Effects of copper chloride on formation of polychlorinated dibenzo-p-dioxins in model waste incineration

Combustion experiments in a laboratory-scale fluidized-bed reactor were conducted to elucidate the effects of copper chloride as a catalyst on polychlorinated dibenzo-p-dioxins (PCDDs) formation in municipal waste incineration. We used model wastes with and without copper chloride (CuCl₂ · 2H₂O), both of which contained polyvinyl chloride as a chlorine source. Combustion temperature was set to 900 °C, and the amount of air supplied was twice the stoichiometric ratio. The experimental setup was carefully planned to suppress the influences of experimental conditions except the waste composition. Results of these experiments showed that copper chloride in the waste increased the amount of PCDDs formed and made the homologue profile to shift towards the highly chlorinated species. Copper chloride contributes to the PCDDs formation by promoting chlorination, whereby the reaction is important in that organic matter is chlorinated directly by copper compounds. Copper chloride did not exert a great influence on the isomer distribution patterns of PCDDs, while there appeared a significant difference in the case of PCDFs. This points out the difference of the major formation mechanisms between PCDDs and PCDFs. PCDDs are less formed by the catalytic reactions from carbon/polycyclic aromatic hydrocarbons than PCDFs in our experimental conditions.     

Effects of copper chloride on formation of polychlorinated dibenzo-p-dioxins in model waste incineration

Combustion experiments in a laboratory-scale fluidized-bed reactor were conducted to elucidate the effects of copper chloride as a catalyst on polychlorinated dibenzo-p-dioxins (PCDDs) formation in municipal waste incineration. We used model wastes with and without copper chloride (CuCl₂ · 2H₂O), both of which contained polyvinyl chloride as a chlorine source. Combustion temperature was set to 900 °C, and the amount of air supplied was twice the stoichiometric ratio. The experimental setup was carefully planned to suppress the influences of experimental conditions except the waste composition. Results of these experiments showed that copper chloride in the waste increased the amount of PCDDs formed and made the homologue profile to shift towards the highly chlorinated species. Copper chloride contributes to the PCDDs formation by promoting chlorination, whereby the reaction is important in that organic matter is chlorinated directly by copper compounds. Copper chloride did not exert a great influence on the isomer distribution patterns of PCDDs, while there appeared a significant difference in the case of PCDFs. This points out the difference of the major formation mechanisms between PCDDs and PCDFs. PCDDs are less formed by the catalytic reactions from carbon/polycyclic aromatic hydrocarbons than PCDFs in our experimental conditions.     

Surface catalyzed formation of polychlorinated dibenzo-p-dioxins/dibenzofurans during municipal waste incineration

A series of reactions was carried out on different surfaces using carbon and CuCl₂, and KCl or HCl as a Cl-source. The PCDD/PCDF congener distribution was seen to vary to a great extent but the isomer distribution remained fairly constant. It is concluded that thermodynamic properties are largely responsible for the PCDD/PCDF isomer distribution. With pentachlorobenzene Cl₂ elimination, assisted by oxygen, appears to be the major pathway for PCDD/PCDF formation.     

Correlation of polychlorinated naphthalenes with polychlorinated dibenzofurans formed from waste incineration

Isomer composition of polychlorinated naphthalenes (PCNs) was measured for municipal waste incinerator fly ash samples and for emission samples produced from soot and copper-deposit experiments conducted at the United States Environmental Protection Agency (US-EPA). Two types of PCN isomer patterns were identified. One pattern contained specific PCN isomers in which chlorine atoms are substituted as if the peri(alpha-) position were dechlorinated from the higher chlorinated PCNs one by one. In another pattern, the isomers had a tendency for the chlorine atoms to assume successive positions on the naphthalene ring, which may be caused by specifically oriented chlorination. Some of these isomers increased, together with several polychlorinated dibenzofuran (PCDF) and a few polychlorinated dibenzo-p-dioxin (PCDD) isomers. The ratios between some specific PCN, PCDF, and PCDD isomers measured for the fly ash samples agree with those obtained from the soot and copper-deposit experiments. The observations suggest that these isomers were formed possibly from de novo synthesis utilizing the carbon structure contained in soot under the catalytic effect of a copper compound. Typical isomers for PCNs and PCDFs produced from incineration emissions were identified.     

The formation of polychlorinated dibenzo-p-dioxins/dibenzofurans from carbon model mixtures containing ferrous chloride

The potential to form polychlorinated dibenzo-p-dioxins/furans (PCDD/F) was investigated in carbon model systems containing ferrous chloride tetrahydrate and a matrix representative of that found in particle emission from the catalytic extraction process (CEP) for wastes. Various types of carbons were used resulting in different PCDD/F yields but, with one exception, similar homologue distributions. Due to the similarity between the turbostratic structure of the carbon in the representative CEP dusts and the carbon blacks used in the model system, experiments were performed using two carbon blacks (termed CBA and CBB). On a mass basis, CBB was more reactive over the temperature range of 275-325 degrees C and reaction times of 20-60 min in the formation of PCDD/F; as well as more adsorptive in terms of the desorption of PCDD/F. On a volume basis, the reactivities and adsorptivities were similar. A maximum in PCDD/F formation occurred at an oxygen concentration of 2% in nitrogen.     

Effects of regional differences in waste composition on the thermal formation of polychlorinated aromatics during incineration

Two artificial wastes (A and B) whose contents reflect regional differences in municipal solid waste composition, were used to investigate the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) during incineration. Flue gas samples were simultaneously collected at three ports in the post-combustion zone corresponding to flue gas temperatures of 400, 300, and 200 °C. The combustion of Waste B, which had a higher chlorine and metal content than Waste A, produced greater levels of highly-chlorinated homologues, as demonstrated by a higher degree of chlorination. The total concentrations of PCDDs, PCDFs, PCBs, and PCNs formed in the combustion of both wastes increased as temperature decreased along the convector. There were no significant differences in total concentrations between Waste A and Waste B combustion at specific temperatures, with exception of PCDFs at 400 °C. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) modeling, used to evaluate the data for all compound groups, suggest that during flue gas quenching at temperatures of 400 °C low-chlorinated homologues are preferentially formed in the presence of copper, which is known to be a very active catalyst for this process. At 300 and 200 °C, the formation of highly-chlorinated homologues is favored.     

Quasi-dynamic leaching characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans from raw and solidified waste incineration residues

Quasi-dynamic leaching characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from raw and solidified air pollution control (APC) residues were examined via a nine-time multiple leaching test. The effect of injected activated carbon in the APC residues on the PCDD/F leachability was also evaluated. When humic acid solution was used as a leachant, the leaching concentrations of PCDD/Fs fluctuated between the first and the fifth leaching, followed by a gradual increase and then suddenly reached maximum values at the leaching sequences around seventh and eighth. This significant enhancement in PCDD/F leachability was mainly due to an increase in the release of highly chlorinated PCDD/Fs. Leaching of PCDD/Fs with n-hexane was, in contrast, primarily caused by the partitioning of hydrophobic PCDD/Fs between the APC residue surface and the liquid phase of n-hexane. Consequently, the largest leaching concentrations for n-hexane tests achieved at the first leaching, followed by a decrease and reached plateaus. Solidification/stabilization (S/S) decreased the PCDD/F leachability up to the fifth leaching by the use of humic acid solution. However, S/S increased the PCDD/F leaching concentrations and rates with n-hexane. The activated carbon in APC residues significantly inhibited the release of PCDD/F with n-hexane. The inhibiting effect provided by activated carbon was, however, less significant by the use of humic acid solution.     

Alumina as a model support in the formation and dechlorination of polychlorinated dibenzo-p-dioxins and dibenzofurans

Alumina was studied as a model matrix for formation and dechlorination reactions of PCDDs and PCDFs. Only small differences in PCDD and PCDF formation were found between de-novo synthesis on alumina and on fly ash. The amounts of PCDDs and PCDFs formed on acidic alumina were much larger than on neutral and alkaline alumina. OCDD and OCDF were rapidly dechlorinated on basic alumina.     

Effects of injected activated carbon and solidification treatment on the leachability of polychlorinated dibenzo-p-dioxins and dibenzofurans from air pollution control residues of municipal waste incineration

To assess the effectiveness of the injected activated carbon, cement, and sulfur-containing chelating agent in controlling polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) release from the surface of air pollution control (APC) residues, this study examined the leachability of PCDD/Fs from APC residues generated by municipal solid waste incinerators. Results showed that PCDD/Fs were stably retained in the APC residues when the samples were leached with acetic acid solution. Highly chlorinated PCDD/F homologues (i.e., hepta- and octa-CDDs and CDFs) were relatively easy to leach. The leaching percentages of PCDD/Fs from raw APC residue samples containing activated carbon were smaller than those from samples without activated carbon, especially when n-hexane was used as the leachant. These results indicate that the flue gas injected activated carbon not only controls PCDD/F emissions, but also suppresses the leachability of PCDD/Fs from the APC residues. Solidification/stabilization (S/S) processes with 30wt% cement and 5wt% sulfur-containing agent can additionally decrease the leachability of PCDD/Fs with humic acid. Using n-hexane as the leachant, S/S processes increased the leachability of PCDD/Fs. Various low chlorinated PCDD/F congeners were moreover leached out of the APC residue samples, markedly increasing the leachate toxicity. The enhancement of leachability and toxicity owing to S/S processes may negatively impact the environment when APC residues are exposed to nonpolar organic solvents.     

High-temperature gas-phase formation and destruction of polychlorinated dibenzofurans

The high-temperature gas-phase decomposition of a PCB isomer was studied using a tubular flow reactor. The formation and destruction of various PCDFs were investigated in atmospheres containing different concentrations of O₂.     

Dechlorination ability of municipal waste incineration fly ash for polychlorinated phenols

Pathways of pentachlorophenol dechlorination have been investigated on municipal waste incineration fly ash at 200 degrees C under nitrogen atmosphere. Thermodynamic calculations have been carried out for these dechlorination conditions using the method of total Gibbs energy minimization for the whole system consisting of gaseous components, i.e., chlorinated phenols, phenol, hydrogen chloride and the Cu3Cl3 trimer and of solid Cu2O and CuCl2 components. The effects of water, temperature and of the amounts of the reaction components on the thermodynamic equilibrium have been discussed and the experimental results compared with the calculated thermodynamic data.     

Concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in soil in the vicinity of a landfill

Estonia still has no waste incineration facilities, which would act as substantial sources of dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) pollution. As landfill fires may serve as sources of dioxins, we focused on the concentrations of PCDD and PCDF in soil samples taken in the vicinity of the landfill located at south-east Estonia in the course of our inventory. Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were studied in five soil samples taken in the vicinity of the Laguja landfill in south-east Estonia. The four soil samples were taken in southern, eastern, western and northern parts not further than 300 m from the landfill, and one sample was taken at the distance of 3 km from the landfill. The PCDD/F concentrations in all soil samples were at background level (0.64-2.33 pg I-TEQ WHO/g dry weight). To maintain this situation, the administrator of the landfill must avoid landfill fires, which are one of the reasons for the generation of dioxins and furans.     

Assessment of polychlorinated dibenzo-p-dioxin and dibenzofuran emissions from a hazardous waste incineration plant using long-term sampling equipment

The aim of this work is to evaluate the performance of a continuous monitoring system for the analysis of the mass concentration of PCDD/Fs from stationary sources. Data was acquired from a modern, state of the art, hazardous waste thermal treatment plant for a period of more than 2 years using a commercial available continuous monitoring system. The study consisted of a total of 16 samples, collected in periods from 1 week to 2 months resulting in an average of 360 m³ sampled flue gas per sample. The study showed the system was able to confirm that for a period of more than 2 years the plant was complying with the limit of 0.1 ng I-TEQ/Nm³. In addition, the data showed the typical fingerprint of such installations which is useful for example in impact studies. Long-term samples were compared to five short-term samples (6 h) collected every 6 months during the study period. Principal component analysis was applied to PCDD/Fs obtained data as useful statistical tool to find out trends and similarities between different samples. Improvement in terms of representativeness of data was achieved through continuous assessment since the starts of the project. The obtained data was further used to determine the emission factor for this activity and the total annual PCDD/Fs release to the atmosphere.     

Depositional flux of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in an urban setting

Dry and wet deposition fluxes of the PCDD/F substituted congeners were measured at two different sites (Clinton Drive and Lang Road) in Houston, TX between December 2003 and April 2004. Average total dry deposition fluxes of 351 and 125pgm(-2)d(-1) were found at Clinton Drive and Lang Road, respectively. A wet deposition flux of 2.873pgm(-2)d(-1) was measured at the Clinton Drive site. The results indicated that the dry deposition process exhibited spatial variability. In addition, the results also demonstrated that precipitation, although intermittent, is the most important mechanism for the removal of dioxins from atmosphere in the area of study. Combining the contributions of the dry and wet deposition processes at Clinton Drive resulted in a total bulk deposition flux of 527pg m(-2)d(-1). The total dry and wet deposition fluxes were dominated by OCDD followed by 1,2,3,4,6,7,8-HpCDD at both sites. Overall average dry deposition velocities of 0.35 and 0.15cms(-1) were calculated at Clinton Drive and Lang Road sites, respectively. While these velocities were similar to velocities observed in other geographical areas, the contribution of OCDD to the total deposition flux in Houston was significantly higher, probably reflecting the unique nature and character of Houston dioxin sources. The results also showed that lower chlorinated congeners, primarily present in the gas phase, are more likely to be removed from the atmosphere by precipitation. Relationships between the detected congeners in the dry deposition samples and other routinely measured air pollutants/meteorological parameters were found. The results showed that in general, the dry deposition of these congeners was consistently negatively correlated with SO(2) and NO(x) concentrations in the air and positively correlated with relative humidity. However, more research is needed to ascertain those correlations.     

The size distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in the bottom ash of municipal solid waste incinerators

In this study, bottom ash was sampled from two Taiwanese municipal solid waste incinerators (MSWIs: A and B) and sieved to size classes of 4.75-9.5 mm, 2.36-4.75 mm, 1.0-2.36 mm, 0.6-1.0 mm, 0.3-0.6 mm, 0.21-0.3 mm, 0.125-0.21 mm, 0.075-0.125 mm and <0.074 mm. For both MSWIs, the major peak in the particle size distribution for the PCDD/F content was found in a particle size <0.21 mm, that is, 16.1 (A) and 4.37 pg I-TEQ/g (B). This is due to the fact that a smaller particle has higher specific surface area thus offering more adsorption sites. The mean cumulative fractions (F%) of PCDD/F I-TEQ in the bottom ash of MSWI A and B in the particle size range below 0.6, 2.36 and 4.75 mm, in sequence, are 40.4%, 77.2% and 95.6%, respectively. We suggest sieving the bottom ash before the subsequent reutilization at the suggested cut size of 0.6 mm. In the view of PCDD/Fs, bottom ash with a particle size larger than 0.6 mm, which is the more non-hazardous part, may be suitable for being the raw material of landfilling soil, road sub-base, and construction blocks. For the minus 0.6 mm fraction, vitrification with fly ash is one of the choices.     

Mechanism of the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans from chlorophenols in gas phase reactions

The pyrolysis of chlorinated phenates at a temperature of about 280 degrees C results in the formation of definite chlorinated dibenzodioxin (PCDD) congeners [1-3]. It is shown that in gas phase reactions chlorophenols react in the presence of oxygen above 340 degrees C not only to PCDD but also to chlorinated dibenzofurans (PCDF). The mechanism of this reaction of chlorophenols to PCDD and PCDF was elucidated. In a first step phenoxyradicals are formed which are capable of forming PCDDs and PCDFs. This is confirmed by the oxygen dependency of the reaction. In an argon atmosphere no dimerization of chlorophenols could be observed at 420 degrees C. By the identification of intermediates and by analyzing the PCDF isomers formed from individual chlorophenols the reaction pathway is elucidated. As intermediates in the formation of PCDFs polychlorinated dihydroxybiphenyls (DOHB) were identified. These are most likely formed by the dimerization of two phenoxy radicals at the hydrogen substituted carbons in ortho-positions under simultaneous movement of the hydrogen atoms to the phenolic oxygen PCDDs are formed in the gas phase via ortho-phenoxyphenols (POP) analogous to the pyrolysis of phenates, but due to the radical mechanism in the first condensation step to POPs not only a chlorine atom is capable for substitution but also the hydrogen atoms. The formation of the DOHBs and their condensation to PCDFs and hydroxylated PCDFs as well as the ratio of PCDD to PCDF formed show a strong dependency on the reaction temperature, the substitution pattern of the chlorophenols and the oxygen concentration.     

Detailed study on the levels of polychlorinated dibenzo-p-dioxins,polychlorinated dibenzofurans and polychlorinated biphenyls in Yusho rice oil

One bottle of Yusho rice oil was obtained from a Yusho family in 1998. The levels of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in the causal oil were investigated with two different approaches and the individual concentrations of all the 17 2,3,7,8-substituted PCDD/F and 14 coplanar PCB (Co-PCB) congeners were elucidated for the first time. The concentrations of PCDDs and PCDFs were found to be 0.60 and 8.8 ppm, respectively. For PCBs, more than 130 PCB peaks were observed and a total concentration of 850 ppm including 170 ppm of Co-PCBs was obtained. The toxic equivalents (TEQs) of PCDDs, PCDFs, and Co-PCBs were calculated to be 17, 470, and 120 ppb, respectively. The relative contribution of these classes to the total TEQ in Yusho oil is 3%, 77%, and 20%, respectively, indicating that PCDFs play a major role in the toxicity of Yusho oil. Furthermore, it was confirmed that 2,3,4,7,8-penta-CDF contributes 58% to the total TEQ, supporting the view that this compound is the principal causal agent in Yusho poisoning. It is noteworthy that the most toxic 2,3,7,8-tetra-CDD was newly discovered, although it contributes only 0.1% to the total TEQ. Based on our data, the smallest TEQ intake during the latent period was estimated to be 0.067 mg for Yusho patients. This value is about 60% of that previously reported, suggesting a lower minimum threshold level for the development of the toxic symptoms of Yusho.     

流化床反应器石灰石固硫特性研究

采集了兖矿地区华聚能源各电厂附近的6种石灰石,在流化床反应器中对其进行固硫实验,研究探讨了石灰石品种、粒径及脱硫温度对石灰石固硫性能的影响.实验结果表明,兖矿地区石灰石粒径小于1.5 mm时,最佳脱硫温度在900℃左右.当粒径小于0.5 mm时,石灰石的钙利用率最高可达43.86%,并且钙利用率对温度的敏感度较高,不同...     

Fate of polychlorinated dibenzo-p-dioxins and dibenzofurans in a fly ash treatment plant

To understand the fate of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in a fly ash treatment plant that used the Waelz rotary kiln process (hereafter the Waelz process), the samples of input and output media were collected and analyzed. The most important PCDD/F source in input mass was electric arc furnace (EAF) fly ash, which had a mean PCDD/F content of 18.51 ng/g and contributed more than 99% of PCDD/F input mass, whereas the PCDD/F input mass fractions contributed by the coke, sand, and ambient air were only 0.04%, 0.02%, and 0.000002%, respectively. For the PCDD/F output mass in the Waelz process, the major total PCDD/F contents of 43.73 and 10.78 ng/g were in bag-filter and cyclone ashes, which accounted for approximately 69% and 17%, respectively, whereas those of stack flue gas and slag were 14% and 0.423%, respectively. The Waelz process has a dechlorination mechanism for higher chlorinated congeners, but it is difficult to decompose the aromatic rings of PCDD/Fs. Therefore, this resulted in the accumulation of lower chlorinated congeners. The output/input ratio of total PCDD/F mass and total PCDD/F international toxicity equivalence (I-TEQ) was 0.62 and 1.19, respectively. Thus, the Waelz process for the depletion effect of total PCDD/F mass was positive but minor, whereas the effect for total PCDD/F I-TEQ was adverse overall.     

Distribution of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and non-ortho coplanar polychlorinated biphenyls in river and offshore sediments

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and non-ortho chlorine substituted coplanar polychlorinated biphenyl (Co-PCBs, non-ortho Cl CBs) in river and offshore sediment samples were analyzed isomer-specifically using (13)C-labeled their respective internal standards and a selected ion monitoring method of high resolution gas chromatograph-mass spectrometry (GC-MS). These compounds were found in all samples analyzed. The average concentrations of the total PCDDs, PCDFs and Co-PCBs in the 23 sediment samples taken from rivers were 11 000, 1300 and 160 pgg(-1) of dry wt, respectively, those in six offshore sediments were 7600, 980 and 52 pgg(-1), respectively. The concentrations of Co-PCBs were much lower than those of PCDDs and PCDFs in all sediment samples. The magnitude of these concentrations was in the order of lower reach of river > offshore area > upper reach of river. The concentrations of PCDDs and PCDFs in the rural river were higher than those in the urban river, whereas the Co-PCB concentration in an urban river was six times higher than that in a rural river. The Co-PCB concentrations in the urban area and industrial area were higher than that in any other area. These findings suggest that the pollution by PCDDs and PCDFs was derived from some kinds of incinerations and herbicides applied in the past and that Co-PCB pollution was caused by PCB preparation used in the past in urban and industrial areas and by municipal waste incineration in urban areas.