respectively. The TEQ concentration in the flue gas of PW averaged 0.050 ng I-TEQ/N·m³. All PCDD/Fs concentrations from the stack flue gas are lower than the Taiwan Environmental Protection Administration emission standard. Furthermore, the mean I-TEQ concentration in the ambient atmosphere ranged from approximately 0.019 to 0.165 pg I-TEQ/N·m³, much lower than the environmental quality standards for dioxins in Japan (0.6 pg TEQ/N·m³). This work classified all sampling sites into three clusters according to k-means cluster analysis. The result shows a probable direct correlation between the GS incinerator and site C. Although the concentration from the PW plant did not exceed the emission standard, it was much higher than that in Fernández-Martínez’s study. For proper environmental management of dioxins, establishing a complete emission inventory of PCDD/Fs is necessary. The government of Taiwan should particularly pay more attention to power plants to address the information shortage.     

Assessment of PCDD/F risk after implementation of emission reduction at a MSWI

Municipal solid waste incinerators (MSWIs) have been shown to be important sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The emission of PCDD/Fs by MSWIs is a controversial subject in human health risk assessment. In this study the effect of a MSWI on a residential area was assessed before and after the installation of an additional treatment system for flue gas. This additional treatment system resulted in a dramatic decrease in PCDD/F concentrations in stack flue gas samples by 99.98%, while the concentrations in air decreased by approximately 50% (36,500 and 0.75 pg I-TEQ m(-3) for air in 1999; 3.5 and 0.38 pg I-TEQ m(-3) in 2002; 1.6 and 0.076 pg I-TEQ m(-3) in 2005 for stack gas and air, respectively). Considering the congener distributions of PCDD/Fs between stack flue gas and air samples, the study area seemed to have been contaminated by other urban sources as well as the MSWI. ISC3 model results support the conclusion that this incinerator became only a minor contributor to the study area after installation of the supplementary systems. This resulted from both proper MSWI operation using modern technology and additional sources of contaminants in this region. Finally, PCDD/F uptake by humans through inhalation of contaminated air was estimated. Assuming that inhalation exposure contributes 10% of total exposure, total exposure was lower than WHO guidelines. These results confirm that proper operation and maintenance of the incinerator led to a reduction in emissions and potential health impacts of PCDD/Fs.     

Air and soil dioxin levels at three sites in Italy in proximity to MSW incineration plants

Levels of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in both air and soil samples were measured at three different sites in Italy, in proximity to three municipal solid waste incinerators (MSWIs) to determine baseline contamination and the contributory role of incinerator emissions. At the first site, located in an agricultural, cattle-breeding, typically flattish area of the Po Valley, the dioxin concentrations had already been measured before the start-up of the new MSWI. These dioxin concentrations were then again measured after two years of continual operation of the incinerator. Despite the presence of the plant, the PCDD/Fs concentrations appear not to have been affected and were found to be in a range of 22-125 fg I-TEQ m(-3) in the air samples and 0.7-1.5 pg I-TEQ g(-1) in the soil samples. The second site is located in an industrial district of the Veneto Region, in the surroundings of an old MSWI that is not equipped with Best Available Technology (BAT) dioxin removal system. The PCDD/Fs concentrations in the air samples were between 144 and 337 fg I-TEQ m(-3). This is a typical range of values for industrial areas, while the soil samples showed contamination levels between 1.1 and 1.4 pg I-TEQ g(-1). The third site lies in the Adige Valley, near a MSWI that has been equipped with BAT for flue gas cleaning. The observed values ranged from 10 to 67 fg I-TEQ m(-3) for the air samples and 0.08-1.2 pg I-TEQ g(-1) for the soil samples. The contributory factors of the varying characteristics of the different areas together with the types of technology adopted at each MSWI plant are discussed. The PCDD/Fs levels are subsequently compared with established values from previous studies.     

PCDD/PCDF emissions from small firing systems in households

This report presents results of emission measurements of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in the flue gas of seven oil, nine gas, and two wood firing systems under laboratory conditions. The burn rate of the combustion was in the range of the rated useful heat output. Two additional test series varied the amount of combustion air and thus the heat output. The PCDD/PCDF emissions for oil- and gas-fired boilers are in the range of 0.0020-0.0142 ng I-TEQ/m3 (referring to 3% O2 in the dry flue gas). No correlation between the combustion technique and the PCDD/PCDF emissions could be established. In the tests with the wood-fired furnaces PCDD/PCDF concentrations in the flue gas ranging from 0.014 to 0.076 ng I-TEQ/m3 (referring to 13% O2 in the dry flue gas) were found. A significant correlation between the firing rate of the heating insert and the measured PCDD/PCDF concentrations was found. On examination of three typical 2,3,7,8-CDD/CDF congener profiles, a comparable pattern could be observed with natural gas and light fuel oil. The congener distribution for wood combustion is considerably different.     

The Spanish dioxin inventory part I: Incineration as municipal waste management system

The main objectives of the Spanish dioxin inventory and the incidence of municipal waste incinerators in the PCDD/Fs releases in the period from January 1997-November 1999 are presented. Preliminary data about the stack emission levels, fly ashes and slags as solid residues and the PCDD/Fs input in the USW are also presented to elaborate an initial balance for the incineration sector. A great decrease, from 20 to 1.2 g I-TEQ/y, from incineration gas emissions has been observed since 1996. The preliminary balance in the MWI sector suggests an overall PCDD/Fs destruction. The calculated emission factor, 1.06 microg I-TEQ/Mg, indicates a high quality of the air pollution control systems. The assumption of PCDD/Fs in the USW permits an initial evaluation of other waste management systems.     

Atmospheric deposition of PCDD/Fs near an old municipal solid waste incinerator: levels in soil and vegetation

The levels of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were determined in soil and vegetation samples taken from 24 sites in the vicinity of an old municipal solid waste incinerator (San Adrià del Besòs, Barcelona, Spain). Duplicate samples were collected within a radius of 3 km from the stack. PCDD/F concentrations in soils ranged from 1.22 to 34.28 ng I-TEQ/kg (d.m.) with median and mean values of 9.06 and 12.24 ng I-TEQ/kg, respectively. In turn, the levels of PCDD/Fs in vegetation samples ranged from 0.33 to 1.98 ng I-TEQ/kg (d.m.), with median and mean values of 0.58 and 0.70 ng I-TEQ/kg, respectively. Although the present PCDD/F concentrations in soil samples were higher than those recently found in soils taken near other incinerators from Catalonia, they are of the same order of magnitude than the levels of these pollutants found in incinerators from other countries. By contrast, the concentrations of PCDD/Fs in herbage samples were comparable to those found in recent surveys carried out in Catalonia.     

Emissions behavior and distribution of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) from cement kilns in China

The production of cement in China is accompanied by various emissions, such as fine particulate matter, heavy metals, nitrogen oxides, sulfur oxides, carbon dioxide…. Moreover, cement kiln presents a potential health risk to its surroundings, linking to emissions of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), in brief dioxins. Flue gas samples were collected from five typical cement kilns during twelve runs and were used to evaluate the levels and distribution of PCDD/Fs in the emissions from cement kilns. The PCDD/Fs concentrations (136 congeners) and I-TEQ values ranged from 2.3 to >40 ng/m³ and 9.3?～?90.8?×?10^?3 ng I-TEQ/m³, respectively, which were lower than the emission standard in China (0.1 ng I-TEQ/m³). In weight units, the dominant congeners were OCDD, 1,2,3,4,6,7,8-HpCDF, and OCDF; 2,3,4,7,8-PeCDF is the largest contributor (36–66 %) to the total I-TEQ value of twelve runs. HxCDF and TCDF were the first two most abundant homologue groups (12–85 and 4–52 %), and the homologue concentration decreased with rising chlorine number for PCDDs. In addition, there was no marked difference in homologue profiles when solid wastes (refuse-derived fuel and municipal solid waste) and hazardous wastes (DDT and POPs) were combusted as supplemental fuels. The use of various supplemental fuels had no obvious effect on the fingerprint of PCDD/F homologues. Moreover, there was no significant difference in levels of PCDD/Fs emission due to the diversity of production capacity, which were consistent with reported previously. Air pollution control device had effect on the homologue profiles, and cement system with electrostatic precipitators (ESP) had more fractions of octachloro congeners to the total.     

Catalytic decomposition of dioxins and other unintentional POPs in flue gas from a municipal waste incinerator (MWI) in China: a pilot testing

Unintentionally produced persistent organic pollutants (UPOPs) include polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), pentachlorobenzene (PeCBz), and hexachlorobenzene (HxCBz). With the booming of municipal waste incinerators (MWIs) in China, the emission of UPOPs has generated great concern. As an alternative technology of dioxin control, catalytic decomposition has not been used in China, mainly due to the absence of national demonstration projects. Also, the simultaneous removal of various UPOPs has not been well investigated.In this study, a pilot-scale selective catalytic oxidative (SCO) system using a self-developed honeycomb catalyst was built and tested in a typical municipal waste incinerator (MWI) of China. The original concentration of PCDD/Fs in flue gas after the treatment of activated carbon injection (ACI) still exceeded the national emission standard (0.1 ng I-TEQ/Nm³), while the concentrations of PeCBz and HxCBz were one order of magnitude higher than that of PCDD/Fs. For the testing temperature varying from 300 to 200 °C, the removal efficiency of PCDD/Fs range from 39 to 95 %, followed by dl-PCBs with the range of 56–89 %. PeCBz and HxCBz were also removed, though their removal efficiencies were lower than those of PCDD/Fs and dl-PCBs. Both temperature and degree of chlorination influence the removal efficiencies.     

Influence of start-up on PCDD/F emission of incinerators

This study aims to evaluate the influence of start-up on polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) concentration in the stack flue gas of incinerators and its contributing PCDD/F emission. The PCDD/F emission of the first sample among three consecutive stack flue gas samples of five intermittent incinerators, which sampled at a stable combustion condition after start-up, is 2-3 times higher than the mean of the others. For verifying the PCDD/F characteristics of incinerators during start-up, one continuous MSWI was investigated for two years. The elevated PCDD/F emissions of the MSWI during start-up could reach 96.9 ng I-TEQN m(-3) and still maintained a high PCDD/F emission (40 times higher than the Taiwan emission limit) even 18 h after the injection of activated carbon, indicating the memory effect. Taking the MSWI for example, which consists of four incinerators, the estimated annual PCDD/F emission from normal operational conditions was 0.112 g I-TEQ. However, one start-up procedure can generate approximately 60% of the PCDD/F emissions for one whole year of normal operations. And the PCDD/F emission, which is the result of the start-ups of four incinerators, was at least two times larger than that of a whole year's normal operations, without consideration for the PCDD/F emission contributed by the long lasting memory effect.