Post-combustion syntheses of PCDD/F and PBDD/F from halogen-rich fuel is suppressed by a pebble heater technology

GOAL, SCOPE AND BACKGROUND: Changes in German and European legislation shifted processing of polymer-rich shredding residues (SR) from landfill to thermal treatment. However, when waste of electric and electronic equipment (WEEE) is the source of SR, thermal treatment is complicated by halogens as well as the presence of polybrominated dioxins and furans (PBDD/F) and brominated flame retardants (BFR). Hence, WEEE requires high temperature incineration with sufficient residence times. Post-combustion synthesis of polyhalogenated dioxins and furans (PXDD/F) is dominant in the temperature range between 250-450 degrees C. Thus, a very rapid gas cooling from 450 degrees to 250 degrees C is important for proper raw gas treatment. The pebble heater technology developed by ATZ Entwicklungszentrum (Sulzbach-Rosenberg, Germany) might serve as an alternative to the state-of-the-art quench cooling. It is based on the application of a pebble bed of natural bulk material, which the exhaust gases flows through radially. It provides an excellent heat transfer and a temperature gradient in the range of 1,500-2,000 K/m. The paper presents data of a pilot application of the pebble heater technology for the treatment of raw gas derived from the incineration of polymeric materials from WEEE. METHODS: A liquid fuel was chosen in order to minimise technical modifications of the plant. It was analysed for halogens by x-ray fluorescence, for brominated flame retardants by HPLC-UV/MS and for PXDD/F by GC-HRMS. Combustion gases were rapidly cooled down to temperatures below 200 degrees C and emissions of PBDD/F and PCDD/ F were estimated without further off-gas treatment. PBDD/F emissions were computed as PCDD/F toxicity equivalents applying two different calculation approaches. RESULTS AND DISCUSSION: PCDD/F emissions accounted for 0.04 ng I-TEQ/Nm3 and are in compliance with European emission limits. Calculated PBDD/F toxicity equivalents exceeded the emission limit of 0.1 ng I-TEQ/Nm3 by factors of 75 and 208 depending on the calculation approach. A mass balance of PBDD/F and PCDD/F congeners revealed an efficient elimination of more than 95% in most cases. Lower reduction rates (76% for 2,3,7,8-TeBDF and 82% for 1,2,3,7,8-PeBDF) were attributed to incomplete combustion. An intended recovery of halogens by one-stage scrubbing downstream of the pebble heater was ineffective, recovering 28% of the applied chlorine and 9% of the bromine, only. CONCLUSIONS: Our pilot incineration test indicates that the pebble heater technology can effectively suppress a post-combustion synthesis of PCDD/F and PBDD/F, resulting in low PCDD/F emission levels without further off-gas treatment. The presented data state that WEEE is sensible to incomplete combustion, which will lead to increased PBDD/F emissions without increasing PCDD/F emission limits. This finding is especially relevant for small and low-technical incineration appliances, which have been reported to treat WEEE in developing countries and are considered to serve as a significant source of PXDD/F these days. RECOMMENDATIONS AND PERSPECTIVES: Monitoring of PCDD/F emissions only might considerably underestimate the total emission of dioxins and dioxin-like compounds. It is therefore an ineffective means for assessing resulting health risks, at least for those waste treatment plants which are considered to handle the increasing amounts of PBDD/ F-containing polymers from WEEE in future. Consequently, it is recommended to initiate a screening programme for PXDD/F emissions in large scale incineration facilities which are capable of treating WEEE shredder residues.     

Investigation on organic pollutants from a domestic heating system using various solid biofuels

Various herbaceous biofuels (straw, whole plant cereals and set aside hay) and spruce wood were tested for their potential to form PCDD/F, PCPh, PCBz and PAH during combustion. The trials were conducted in an automatically charged multi-fuel furnace for domestic applications (50 kWth). Both, flue gas and the different ash fractions were analysed. CO-emission results show, that combustion conditions were relatively uniform (mean CO-level: 200 mg/m3 at 13% O2 in flue gas). Likewise, the TOC- and PAH-emissions in the fuel gas remained constantly on a relatively low level. However, for the PCDD/F, PCPh and PCBz increased emissions were detected when herbacious fuels were applied. This may be attributed to their higher chlorine concentration and the high ash content, which is responsible for increased dust emissions during combustion. Similar observations were also found for the PCDD/F-concentrations in the ashes. Combustion chamber ashes usually showed a drastically reduced contamination with highly toxical compounds, compared to the ash fraction from the heat exchanger ash or to chimney soot.     

Correlation between PCDD/F, PCB and PCBz in coal/waste combustion. Influence of various inhibitors

In the flue gas of co-combustion of solid waste and coal in a laboratory scale furnace high concentrations of polychlorinated dibenzo-p-dioxin and furans (PCDD/F), polychlorinated biphenyls (PCB) and polychlorinated benzenes (PCBz) have been detected. These toxic emissions have been reduced by the help of various inhibitors added to fuel before incineration. Knowledge of the congener pattern and homologue profiles of PCDD/F, PCB and PCBz is important to elaborate the mechanism of formation and inhibition of the toxic compounds formed during co-combustion of solid waste and coal. Principle component analysis (PCA) is used in order to find the similarity between the samples and separate them according their toxicity. By the help of the component analysis (CA) the best correlated congeners are effectively detected. Using linear regression between the independent variables and the indicator parameters various good correlated pairs between PCDD/F, PCB and PCBz have been elaborated. Generally it was found that the samples with higher toxicity show a good correlation between tetra- and pentachlorinated benzenes and tetra- and pentachlorinated dibenzo-p-furans. The best indicator parameter for PCDD/F World Health Organization toxic equivalent (WHO-TEQ) among the PCBz congeners investigated is 1,2,4,5-TCBz. This isomer is also significantly correlated with PCDD/F WHO-TEQ and with the sum of PCDD/F WHO-TEQ and PCB WHO-TEQ. However for samples with higher percentage of inhibitors the above mentioned relationship between the surrogate and WHO-TEQ disappeared. The PCB homologues and congeners show no correlation with PCBz and PCDD/F homologues and congeners.     

Release of polychlorinated dibenzo-p-dioxins and dibenzofurans by setting off fireworks.

Selected pyrotechnic articles were set off under laboratory conditions. Residues and vapors of smoke as well as unburnt charges were analyzed for polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F) and their precursors chlorinated benzenes and phenols. The contamination of the selected products with these organic xenobiotics proved to be very variable. Remains of fireworks contained octachlorinated dioxins and furans up to 142 ng I-TEQ/kg as well as hexachlorobenzene in the range of 0.05 to 1,400 mg/kg. The deflagration of detonating compositions usually resulted in a dispersion of contaminants, whereas continuously burning flare compositions partially led to a thermal decomposition of organic pollutants. A significant rate of formation of polychlorinated dioxins and furans was observed when setting off blue-lightning rockets and fountains. Further investigations revealed that even high temperatures during the deflagration of black powder charges could not suppress the formation of PCDD/F from appropriate precursors.     

Influence of combustion conditions on the PCDD/F-, PCB-, PCBz- and PAH-concentrations in the post-combustion chamber of a waste incineration pilot plant

Experiments at a pilot scale waste incinerator (0.5 MW thermal power) showed that the conditions in the post-combustion chamber (650-900 degrees C) are strongly influencing the formation of chlorinated and non-chlorinated aromatics. Non-optimal combustion conditions resulted in increased concentrations of mono- to trichlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and polycyclic aromatic hydrocarbons (PAH), while chlorinated benzenes (PCBz), polychlorinated biphenyls (PCB) and the higher chlorinated PCDD/F are only weakly affected or even decrease. The changes in concentration of the compounds investigated over a time span of hours gave hints on 'memory effects' in this combustion zone. For mono- and dichlorinated benzenes, a high correlation (r2 = 0.80) with the international toxicity equivalent (I-TEQ) value of PCDD/F was observed. As recently has been demonstrated, this correlation can be utilized for an indirect on-line measurement of the I-TEQ by a novel laser mass spectrometric technique (REMPI-TO-FMS).     

Microbial degradation of chlorinated dioxins

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were introduced into the biosphere on a large scale as by-products from the manufacture of chlorinated phenols and the incineration of wastes. Due to their high toxicity they have been the subject of great public and scientific scrutiny. The evidence in the literature suggests that PCDD/F compounds are subject to biodegradation in the environment as part of the natural chlorine cycle. Lower chlorinated dioxins can be degraded by aerobic bacteria from the genera of Sphingomonas, Pseudomonas and Burkholderia. Most studies have evaluated the cometabolism of monochlorinated dioxins with unsubstituted dioxin as the primary substrate. The degradation is usually initiated by unique angular dioxygenases that attack the ring adjacent to the ether oxygen. Chlorinated dioxins can also be attacked cometabolically under aerobic conditions by white-rot fungi that utilize extracellular lignin degrading peroxidases. Recently, bacteria that can grow on monochlorinated dibenzo-p-dioxins as a sole source of carbon and energy have also been characterized (Pseudomonas veronii). Higher chlorinated dioxins are known to be reductively dechlorinated in anaerobic sediments. Similar to PCB and chlorinated benzenes, halorespiring bacteria from the genus Dehalococcoides are implicated in the dechlorination reactions. Anaerobic sediments have been shown to convert tetrachloro- to octachlorodibenzo-p-dioxins to lower chlorinated dioxins including monochlorinated congeners. Taken as a whole, these findings indicate that biodegradation is likely to contribute to the natural attenuation processes affecting PCDD/F compounds.     

Establishing the propensity for dioxin formation using a plume temperature model for medical waste incinerator emissions in developing countries

Air pollution control devices (APCDs) are not compulsory for medical waste incinerators (MWIs) in developing countries. In South Africa, combustion gases are usually vented directly to the atmosphere at temperatures greater than the formation temperature of dioxin. The possibility of dioxin formation outside the incinerator stack has been hypothesized. A plume model has been developed and tested in the wind tunnel with a scale model of an incinerator stack. The plume temperature and trajectory predictions of the plume model were verified within a +/- 3% experimental accuracy. Using South African data, the plume model predicts that the residence time of gases in the temperature range of 150-450 degrees C in a plume is 1.3 sec on average for 5% of a year (18 days) at meteorological conditions resulting in wind speeds of less than 1 m/sec. Two published dioxin formation models were used to assess the probability of dioxin formation in the plume. The formation models predict that the average polychlorinated dibenzodioxins/furans (PCDD/Fs) formed in the plume will exceed the stack emission regulations in South Africa of 0.2 ng/Nm3 toxic equivalent quotient (TEQ) by between 2 and 40 times. The calculated concentrations do not include additional gaseous PCDD/F compounds that may be formed at high-temperature post-combustion zones through pyrosynthesis mechanisms.     

CuCl2-catalyzed PCDD/F formation and congener patterns from phenols

Homologue and isomer patterns of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) in CuCl2-catalyzed formation were studied in an isothermal flow reactor using a distribution of 20 phenols as measured in municipal waste incinerator (MWI) exhaust gases. A mixture of 20 phenols was synthesized and used as reactants for this study because phenols are known to be key precursors in the formation of PCDD/F. Experiments were conducted at 400 degrees C. The 92% of nitrogen (N2) and 8% of oxygen (O2) were used as a carrier gas. PCDD/F homologue and isomer patterns with dibenzo-p-dioxin (DD) and dibenzofuran (DF) were obtained from a mixture of 20 phenols. DF+PCDF formation was favored over DD+PCDD formation. The major homologue groups formed were non-chlorinated DD and DF, and PCDD/F homologue fraction decreased with the degree of chlorination. PCDD/F homologue and isomer distributions were almost constant. Phenol and lower chlorinated phenols present in high amount played an important role in PCDD/F congener distributions. The results presented here can be used as characteristics or fingerprints for homologue and isomer patterns of PCDD/F formation attribution in CuCl2-catalyzed reaction from phenols.     

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.     

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.     

Thermal formation of PBDD/F from tetrabromobisphenol A--a comparison of polymer linked TBBP A with its additive incorporation in thermoplastics

For a long period, polybrominated flame retardants are under discussion because of the formation of polybrominated dibenzo-p-dioxins (PBDD)/dibenzofurans (PBDF) (PBDD/F) in case of thermal stress. Concerning polymer linked tetrabromobisphenol A (TBBP A), formation of PBDD/F was commonly presumed to be sterically hindered because of the covalent fixation into the polymer backbone. Combustion experiments with additively incorporated TBBP A compared with its polymer linkage revealed, that this assumption is incorrect and has to be revised. Under same conditions, similar PBDD/F concentrations in the range of 17.5-19.6 mg PBBD/F per kg TBBP A applied were analyzed. PBDD/F homologue distribution patterns were almost identical predominated by low brominated PBDF. These findings for PBDD/F formation have to be considered in future discussions regarding thermal stress caused by combustion or recycling processes, including other flame retardants bound in polymer matrix, e.g. polybrominated polystyrene (PS), or those with molecular structures showing less analogy to PBDD/F, like hexabromocyclododecane. The second aspect introduced, is the influence of different plastics on the formation rates of PBDD/F. In this context, combustion experiments were performed in an atmosphere consisting of synthetic air and HBr. PBDD/F concentrations were 8.47 mg/kg polyethylene, 1.67 mg/kg PS, 3.92 mg/kg phenolic resin and 18.1 mg/kg epoxy resin. Distribution patterns of PBDD/F homologues could partly be correlated with the occurrence of the precursors polybrominated benzenes and phenols.     

Formation and inhibition of chloroaromatic micropollutants formed in incineration processes

The formation pathways for chlorinated aliphatic and chlorinated aromatic compounds in technical incineration processes are reviewed. It is shown that acetylene is converted to chloroaromatic compounds including PCDD/F in a special flow reactor by catalytic activity of CuCl2 in the temperature regime of a post-combustion zone of technical incinerators. Mechanistic pathways begin with chlorination of acetylene. Dichloroacetylene is further condensed to C-4 and C-6 units. Hexachlorobenzene is the dominant aromatic compound and a likely precursor to chlorinated phenols and PCDD/F. Two specific mechanisms of formation of chlorinated aromatic compounds including PCDD/F have been advanced. Both mechanisms begin with the formation of dichloroacetylene from flame pyrolysis products like acetylene. Condensation of dichloroacetylene is mediated by copper species via metallacyclic intermediates and/or a catalytic cycle involving copper stabilized trichlorovinyl radicals. The final pathways of conversion of chlorinated benzenes to PCDD/F via chlorophenols are under active investigation.     

Modified clean-up for PBDD,PBDF and PBDE with an active carbon column--its application to sediments

A clean-up method for polybrominated dibenzo-p-dioxins (PBDDs), dibenzofurans (PBDFs) and diphenyl ethers (PBDEs) was modified using combinations of multi-layered silica gel, Florisil and active carbon columns. By using active carbon column chromatography in the final procedure, PBDEs were well separated from PBDD/Fs in an elution test with reference standards. We report the application of this method to sediment samples taken from industrialized areas in Japan. These sediments contained PBDEs ranging in concentration from 13 to 2394 pg/g, dry wt. PBDEs did not interfere with the quantification of PBDD/Fs. In addition, PBDEs found in the PBDD/F fraction did not interfere with the identification of PBDFs using the HRGC/HRMS separation method. Some 2,3,7,8-tetra- to hexabrominated dioxins and furans were also detected in the sediment samples.     

Identification of surrogate compounds for the emission of PCdd/F (I-TEQ value) and evaluation of their on-line real-time detectability in flue gases of waste incineration plants by REMPI-TOFMS mass spectrometry

Correlations between products of incomplete combustion (PIC), e.g., chloroaromatic compounds, can be used to characterise the emissions from combustion processes, like municipal or hazardous waste incineration. A possible application of such relationships may be the on-line real-time monitoring of a characteristic surrogate, e.g., with Resonance-Enhanced Multiphoton Ionization-Time-of-Flight Mass Spectrometry (REMPI-TOFMS). In this paper, we report the relationships of homologues and individual congeners of chlorinated benzenes (PCBz), dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and phenols (PCPh) to the International Toxicity Equivalent (I-TEQ) of the PCDD/F (I-TEQ value) in the flue gas and stack gas of a 22 MW hazardous waste incinerator (HWI). As the REMPI detection sensitivity is decreasing with the increase of the degree of chlorination, this study focuses on the lower chlorinated species of the compounds mentioned above. Lower chlorinated species, e.g., chlorobenzene (MCBz), 1,4-dichlorobenzene, 2,4,6-trichlorodibenzofuran or 2,4-dichlorophenol, were identified as I-TEQ surrogates in the flue gas. In contrast to the higher chlorinated phenols, the lower chlorinated phenols (degree of chlorination <4) were not reliable as surrogates in the stack gas. The identified surrogates are evaluated in terms of their detectability by REMPI-TOFMS laser mass spectrometry. The outcome is that MCBz is the best suited surrogate for (indirect) on-line measuring of the I-TEQ value in the flue gas by REMPI-TOFMS. The correlation coefficient r of the MCBz concentration to the I-TEQ in the flue gas was 0.85.     

Dioxins and furans formation in pilot incineration tests of sewage sludge spiked with organic chlorine

The factors affecting polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) formation were studied in sewage sludge incineration tests carried out on a demonstrative plant. The plant includes a circulating fluidised bed furnace (FBF) and a rotary kiln furnace (RKF), operating alternatively. During the tests sewage sludge was spiked with chlorinated hydrocarbons and the operating parameters of the afterburning chamber were varied. PCDD/F were sampled in each test before the bag filter, thus collecting the above contaminants before abatement systems. From the tests it appeared that PCDD/F were always produced in more abundance in the tests carried out by FBF than by RKF. The higher PCDD/F concentrations in the tests by FBF were reached when sewage sludge was spiked with a high dosage of a surrogate organic mixture of chlorinated hydrocarbons and when the afterburning chamber was used only as transit equipment with the burner off. The distribution of the different PCDD/F homologues was compared. P5CDFs were generally the prevalent fraction, with very few exceptions for the tests by RKF at high temperature of the afterburning chamber. As for FBF tests, it was found that the PCDD/F homologue profile depends on the afterburning chamber temperature.     

PCDD/F formation from oxy-PAH precursors in waste incinerator flyash

The yield of PCDD/F in relation to the presence of oxygenated PAH in model waste incinerator flyash has been investigated in a fixed bed laboratory scale reactor. Experiments were undertaken by thermal treatment of the model flyash at 250 and 350 °C under a simulated flue gas stream for 2 h. After reaction, the PCDD/F content of the reacted flyash and the PCDD/F released into the exhaust gas, and subsequently trapped by XAD-II resin in a down-stream condensation system were analyzed. The PAHs investigated were, dibenzofuran and benzo[b]naphtho[2,3-d]furan and were spiked onto the model flyash as reactant precursors for PCDD/F formation. The results showed significant formation of furans from both of the PAH investigated, however except from some highly chlorinated dioxin congeners, the formation of dioxins was not so common. Benzonaphthofuran was significantly more reactive than dibenzofuran in PCDD/F formation, in spite of the fact that dibenzofuran is structurally more similar to that of PCDD/F. Thus, there was no clear attribution between the chemical structure of PAH used and the formation of PCDD/F. There were considerable differences between the yields of PCDD/F congeners in the gaseous species and those in the reacted flyash under the same operational conditions. The concentration of PCDD/Fs was reduced at the higher reaction temperature of 350 °C; however, the higher temperature resulted in the majority of the PCDD/F formed on the flyash being released into the gas phase.     

An assessment of dioxin contamination from the intermittent operation of a municipal waste incinerator in Japan and associated remediation

Significant dioxin (polychlorinated dibenzo-para-dioxins (PCDDs)/polychlorinated dibenzo-furans (PCDFs)) pollution from a municipal solid waste incinerator was discovered in 1997 in Osaka prefecture/Japan. The cause and mechanism of pollution was identified by a detailed assessment of the environment and incinerator plant. The primary sources of PCDD/PCDF pollution were high dioxin releases from an intermittently operated waste incinerator with PCDD/PCDF emissions of 150 ng-TEQ/Nm³. PCDD/PCDF also accumulated in the wet scrubber system (3,000 μg TEQ/L) by adsorption and water recirculation in the incinerator. Scrubber water was air-cooled with a cooling tower located on the roof of the incinerator. High concentrations of dioxins in the cooling water were released as aerosols into the surrounding and caused heavy soil pollution in the area near the plant. These emissions were considered as the major contamination pathway from the plant. Decontamination and soil remediation in and around the incinerator plant were conducted using a variety of destruction technologies (including incineration, photochemical degradation and GeoMelt technology). Although the soil remediation process was successfully finished in December 2006 about 3 % of the waste still remains. The case demonstrates that releases from incinerators which do not use best available technology or which are not operated according to best environmental practices can contaminate their operators and surrounding land. This significant pollution had a large impact on the Japanese government’s approach toward controlling dioxin pollution. Since this incident, a ministerial conference on dioxins has successfully strengthened control measures.     

Toxic chlorinated and polyaromatic hydrocarbons in simulated house fires

Toxic chlorinated hydrocarbons (polychlorinated biphenyls, benzenes and dioxins and furans) and polyaromatic hydrocarbons were examined in combustion gas and deposited soot wipe samples from simulated house fires. Concentrations of these substances were high during the fires, the amounts of polychlorinated dioxins and furans (PCDD/Fs) in the combustion gas varying from 1.0 to >7.2 ng/m3 (I-TEQ) and those of polyaromatic hydrocarbons from 6.4 to 470 mg/m3. Thus large amounts of organic compounds may be released in house fires. As a result, there is a need for careful personal protection of fire-fighters and remediation workers against combustion gases during a fire and on contaminated surfaces after it.     

Polybrominated diphenyl ethers (PBDEs), polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) and monobromo-polychlorinated dibenzo-p-dioxins/dibenzofurans (MoBPXDD/Fs) in the atmosphere and bulk deposition in Kyoto, Japan

Polybrominated diphenyl ethers (PBDEs), polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs) and monobromo-polychlorinated dibenzo-p-dioxins/dibenzofurans (MoBPXDD/Fs) in atmosphere, bulk atmospheric deposition and soil in Kyoto, which is an urban city in Japan, were measured. Decabromodiphenyl ether (D(10)BDE, BDE-209) was detected in relatively high concentrations compared to other PBDE congeners in most samples. Similar results, in which D(10)BDE was predominantly detected, were reported in other studies in Japan. However, these homologue profiles differ from those of studies conducted in North America. The partitioning of semivolatile organic compounds between atmospheric gas phase and particulate-associated phase is an important factor in their environmental behavior. In this study, atmospheric particulate phase fraction (f(P)) of the brominated compounds increased with increasing bromine number, and f(P) was higher in samples collected in winter than in those collected in summer. Moreover, f(P) of PBDFs and MoBPXDFs was higher than that of PCDFs with the same halogen number. These results agree well with expectations from the vapor pressure of the brominated compounds and PCDD/Fs. Among the brominated compounds in the atmosphere, the level of MoBPXDD/Fs correlates positively with that of PCDD/Fs. This relationship has been previously observed in waste incineration samples. These results suggest that one of the sources of MoBPXDD/Fs in the atmosphere is incineration byproduct. The level of PBDD/Fs seems to correlate positively with that of PBDEs. This relationship suggest that the PBDD/Fs in the atmosphere relate to PBDEs, which is an impurity of PBDE products, or formed by the manufacture or combustion of plastics containing PBDEs.     

PCDD/F formation from oxy-PAH precursors in waste incinerator flyash

The yield of PCDD/F in relation to the presence of oxygenated PAH in model waste incinerator flyash has been investigated in a fixed bed laboratory scale reactor. Experiments were undertaken by thermal treatment of the model flyash at 250 and 350 °C under a simulated flue gas stream for 2 h. After reaction, the PCDD/F content of the reacted flyash and the PCDD/F released into the exhaust gas, and subsequently trapped by XAD-II resin in a down-stream condensation system were analyzed. The PAHs investigated were, dibenzofuran and benzo[b]naphtho[2,3-d]furan and were spiked onto the model flyash as reactant precursors for PCDD/F formation. The results showed significant formation of furans from both of the PAH investigated, however except from some highly chlorinated dioxin congeners, the formation of dioxins was not so common. Benzonaphthofuran was significantly more reactive than dibenzofuran in PCDD/F formation, in spite of the fact that dibenzofuran is structurally more similar to that of PCDD/F. Thus, there was no clear attribution between the chemical structure of PAH used and the formation of PCDD/F. There were considerable differences between the yields of PCDD/F congeners in the gaseous species and those in the reacted flyash under the same operational conditions. The concentration of PCDD/Fs was reduced at the higher reaction temperature of 350 °C; however, the higher temperature resulted in the majority of the PCDD/F formed on the flyash being released into the gas phase.