Correlations between homologue concentrations of PCDD/Fs and toxic equivalency values in laboratory-, package boiler-, and field-scale incinerators

The toxic equivalency (TEQ) values of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are predicted with a model based on the homologue concentrations measured from a laboratory-scale reactor (124 data points), a package boiler (61 data points), and operating municipal waste incinerators (114 data points). Regardless of the three scales and types of equipment, the different temperature profiles, sampling emissions and/or solids (fly ash), and the various chemical and physical properties of the fuels, all the PCDF plots showed highly linear correlations (R(2)>0.99). The fitting lines of the reactor and the boiler data were almost linear with slope of unity, whereas the slope of the municipal waste incinerator data was 0.86, which is caused by higher predicted values for samples with high measured TEQ. The strong correlation also implies that each of the 10 toxic PCDF congeners has a constant concentration relative to its respective total homologue concentration despite a wide range of facility types and combustion conditions. The PCDD plots showed significant scatter and poor linearity, which implies that the relative concentration of PCDD TEQ congeners is more sensitive to variations in reaction conditions than that of the PCDF congeners.     

Formation of chlorinated organics during solid waste combustion

The formation mechanisms of the precursors of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) were examined in a laboratory reactor. Both homogeneous and heterogeneous reactions were studied between 200 and 800 °C with HCl, Cl₂, and phenol as reactants in a simulated flue gas containing oxygen. Analysis of the reactor effluent showed that homogeneous phase production of chlorophenols and non-chlorinated dioxin and dibenzopdioxin and dibenzofuran, benzofuran potential precursors to PCDD and PCDF, was related to HCl concentration, reaching a maximum formation level around 650 °C. However, Cl₂ produced a greater variety of chlorinated aromatics at levels over three orders of magnitude greater than with HCl, with product concentrations reaching maximum formation levels around 350 °C. Heterogeneous tests at 450 °C using a CuCl catalyst increased formation of chlorinated organics and PCDDs and identified the major chlorinating reactant to be Cl₂.     

Recommended methodology for measurements of PCDD and PCDF in the nordic countries

In April 1986 the Nordic Council of Ministers recommended that the Nordic countries use a specific method for measurements of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) in flue gas emissions from waste combustion. The recommended protocol, which will be re-evaluated in a years time, includes the following.A one week registration period during which the plant is studied by continuous registration of a number of operating and emission parameters. The sampling period is included in this time.A sampling procedure based on a heated filter followed by a condenser, a bottle for the condensate and an adsorbent column. Before the sampling, at least two labelled PCDD are added to the filter.No specified analytical procedure. A labelled PCDF is added before the clean-up procedure and an injection standard before the final analysis. The laboratory is free to use any method that gives at least 25% recovery of the sampling standards and 50% recovery of the clean-up standard.Reporting requirements include homologue specific results for PCDD and PCDF containing four to eight chlorine atoms as well as isomer-specific results for the “dirty dozen”. The results should be compensated for incomplete recoveries and the factors used should be reported.     

An investigation on pollutant emissions from co-firing of RDF and coal

Pollutant emissions from co-firing of refuse derived fuel (RDF) and coal were investigated in a vortexing fluidized bed combustor (VFBC). RDF-5 was made of common municipal solid waste (MSW). CaCO₃ was injected in the combustor to absorb HCl at 850 °C. The results show that NO_x and HCl emissions increase with RDF-5 co-firing ratio. The NO_x concentration in flue gas at the bottom of the combustor is higher than that at the top. However, the trend of HCl released is reverse compared with NO_x emissions. It was found that the HCl concentration decreases with increasing the molar ratio of Ca/Cl. However, the effect of CaCO₃ addition on HCl retention is not significant when the molar ratio of Ca/Cl is higher than 5. The chlorine content in fly ash increases obviously with the molar ratio of Ca/Cl. PCDD/Fs emissions decrease slightly with an addition of CaCO₃. In this study incomplete combustion is regarded as the main cause for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) formation.     

De-novo formation of dioxins and furans and the memory effect in waste incineration flue gases

The formation of dioxin (polychlorinated-rho-dibenzodioxins - PCDD) and furan (polychlorinated dibenzofurans - PCDF) in waste incineration flyash in relation to temperature has been investigated in a bench scale reactor. The PCDD/PCDF released into the exhaust gases of the reactor and trapped in a condensation and vapour phase adsorption system were also determined. The concentrations of PCDD/PCDF in the flyash were analysed in detail for all congeners and isomers including the mono-, di- and tri-PCDD/PCDF. De-novo synthesis of PCDD/PCDF was clearly seen in the flyash with large changes in concentrations of PCDD/PCDF with only small changes in temperature. Exhaust gas PCDD/PCDF were detected at all temperatures, with the maximum emission occurring at a flyash temperature of 350 degrees C, where the equivalent of over 42 times the total dioxin/furan concentration of the original flyash was lost to the vapour phase per unit mass of initial flyash. Although the desorbed species were mainly the lower mono- to tri-congener group of dioxins and furans, the desorbed dioxin/furans had a considerable toxic equivalent value.     

Optimization of combustion conditions to minimize dioxin emissions

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) may enter an incinerator with the waste, be created in poor combustion or form in post-combustion zones under certain conditions of temperature and oxygen. Tests of MSW burning plants show a wide range of emissions of PCDD and PCDF. Diagnostic tests show the relationship between combustion conditions and the emission of PCDD/DF before and after emission controls. Mixing effectiveness, tightness of control, moisture, furnace and post-furnace temperatures, and the use of lime and reduced temperatures for acid-gas control all have an effect on emissions of trace organics. Carbon monoxide (CO), oxygen, moisture and furnace temperature have been found to be closely related to PCDD/PCDF emissions. By control of temperature and/or oxygen, and the use of CO as an indicator, it is possible to find and maintain optimum combustion conditions so as to minimize dioxins and furans. Plants having acid-gas controls reduce emissions below those achieved by good combustion alone.     

Problems associated with the measurement of PCDD and PCDF emissions from waste incineration plants

Fly ash and stack gases from municipal waste and industrial incinerators in the F.R.G. have been analyzed for dioxins (PCDD and PCDF). Most of the currently used procedures of stack gas sampling for PCDD/PCDF have been compared and were found to be equally effective. Differences are found, however, in the recovery of surrogates added to the sampling train before sampling, which makes it difficult to validate the sampling procedure. The analysis for PCDD%PCDF in stack gas or fly ash samples from municipal waste incinerators can no longer be considered an analytical problem. Thirty samples of stack gas from a single (old) municipal waste incinerator showed wide variation in PCDD/PCDF emission, indicating that single measurements are not useful in characterizing a plant for average PCDD/PCDF emission. It will be extremely difficult to correlate plant operating conditions to PCDD/PCDF stack gas emissions or PCDD/PCDF fly ash concentrations, because the effects produced by changing conditions are obscured by the variations which occur in PCDD/PCDF concentrations during steady conditions. The variations found under steady conditions can be explained by the proposed mechanisms of PCDD/PCDF formation and decomposition at low temperatures catalyzed by fly ash. Incineration of hospital waste and pyrolytic reclamation of copper in cables and aluminium produced significant emission of PCDD/PCDF. A major noncombustion source of higher chlorinated PCDD/PCDF (tetra- to octa-isomers) is pentachlorophenol, a widespread preservative which contributes to the PCDD/PCDF concentrations found, for example, in sewage sludge, river sediments and house dust.     

Pilot-scale studies on the effect of bromine addition on the emissions of chlorinated organic combustion by-products

The addition of brominated organic compounds to the feed of a pilot-scale incinerator burning chlorinated waste has been found previously, under some circumstances, to enhance emissions of volatile and semivolatile organic chlorinated products of incomplete combustion (PICs) including polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs). This phenomenon appears to be sensitive to temperature and combustion conditions. This paper reports on a study to evaluate the emissions of organic combustion by-products while varying amounts of bromine (Br) and chlorine (Cl) are being fed into a pilot-scale incinerator burning surrogate waste materials. The surrogate waste was fed at a constant molar halogen input rate, with varying Br/Cl molar ratios. In these tests, an approximately 30% decrease in the total PCDD/F concentrations due to the addition of Br was observed. This decrease appears to be a decrease only in the chlorinated dioxin and furan species; other halogenated dioxins and furans were formed instead. PCDD/F homologue distribution shifted towards the higher chlorinated species. Perhalogenated or nearly perhalogenated mixed bromo-chloro furans were also observed in quantities that could potentially account for the observed decrease in PCDDs/Fs. This research illustrates the need for careful trial burn planning if Br will be present in the facility's feed-stock during normal operation.     

Bench-scale studies on the simultaneous formation of PCBs and PCDD/Fs from combustion systems

The presence of endocrine disrupting chemicals (EDCs) in the environment has wide-ranging potential ecological and health impacts on animals and humans. A significant amount of experimental and theoretical work has been performed the examining formation and control of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), which account for only part of the EDCs being emitted from combustion devices. Generally accepted mechanistic theories for PCDD/F formation propose heterogeneous reactions in the cooler regions of the combustor involving gas-phase organic precursors (such as chlorobenzenes or chlorophenols), a chlorine donor [such as hydrogen chloride (HCl)], and a flyash-bound metallic catalyst (such as copper chloride). There is evidence that some other proposed EDCs, including polychlorinated biphenyls (PCBs), are formed through a similar mechanistic pathway as PCDD/Fs. In addition, there is evidence that certain important steps in the catalytic reaction between the copper catalyst and the organic precursors may suggest a common rate limiting step for the heterogeneous formation of the previously mentioned EDCs. This paper reports on a bench-scale experimental study to characterize a newly built reactor system that was built to: produce levels and distributions of PCDD/F production similar to those achieved by previous researchers; verify similar responses to changes in independent variables; examine the hypothesis that PCB formation rates exhibit trends similar to PCDD/F formation rates as reactor variables are changed; and begin to explore the dependence of PCB formation on temperature and precursor type. The reactor system has been built, and initial reactor characterization studies have been performed. Initial experiments yielded results that support the hypothesis of a similar formation mechanism of PCBs and PCDD/Fs in combustors. Initial experiments uncovered potential deficiencies with the reactor system and the experimental procedures and have suggested corrective action to improve the experimental system.     

Determination of inorganic and organic priority pollutants in biosolids from meat processing industry

The biosolids (BS) generated in the wastewater treatment process of a meat processing plant were monitored and the priority pollutant content was characterized. The trace metal and organic pollutant content – polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) – were determined quantitatively and compared to guideline limits established by the US EPA and EU. PCBs were not detected in the solid samples, while trace metals, PAHs and PCDD/PCDF were detected in concentrations below the limits established by international standards. Toxic equivalent factors were evaluated for the biosolids, and the results proved that these wastes can be safely deposited on land or used in combustion/incineration plants. Since no previous data were found for meat processing waste, comparisons were made using municipal sewage sludge data reported in the literature. Since, this report monitored part of the priority pollutants established by the US EPA for meat and poultry processing wastewater and sludge, the results verified that low pollution loads are generated by the meat processing plant located in the southern part of Brazil. However, the BS generated in the treatment processes are in accordance with the limits established for waste disposal and even for soil fertilizer.     

An investigation of halogens in Izmit hazardous and clinical waste incinerator

In the combustion facilities, halogens (Cl, F, Br, I) should be considered with regard to the control of the compounds such as polychlorinated dibenzodioxins (PCDD), polychlorinated dibenzofurans (PCDF), halogenated polyaromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and volatile heavy metals formed as a result of incomplete combustion and caused adverse environmental effects. In this study halogens were observed in Izmit Hazardous and Clinical Waste Incinerator (IZAYDAS). Halogen contents of the combustion menu, flue gas, fly ash, bottom ash and filter cake were measured and their distributions in these exit streams were determined. Results showed that the major part of the halogens was partitioned to solid residues, i.e., bottom ash and filter cake which represents the removal by wet scrubbers. Fly ash and flue gas fractions of halogens were much lower due to the reduced formation of volatile compounds.     

Formation of persistent chlorinated aromatic compounds in simulated and real fly ash from iron ore sintering

Effects of carbon concentration and Cu additive in simulated fly ash (SFA) and real fly ash (RFA) on the formation of polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs), chlorobenzenes, and polychlorinated biphenyls which were all regarded as persistent chlorinated aromatics in iron ore sintering were investigated. In the annealing process of SFA with various carbon contents, the yield of chlorinated aromatics and the I-TEQ obtained their maximum at 10 wt% carbon content. Active carbon in SFA acted as the carbon source as well as an adsorbent which led to higher production of PCDD/F in solid phase at 10 wt% carbon content. The increase of carbon content will be beneficial on the formation of 2,3,7,8-Chloro-substituted PCDF compared with 2,3,7,8-Chloro-substituted PCDD. In addition, the CuCl₂·2H₂O was a much more powerful catalyst in the formation of chlorinated aromatic compounds compared with elementary Cu, since it served as both a catalyst and a chlorine donor. However, the RFA behaved similarly with SFA with elementary Cu in the formation of chlorinated aromatic compounds. The effect of carbon content and copper additives on formation of 2,3,7,8-chloro-substituted congeners displayed similar characteristics with the tetra- to octa-PCDD/F isomers and even the total PCDD/Fs.     

Decreased PCDD/F formation when co-firing a waste fuel and biomass in a CFB boiler by addition of sulphates or municipal sewage sludge

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are formed during waste incineration and in waste-to-energy boilers. Incomplete combustion, too short residence times at low combustion temperatures (<700 °C), incineration of electronic waste and plastic waste containing chlorine are all factors influencing the formation of PCDD/Fs in boilers. The impact of chlorine and catalysing metals (such as copper and iron) in the fuel on PCDD/F formation was studied in a 12 MW_th circulating fluidised bed (CFB) boiler. The PCDD/F concentrations in the raw gas after the convection pass of the boiler and in the fly ashes were compared. The fuel types were a so-called clean biomass with low content of chlorine, biomass with enhanced content of chlorine from supply of PVC, and solid recovered fuel (SRF) which is a waste fuel containing higher concentrations of both chlorine, and catalysing metals. The PCDD/F formation increased for the biomass with enhanced chlorine content and it was significantly reduced in the raw gas as well as in the fly ashes by injection of ammonium sulphate. A link, the alkali chloride track, is demonstrated between the level of alkali chlorides in the gas phase, the chlorine content in the deposits in the convection pass and finally the PCDD/F formation. The formation of PCDD/Fs was also significantly reduced during co-combustion of SRF with municipal sewage sludge (MSS) compared to when SRF was fired without MSS as additional fuel.     

Recent findings on the formation and decomposition of PCDD/PCDF in municipal solid waste incineration

The thermal formation of PCDD/PCDF in fly ashes of refuse incineration plants preferably in the low-temperature region of the boiler at 3002C is fully confirmed. Important parameters for the reaction of formation are the oxygen content and the water vapor in the offgas. Elemental carbon in the fly ash acts as an adsorbent to the precursor compounds. The oxidation of carbon may serve as a basis for the mechanism of PCDD/PCDF formation. Both reactions proceed by the Deacon process scheme. The catalytic action of CuCl₂ can be counteracted by the addition of NH₃.     

The toxicity equivalency factor scheme applied to municipal incinerator PCDD/PCDF emissions when specific congener information is lacking

The 2,3,7,8-TODD Toxicity EQuivalents (TEQ) approach provides a useful method for estimating the environmental risk of polychlorodibenzodioxin and polychlorodibenzofuran complex mixtures, thus making it possible to express their toxicological significance with only one number. Generally the conversion of the concentration units into those of TEQ requires an isomer-specific analysis and the appropriate Toxicity Equivalency Factors (TEF). In this paper we propose a “theoretical” model for estimating TEQ values of PCDD + PCDF mixtures which, starting from the experimental value of the PCDD + PCDF concentration (μg Nm⁻³) and the theoretical value of PCDD and PCDF fingerprints in the emissions from municipal incinerators, to make an estimate of the global toxicity in terms of ng TEQ Nm⁻³. The TEQ values estimated for a number of samples are in good agreement with those calculated from the isomer and congener experimental data. Given the investment and running costs plus the time and the analytical complexity in determining the congeners and single isomer concentrations, it seems that the proposed “theoretical” model is a reasonable tool for estimating the exposure hazard related to a complex mixture of PCDD/PCDFs emitted from municipal solid waste (MSW) incinerators. Another objective of this paper is to explore the consistency between scientific knowledge and the authority regulatory guidelines. This work shows that the Italian national emission standard (4 μg Nm⁻³) for the total PCDD+PCDF concentration is higher than the international target of 0.1 ng TEQ Nm⁻³. We suggest a value of 1 μg Nm⁻³ for TCDD + TCDF concentration if Italian regulators want to add a further constraint.     

Effects of gaseous NH(3) and SO(2) on the concentration profiles of PCDD/F in flyash under post-combustion zone conditions

The influence of gaseous ammonia and sulphur dioxide on the formation of 2378-substituted PCDD/F on a reference flyash from a municipal waste incinerator has been investigated using a laboratory scale fixed-bed reactor. The reference flyash samples (BCR-490) was reacted under a simulated flue gas stream at temperatures of 225 and 375°C for 96h. The experiments were carried out in two series: first with simulated flue gas alone, and then with injection of NH(3) or SO(2) gas into the flue gas just before the reactor inlet. It was found that the injection of gaseous ammonia into the flue gas could decrease the concentration of both PCDD and PCDF by 34-75% from the solid phase and by 21-40% from the gas phase. Converting the results to I-TEQ values, it could reduce the total I-TEQ values of PCDD and PCDF in the sum of the flyash and exhaust flue gas by 42-75% and 24-57% respectively. The application of SO(2) led to 99% and 93% reductions in the PCDD and PCDF average congener concentrations, respectively in the solid phase. In the gas phase, the total reductions were 89% and 76% for PCDD and PCDF, respectively. Moreover, addition of SO(2) reduced the total I-TEQ value of PCDD and PCDF in the flyash and exhaust flue gas together by 60-86% and 72-82% respectively. Sulphur dioxide was more effective than ammonia in suppressing PCDD/F formation in flyash under the conditions investigated.     

Characterizing emissions from open burning of military food waste and ration packaging compositions

Emissions from open burning of military food waste and ration packaging compositions were characterized in response to health concerns from open burning disposal of waste, such as at military forward operating bases. Emissions from current and prototype Meals, Ready-to-Eat (MREs), and material options for their associated fiberboard packaging were quantified to assess contributions of the individual components. MREs account for 67–100% of the particulate matter (PM), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated dibenzo-p-dioxins and -furans (PCDDs/PCDFs) emissions when burned in unison with the current fiberboard container and liner. The majority of the particles emitted from these burns are of median diameter 2.5 µm (PM_2.5). Metal emission factors were similar regardless of waste composition. Measurements of VOCs and PAHs indicate that targeted replacement of MRE components may be more effective in reducing emissions than variation of fiberboard-packaging types. Despite MRE composition variation, equivalent emission factors for PM, PAH, VOC, and PCDD/PCDF were seen. Similarly, for fiberboard packaging, composition variations exhibited essentially equivalent PM, PAH, VOC, and PCDD/PCDF emission factors amongst themselves. This study demonstrated a composition-specific analysis of waste burn emissions, assessing the impact of waste component substitution using military rations.     

Verification results of jet resonance-enhanced multiphoton ionization as a real-time PCDD/F emission monitor

A jet resonance-enhanced multiphoton ionization (REMPI) monitor was tested on a hazardous-waste-fired boiler for its ability to determine concentrations of polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs). Jet REMPI is a real-time instrument capable of highly selective and sensitive (from parts per billion to parts per trillion) detection of a broad range of aromatic compounds, including a number of air toxic compounds. The PCDD/F toxic equivalency (TEQ) value was derived from a predetermined correlation (R ² = 0.74) with monochlorobenzene (MClBz). This relationship was applied to nine subsequent jet REMPI on-line measurements of MClBz and parallel, standard extractive sampling for PCDD/F TEQ. For high waste-firing rates, with a range of PCDD/F TEQ values between 3.9 and 6.0 ng TEQ/m³, the TEQ values predicted by jet REMPI had a relative difference of 26% with the standard EPA Method 23 results. At low waste-firing rates (0.9–1.6 ng TEQ/m³), the relative difference increased to 219%. This limited testing shows that jet REMPI has promise as an on-line diagnostic monitor, providing feedback on the effects on PCDD/F emissions of operating parameter changes such as fuel feed interruptions or air pollution control failures.     

Balance of NH3 and behavior of polychlorinated dioxins and furans in the course of the selective non-catalytic reduction of nitric oxide at the TAMARA waste incineration plant

Investigations were performed on the selective non-catalytic reduction (SNCR) of nitric oxide (NO) at TAMARA, the pilot-scale waste incineration plant of the Karlsruhe Research Center. Aqueous ammonia (NH₃) was injected into the combustion chamber as reductant. The influence of NH₃ on various inorganic and organic compounds in the flue gas was investigated. The concentrations of NO were reduced by up to about 90% by NH₃ injection. The concentrations of most of the other inorganic and organic compounds, including in particular PCDD and PCDF, did not change significantly.     

PCBs,PBDEs and dioxin-related compounds in floor dust from an informal end-of-life vehicle recycling site in northern Vietnam: contamination levels and implications for human exposure

Floor dusts from Vietnamese end-of-life vehicle (ELV)-processing households were investigated to elucidate the contamination levels and exposure risk of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and dioxin-related compounds (DRCs). The concentrations were in order of PBDEs (260–11,000, median 280 ng/g overall) > PCBs (19–2200, median 140 ng/g) > dioxin-like PCBs (8.8–450, median 22 ng/g) ? polybrominated dibenzo-p-dioxin/dibenzofurans (PBDD/Fs, 2000–28,000, median 8500 pg/g) > polychlorinated dibenzo-p-dioxin/dibenzofurans (PCDD/Fs, 440–4100, median 1800 pg/g) > MoBPCDD/Fs (1.9–1200, median 250 pg/g). Concentrations of PCBs and DRCs were higher than those reported for Vietnamese urban houses, indicating ELV processing as a significant source of these contaminants. Higher concentrations of PCBs relative to PBDEs suggest the abundance of old electrical capacitors/transformers in ELVs. The PBDD/F and PCDD/F profiles were indicative of DecaBDE-containing materials and combustion sources, respectively. PBDFs, PCDFs and DL-PCBs were the most important dioxin-like toxic equivalent (TEQ) contributors. The estimated PCB and TEQ intake doses from dust ingestion approached or exceeded the reference doses for children living in some ELV-processing households, indicating potential health risk. More comprehensive risk assessment of the exposure to PCBs and DRCs is required for residents of informal ELV recycling sites.