Variations of PCDD/Fs emissions from secondary nonferrous smelting plants and towards to their source emission reduction

Free radical mechanisms of ammonium sulfate as intensively used industrial materials on suppressing organic pollutants

Organic free radicals are critical intermediates for the generation and inhibition of organic pollutants during industrial processes. Clarifying the free radical mechanism of pollutant inhibition is significant for their efficient control. Ammonium sulfate is intensively used in industrial materials to suppress organic pollutants. In this study, organic free radical intermediate species in metal-catalyzed reactions inhibited by ammonium sulfate were identified using continuous-wave electron paramagnetic resonance (EPR) spectroscopy, providing direct evidence for the free radical mechanisms of organic pollutants inhibition. The transverse (T2) and longitudinal (T1) relaxation time variations catalyzed by different metal catalysts in the presence of ammonium sulfate were compared using pulsed-wave EPR. Consequently, after the addition of ammonium sulfate, the observed increase in T2 suggests that ammonium sulfate leads to radical concentration reduction. A decrease in the T1 relaxation time suggests the enhanced interaction between organic radicals and metals, which is an obstacle to subsequent radical reactions. Therefore, ammonium sulfate dominantly changed the free radical intermediates species, concentrations, and their reactivity, and then inhibited the organic pollutants formations. The inhibition mechanisms of ammonium sulfate on metal-catalyzed pollutants were then proposed combining EPR analysis, X-ray characterization, and high-resolution mass spectrometry screening. As a result, (1) occupying the active sites of metal catalysis and (2) inhibiting free radical intermediates are the two main intrinsic inhibition mechanisms of ammonium sulfate. The findings provide new perspectives on the efficient inhibition of organic pollutants in industrial processes involving various metal catalysts.

Unintentional persistent organic pollutants in cremation process: Emissions, characteristics, and inventory

Pollutants produced by cremation furnaces have gradually caused concern because of the increasing rate of cremation around the world. In this study, the levels, patterns, and emission factors of unintentional persistent organic pollutants (UPOPs) from cremation were investigated. The toxic equivalent (TEQ) concentrations (11 % O2 normalized) of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in flue gas ranged from 0.036 to 22 ng TEQ/Nm3, while the levels of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) in flue gas samples ranged from 0.0023 to 1.2 ng TEQ/Nm3 and 0.17-44 pg TEQ/Nm3, respectively. The average concentrations of UPOPs in flue gas from car-type furnaces were higher than those from flat-panel furnaces. Secondary chambers and air pollution control devices were effective for controlling UPOPs emissions. However, heat exchangers were not as effective for reducing UPOPs emissions. It was observed that the UPOPs profiles exhibited dissimilarities between fly ash and flue gas samples. HxCDF, OCDD, and PeCDF were the dominant homologs of PCDD/Fs in flue gas, while HxCDF, PeCDF, and HpCDF were the dominant homologs in fly ash. The fractions of MoCBs and MoCNs in fly ash were higher than those in flue gas. Finally, we conducted an assessment of the global emissions of UPOPs from cremation in the years of 2019 and 2021. The total emission of UPOPs in 47 countries was estimated at 239 g TEQ in 2021, which was during the peak period of the COVID-19 pandemic worldwide. The emissions in 2021 increased by approximately 24 % compared to 2019, with the impact of COVID-19 being a significant factor that cannot be disregarded.

Health assessment of emerging persistent organic pollutants (POPs) in PM2.5 in northern and central Taiwan

Over the last two decades, Taiwan has effectively diminished atmospheric concentrations of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) through the adept utilization of advanced technologies and the implementation of air pollution control devices. Despite this success, there exists a dearth of data regarding the levels of other PM2.5-bound organic pollutants and their associated health risks. To address this gap, our study comprehensively investigates the spatial and seasonal variations, potential sources, and health risks of PCDD/Fs, Polychlorinated biphenyls (PCBs), and Polychlorinated naphthalene (PCNs) in Northern and Central Taiwan. Sampling collections were conducted at three specific locations, including six municipal waste incinerators in Northern Taiwan, as well as a traffic and an industrial site in Central Taiwan. As a result, the highest mean values of PM2.5 (20.3-39.6 μg/m3) were observed at traffic sites, followed by industrial sites (14.4-39.3 μg/m3), and the vicinity of the municipal waste incinerator (12.4-29.4 μg/m3). Additionally, PCDD/Fs and PCBs exhibited discernible seasonal fluctuations, displaying higher concentrations in winter (7.53-11.9 and 0.09-0.12 fg I-TEQWHO/m3) and spring (7.02-13.7 and 0.11-0.16 fg I-TEQWHO/m3) compared to summer and autumn. Conversely, PCNs displayed no significant seasonal variations, with peak values observed in winter (0.05-0.10 fg I-TEQWHO/m3) and spring (0.03-0.08 fg I-TEQWHO/m3). Utilizing a Positive Matrix Factorization (PMF) model, sintering plants emerged as the predominant contributors to PCDD/Fs, constituting 77.9% of emissions. Woodchip boilers (68.3%) and municipal waste incinerators (21.0%) were identified as primary contributors to PCBs, while municipal waste incinerators (64.6%) along with a secondary copper and a copper sludge smelter (22.1%) were the principal sources of PCNs. Moreover, the study specified that individuals aged 19-70 in Northern Taiwan and those under the age of 12 years in Central Taiwan were found to have a significantly higher cancer risk, with values ranging from 9.26 x 10-9-1.12 x 10-7 and from 2.50 x 10-8-2.08 x 10-7respectively.

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.

Variation in the formation characteristics of PBDD/F, brominated PAH, and PBDE congeners along the secondary copper smelting processes

Simultaneous determination of 58 congeners of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), brominated polycyclic aromatic hydrocarbons (Br-PAHs), and polybrominated diphenyl ethers (PBDEs) from multiple stages of industrial-scale secondary copper smelting plants was conducted with the aim of understanding their variations and control. In addition to the historical manufacture of PBDEs as brominated flame retardants, this study confirmed that PBDEs can be unintentionally produced and released from the secondary copper industry. The average mass emission factors of PBDD/Fs, PBDEs, and Br-PAHs from different sources were 10.0, 5.21 × 10³, and 7.24 × 10³ μg t^-1, respectively. Therefore, the emission of brominated persistent organic pollutants (POPs) in the secondary copper industry should be of concern. The concentration of brominated POPs increased from the gas cooling stage to stack outlet due to the possible "memory effect" and the regenerated POPs were mainly low-brominated homologs. A comparison of brominated POPs with corresponding chlorinated analogs in the same process indicated that the formation pathway of Br-PAHs was consistent with that of chlorinated PAHs. However, unlike chlorinated dioxins and furans, PBDD/Fs can also be formed from PBDEs as precursors, leading to obvious increases in highly brominated furans. Therefore, inhibiting the unintentional formation of PBDEs is important for controlling brominated POPs emissions.

Investigation on Pollution Control Device (PCD) in iron foundry industry to reduce environmental chemicals

Right from the olden days, many products have been made according to foundry practices in order to generate prosperity in the societies in which they operate while reaping these types of benefits through the operation of foundries. It is alarming that the emissions released by foundries affect human health. Therefore, foundries installed Pollution Control devices (PCDs), in accordance with this development; researchers examined the effectiveness of these PCDs in controlling emissions from foundries in different parts of the world. The emission control obtained by installing these PCDs is explained in this article based on the data gathered from the survey. The cartridge filter equipped with an induction furnace reduced the concentration of SPM to less than 20 mg/Nm³. This result of the investigation indicates that the cartridge filter built into the induction furnace achieves the best efficiency in controlling contaminants from iron foundries. Interestingly, the operation of the cartridge filter has yet to be documented. Therefore, the construction operation, the performance of the cartridge filter, and its efficiency in achieving contaminations control in foundries are described. This will provide useful information on the use of cartridge filters in an induction furnace to reduce Iron foundry emissions.

Reduction of environmental chemicals, toxicity and particulate matter in wet scrubber device to achieve zero emissions

The fine particles generated by the foundry industry are present in the atmosphere; they have an impact on the climate because of their influence on atmospheric radioactive phenomena. As a result of this scenario, there is a rising amount of legislation restricting the emission of pollutants from foundry industries and related businesses. In response to this situation, many researchers have concentrated on end-of-pipe technologies, one of which is the wet scrubber, which is a device that is primarily used in foundries to control pollution and is one of the devices that has been incorporated. The disadvantage of using this wet scrubber, on the other hand, is that it contributes to secondary pollution when it is used. In order to combat secondary pollution, a model of an enhanced wet scrubber system that incorporates a multi-sand filtering technology was developed. The performance of this redesigned wet scrubber system was evaluated with the use of computational fluid dynamics (CFD) software. In CFD, the Reynolds stress model was applied for simulation. The pressure magnitudes and velocity magnitudes are obtained by this simulation. The volume fraction of the dust was evaluated through the DPM approach. Because of the introduction of the filtration tank's computation, it was discovered that successful filtration was accomplished using sand filters, meaning that environmental chemicals and particles were totally filtered from 0.17 kg at the entrance to zero kg of particles at the outflow.

Profiles, spatial distributions and inventory of brominated dioxin and furan emissions from secondary nonferrous smelting industries in China

Nonferrous metallurgical processes are important sources of carcinogenic polybrominated dibenzo-p-dioxin and dibenzofuran (PBDD/Fs) that transport globally. Studies on the profiles, spatial distributions and inventory of PBDD/F emissions into the atmosphere from nonferrous metallurgical plants are needed for better source control. In this study, field investigations on PBDD/F emissions from typical nonferrous metallurgical plants were conducted to characterize the PBDD/F profiles and derive their emission factors. Based on the PBDD/F profiles, diagnostic ratios of PBDD/Fs for secondary copper, zinc and lead smelting were proposed for identifying the potential sources of PBDD/Fs in environment. The PBDD/F emission factors for the secondary copper, lead, and zinc smelting plants were 0.71, 1.65, and 1.54 μg toxic equivalents/t, respectively. The estimated annual input of PBDD/Fs into atmosphere by secondary nonferrous metallurgical plants in China was 212.4 g by mass and 3511.3 mg by toxic equivalents, which is of significance for further evolving a global inventory. The spatial distribution of PBDD/F emissions from nonferrous metallurgical plants in China was mapped. Larger amounts of PBDD/Fs were emitted in the southeastern coastal region and northern China than elsewhere in China.

Particle size distributions and health risks of polychlorinated dibenzo-p-dioxin/furans, polychlorinated biphenyls, and polychlorinated naphthalenes in atmospheric particles around two secondary copper smelters in Shandong Province, China

Sixteen samples of atmospheric particles in four size fractions (diameter: > 10 μm, 5-10 μm, 2.5-5 μm, and <2.5 μm) were collected around two secondary copper smelters in Shandong Province, China. The levels, particle size distributions, and potential health risks of polychlorinated dibenzo-p-dioxin/furans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), and polychlorinated naphthalenes (PCNs) in these samples were analyzed. The concentration ranges for the PCDD/Fs, dl-PCBs, and PCNs were 3.13-5.77 pg m^-3, 0.43-0.56 pg m^-3, and 4.76-9.89 pg m^-3, respectively. All of the compounds accumulated strongly in the particles with diameters of <2.5 μm. The congener profiles of PCDD/Fs in particles of various sizes were similar, and were consistent with those in stack gases from local secondary copper smelters. However, the congener profiles of dl-PCBs and PCNs in the particles with diameters of <2.5 μm differed from those for the other particle size fractions. The proportion of highly chlorinated homologs in particles with diameters of <2.5 μm was much higher than that of particles with diameters of >2.5 μm. The results of a risk assessment indicated that the contribution of PCDD/Fs to the total carcinogenic risk (PCDD/Fs + dl-PCBs + PCNs) was >95%. For the PCDD/Fs, dl-PCBs, and PCNs, 78%, 71%, and 86% of the carcinogenic risk was associated with the <2.5 μm fraction, respectively. This study improves our understanding of the particle size distributions and human health risks of exposure to PCDD/Fs, dl-PCBs, and PCNs in the atmosphere around secondary copper smelters.

Occurrence of dioxin-like POPs in soils from urban green space in a metropolis, North China: implication to human exposure

Urban green space is a special space for urban life and natural contact and has an important impact on human health. However, little information is available on dioxin-like persistent organic pollutants (POPs) in the soils from the specific areas. We measured the concentrations of polychlorinated naphthalenes (PCNs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polychlorinated biphenyls (PCBs) in the soils from urban green space in a metropolis, North China, and found total concentrations of PCDD/Fs, PCBs, and PCNs in the range of 11.5-91.4, 14.7-444, and 82.5-848 pg/g, respectively. It was worth to notice that the concentrations of PCDD/Fs in public park soil from urban center were significantly higher than those in the road greenbelts and resident lawns (Kruskal-Wallis test, p = 0.004). The source analysis indicated that sewage sludge from wastewater treatment plants were important sources of PCNs and PCDD/Fs in urban green land soils, and atmospheric deposition from municipal solid waste incinerator (MSWI) also play an important role in PCDD/F sources. The rough exposure risk evaluation showed that the residents were at a safe level with the daily doses being 0.172-3.144 fg/kg BW/day for children and 0.022-0.406 fg/kg BW/day for adult. Due to the complex and variable sources of PCDD/Fs in urban areas, dioxin-like POPs in urban green land should be given more attention to weaken human exposure.

Process tracing of PCDD/Fs from economizer to APCDs during solid waste incineration: Re-formation and transformation mechanisms

The emission of PCDD/Fs is a crucial factor for the aggravation of the Not-In-My-Back-Yard (NIMBY) syndrome, especially for the incineration plants that fail to meet the emission standard. It is well known that physicochemical processes in the boiler can notably affect the discharge of dioxins, especially under transient, non-steady conditions. However, few studies paid attention to the important operational parameters that influence PCDD/Fs formation and transformation in the boiler when an incinerator is in its daily steady operation. In this study, 36 samples were analyzed to achieve process tracing of PCDD/Fs. The concentration, congener profile and vapor/solid partitions of PCDD/Fs from the economizer to air pollution control devices (APCDs) under two typical steady conditions were investigated. Results indicated that increasing air supply aggravated the formation of PCDD/Fs, disturbed the vapor/solid partitions, and triggered a substandard emission. Quantitative structure-activity relationship (QSAR) modeling was firstly performed for the formation mechanism and orbital energy factors were identified as dominating factors. Besides, the removal rates of PCDD/Fs significantly correlated with the saturated vapor pressure and proportions of different isomers. This study is beneficial for operators to optimize relevant operational parameters of the incineration plants so as to get rid of substandard problems.

Concentrations and profiles of persistent organic pollutants unintentionally produced by secondary nonferrous metal smelters: Updated emission factors and diagnostic ratios for identifying sources

Secondary nonferrous metal smelters are important sources of unintentionally produced persistent organic pollutants (UPOPs) including polychlorinated biphenyls (PCBs), polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene. Quantifying UPOP emissions by the main sources is an important step when evaluating UPOP emissions and establishing an inventory. In this study, field investigations were performed to allow UPOP emissions and distributions in stack gases emitted by secondary nonferrous metal smelters to be compared. A total of 25 stack gas samples were collected from secondary copper smelters (SCus), secondary zinc smelters, and secondary lead smelters in China. The mean toxic equivalent concentrations (TEQs) and mass concentrations of most of the UPOPs were highest in the secondary zinc smelter stack gas samples, next highest in the SCu stack gas samples, and lowest in the secondary lead smelter stack gas samples. The mean dioxin-like PCB and polychlorinated naphthalene TEQs were ∼8.9 and ∼6.6 times higher in stack gases from a SCu equipped with an oxygen-enriched smelting furnace than in stack gases from a SCu with a converter furnace. The mean PCB-118 to PCB-123 ratios and CN-10 to CN-35 ratios varied strongly and could be used as diagnostic ratios for apportioning the sources of UPOPs in the environment. Emission factors for dioxin-like PCBs, polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene in stack gases from secondary nonferrous metal smelters were derived and updated. The results improve our understanding of UPOP emission and provide data for establishing UPOP emission inventories for secondary nonferrous metal smelters.