Insight into the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans in hazardous waste incineration and incinerators: Formation process and reduction strategy

Incineration technology has been widely adopted to safely dispose of hazardous waste (HW). While the incineration process causes the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Due to its extreme toxicity, many scholars have been committed to determining the PCDD/F formation process and reducing emissions in incinerators. Previous studies ignored the impact of incineration and fluctuation of feeding materials on PCDD/F formation in hazardous waste incinerators (HWIs). In this study, differences in PCDD/F formation between HWIs and municipal solid waste incinerators (MSWIs) were pointed out. The incineration section in HWIs should be carefully considered. Laboratory experiments, conventional analysis and thermogravimetry experiments were conducted. An obvious disparity of PCDD/F formation between 12 kinds of HWs was found. Distillation residue was found with remarkably higher PCDD/F concentrations (11.57 ng/g). Except for the Cl content, aromatic rings and C-O bond organics were also found with high correlation coefficients with PCDD/F concentrations (>0.92). And PCDD/Fs were formed through a chlorination process and structure formation process. All of these are helpful to further understand the PCDD/F formation process during HW incineration, optimize the operation conditions in HWIs and reduce the emission pressure of PCDD/Fs in the future.

Emission reduction of PCDD/Fs by flue gas recirculation and activated carbon in the iron ore sintering

One of the main sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the environment is the sintering of iron ore. Both flue gas recirculation (FGR) and activated carbon (AC), which have the impact of decreasing both PCDD/Fs and conventional pollutants (NOx, SO2, etc.), are significant technologies for the abatement of PCDD/Fs from the sintering exhaust gas. This work involved the first measurement of PCDD/Fs emissions during FGR and a thorough analysis of the impact of PCDD/Fs reduction following the coupling of FGR and AC technologies. According to the measured data, the ratio of PCDFs to PCDDs in the sintered flue gas was 6.8, indicating that during the sintering process, the PCDD/Fs were primarily produced by de novo synthesis. Further investigation revealed that FGR initially removed 60.7% of PCDD/Fs by returning it to the high temperature bed, and AC further removed 95.2% of the remaining PCDD/Fs through physical adsorption. While AC is better at removing PCDFs and can efficiently remove tetra-to octa-chlorinated homologs, FGR is more effective at removing PCDDs and has higher removal efficiency for hexa-to octa-chlorinated PCDD/Fs. Together, they complement each other with a removal rate of 98.1%. The study's findings are instructional for the process design of combining FGR and AC technologies to reduce PCDD/Fs in the sintered flue gas.

Formation and Inventory of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans and Other Byproducts along Manufacturing Processes of Chlorobenzene and Chloroethylene

Chlorinated organic chemicals are produced and used extensively worldwide, and their risks to the biology and environment are of increasing concern. However, chlorinated byproducts [e.g., polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)] formed during the commercial manufacturing processes and present in organochlorine products are rarely reported. The knowledge on the occurrences and fate of unintentional persistent organic chemicals in the manufacturing of organochlorine chemical is necessary for accurate assessment of the risks of commercial chemicals and their production. Here, PCDD/Fs were tracked throughout chlorobenzene and chloroethylene production processes (from raw materials to final products) by target analysis. Other byproducts that can further transform into PCDD/Fs were also identified by performing non-target screening. As a result, the PCDD/F concentrations were mostly the highest in bottom residues, and the octachlorinated congeners were dominant. Alkali/water washing stages may cause the formation of oxygen-containing byproducts including PCDD/Fs and acyl-containing compounds, so more attention should be paid to these stages. PCDD/Fs were of 0.17 and 0.21-1.2 ng/mL in monochlorobenzene and chloroethylene products, respectively. Annual PCDD/F emissions (17 g toxic equivalent in 2018) during chlorobenzene and chloroethylene production were estimated using PCDD/F emission factors. The results can contribute to the improvement of PCDD/F inventories for the analyzed commercial chemicals.

Inhibition of polychlorinated dibenzo-p-dioxins and dibenzofurans by phosphorus-containing compounds in model fly ash

Waste incineration is a preferred method in China to dispose the municipal solid waste, but controlling the production of highly toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans effectively during incineration is both challenging and imperative. In this study, the suppression of PCDD/Fs by various phosphorus-containing compounds was explored, and the mechanisms responsible for the inhibition were studied in detail. The experiments took place in a lab-scale vertical tubular reactor at 350 °C under a simulated flue gas (12 vol% O₂ in N₂ flow), and both the off-gases and residues were collected for PCDD/Fs analysis. The scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the reaction residues. The experimental results revealed that NH₄H₂PO₄ and (NH₄)₂·HPO₄ showed the highest inhibitory effect (57.2% and 57.3%, respectively) on the PCDD/Fs formation, followed by CaHPO₄ with inhibition efficiency of 39.1%. In contrast, KH₂PO₄ and K₂HPO₄ barely inhibited the generation of the PCDD/Fs. The inhibitory effect of NH₄H₂PO₄ and (NH₄)₂·HPO₄ was similar to that of nitrogen-based inhibitors. At the same time, it was proven that the inhibitory activity of CaHPO₄ might be due to the reaction of it with Cu²⁺ forming stable compounds.

Alteration in formation behaviors of chloroaromatic precursors of PCDD/Fs: An experimental study on the effect of extrinsic and intrinsic oxygen on chlorination

Due to the promotion on Cl radical generation by enhanced oxidation, chlorination of hydrocarbon intermediates becomes a potential formation path for chloroaromatic precursors of PCDD/Fs (polychlorinated dibenzo-p-dioxins and dibenzofurans) in both MSW (municipal solid waste) incineration and gasification-combustion processes, in which intrinsic oxygen might have a significant effect on the competition between oxidation and chlorination. Thus, chlorination of benzene and phenol was experimentally studied on a homogeneous flow reaction system. Effects of temperature and ER (equivalence ratio) were assessed, and comparison was carried out to clarify the alteration in formation behaviors of chloroaromatics by extrinsic and intrinsic oxygen. At 600 °C, chlorobenzenes were already largely formed in benzene chlorination, and the addition of extrinsic oxygen barely affected it. On the contrary, with intrinsic oxygen, phenol tended to decompose to light compounds. With rising temperature, oxidation was promoted and extrinsic oxygen strongly inhibited the formation of chloroaromatics in benzene chlorination at 900 °C and higher temperature. For phenol chlorination, chlorobenzenes were still rarely generated. However, high proportions of octachloronaphthalene and octachlorodibenzofuran were observed, due to the enhancement in polymerization by high temperature. When increasing ER, oxidative decomposition was also promoted in both the chlorination of benzene and phenol. Extra extrinsic oxygen led to a further reduction of chloroaromatics during benzene chlorination, and till ER = 1.0 at 1000 °C, comparable performance to intrinsic oxygen could be achieved in the control of chloroaromatics. Based on these results, formation pathways of the major chloroaromatics from chlorination, oxidation and polymerization were summarized, and the roles of extrinsic and intrinsic oxygen in altering their formation behaviors were revealed.

Industrial disposal processes for treatment of polychlorinated dibenzo-p-dioxins and dibenzofurans in municipal solid waste incineration fly ash

Hazardous waste disposal is a serious environmental concern in China. Therefore, in this study, industrial trials were conducted in a low-temperature thermal degradation facility, a tunnel kiln, and a shaft kiln to effectively treat dioxins in municipal solid waste incineration (MSWI) fly ash. The results indicated that the low-temperature thermal degradation facility efficiently decomposed polychlorinated dibenzo-p-dioxins and dibenzofurans in the MSWI fly ash. Additionally, the concentrations of dioxins in the treated fly ash and exhaust gas were lower than the suggested standard limits and the degradation ratio of dioxins was ∼99%. Therefore, treated fly ash characterized by acceptable dioxin risks could be utilized for the production of non-fired building materials. The results from the tunnel kiln indicated complete decomposition of the dioxins in the firing and insulating sections. However, the addition of fly ash in the tunnel kiln increased the concentration of dioxins in the flue gas. This can be primarily attributed to the heterogeneous catalytic synthesis reaction in the low-temperature section of the tunnel kiln. The results from the shaft kiln indicated degradation of at least 22% of the dioxins in the ash. The dioxin concentration in the flue gas was lower than the national standard while that in the clinker was within a reasonable limit. Furthermore, the environmental risks were significantly reduced at fly ash addition ratios lower than 3%.

Bioaccumulation of PCDD/Fs in foodstuffs near Bien Hoa and Da Nang airbases: assessment on sources and distribution

In this survey, food items were collected from vicinities of Bien Hoa and Da Nang airbase and determined for polychloro-dibenzo-dioxins and polychloro-dibenzo-furans (PCDD/Fs) to assess their accumulation, distribution in the local food items, and risk of PCDD/F exposure through consumption of the local foods. Dioxin compounds were determined using isotope dilution method which is slightly modified from US-EPA method 1613B. The dioxin concentration was the highest in fish followed by eggs, chicken, meat (pork and beef), and vegetables. Particularly, in Bien Hoa airbase, the mean concentrations of dioxin on TEQ and lipid basis (except for vegetables) were 26 pg/g for fish, 13 pg/g for eggs, 20 pg/g for chicken, 4.5 pg/g for meat, and 0.34 pg/g fresh wt for vegetables. In Da Nang airbase, the mean levels of dioxin on TEQ and lipid basis were slightly lower, 12.9 pg/g for fish, 8.7 pg/g for eggs, 5.9 pg/g for chicken, 6.7 pg/g for meat, and 0.17 pg/g for vegetables. It has been interesting to observe that free-range chicken expose to higher level of dioxin than caged chicken. In some free-range chicken, the portion of 2,3,7,8-TCDD was relatively high and implying recent exposure to dioxin.

Thermal oxidation of dieldrin and concomitant formation of toxic products including polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F)

This paper examines the gas phase thermal decomposition of dieldrin and associated formation of toxic combustion products including polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F). Volatile Organic Carbon (VOC) analysis revealed the formation of pentachlorostyrene (PCS), hexachlorostyrene (HCS) and polychlorinated naphthalene as toxic combustion products generated during the combustion of dieldrin. The thermal pyrolysis of dieldrin resulted in the formation of chlorinated benzenes and chlorinated phenols, which are known PCDD/F precursors. The formation of PCDD/F commenced around 823 K @ 5s residence time and results indicate a preference for the formation of PCDF over PCDD under all experimental conditions studied. Subsequent experiments, to examine the yield of PCDD/F as a function of temperature, reveal the progressive chlorination of PCDD/F with temperatures up to 923 K. Octachlorodibenzofuran (OCDF) was the major dioxin congener detected in the oxidation of dieldrin. The highest toxicity factor for dioxin formation was recorded at 923 K with a 6% O₂ content in the feed gas and corresponds to 6.24 ng TEQ WHO 2005/mg of dieldrin and total PCDD/F concentration of 96.8 ng/mg of dieldrin.

Mechanochemical degradation of PCDD/Fs in fly ash within different milling systems

Two distinct mechanochemical degradation (MCD) methods are adopted to eliminate the polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) from fly ash in municipal solid waste incinerators. First, experiments are conducted in a planetary ball mill for selecting suitable additives, and an additive system of SiO₂-Al is chosen for its high-efficiency, low-price, and good practicability. The I-TEQ value of PCDD/Fs in washed fly ash decreases dramatically from 6.75 to 0.64 ng I-TEQ/g, after 14 h of milling with 10 wt % SiO₂-Al, and dechlorination is identified as the major degradation pathway. Then, this additive is applied in a horizontal ball mill, and the results indicate that the degradation of PCDD/Fs follows the kinetic model established in planetary ball mills. However, longer milling time is required for the same supplied-energy because of the lower energy density of horizontal ball mills, resulting in partial loss of Al reactivity and a lower degradation efficiency of PCDD/Fs. During MCD, the evolution of PCDD/F-signatures is analogous, indicating a similar acting mechanism of all additives in both the two milling systems. Finally, a major dechlorination pathway of PCDD-congeners is proposed based on the signature analysis of congeners synthesized from chlorophenols.

Emissions of 2,3,7,8-substituted and non-2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans from secondary aluminum smelters

The secondary aluminum smelting industry is an important source of polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs). However, the formations and emissions of non-2,3,7,8-PCDD/Fs have rarely been studied. Non-2,3,7,8-PCDD/Fs may also be metabolically toxic to mammalians. In this study, four typical secondary aluminum smelters were selected as demonstration smelters and the composition of the raw material they used was adjusted to investigate the influence on PCDD/F emissions and profiles. In addition to 17 congeners of 2,3,7,8-PCDD/Fs, 64 congeners of non-2,3,7,8-PCDD/Fs were firstly reported. Strong, positive correlations were found between non-2,3,7,8-PCDD/Fs and 2,3,7,8-PCDD/Fs. The concentrations of 2,3,7,8-PCDD/Fs in stack gas and fly ash samples were 120.7-870.4 pg/Nm³ and 13.40-292.9 ng/g, respectively. Those of non-2,3,7,8-PCDD/Fs in the stack gas and fly ash samples were 84.03-1183.7 pg/Nm³ and 7.20-344.7 ng/g, respectively. The raw material composition was a key factor affecting PCDD/F emissions and profiles. An analysis of Gibbs free energies (ΔG_f) showed that non-2,3,7,8-PCDD/Fs could be transformed into 2,3,7,8-PCDD/Fs, which would increase the PCDD/F environmental risks. The emission inventories of 2,3,7,8-PCDD/Fs, non-2,3,7,8-PCDD/Fs, and International Toxic Equivalents from Chinese secondary aluminum smelters in 2013 were 8247 g, 7253 g, and 608.6 g, respectively. The results of this study could contribute to potential risk evaluations and effective reduction of non-2,3,7,8-PCDD/Fs.

TCDD Toxicity Mediated by Epigenetic Mechanisms

Dioxins are highly toxic and persistent halogenated organic pollutants belonging to two families i.e., Polychlorinated Dibenzo-p-Dioxins (PCDDs) and Polychlorinated Dibenzo Furans (PCDFs). They can cause cancer, reproductive and developmental issues, damage to the immune system, and can deeply interfere with the endocrine system. Dioxins toxicity is mediated by the Aryl-hydrocarbon Receptor (AhR) which mediates the cellular metabolic adaptation to these planar aromatic xenobiotics through the classical transcriptional regulation pathway, including AhR binding of ligand in the cytosol, translocation of the receptor to the nucleus, dimerization with the AhR nuclear translocator, and the binding of this heterodimeric transcription factor to dioxin-responsive elements which regulate the expression of genes involved in xenobiotic metabolism. 2,3,7,8-TCDD is the most toxic among dioxins showing the highest affinity toward the AhR receptor. Beside this classical and well-studied pathway, a number of papers are dealing with the role of epigenetic mechanisms in the response to environmental xenobiotics. In this review, we report on the potential role of epigenetic mechanisms in dioxins-induced cellular response by inspecting recent literature and focusing our attention on epigenetic mechanisms induced by the most toxic 2,3,7,8-TCDD.

PCDD/PCDF formation in the chlor-alkali process-laboratory study and comparison with patterns from contaminated sites

Studies on the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) during the electrolysis of sodium chloride solution (brine) using graphite or titanium electrodes were carried out at a laboratory scale. High concentrations of PCDFs but no PCDDs were formed in tests using graphite electrodes. With titanium electrodes, PCDFs were only formed when tar pitch was added and mainly originated from the dibenzofuran present in the tar. For the first time, a detailed assessment of the formation of mono- to octachlorinated PCDD/PCDF from tar pitch was investigated. The assessment included of the chlorination steps proved that PCDFs were formed by successive lateral chlorinated from dibenzofuran to MonoCDFs, DiCDFs, and TriCDFs to form the typical known "chlorine pattern" of TetraCDF to OctaCDF with a dominance of 1,2,7,8- and 2,3,7,8-TetraCDFs, 1,2,3,7,8-PentaCDF, and 1,2,3,4,7,8-HexaCDF as marker congeners. The final homologue distributions depended on reaction time and reaction temperature. In addition, electrolysis with non-chlorinated dibenzo-p-dioxins, dibenzofuran, and biphenyl was carried out. As a result, PCDDs, PCDFs, and PCB were formed at comparable yields. Congener patterns in soil samples from a PCDD/F-contaminated site where chlor-alkali electrolysis had been operated for decades in Japan had identical isomer distribution demonstrating the source and contamination potential and risk of these processes. Therefore, sites where in the past 120 years chlor-alkali electrolysis has been operated or where residues from chlor-alkali production or other chlorine using industries have been disposed should be assessed for their pollution level and exposure relevance. The assessment of total organohalogen content revealed that PCDF is only a small fraction of organohalogens in the contaminated soils. For an appropriate risk assessment, also other chlorinated aromatic compounds such as PCBs or PCNs need to be considered.

Polychlorinated dibenzo-p-dioxin and dibenzofuran precursors and formation mechanisms during non-woodpulp chlorine bleaching process

There is great concern about decreasing the amounts of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) that are formed and emitted during the chlorine bleaching of pulp. The formation of PCDD/Fs during non-woodpulp chlorine bleaching was investigated in the study described here. Wheat straw was separated into three components, cellulose, hemicellulose, and lignin. Chlorination experiments were performed, and lignin and hemicellulose contributed more than cellulose to PCDD/F formation when the pulp was bleached using chlorine. The chemical components of lignin were identified by gas chromatography mass spectrometry, and nine possible PCDD/F precursors were quantified by gas chromatography tandem mass spectrometry. Spiked chlorination experiments were performed to investigate the effects of these compounds on PCDD/F formation. 4-Ethyl-2-methoxyphenol had the strongest effect on PCDD/F formation, followed by p-chlorophenol, and guaiacol. All the test compounds promoted polychlorinated dibenzofuran formation but had limited effects on polychlorinated dibenzo-p-dioxin formation. The results allowed mechanisms for the formation of PCDD/Fs from phenol, chlorophenol, catechol, and guaiacol to be proposed.

Destruction and formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during pretreatment and co-processing of municipal solid waste incineration fly ash in a cement kiln

During a three-day industrial trial, municipal solid waste incineration fly ash (FA) was co-processed in a cement kiln after water-washing pretreatment for waste-to-resource conversion. All inputs and outputs were sampled to obtain the dioxin fingerprints. During washing, the relative contents of polychlorinated dibenzo-p-dioxins and dibenzofurans in FA, washed FA and sludge were basically the same and only a simple physical migration resulted. During drying, only physical processes resulted, which included volatilization and migration. Minimal dioxins residue remained in the clinker, cement kiln dust and flue gas, and the dioxins degraded completely. Through co-processing, the dioxins degraded obviously. The main compounds synthesized include 1,2,3,4,7,8-hepta-chlorodibenzo-p-dioxin, 2,3,7,8-tetra- chlorodibenzofuran and octa-chlorodibenzofuran. A comparison of dioxins fingerprints in the clinker, cement kiln dust and flue gas under baseline and co-processing conditions showed that co-processing had no effect on the cement kiln production. The baseline sample also contained a certain amount of dioxins, possibly because of the 'memory effect' and heterogeneous formations. The dioxins concentrations in the clinker and FA were far lower than the national standards. Thus, no environmental risk results during co-processing.

Evolution of PCDD/F-signatures during mechanochemical degradation in municipal solid waste incineration filter ash

Mechanochemical degradation (MCD) is employed for the dechlorination of polychlorinated dibenzo-p-dioxins (PCDD) and -furans (PCDF) in filter ashes from municipal solid waste incinerators, respectively with the assist of six additive systems. The evolution of PCDD/F-signatures in all eleven samples are systematically monitored and studied at the level of individual congeners, and special attention is paid to CP-route congeners, 2,3,7,8-substitution, 1,9-substitution, and 4,6-PCDF. The PCDD/F-isomers distribution follows an analogous pattern, indicating the similar acting mechanism for all additives: additives transfer electrons to attack the CCl bond and then expulse chlorine. MC dechlorination is not favored for the chlorine on β-position (2,3,7,8-position). The oxygen with stronger electronegativity in PCDD/Fs negatively influences CCl bond to accept donated electrons, hindering the removal of chlorine on 1,9-position for PCDD, and chlroine on 4,6-position for PCDF. Finally, two fair dechlorination pathways for PCDD and PCDF are respectively proposed based on the detailed analysis of CP-route congeners. The evolution of PCDD-signatures is clear, yet obscure for PCDF-signatures, which still requires further investigations.

Removal of PCDD/Fs, PCP and mercury from sediments: Thermal oxidation versus pyrolysis

A continuous pilot-scale system (CPS) equipped with effective air pollution control devices (APCDs) is used for remediating the sediments contaminated with PCDD/Fs, PCP and Hg simultaneously. The removal efficiencies of these three pollutants in sediments collected from seawater pond and river, respectively, are evaluated via thermal treatment processes. PAHs and CBz formed during thermal oxidation and pyrolysis are also analyzed for better understanding the behaviors of chlorinated organic compounds. Experimental results indicate that low-molecular-weight PAHs are closely related to the formation of CBz, PCDD/Fs, and CPs, while low chlorinated PCDD/Fs and CBz are predominant in flue gas with thermal oxidation. However, the PM concentration is higher in thermal oxidation than pyrolysis due to the higher air flow rate of thermal oxidation. It may bring more particles out of the furnace and have a greater potential to form PCDD/Fs within APCDs. Besides, the high air flow also dilutes the Hg vapor in flue gas and would require more energy to condense and collect Hg with the quench tower. Furthermore, for removal of total amount of PCDD/Fs, pyrolysis is better than thermal oxidation. Thus, pyrolysis is more suitable for remediating the contaminated sediment. The removal efficiencies of PCDD/Fs, PCP and Hg in sediments achieved with pyrolysis increase with increasing operating temperature and retention time in CPS. Overall, the residual concentrations of PCDD/Fs and PCP in river sediment are higher than that in seawater-pond sediment since significant formation of tar is observed due to higher organic matter content in river sediment.

Occurrence and characteristics of PCDD/Fs formed from Chlorobenzenes production in China

China had a large production capacity of chlorobenzenes. An extensive investigation was conducted to understand the occurrence and characteristics of PCDD/Fs from four chlorobenzene production plants. The concentrations of PCDD/Fs in mono-CB production and in a new di-CB production routine were revealed. Concentrations of PCDD/Fs in residues, byproducts, products and wastewater varied between 8.4*10³-4.0*10⁶ ng TEQ/kg, 1.5-5.0*10⁴ ng TEQ/kg, ND∼0.12 ng TEQ/kg and 6.0*10⁴-9.1*10⁴ pg TEQ/L, respectively. OCDF, 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, and 2,3,7,8-TeCDF were the most abundant congeners of the 17 2,3,7,8-substituted PCDD/Fs. In most samples, PCDFs contributed more than 99% of the total TEQs of PCDD/Fs, in which 2,3,4,7,8-PeCDF was the dominating contributor. It is inferred PCDFs were mainly formed in the chlorination reactions. The emission factors were suggested and the amount of PCDD/Fs formed in CB production was estimated to be 450 g TEQ in 2012. Residue, byproduct and wastewater were potentially the main pathways of PCDD/Fs to the environmental releases.

Mechanochemical treatment of fly ash and de novo testing of milled fly ash

Mechanochemical (MC) treatment has been widely proposed to degrade chlorinated organics in various matrix materials. In this study, fly ash from municipal solid waste incineration was grinded without any addition, using an all-dimensional planetary ball mill. The treated fly ash samples were characterised using X-ray diffraction, Raman spectra, scanning electron microscopy and X-ray energy-dispersive spectroscopy. The residual content of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) was monitored, as well as polycyclic aromatic hydrocarbons (PAH), a potential precursor of PCDD/F and amorphous carbon or graphite. Finally, de novo formation experiments were performed to test the chemical reactivity of the treated fly ash. The PCDD/F in milled samples was compared to those resulting from de novo tests on these same samples. The results suggest that both milling as well as de novo tests significantly alter the PCDD/F signature, suggesting substantial differences in the mechanisms of formation and destruction.

Current state of yusho and prospects for therapeutic strategies

The mass food poisoning incident yusho occurred in Japan in 1968. It was caused by the ingestion of rice bran oil contaminated with polychlorinated biphenyls and various dioxins and dioxin-like compounds including polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDFs). Notably, PCDFs were found to contribute to approximately 65% of the total toxicity equivalent in the blood of yusho patients. Lipophilic dioxins are retained in the body for a longer period than previously estimated. Victims suffered from characteristic skin manifestations associated with non-specific systemic symptoms, neurological symptoms, and respiratory symptoms. The severe symptoms seen in the initial phase subsequently faded, but recently, improvements have scarcely been observed. The Yusho Group has been researching treatments for this condition. Several clinical trials with chelating agents or dietary fibers aimed at accelerating the excretion of compounds. While some treatments increased dioxin excretion, none provided satisfactory symptom relief. Concurrently, various phytochemicals and herbal extracts have been found to possess biological activities that suppress dioxin-induced toxicity via aryl hydrocarbon receptor or activate the antioxidant nuclear factor-erythroid 2-related factor-2 (NRF2) signal pathway, making them promising therapeutic candidates. Here, we summarize the current status of yusho and findings of clinical trials for yusho patients and discuss the treatment prospects.

Emission characteristics of PCDD/Fs in stack gas from municipal solid waste incineration plants in Northern China

Emission characteristics including congener's profile, gas emissions and toxic equivalent concentration (TEQ) indicators of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in 57 stack gas samples from 6 municipal solid waste incinerators (MSWIs) in Northern China were investigated by gas chromatography-high resolution mass spectrometry (HRGC-HRMS). Additionally, PCDD/Fs formation mechanisms from the MSWIs were briefly discussed. Results revealed that the concentrations and equivalent concentrations of PCDD/Fs emissions in stack gas from 6 MSWIs were in the range of 0.11-2.53 ng Nm^-3 and 0.007-0.059 ng TEQ Nm^-3, respectively. The emission factors of PCDD/Fs from 6 MSWIs varied from 0.027 to 0.225 μg I-TEQ tonne^-1, with a mean value of 0.17 μg I-TEQ tonne^-1 waste, which was estimated to an annual emission of 234.96 mg I-TEQ of PCDD/Fs from 6 MSWIs to the atmosphere. O8CDD, O8CDF and 1,2,3,4,6,7,8-H7CDD were the indicatory compounds of PCDD/Fs to apportion the sources of PCDD/Fs in environmental medium especially in ambient environment of MSWIs. 1,2,3,7,8,9-H6CDF and 1,2,3,4,7,8-H6CDF can be used as TEQ indicators for monitoring PCDD/Fs emission. Based on the positive matrix factorization (PMF) model, eight factors were extracted by the PMF analysis. Formation of low-chlorinated PCDDs (1,2,3,7,8-P5CDD, 1,2,3,4,7,8-H6CDD, 1,2,3,6,7,8-H6CDD and 1,2,3,7,8,9-H6CDD) possessed strong correlation, and the chlorophenols maybe the important precursors of low-chlorinated PCDDs, which were generated within the low chlorinated content. Penta- and hexa-PCDFs formation in stack gas from MSWI may block catalytic sites for PCDFs formation from carbon. Meanwhile, possible formation mechanisms of high-chlorinated PCDDs (hepta- and octa-PCDDs) and high-chlorinated PCDFs (hepta- and octa-PCDFs) were respectively dependent.

Evaluating the effect of rain on the fate of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) accumulated in polluted trees in Amman, Jordan

Open combustion of solid waste is one of the main sources of the emission of dioxin and dioxin-like compounds (DLCs). Ambient dioxin will eventually undergo depositions on soils and tree leaves. Pine trees have shown an ability to store dioxin in their needles allowing biomonitoring of dioxin atmospheric concentrations. Infiltration can transport dioxin to greater depths into the ground, on one hand, while vaporization can allow dioxin to return back to the atmosphere on the other. Several studies evaluated the migration of dioxin between two compartments; however, few studies have attempted to understand the fate of non-conservative PCDDs and PCDFs in an unsteady state system of more than two mediums. This study focused on the transportation of dioxin between polluted trees and the underlying soil through the effect of rain water. For approximately 10 years, pine trees in this study have been exposed to emissions generated by the open combustion of municipal solid waste (MSW) from a fixed location. Soil samples located further from the point source had generally lower dioxin concentrations. Dioxin concentrations were correlated to distance from the source using least square regression. Soil samples below contaminated trees had dioxin concentrations 10-35% greater than the calculated measurements for the same spots using the regression model. By detecting these spikes in concentrations, it was possible to identify pools of dioxin found directly under the contaminated trees-indicating a rinsing effect of rain water on the stored dioxin on the trees' needles.

The fingerprint nature of PCDD in iron ore sinter strand emissions, the effect of suppressants and alternative fuels, and the potential for comparison with the isomer profile of PCDF

It has been previously shown that the isomer profile of PCDF emissions from iron ore sinter plant only varies within limits even when suppressants or alternative fuels are added, to the extent that it can be said to have a 'fingerprint'. The isomer profiles of PCDD from tetra- to hexacholrodibenzo-p-dioxin from the same samples examined for PCDF emissions have been obtained, and show the same tendency for a 'fingerprint ' isomer distribution to occur. Occasional exceptionally high isomer abundances are observed, but these are uncommon. The potential for comparison of the abundances of PCDF and PCDD isomers with similar chlorination patterns to determine whether the same formation process is involved has been examined. It is found that co-elutions prevent extensive comparisons irrespective of whether the SP2331 or DB5ms column is used in the analyses for separation of isomers to provide the results used for comparisons, although they allow limited results to be obtained. It is suggested that analyses using the two chromatography columns to analyse the same sample in parallel could provide more resolution of the isomer profiles for use in comparisons. A pilot study using samples analysed using each column is limited because of detailed differences in the emissions profiles, but demonstrates that greater resolution is possible if the two columns are used to analyse one sample.

Thermochemical formation of polychlorinated dibenzo-p-dioxins and dibenzofurans on the fly ash matrix from metal smelting sources

Metal smelting processes are important sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The present work aims to clarify the formation characteristics of PCDD/Fs by heterogeneous mechanisms on fly ash from typical multiple secondary aluminum (SAl), secondary lead (SPb) smelting, and iron ore sintering (SNT) sources in China. The formation characteristics of PCDD/Fs on fly ash were studied in the temperature range 250-450 °C for 10-150 min. Substantial thermochemical formation of PCDD/Fs on SAl and SNT ash was observed. The maximum increase of PCDD/F concentrations under 350 °C for 30 min was 604 times greater than the initial concentration in SAl ash. The concentration of PCDD/Fs was 77 times greater than that of SNT fly ash under 350 °C for 30 min. However, the maximum increase of PCDD/F concentrations was less than 8 times that in raw SPb ash under 350 °C. Contents of total organic carbon (TOC), Cu, Al, Zn and Cl, which are widely recognized as important elements for promoting PCDD/F formation, were obviously higher in SAl and SNT ash than in SPb ash. This may explain the greater observed formation times of PCDD/Fs on SAl and SNT ash than that on SPb ash. It was found that several congeners tended to form at higher temperatures than those for SAl ash. Activation energy calculation according to the Arrhenius equations could explain the dominant formation of those congeners at much higher temperatures on SAl ash.

Comparative analyses of catalytic degradation of PCDD/Fs in the laboratory vs. industrial conditions

This study investigates the efficiencies and mechanisms of the catalytic degradation of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) first, in simulated laboratory conditions and then, in a commercial municipal solid waste incineration (MSWI) plant. Five commercially available V₂O₅-WO₃/TiO₂ (VWTi) catalysts were tested. The degradation efficiency of PCDD/Fs in the simulated flue gas ranged 22.8-91.7% and was generally higher than that in the MSWI flue gas of 8.0-85.4%. The degradation efficiency of PCDD/Fs in the real flue gas of the MSWI plant was largely hindered by the complex composition of the flue gas, which could not be completely reproduced in the simulated laboratory conditions. Furthermore, the degradation of the higher chlorinated PCDD/Fs was easier compared to the lower chlorinated ones in the presence of the VWTi catalysts, which was primarily driven by the tendency of the higher chlorinated PCDD/Fs to be adsorbed on the surface of the catalyst and further destructed due to their lower vapor pressure. In addition, powdered catalysts should be preferred over the honeycomb shaped ones as they exposed higher PCDD/Fs degradation efficiencies under equal reaction conditions. The chemical composition and a range of the relevant to the study properties of the catalysts, such as surface area, crystallinity, oxidation ability, and surface acidity, were analyzed. The study ultimately supports the identification of the preferred characteristics of the VWTi catalysts for the most efficient degradation of toxic PCDD/Fs and elucidates the corresponding deactivation reasons of the catalysts.

Source contributions to total concentrations and carcinogenic potencies of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in ambient air: a case study in Suzhou City, China

The potential source categories and source contributions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in ambient air from Suzhou City, China, were performed by principal component analysis-multiple linear regression (PCA-MLR) and positive matrix factorization (PMF). The carcinogenic potencies of PCDD/Fs were quantitatively apportioned based on the positive matrix factorization-toxic equivalent concentration (PMF-TEQ) method. The results of the present study were summarized as follows. (1) The total concentrations and toxic equivalent concentrations of PCDD/Fs (∑PCDD/Fs and TEQ) in ambient air from Suzhou City were 1.34-42.80 pg N m^-3 and 0.081-1.22 pg I-TEQ N m^-3, respectively. (2) PCA-MLR suggested that industrial combustion (IC), electric arc furnaces (EAFs) and secondary aluminum smelters (ALSs), unleaded gas-fueled vehicle sources (UGFVs), ALSs, and hazardous solid waste incinerators (HSWIs) could be the primary PCDD/F contributors, accounting for 13.2, 16.7, 35.5, 19.4, and 15.2% of ∑PCDD/Fs, respectively. (3) PMF and PMF-TEQ indicated that EAFs (carbon steel), UGFVs, IC, ALSs, municipal solid waste incinerators (MSWIs) and hospital waste incinerators (HWIs), and HSWIs contributed 10.9, 10.9, 42.8, 11.3, 10.7, and 13.4% to ∑PCDD/Fs, but contributed 8.3, 12.3, 50.3, 12.7, 6.0, and 10.4% to carcinogenic potencies of PCDD/Fs. This study was the first attempt to quantitatively apportion the source-specific carcinogenic potencies of PCDD/Fs in ambient air.

Dioxins degradation and reformation during mechanochemical treatment

Mechanochemical dechlorination and destruction of polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) on fly ash from Municipal Solid Waste Incineration was tested with and without additives (CaO and CaO/aluminium powder). The first results disappointed because of obvious PCDD/F-reformation and a second test series was conducted after removing soluble salts (NaCl, KCl …) by thorough two-stage water washing. This second test series was successful and demonstrated good destruction results, especially with combined CaO/aluminium powder as additive. In a third test series salt was again added to the water-washed fly ash, and the first, poor results were largely reconstituted. For all tests a fairly complete (94 out of 136 congeners) isomer-specific analysis was conducted and analysed, allowing to differentiate between, e.g., 2,3,7,8-substituted PCDD/F and congeners formed following the chlorophenol route. The first became more important in the samples series Fly Ash, Milled Fly Ash, milling with added CaO, and milling with CaO/aluminium-addition. The second follow the opposite trend. This isomer-specific analysis will form the basis for further study using Principal Component Analysis.

A full-scale study on thermal degradation of polychlorinated dibenzo- p-dioxins and dibenzofurans in municipal solid waste incinerator fly ash and its secondary air pollution control in China

Degradation of polychlorinated dibenzo- p-dioxins and dibenzofurans in municipal solid waste incinerator fly ash is beneficial to its risk control. Fly ash was treated in a full-scale thermal degradation system (capacity 1 t d^-1) to remove polychlorinated dibenzo- p-dioxins and dibenzofurans. Apart from the confirmation of the polychlorinated dibenzo- p-dioxin and dibenzofuran decomposition efficiency, we focused on two major issues that are the major obstacles for commercialising this decomposition technology in China, desorption and regeneration of dioxins and control of secondary air pollution. The toxic equivalent quantity values of polychlorinated dibenzo- p-dioxins and dibenzofurans decreased to <6 ng kg^-1 and the detoxification rate was ⩾97% after treatment for 1 h at 400 °C under oxygen-deficient conditions. About 8.49% of the polychlorinated dibenzo- p-dioxins and dibenzofurans in toxic equivalent quantity (TEQ) of the original fly ash were desorbed or regenerated. The extreme high polychlorinated dibenzo- p-dioxin and dibenzofuran levels and dibenzo- p-dioxin and dibenzofuran congener profiles in the dust of the flue gas showed that desorption was the main reason, rather than de novo synthesis of polychlorinated dibenzo- p-dioxins and dibenzofurans in the exhaust pipe. Degradation furnace flue gas was introduced to the municipal solid waste incinerator economiser, and then co-processed in the air pollution control system. The degradation furnace released relatively large amounts of cadmium, lead and polychlorinated dibenzo- p-dioxins and dibenzofurans compared with the municipal solid waste incinerator, but the amounts emitted to the atmosphere did not exceed the Chinese national emission limits. Thermal degradation can therefore be used as a polychlorinated dibenzo- p-dioxin and dibenzofuran abatement method for municipal solid waste incinerator source in China.

Field study and theoretical evidence for the profiles and underlying mechanisms of PCDD/F formation in cement kilns co-incinerating municipal solid waste and sewage sludge

A field study and theoretical calculations on the profile and formation mechanism of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from two cement kilns co-incinerating municipal solid waste and sewage sludge were performed, and the PCDFs were mainly focused. The back-end areas of the cement kilns were identified to be the major sites of PCDD/F formation according to their distributions in particulate samples from different process stages. The proportions of tetra- to hexa-chlorinated dibenzofurans (∑Cl_4-6CDFs) at the kiln back-end areas were in the range of 50-80% of the total PCDD/Fs in mass concentrations and 62-87% in toxic equivalent concentrations. These results indicated that ∑Cl_4-6CDFs are the dominant homologs that should be the focus for reducing PCDD/F emissions in cement kilns that co-incinerate municipal solid waste and sewage sludge. It is speculated that the low contents of oxygen and copper compounds, as well as the alkaline conditions, may contribute to the dominance of ∑Cl_4-6CDFs in the PCDD/Fs formed. Chlorination was assumed to be the mechanism of formation of PCDFs. The results from model predictions and thermodynamic calculations used to test this assumption were consistent with the PCDF profiles observed from the field study.

The OH-initiated atmospheric chemical reactions of polyfluorinated dibenzofurans and polychlorinated dibenzofurans: A comparative theoretical study

The atmospheric chemical reactions of some polyfluorinated dibenzofurans (PFDFs) and polychlorinated dibenzofurans (PCDFs), initiated by OH radical, were investigated by performing theoretical calculations using density functional theory (DFT) and B3LYP/6-311++G(2df,p) method. The obtained results indicate that OH addition reactions of PFDFs and PCDFs occurring at C_1∼4 and C_A sites are thermodynamic spontaneous changes and the branching ratio of the PF(C)DF-OH adducts is decided primarily by kinetic factor. The OH addition reactions of PFDFs taking place at fluorinated C_1∼4 positions are kinetically comparable with those occurring at nonfluorinated C_1∼4 positions, while OH addition reactions of PCDFs occurring at chlorinated C_1∼4 sites are negligible. The total rate constants of the addition reactions of PFDFs or PCDFs become smaller with consecutive fluorination or chlorination, and substituting at C₁ position has more adverse effects than substitution at other sites. The succedent O₂ addition reactions of PF(C)DF-OH adducts are thermodynamic nonspontaneous processes under the atmospheric conditions, and have high Gibbs free energies of activation (Δ_rG^≠). The substituted dibenzofuranols are the primary oxidation products for PCDFs under the atmospheric conditions. However, other oxidative products may also be available for PFDFs besides substituted dibenzofuranols.

The rate-determining step in a low temperature PCDD/F formation from oxidative breakdown of native carbon in MSWI fly ash

We developed a phenomenological approach to explain the kinetic experimental data of PCDD/F formation/destruction based on a reaction mechanism model at the congener group level. In the present work, we investigated the formation and destruction of PCDD/F on fly ash as a function of time at 280 °C, chlorine mass balance, evolution of the total equivalent toxicity and kinetic modelling. We determined that the volatilization process is negligible and that the reactive processes at short reaction times only become important above 300 °C. The results provide a substantial improvement on existing studies. We experimentally demonstrated, for the first time, that there is a correlation between the oxidative breakdown of native carbon and PCDD/F de novo synthesis. Data processing by our kinetic model showed that the formation of oxygen complexes C(O) was the determining step for de novo synthesis of PCDD/F. Indeed, the calculated reaction time at which the PCDD/F concentration was at a maximum (850 min) was greater than that calculated for the oxygen complexes C(O) (435 min). Moreover, the experimental carbon conversion efficiency for PCDD/F production (0.0032% at 600 min maximum) was in a very good agreement with the theoretical conversion (0.0041%).

Suppression of PCDD/Fs during thermal desorption of PCBs-contaminated soil

Thermal treatment of polychlorinated biphenyls (PCBs) contaminated soil was shown in earlier work to generate new PCBs, as well as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). In this study, this thermal desorption was conducted with addition of three distinct inhibitors, including ammonium sulphate, urea and calcium oxide, to inhibit the formation of PCDDs and PCDFs when remediating PCBs-contaminated soil. Experiments were conducted for 40 min at 400 °C after adding 1 wt.% of inhibitor. Both the total PCDD/Fs and international toxic equivalent quantity (I-TEQ) reduced when inhibitors were introduced. Of the three compounds tested, CaO shows the highest inhibition efficiency, 92.2 % for total PCDD/Fs and 95.6 % for I-TEQ. The amount of CaO added also influences the suppression efficiency of PCDD/Fs. These results suggest that promoting desorption and destruction of precursors is probably the mechanism of suppression.

Concentrations and patterns of polychlorinated biphenyls at different process stages of cement kilns co-processing waste incinerator fly ash

Cement kilns can be used to co-process fly ash from municipal solid waste incinerators. However, this might increase emission of organic pollutants like polychlorinated biphenyls (PCBs). Knowledge of PCB concentrations and homolog and congener patterns at different stages in this process could be used to assess the possibility of simultaneously controlling emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and "dioxin-like" compounds. To date, emissions from cement kilns co-processing fly ash from municipal solid waste incinerators have not been analyzed for PCBs. In this study, stack gas and particulate samples from two cement kilns co-processing waste incinerator fly ash were analyzed for PCBs. The average total tri- to deca-chlorinated biphenyl (∑_3-10PCB) concentration in the stack gas samples was 10.15ngm^-3. The ∑_3-10PCB concentration ranges in particulate samples from different stages were 0.83-41.79ngg^-1 for cement kiln 1and0.13-1.69ngg^-1 for cement kiln 2. The ∑_3-10PCB concentrations were much higher in particulate samples from the suspension pre-heater boiler, humidifier tower, and kiln back-end bag filters than in particulate samples from other stages. For these three stages, PCBs contributed to 15-18% of the total PCB, PCDD/F, and polychlorinated naphthalene toxic equivalents in stack gases and particulate matter. The PCB distributions were similar to those found in other studies for PCDD/Fs and polychlorinated naphthalenes, which suggest that it may be possible to simultaneously control emissions of multiple organic pollutants from cement kilns. Homolog patterns in the particulate samples were dominated by the pentachlorobiphenyls. CB-105, CB-118, and CB-123 were the dominant dioxin-like PCB congeners that formed at the back-end of the cement kiln. A mass balance of PCBs in the cement kilns indicated that the total mass of PCBs in the stack gases and clinker was about half the mass of PCBs in the raw materials.

Theoretical and experimental formation of low chlorinated dibenzo-p-dioxins and dibenzofurans in the Fenton oxidation of chlorophenol solutions

The formation of chlorinated and non-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) has been experimentally investigated after the Fenton oxidation of 2-chlorophenol (2-CP, 15.56 mM) aqueous solutions by assessing the influence of iron concentration (0.09-2.88 mM), hydrogen peroxide dose (40.44-202.20 mM), temperature (20-70 °C) and chloride concentration (0-56.35 mM). The presence of chloride in the medium together with room temperature and substoichiometric Fenton conditions (40.44 mM H2O2) led to an increase in total PCDD/Fs concentration from less than 1 ng L(-1) to 2 μg L(-1). Results showed a dominance of the dichlorinated species (DCDD/Fs) in the homologue profile of total PCDD/Fs reaching values up to 1.5 μg L(-1). Furthermore, the products distribution exhibited a gradual decrease in the homologue concentration as the chlorination degree increased from di-to octachloro-substituted positions. Considering the characteristics of the reaction medium, the experimental results, and the information gathered in bibliography with regard to the generation of active radicals from 2-chlorophenol, a mechanism describing the formation of low chlorinated PCDD/Fs in a Fenton oxidizing aqueous system has been proposed.

Catalytic decomposition of gaseous PCDD/Fs over V2O5/TiO2-CNTs catalyst: Effect of NO and NH3 addition

There is a strong need for a control technology that simultaneously achieving the abatement of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) and nitrogen oxides (NOx) emissions in waste incineration industry. TiO2 and carbon nanotubes (CNTs) were used as composite carriers to support vanadium oxide as an innovative catalyst to simultaneously control PCDD/Fs and NO emissions. The removal efficiencies (RE) of PCDD/Fs by V2O5/TiO2-CNTs catalyst under a space velocity (SV) of 20,000 h(-1) reaches 99.9% at 150 °C and adsorption is supposed to be the main mechanism at this temperature. The influence of NONH3 reaction on PCDD/Fs catalytic reaction is investigated. The kinetics analysis exhibits that the addition of NO and NH3 reduces the activation energies for OCDD (octachlorodibenzo-p-dioxin) and OCDF (octachlorodibenzofuran) decomposition to 3.6 kJ/mol and 5.4 kJ/mol respectively.

Catalytic destruction of PCDD/Fs over vanadium oxide-based catalysts

Vanadium oxide-based catalysts were developed for the destruction of vapour phase PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans). A vapour phase PCDD/Fs generating system was designed to supply stable PCDD/Fs steam with initial concentration of 3.2 ng I-TEQ Nm(-3). Two kinds of titania (nano-TiO2 and conventional TiO2) and alumina were used as catalyst supports. For vanadium-based catalysts supported on nano-TiO2, catalyst activity is enhanced with operating temperature increasing from 160 to 300 °C and then reduces with temperature rising further to 350 °C. It is mainly due to the fact that high volatility of organic compounds at 350 °C suppresses adsorption of PCDD/Fs on catalysts surface and then further inhibits the reaction between catalyst and PCDD/Fs. The optimum loading of vanadium on nano-TiO2 support is 5 wt.% where vanadium oxide presents highly dispersed amorphous state according to the Raman spectra and XRD patterns. Excessive vanadium will block the pore space and form microcrystalline V2O5 on the support surface. At the vanadium loading of 5 wt.%, nano-TiO2-supported catalyst performs best on PCDD/Fs destruction compared to Al2O3 and conventional TiO2. Chemical states of vanadium in the fresh, used and reoxidized VOx(5 %)/TiO2 catalysts at different operating temperature are also analysed by XPS.

Development of new transition metal oxide catalysts for the destruction of PCDD/Fs

Various transition metal oxide and vanadium-containing multi-metallic oxide catalysts were developed for the destruction of PCDD/Fs (polychlorinated dibenzo-p-dioxins and furans). A stable PCDD/Fs generating system was installed to support the catalytic destruction tests in this study. Nano-titania supported vanadium catalyst (VOx/TiO2) showed the highest activity, followed by CeOx, MnOx, WOx and finally MoOx. Multi-metallic oxide catalysts, prepared by doping WOx, MoOx, MnOx and CeOx into VOx/TiO2 catalysts, showed different activities on the decomposition of PCDD/Fs. The highest destruction efficiency of 92.5% was observed from the destruction test over VOxCeOx/TiO2 catalyst. However, the addition of WOx and MoOx even played a negative role in multi-metallic VOx/TiO2 catalysts. Characterizations of transition metal oxides and multi-metallic VOx/TiO2 catalysts were also investigated with XRD and TPR. After the catalysts were used, the conversion from high valent metals to low valence states was observed by XPS.

Bioremediation of polychlorinated-p-dioxins/dibenzofurans contaminated soil using simulated compost-amended landfill reactors under hypoxic conditions

Compost-amended landfill reactors were developed to reduce polychlorinated-p-dioxins and dibenzofurans (PCDD/Fs) in contaminated soils. By periodically recirculating leachate and suppling oxygen, the online monitoring of the oxidation reduction potential confirmed that the reactors were maintained under hypoxic conditions, with redox levels constantly fluctuating between -400 and +80mV. The subsequent reactor operation demonstrated that PCDD/F degradation in soil could be facilitated by amending compost originating from the cow manure and waste sludge and that the degradation might be affected by the availability of easily degradable substrates in the soil and compost. The pyrosequencing analysis of V4/V5 regions of bacterial 16S rRNA genes suggested that species richness of the soil microbial community was increased by a factor of 1.37-1.61. Although the bacterial community varied with the compost origin and changed markedly during reactor operation, it was dominated by Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, and Firmicutes. The aerotolerant anaerobic Sedimentibacter and Propionibacterium spp., and the uncultured Chloroflexi group could be temporarily induced to a high abundance by amending the cow manure compost; the bacterial growths were associated with the rapid degradation of PCDD/Fs. Overall, the novel bioremediation method for PCDD/F-contaminated soils using hypoxic conditions was effective, simple, energy saving, and thus easily practicable.

The polychlorinated dibenzofuran fingerprint of iron ore sinter plant: Its persistence with suppressant and alternative fuel addition

An earlier demonstration that the relative concentrations of isomers of polychlorinated dibenzofuran do not vary as the flamefront of an iron ore sinter plant progresses through the bed, and profiles are similar for two sinter strands has been widened to include studies of the similarity or otherwise between full scale strand and sinter pot profiles, effect of addition of suppressants and of coke fuel substitution with other combustible materials. For dioxin suppressant addition, a study of the whole of the tetra- penta- and hexaCDF isomer range as separated by the DB5MS chromatography column, indicates no significant change in profile: examination of the ratios of the targeted penta- and hexaCDF isomers suggests the profile is similarly unaffected by coke fuel replacement. Addition of KCl at varied levels has also been shown to have no effect on the 'fingerprint' and there is no indication of any effect by the composition of the sinter mix. The recently published full elution sequence for the DB5MS column is applied to the results obtained using this column. It is confirmed that isomers with 1,9-substitution of chlorine atoms are invariably formed in low concentrations. This is consistent with strong interaction between the 1 and 9 substituted chlorine atoms predicted by DFT thermodynamic calculations. Non-1,9-substituted PCDF equilibrium isomer distributions based on DFT-derived thermodynamic data differ considerably from stack gas distributions obtained using SP2331 column separation. A brief preliminary study indicates the same conclusions (apart from the 1,9-interaction effect) hold for the much smaller content of PCDD.

Identification, Quantification, and Toxicity of PCDDs and PCDFs in Soils from Industrial Areas in the Central and Eastern Regions of Saudi Arabia

This study was conducted to identify and quantify polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in soil samples collected from selected industrial areas in the central and eastern regions of Saudi Arabia. All the investigated compounds of PCDDs/PCDFs were identified in the studied locations. The average concentrations of PCDDs (sum of seven congeners measured) ranged from 11.5 to 59.6 pg g(-1), with a maximum concentration of 125.7 pg g(-1) at an oil refinery station followed by 100.9 pg g(-1) at a cement factory. The average concentrations of PCDFs (sum of 10 congeners measured) accounted for 11.68-19.35 pg g(-1), with a maximum concentration of 38.67 pg g(-1) at the cement factory. It was generally observed that the soil samples collected from industrial areas have substantially high toxicity equivalence (TEQ) values of PCDDs/PCDFs compared to soils of remote areas. Principal component analysis revealed that the cement factories and oil refineries were the primary sources of PCDDs and PCDFs.

Mechanistic evaluation of polychlorinated dibenzo-p-dioxin, dibenzofuran and naphthalene isomer fingerprints in microwave pyrolysis of biomass

Isomer distribution patterns of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs) were investigated in microwave-assisted pyrolysis (MAP) products of woody biomass. The feedstocks included bark and impregnated wood. The results indicated that isomer distributions in MAP are more selective compared to those reported from wood burning and waste incineration. Favored formation of 4-MoCDF and highly selective chlorine substitution at the 2,4-position observed during MAP suggested a preferred formation pathway of PCDFs involving (chloro)phenol precursors followed by subsequent chlorination. The PCDD distribution was dominated by isomers typically formed from chlorophenol condensation at relatively low temperature. The PCN isomer distributions showed a tendency for sequential chlorination from non-substituted naphthalene at successive positions. The presence of isomers such as 1-MoCDD, 4-MoCDF, 1,2,3-TriCN with low thermodynamic stability indicates that kinetic factors may be important in the MAP process.

PCDD/F and PCB water column partitioning examination using natural organic matter and black carbon partition coefficient models

A 9-year water dataset from the Houston Ship Channel (HSC) was analyzed to understand partitioning in polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs). Total PCBs had more mass as dissolved (74%) whereas total PCDD/Fs did not (11%). Generally, the limited number of PCDD/Fs (only 2378 substituted) explained these differences though differences in chemical behavior beyond log K ow also likely influence partitioning. The particular fractionation seen in the HSC also seemed related to a wide variation in particulate organic carbon (POC)/dissolved organic carbon (DOC) ratio (0.42-180%). Published and unaltered linear free energy and linear solvation energy relationships for DOC, POC, and particulate black carbon (BC) resulted in predictions that were at best 27% (PCB) and 25% root-mean-square error (RMSE) (PCDD/F) partition fraction compared to observed (using estimated BC/POC fractions of 10 and 25%, respectively). These results show, at least in light of the uncertainties in this data (e.g., precise fraction of BC), that a 25% accuracy in model prediction of operationally dissolved or suspended fraction for any one PCB or PCDD/F congener is the best prediction that may be expected. It is therefore recommended that site-specific data be used to calibrate most any water column-partitioning model if it is to be expected to describe what actually occurs in field conditions.

Size fractionation of waste-to-energy boiler ash enables separation of a coarse fraction with low dioxin concentrations

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) formed in modern Waste-to-Energy plants are primarily found in the generated ashes and air pollution control residues, which are usually disposed of as hazardous waste. The objective of this study was to explore the occurrence of PCDD/F in different grain size fractions in the boiler ash, i.e. ash originating from the convection pass of the boiler. If a correlation between particle size and dioxin concentrations could be found, size fractionation of the ashes could reduce the total amount of hazardous waste. Boiler ash samples from ten sections of a boiler's convective part were collected over three sampling days, sieved into three different size fractions - <0.09 mm, 0.09-0.355 mm, and >0.355 mm - and analysed for PCDD/F. The coarse fraction (>0.355 mm) in the first sections of the horizontal convection pass appeared to be of low toxicity with respect to dioxin content. While the total mass of the coarse fraction in this boiler was relatively small, sieving could reduce the amount of ash containing toxic PCDD/F by around 0.5 kg per tonne input waste or around 15% of the collected boiler ash from the convection pass. The mid-size fraction in this study covered a wide size range (0.09-0.355 mm) and possibly a low toxicity fraction could be identified by splitting this fraction into more narrow size ranges. The ashes exhibited uniform PCDD/F homologue patterns which suggests a stable and continuous generation of PCDD/F.