Evaluation of PCDD/F partitioning between vapor and solid phases in MWI flue gases with temperature variation

Partitioning of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofuran) between vapor and solid phases in flue gas is affected by several factors including temperature variation. In this study, PCDD/F removal efficiencies achieved with activated carbon injection (ACI) and partitioning of vapor/solid phase PCDD/Fs in flue gases with temperature variation in a municipal waste incinerator (MWI) are evaluated via intensive flue gas sampling. Results indicate that most PCDD/Fs in flue gas downstream of the ACI+bag filter (BF) exist in vapor phase (over 90%) while the removal efficiencies of vapor and solid phase PCDD/Fs are 98.5-99.6% and 99.8-99.9%, respectively. The results of flue gas samplings also indicate that there is optimal operating temperature for PCDD/F removal achieved with ACI. Additionally, a pilot-scale adsorption system (PAS) is constructed in this study to evaluate the PCDD/F partitioning affected by temperature. The results of the PAS experimentation indicate that about 55% and 25% vapor phase PCDD/Fs passing through the filter cake (adsorbent) are transferred to solid phase at 150 and 200 degrees C, respectively. As the temperature is increased to 250 degrees C, filter cake (adsorbent) cannot effectively adsorb vapor phase PCDD/Fs and significant PCDD/Fs are formed via de novo synthesis.     

Chlorobenzene oxidation using ozone over iron oxide and manganese oxide catalysts

A low-temperature catalytic oxidation of chlorobenzene (CB) has been performed at temperatures of 60-210°C using ozone (O(3)) over iron oxide and manganese oxide, respectively. In the absence of ozone, CB conversion achieved with these two catalysts at 200°C was below 10%. However, addition of 1200 ppm ozone results in a remarkable increase in CB conversion and the conversion reaches 91.7% at 150°C for iron oxide, while 81.5% conversion is achieved with manganese oxide at 90°C. The activation energy of manganese oxide (48 kJ mol(-1)) is higher than that of iron oxide (43 kJ mol(-1)) without ozone. However, as ozone is added, the activation energy is significantly reduced to 20.0 kJ mol(-1) for iron oxide. CO and CO(2) are the only carbon-containing products detected in the effluent gas stream. For the long-term test, no obvious deactivation was found in iron oxide and ozone. However, in the case of manganese oxide and ozone, 3% reduction of CB conversion was observed. Slight deactivation might be attributed to a small amount of reaction byproducts (carboxylic acid species) and residual chloride (MnCl(2)) being deposited on the active sites of the catalysts.     

Evaluation of gas-particle partition of dioxins in flue gas I: evaluation of gasification behavior of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in fly ash by thermal treatment

The gasification behavior of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in fly ash by thermal treatment has been investigated to estimate gas-particle partition in flue gas. The results obtained in thermal experiments under various conditions showed that gasification of PCDD/Fs depends on air flow rate and treatment weight of fly ash as well as treatment temperature. On the other hand, the results obtained in the thermal experiments using dioxin-free fly ash revealed that during thermal treatment, the de novo synthesis, gasification, and decomposition of PCDFs proceeded at different rates. This difference in the reaction rates indicates that thermal treatment time is also a factor in determining the gas-particle partition of PCDD/Fs in fly ash. Therefore, reasonable thermal treatment conditions were established and applied to three ash samples. For all samples, PCDD/Fs started to gasify at 350 degrees C treatment, whereas 53-98% of PCDD/F homologs gasified at 400 degrees C treatment, implying that gaseous PCDD/Fs are dominant in flue gas at temperatures in the range 350-400 degrees C regardless of particle concentration.     

Thermal treatment of polychlorinated dibenzo-p-dioxins and dibenzofurans from contaminated soils

Thermal treatment technology was used to remove polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from heavily contaminated soil. For a soil with an original PCDD/F content of 35,970ng International Toxic Equivalents (I-TEQ)/kg, >99.99% PCDD/F removal efficiency was obtained with a primary furnace at two different treatment temperatures (750 degrees C and 850 degrees C), while a secondary furnace at 1200 degrees C gave >98% decomposition efficiency. The total PCDD/F I-TEQ contents in treated soils at 750 degrees C and 850 degrees C were 1.56ngI-TEQ/kg and 2.15ngI-TEQ/kg, respectively, which were far below the soil pollution standard of Taiwan (1000ngI-TEQ/kg soil). Although air pollution control devices had significant effects on the removal of PCDD/Fs, the total I-TEQ concentrations in the upstream flue gas of PUF cartridge at 750 degrees C and 850 degrees C (2.61ngI-TEQ/Nm(3) and 2.38ngI-TEQ/Nm(3), respectively) were still higher than the stationary emission limit of the Taiwan EPA (0.5ngI-TEQ/Nm(3)). The above results also suggested that additional APCDs, such as activated carbon injection in front of the filter are needed to enhance PCDD/F removal efficiency.     

Removal of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by three coagulants in simulated coagulation processes for drinking water treatment

Surface water from Guangzhou to which standard polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were added was treated by coagulation with ferric chloride (FC), polyaluminium chloride (PAC), and aluminium sulfate (AS) at optimum removal dosages for nature organic matter (NOM) to assess the polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) removal efficiencies. PCDD/Fs in suspended particulate matter (SPM) and treated water (TW) after coagulation were analysed. Low residual levels of PCDD/Fs were found in treated water after coagulation: 0.8% for FC, 0.9% for PAC, and 3.1% for AS. The removal efficiency calculated using these results was >99% for FC and PAC and 97-98% for AS. Most PCDD/Fs congeners could be removed by the three coagulation processes; the removal efficiency of FC and PAC was similar, and slightly higher than that of AS. The results also demonstrate that coagulation with FC preferentially removed tetra- and penta-substituted PCDD/Fs from raw water.     

A novel method to enhance polychlorinated dibenzo-p-dioxins and dibenzofurans removal by adding bio-solution in EAF dust treatment plant

In order to understand the effect of different amounts of powder-activated carbon (PAC) injection and bio-solution (NOE-7F) addition on the removal efficiencies of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in a fly ash treatment plant with Waelz rotary kiln process, the PCDD/F concentrations in the stack flue gasses were measured and discussed. In the amount of 20, 40 and 50 kg/h PAC injection, the removal efficiencies of PCDD/Fs in the stack flue gas were 86, 96 and 97%, respectively. While adding more amounts of PAC did enhance the removal efficiencies, the reduction fractions of low chlorinated PCDD/F congeners were much higher than those of highly chlorinated PCDD/F congeners. Particularly, a lower amount of PAC injection (20 kg/h), not only cannot remove highly chlorinated PCDD/Fs, but also the carbon surface of the PAC can act as a precursor for the formation promotion of highly chlorinated PCDD/F congeners. The addition of NOE-7F in the raw materials had the dechlorination effect on the PCDD/F removal and mainly inhibited highly chlorinated PCDD/F formation. The combination of both PAC injection and NOE-7F addition has a high potential for practical application.     

Polychlorinated dibenzo-p-dioxins/dibenzofurans distributions in ash from different units in a municipal solid waste incinerator

This study determined the polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) contents in ash in the super heater (SH), economizer (EC), semi-dryer absorber (SDA), fabric filter (FF), fly ash pit (FAP) and bottom residue (BR) in a municipal solid waste incinerator (MSWI). A high-resolution gas chromatograph/high-resolution mass spectrometer (HRGC/HRMS) was utilized for analyzing 17 PCDD/F species. Experimental results showed that average PCDD/F contents in ash samples from the SH, EC, SDA, FF, FAP and BR were 0.102, 0.788, 0.210, 1.95, 2.04 and 0.0218 ng I-TEQ g(-1), respectively. PCDD/F content was very low in the SH and BR due to high temperatures (around 461 degrees C in the SH and 914 degrees C in combustion chamber). Conversely, total PCDD/F content was significantly high in ash samples from the EC (around 340 degrees C), mainly because the temperature is within the favorable range of 250-400 degrees C for PCDD/F formation due to de nova reformation mechanisms. Although the SDA operated at 245 degrees C, the PCDD/F content decreased very significantly, mainly because the temperature was relatively low and because calcium carbonate was introduced into flue gases to dechlorinate and dilute chlorine-containing species. PCDD/Fs were captured by the active carbon in the FF. Furthermore, the duration that fly ash remained in the FF was longer than that for other incinerator units, and thus causing an increasing trend of PCDD/Fs level downstream (except the SDA). Total PCDD/Fs emission factors (microg tonnes-waste(-1); microg I-TEQ tonnes-waste(-1)) in ash samples from different units were: SH (42.3; 0.846), EC (326; 6.12), SDA (58.1; 1.10), FF (1540; 61.3), FAP (2950; 107) and BR (537; 4.31). Most PCDD/Fs in ash were contributed by the FF (about 56%), and the generation of PCDD/Fs in ash was significant (about 35%) during the transfer process from different units to the FAP. A strong and positive correlation in a logarithmic form existed between PCDD/Fs and chlorine (Cl(-1)) contents in ash. In Taiwan, the government policy for incineration residues advocates their reuse as road sub-bases or secondary building materials provided that total PCDD/Fs content is below the legal limit (1 ng I-TEQ g(-1)). Thus, ash with total PCDD/Fs content below the legal limit, such as that from the SH, EC, SDA and BR, can be collected and transferred to the FAP and reused. Ash with total PCDD/Fs content exceeding the legal limit, such as that from the FF, should be collected separately and be treated properly before being disposal in a landfill.     

Benzene oxidation with ozone over supported manganese oxide catalysts: effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO(2)-supported catalyst than Al(2)O(3)-, TiO(2)-, and ZrO(2)-supported catalysts. The rate for benzene oxidation and CO(x) selectivity increased with the reaction temperature (22-100 degrees C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.     

Catalytic combustion of volatile organic compounds

Despite the success of adsorption and thermal incineration of (C)VOC emissions, there is still a need for research on techniques which are both economically more favorable and actually destroy the pollutants rather than merely remove them for recycling elsewhere in the biosphere. The catalytic destruction of (C)VOC to CO2, H2O and HCl/Cl2 appears very promising in this context and is the subject of the present paper. The experiments mainly investigate the catalytic combustion of eight target compounds, all of which are commonly encountered in (C)VOC emissions and/or act as precursors for the formation of PCDD/F. Available literature on the different catalysts active in the oxidation of (C)VOC is reviewed and the transition metal oxide complex V2O5-WO3/TiO2 appears most suitable for the current application. Different reactor geometries (e.g. fixed pellet beds, honeycombs, etc.) are also described. In this research a novel catalyst type is introduced, consisting of a V2O5-WO3/TiO2 coated metal fiber fleece. The conversion of (C)VOC by thermo-catalytic reactions is governed by both reaction kinetics and reaction equilibrium. Full conversion of all investigated VOC to CO2, Cl2, HCl and H2O is thermodynamically feasible within the range of experimental conditions used in this work (260-340 degrees C, feed concentrations 30-60 ppm). A first-order rate equation is proposed for the (C)VOC oxidation reactions. The apparent rate constant is a combination of reaction kinetics and mass transfer effects. The oxidation efficiencies were measured with various (C)VOC in the temperature range of 260-340 degrees C. Literature data for oxidation reactions in fixed beds and honeycomb reactors are included in the assessment. Mass transfer resistances are calculated and are generally negligible for fleece reactors and fixed pellet beds, but can be of importance for honeycomb monoliths. The experimental investigations demonstrate: (i) that the conversion of the hydrocarbons is independent of the oxygen concentration, corresponding to a zero-order dependency of the reaction rate; (ii) that the conversion of the hydrocarbons is a first-order reaction in the (C)VOC; (iii) that the oxidation of the (C)VOC proceeds to a higher extent with increasing temperature, with multiple chlorine substitution enhancing the reactivity; (iv) that the reaction rate constant follows an Arrhenius dependency. The reaction rate constant kr (s(-1)) and the activation energy E (kJ/mol) are determined from the experimental results. The activation energy is related to the characteristics of the (C)VOC under scrutiny and correlated in terms of the molecular weight. The kr-values are system-dependent and hence limited in design application to the specific VOC-catalyst combination being studied. To achieve system-independency, kr-values are transformed into an alternative kinetic constant K (m3/(m2u)) expressed per unit of catalyst surface and thus independent of the amount of catalyst present in the reactor. Largely different experimental data can be fitted in terms of this approach. Results are thereafter used to define the Arrhenius pre-exponential factor A*, itself expressed in terms of the activation entropy. Destruction efficiencies for any given reactor set-up can be predicted from E- and A*-correlations. The excellent comparison of predicted and measured destruction efficiencies for a group of chlorinated aromatics stresses the validity of the design approach. Since laboratory-scale experiments using PCDD/F are impossible, pilot and full-scale tests of PCDD/F oxidation undertaken in Flemish MSWIs and obtained from literature are reported. From the data it is clear that: (i) destruction efficiencies are normally excellent; (ii) the efficiencies increase with increasing operating temperature; (iii) the higher degree of chlorination does not markedly affect the destruction efficiency. Finally, all experimental findings are used in design recommendations for the catalytic oxidation of (C)VOC and PCDD/F. Predicted values of the a)VOC and PCDD/F. Predicted values of the acceptable space velocity correspond with the cited industrial values, thus stressing the validity of the design strategy and equations developed in the present paper.     

Degradation of PCDD/Fs by mechanochemical treatment of fly ash from medical waste incineration

The potential of mechanochemical treatment (MC) to degrade PCDD/Fs contained in fly ash was tested via grounding with and without calcium oxide (CaO) under atmospheric pressure. Three types of fly ash collected from medical waste incineration were compared, originating either from rotary kiln fluidized bed multi-stage incinerator using activated carbon spray (FA1, FA2), or a simple stoker incinerator without activated carbon spray (FA3). In test I: CaO to FA1 mixed at ratio of 6-60% was milled at rotational speed of 350 rpm; in test II: FA2 and FA3 without CaO were milled at rotational speed of 400 rpm. The duration of the tests was 2h. The results from the present study indicate that (1) under two test conditions of with and without CaO, PCDD/Fs contained in real fly ash both can be degraded by mechanochemical treatment, (2) under condition of blending with CaO, the degradation efficiency of PCDD/Fs increased with increasing ratio of CaO, (3) the degradation efficiency of PCDD/Fs may increase with rotational speed increasing and (4) the destruction and dechlorination are major mechanism for PCDD/Fs degradation. These results show that mechanochemical treatment is a high potential technology for PCDD/Fs degradation in fly ash.     

Evaluation of gas-particle partition of dioxins in flue gas II: estimation of gas-particle partition of dioxins in dust-rich flue gas by parallel sampling with different conditions

For an accurate determination of the gas-particle partition of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like biphenyls (DLPCBs) in dust-rich flue gas, a parallel monitoring procedure with an isokinetic and a non-isokinetic train was used. For four flue gas samples, the two trains gave a significantly different weight of the collected fly ash particles despite the equal gas volume sampled. On the basis of the quantitative values of PCDD/F and DLPCB homologues and the weight of the collected particles, ratios of each homologue in the real flue gas samples in gaseous form were predicted using simultaneous equations. For the four flue gas samples examined, the predicted gaseous ratios were considerably higher that those calculated using a previously reported equation, suggesting that there are some properties which affect partitions of PCDD/Fs in flue gas besides their saturation vapor pressures and fly ash concentration. The partitions for higher temperature flue gases obtained by fractional determinations of each collection device were additionally different from those predicted by the parallel collection, indicating that conventional determination by fractional measurements is subjected to large errors in dust-rich flue gas due to severe adsorption of gaseous PCDD/Fs and DLPCBs onto particles collected on a low-temperature collection device.     

Dioxins and dioxin-like PCBs in different fish from the river Elbe and its tributaries, Germany

In a long-term program polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) as well as dioxin-like polychlorinated biphenyls (DL-PCBs) were analyzed in the muscle tissue of eels (Anguilla anguilla), bream (Abramis brama), European chub (Leuciscus cephalus) and ide (Leuciscus idus) from the river Elbe and its tributaries Mulde and Saale. The variation of the PCDD/F and DL-PCB concentrations in all fish samples is very large, whereby the DL-PCBs predominate in comparison to the PCDD/Fs. In the eels, the concentrations (pg WHO-TEQ/g ww) for the PCDD/Fs lie in the range of 0.48-22 and for the DL-PCBs between 8.5 and 59. In the whitefish, the concentration range is 0.48-12 for the PCDD/Fs and 1.2-14 for the DL-PCBs. Statistical analysis using relative congener patterns for PCDD/Fs allow spatial correlations to be examined for sub-populations of eels and whitefish. The results are compared to the maximum levels laid down in the European Commission Regulation (EC) No. 466/2001 and the action levels of the European Commission Recommendation 2006/88/EC. Eels caught directly after the major flood in August 2002 as well as eels near Hamburg (years 1996 and 1998) show high concentration peaks. Compared to the eels whitefish is less contaminated with PCDD/Fs and DL-PCBs.     

Evaluation of PCDD/Fs emission from fluidized bed incinerators co-firing MSW with coal in China

The levels and homologue profile of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from stack gas of three typical fluidized bed incinerators co-firing municipal solid waste (MSW) with Chinese coal were measured. The PCDD/Fs emission was in the range of 0.0054-0.1961 ng I-TEQ/N m(3). Comparison of PCDD/Fs detection results by HRGC/HRMS and HRGC/LRMS suggested that it was feasible to detect fly ash with high PCDD/Fs concentration by HRGC/LRMS. Several factors on PCDD/Fs emission were discussed. The primary reason for the lower PCDD/Fs emission was the inhibition mechanism of relatively high sulfur in feeding coal on PCDD/Fs formation. The emission results also showed that there was no directly correlation between PCDD/Fs levels and CO, O(2) and HCl concentration in flue gas. It was estimated that about 0.1034 g I-TEQ was annually emitted to atmosphere from the tested three MSW incinerators (total daily treatment capacity is 800 tonnes MSW).     

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from a heavy oil-fueled power plant in northern Taiwan

We measured the concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the flue gas and the ambient atmosphere of a power plant fueled by heavy oil in northern Taiwan. The mean emission concentration and I-TEQ concentration of total PCDD/Fs were 0.292 ng/Nm(3) and 0.016 ng I-TEQ/Nm(3), respectively. All PCDD/F emission concentrations in the flue gas were supposed to meet the Environmental Protection Administration Executive Yuan, R.O.C. standard (1.0 ng I-TEQ/Nm(3) from 2008). Furthermore, the mean I-TEQ concentration in the ambient atmosphere was 0.011 pg I-TEQ/Nm(3), which was much lower than the environmental quality standards for dioxins in Japan (0.6 pg TEQ/Nm(3)). Also, the PCDD/F emission factor was 0.188 ng I-TEQ/L fuel, which was comparable to the data issued in US EPA [EPA, Locating and estimating air emissions from sources of dioxins and furans, Office of Air Quality Planning and Standards, Research Triangle Park, NC, DCN No. 95-298130-54-01, 1997] (0.2 ng I-TEQ/L of fuel). Also, the result of the correlations of PCDD/Fs and operational parameters illustrated that the positively significant correlation (r=0.502, p=0.048) was found only between PCDD/Fs (I-TEQ) and the flue gas emission temperature (125-157 degrees C). However, PCDD-TEQ/PCDF-TEQ ratios were statistically significantly associated with the decreased flue gas flow (r=-0.659, p=0.006), moisture (r=-0.612, p=0.012) and flue gas temperature (r=-0.503, p=0.047). For proper environmental management of dioxins, it is necessary to establish a complete emission inventory of PCDD/Fs, and, in particular, the government should pay more attention to power plants to address the information shortage.     

Removal characteristics of PCDD/Fs by the dual bag filter system of a fly ash treatment plant

In this study, a dual bag filter system was established to decrease the concentration of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in the stack flue gases of a fly ash treatment plant, which retained zinc from the fly ash of electric arc furnaces. Compared to the original single bag filter system with activated carbon injection (ACI) of 40 kg h(-1), the PCDD/F concentrations in the stack flue gas after the plant was equipped with the dual bag filter system dropped enormously from 3.38-7.73 ng I-TEQNm(-3) to 0.03 ng I-TEQNm(-3), and the total PCDD/F I-TEQ removal efficiency increased from 97.6% to 99.3% with ACI of 16 kg h(-1), that is, about 40% of the original AC usage. The AC utilization efficiency (0.560 mg I-TEQ absorbed kg ACI(-1)) of the dual bag filter system (AC: 16 kg h(-1)) was estimated about three times higher than that (0.192 mg I-TEQ absorbed kg ACI(-1)) of single bag filter system with ACI (40 kg h(-1)). The reason is that the particulate phase PCDD/Fs and some gas phase PCDD/Fs (captured by the recycled AC/ash mixture) were removed first by the first bag filter, and the rest of the gas phase PCDD/Fs were able to be adsorbed more completely by the AC/ash mixture due to a lower fly ash load, and then were removed by the second bag filter.     

Optimization of accelerated solvent extraction for polyhalogenated dibenzo-p-dioxins and benzo-p-furans in mineral and environmental matrixes using experimental designs

This paper deals with the optimization of accelerated solvent extraction (ASE) for the analysis of the polychlorinated dibenzo-p-dioxins, benzo-p-furans (PCDD/Fs), mixed bromine/chlorine-dibenzo-p-dioxins, and benzo-p-furans (so-called MXDD/Fs) in solid samples. Previous theoretical studies have shown that these compounds exhibit similar electronic properties. It is reasonable to assume that there is little difference in the behavior, formation, and toxicity of PCDD/Fs and MXDD/Fs. Indeed, for most of the cases, the affinity is defined by these weak interactions. Only eight native standards are available for the MXDD/Fs; hence, the use of similar compounds (native and (13)C(12)-labeled), such as PCDD/Fs, is required to optimize and to validate experimental methods. This would allow conclusions to be applied for the MXDD/Fs without extended studies involving complex synthesis methods. Experimental design methodology was used to evaluate the influence of five parameters (temperature, pressure, static time, number of cycles, and solvent nature) on the polyhalogenated dibenzodioxin and -furan (PXDD/Fs) extractions in different materials. The extraction profiles and the optimal operating conditions were determined for each matrix from the modeling of extraction performance. The two following effects, the relative peak area and the co-extracted matrix (CEM), were screened in this study. The temperature of extraction was found to be the most important parameter. ASE offers automation and appears to be as efficient as Soxhlet or Soxtet; however, a major benefit was that a 4-fold decrease in extraction time was obtained. Results suggest that extraction efficiency was quantitative with extraction times as low as 15 min for all congeners at 130 degrees C with a mixed solvent (n-hexane/acetone (1/1)). Under these operating conditions, the CEM and the degradation of the highly brominated compounds were minimized. The analysis of some real life samples from municipal solid waste incinerators showed significant amounts of PXDD/Fs.     

Oxidative destruction of o-DCB on supported manganese oxide catalyst

An active catalyst, MnO(2)/Al(2)O(3), was prepared by a novel technique as well as wet impregnation method. Total oxidation of chlorinated aromatics on supported manganese oxide catalysts was investigated. It is seen that MnO(2) supported on Al(2)O(3) is an effective catalyst for the oxidative destruction of o-DCB in the concentration range of 1611-2263ppm at temperatures over 350 degrees C. It is also seen that for the catalyst with 0.029% MnO(2), the activity per unit amount of MnO(2) is much higher than that for the other catalysts and the activity per unit amount of MnO(2) decreases sharply for MnO(2)-loading above 0.5%. This high activity may be attributed to a high degree of dispersion of MnO(2) achieved by deposition from colloidal solution. No chlorinated byproducts are detected in the effluent during the oxidative destruction of o-DCB. It is proposed that catalyst with MnO(2)-loading less than 0.5% MnO(2) can be effective for the oxidative degradation of o-DCB. Such catalysts will be less difficult to dispose of after use in view of their low heavy-metal content, and consequently, less harmful to the environment. The possibility of supporting MnO(2) on clay materials may be explored and very cheap catalysts are likely to be obtained by depositing MnO(2) from colloidal solutions.     

Patterns and sources of PCDD/Fs and dioxin-like PCBs in surface sediments from the East River, China

The contamination status of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) was preliminarily investigated in surface sediments collected from the East River during April 2007. The contamination levels of PCDD/Fs and DL-PCBs ranged from 2.1 to 9.8 with mean concentration of 4.5 pg WHO₉₈-TEQ g⁻¹ and ranged from 0.042 to 0.45 with mean concentration of 0.19 pg WHO₉₈-TEQ g⁻¹, respectively. All sediments were characterized by the elevated levels of PCDDs, especially OCDD. Higher concentrations of PCDD/Fs were found in the sediments from Guangzhou and Dongguan. Source analysis revealed that PCDD/Fs in the sediments from Guangzhou were mainly from the secondary copper smelters and steel-making plants, and PCDD/Fs in the sediment from Dongguan were mainly from MSWIs. PCP and paper mills were unlikely to be the main sources.     

Shape-selective extraction of PCBs and dioxins from fish and fish oil using in-cell carbon fractionation pressurized liquid extraction

This paper describes a new shape-selective, pressurized liquid extraction (PLE) procedure for extracting polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and PCBs from food and feed samples with an integrated carbon fractionation step. Initially this was done using specially designed inserts for 34-mL cells, but subsequently, large solid cells (66 mL) were machined to increase the capacity and robustness of the system. Depending on the carbon load and extraction solvent strength, the non-ortho PCBs were recovered either with the bulk of the PCBs or with the PCDD/Fs. The former is preferable if PCDD/Fs are the targets. In most cases, however, data are required for all indicator PCBs, WHO-PCBs, and PCDD/Fs. Therefore, further efforts focused on developing, optimizing, and validating a cost- and time-efficient PLE procedure that can extract these targets, separate non-ortho PCBs and PCDD/Fs from the bulk of the PCBs, allow gravimetric fat determinations, and requires a minimum of postextraction cleanup. The performance of the resulting procedure was assessed in experiments with a fish tissue reference material. The trueness of the WHO-PCB-TEQ, PCDD/F-TEQ, and total-TEQ data were -8, -5, and -7%, respectively, and the corresponding CVs were 1.5, 0.5, and 1.3%; within the limits set by the European community for gas chromatography-high-resolution mass spectrometry methods for food and feed control.     

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in water and suspended particulate matter from the Xijiang River, China

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in water and suspended particulate matter (SPM) collected from the Xijiang River, China, were measured by the quarter from September 2005 to June 2006. Total PCDD/F concentration ranged from 2.659 to 4.596pg/L for water and from 562.4 to 3259.5pg/g for SPM. Concentrations were high in summer and low in winter. I-TEQ values in water and SPM were low, ranging from 0.012 to 0.075pg/L, with a mean value of 0.039pg/L. Calculated annual loadings of total PCDD/Fs and I-TEQ were 8.55kg and 0.026kg, respectively. Composition and homologue distribution of PCDD/Fs were varied because of large seasonal differences in discharge from the Xijiang River into the South China Sea. Comparison of the PCDD/Fs homologue and congener profiles of atmospheric deposition, soil, and water revealed that soil was the dominant source of PCDD/Fs in the Xijiang River. Industrial effluents were also possible sources of PCDD/Fs. A good correlation between logK(oc) and logK(ow) was observed for 2,3,7,8-substituted PCDDs and PCDFs and correlation coefficients were 0.71 and 0.84, indicating organic matter in SPM played a dominant role in PCDD/Fs partition between SPM and water.