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| 2. |
- Duong Phan, Ngoc Chau, et al.
(författare)
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Accurate sampling of PCDD/F in high temperature flue-gas using cooled sampling probes
- 2012
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 88:7, s. 832-836
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Tidskriftsartikel (refereegranskat)abstract
- In a laboratory-scale combustion reactor, flue-gas samples were collected at two temperatures in the post-combustion zone, 700 °C and 400 °C, using two different water-cooled sampling probes. The probes were the cooled probe described in the European Standard method EN-1948:1, referred to as the original probe, and a modified probe that contained a salt/ice mixture to assist the cooling, referred to as the sub-zero probe. To determine the efficiency of the cooling probes, internal temperature measurements were recorded at 5 cm intervals inside the probes. Flue-gas samples were analyzed for polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs). Samples collected at 700 °C using the original cooling probe showed higher concentrations of PCDD/Fs compared to samples collected using the sub-zero probe. No significant differences were observed between samples collected at 400 °C. The results indicated that artifact formation of PCDD/Fs readily occurs during flue-gas sampling at high temperatures if the cooling within the probe is insufficient, as found for the original probe at 700 °C. It was also shown that this problem could be alleviated by using probes with an enhanced cooling capacity, such as the sub-zero probe.Although this may not affect samples collected for regulatory purposes in exit gases, it is of great importance for research conducted in the high-temperature region of the post-combustion zone.
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| 3. |
- Fick, Jerker, et al.
(författare)
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Contamination of surface, ground, and drinking water from pharmaceutical production
- 2009
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Ingår i: Environmental Toxicology and Chemistry. - : SETAC Journals. - 0730-7268 .- 1552-8618. ; 28:12, s. 2522-2527
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Tidskriftsartikel (refereegranskat)abstract
- Low levels of pharmaceuticals are detected in surface, ground, and drinking water worldwide. Usage and incorrect disposal have been considered the major environmental sources of these micro-contaminants. Recent publications, however, suggest that wastewater from drug production can potentially be a source of much higher concentrations in certain locations. We investigated the environmental fate of active pharmaceutical ingredients in a major production area for the global bulk-drug market. Water samples were taken from a common effluent treatment plant near Hyderabad, India, which receives process water from about 90 bulk drug manufacturers. Surface water was analyzed from the recipient stream and from two lakes that are not contaminated by the treatment plant. Water samples were also taken from wells in six nearby villages. The samples were analyzed for the presence of twelve pharmaceuticals with LC-MS/MS. All wells were determined to be contaminated with drugs. Ciprofloxacin, enoxacin, cetirizine, terbinafine and citalopram were detected at >1microg l-1 in several wells. Very high concentrations of ciprofloxacin (up to 14 mg L-1) and other pharmaceuticals (up to 2 mg L-1) were found in the effluent of the treatment plant and in the two lakes (up to 6.5 mg L-1). Thus, insufficient wastewater treatment in one of the world's largest centers for bulk drug production leads to unprecedented drug contamination of surface, ground, and drinking water. This raises serious concerns regarding the development of antibiotic resistance, and it creates a major challenge for producers and regulatory agencies to improve the situation.
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| 5. |
- Phan, Duong Ngoc Chau, 1985-, et al.
(författare)
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A link between fly ash chemistry and the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during waste incineration
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The relationship between the properties of fly ash generated during waste incineration and the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) was investigated using a laboratory incinerator and two artificial wastes that were designed to reflect regional differences in municipal solid waste composition. Flue gas and fly ash samples were collected isokinetically via a sampling port in the post-combustion zone at a flue gas temperature of 300 °C. The mineralogical properties, morphology and sub-surface composition, surface composition and elemental oxidation states of the fly ash samples were determined. The flue gas samples were analyzed for Mo-OCDDs, Mo-OCDFs, Tri-DCBs, and Di-OCNs. Orthogonal Projections to Latent Structures (OPLS) modeling was used to study the relationship between the properties of the fly ash and the post-combustion formation of polychlorinated aromatics. The presence of high levels of ash-forming elements (i.e. Na, Mg, Fe, Ti, etc…) in the waste reduced the S content of the flue gas and thereby promoted the production of Cl2 via the Deacon process. Because this process is vital for the formation of polyaromatic species, wastes with depleted levels of fly ash-building elements should be favored to minimize the release of toxic PCDDs, PCDFs, PCBs, and PCNs during incineration.
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| 6. |
- Phan, Duong Ngoc Chau, 1985-, et al.
(författare)
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Effects of regional differences in waste composition on the thermal formation of polychlorinated aromatics during incineration
- 2013
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 93:8, s. 1586-1592
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Tidskriftsartikel (refereegranskat)abstract
- Two artificial wastes (A and B) whose contents reflect regional differences in municipal solid waste composition, were used to investigate the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) during incineration. Flue gas samples were simultaneously collected at three ports in the post-combustion zone corresponding to flue gas temperatures of 400, 300, and 200 °C. The combustion of Waste B, which had a higher chlorine and metal content than Waste A, produced greater levels of highly-chlorinated homologues, as demonstrated by a higher degree of chlorination. The total concentrations of PCDDs, PCDFs, PCBs, and PCNs formed in the combustion of both wastes increased as temperature decreased along the convector. There were no significant differences in total concentrations between Waste A and Waste B combustion at specific temperatures, with exception of PCDFs at 400 °C. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) modeling, used to evaluate the data for all compound groups, suggest that during flue gas quenching at temperatures of 400 °C low-chlorinated homologues are preferentially formed in the presence of copper, which is known to be a very active catalyst for this process. At 300 and 200 °C, the formation of highly-chlorinated homologues is favored.
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| 7. |
- Phan, Duong Ngoc Chau, et al.
(författare)
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Link between fly ash properties and polychlorinated organic pollutants formed during simulated municipal solid waste incineration
- 2014
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 28:4, s. 2761-2769
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the properties of fly ash generated during waste incineration and the thermal formation of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs), was investigated on two artificial wastes using a laboratory incinerator. Fly ash particles were sampled in the post-combustion zone at approximately 300 degrees C and were characterized with the following complementary techniques: X-ray diffraction (XRD), scanning electron microscopy energy-dispersive X-ray (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Flue gas samples were collected at the same location and analyzed for Mo-OCDDs, Mo-OCDFs, Tri-DCBs, and Di-OCNs. A strong correlation between fly ash characteristics and waste composition exists for several of the elements considered in this work. For instance, the waste containing the highest levels of Al produced more abundant Al-bearing minerals and elemental Al in the resulting fly ashes. Copper, an especially important POP formation catalyst, was not detected in the top 10 nm surface of fly ash particles but rather occurred within the top 2 pm, indicating that surface copper of catalytic importance for POP formation reactions was not available. Important contributions of ferric iron present in the abundant fly ash-building hematite phase could have also played an important role, especially given its documented contributions in chlorination pathways. Orthogonal projections to latent structures (OPLS) modeling resolved the relationship between fly ash properties and the post-combustion POP formation. These efforts showed that low levels of ash-forming elements (i.e., Na, Mg, Fe, Ti, etc.) were associated with an increase in flue gas S levels, which, in turn, poison the Cl-2 production via the Deacon process. Wastes with depleted levels of fly-ash-building elements should therefore be favored for minimizing PCDD, PCDF, PCB, and PCN release caused by incineration.
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| 8. |
- Phan, Duong Ngoc Chau, 1985-, et al.
(författare)
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Physicochemical properties of fly ash particles formed during municipal solid waste combustion
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Fly ashes generated from two artificial wastes were investigated with regard to physicochemical properties of importance for thermal formation of persistent organic pollutants (POPs). The ash samples were collected in the post-combustion zone at approximately 300 °C and were characterized using complementary techniques: X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray (SEM/EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results showed a strong correlation between ash chemistry and waste composition. The waste containing higher levels of Al resulted in more abundant Al-bearing minerals, as well as the element Al, in the fly ash. In the case of Fe, no such correlation was found. Copper, an especially important reaction catalyst, was not detected by in the top 10-nm layer of ash but rather occurred within the top 2-µm, indicating that POPs formation reactions may have depleted the available surface Cu. The possibly inaccessible buried forms of Cu may also be a limiting factor in the production of POPs. Furthermore, organic forms of carbon were present at fly ash surfaces, although not significantly in their chlorinated forms. Taken collectively, these results contribute to understanding the correlations between fly ash chemistry and the thermal formation of POPs.
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| 9. |
- Phan, Duong Ngoc Chau, 1985-
(författare)
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The relationship between fly ash chemistry and the thermal formation of polychlorinated pollutants during waste incineration
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) is a major problem in waste incineration. Ideally, rather than relying on air cleaning systems and treatment techniques, their formation should be minimized or, if possible eliminated. The work presented in this thesis was conducted to obtain a deeper understanding of the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during incineration using a 5 kW laboratory scale incinerator and two artificial wastes that were designed to reflect regional differences in waste composition.The first part of the thesis focuses on the validation of a recently-developed flue-gas sampling probe with enhanced cooling capabilities. Artifact formation of PCDDs and PCDFs can occur during the sampling of hot flue gases if the cooling is insufficient. The new probe was successfully used to collect samples at 700 °C without biasing the measured POP levels. The thermal formation of PCDDs, PCDFs, PCBs, and PCNs in the post-combustion zone of the incinerator was then studied by collecting flue gas samples at 400 °C, 300 °C, and 200 °C during the incineration of the two artificial wastes. Highly chlorinated POPs were formed in larger quantities when burning the waste with the higher content of metals and chlorine, which suggests that high metal levels in the waste favor the chlorination of less chlorinated POPs or otherwise facilitate the formation of highly chlorinated polyaromatics, possibly via the condensation of highly chlorinated phenols. The concentrations of these pollutants and the abundance of highly chlorinated homologues increased as the flue gas cooled. Fly ash particles play an important role in thermal POP formation by providing essential elements (carbon, chlorine, etc.) and catalytic sites. The chemical and mineralogical properties of fly ash samples were studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX), and X-ray photoelectron spectroscopy (XPS) to determine their impact on thermal POP formation. Orthogonal Partial Least Squares (OPLS) modeling was used to identify correlations between the observed POP distributions and the physicochemical data. This investigation provided new insights into the impact of fly ash chemistry on thermal POP formation.In addition, the POP isomer distribution patterns generated during waste combustion were examined. These patterns are used to “fingerprint” mechanisms of POP formation. It was found that wastes containing large quantities of metals and chlorine favored the formation of highly chlorinated homologues including the very toxic 2,3,7,8-congeners. The data suggest that reducing fly ash emissions might increase the SO2 content of the flue gas and thereby suppress the Deacon process and the formation of harmful highly chlorinated aromatic species.
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| 10. |
- Phan, TC, et al.
(författare)
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Determinants of mental health among youths and adolescents in the digital era: Roles of cyber and traditional bullying, violence, loneliness, and environment factors
- 2022
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Ingår i: Frontiers in public health. - : Frontiers Media SA. - 2296-2565. ; 10, s. 971487-
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Tidskriftsartikel (refereegranskat)abstract
- Although the pathogenesis of depressive disorders is not fully elucidated, untreated adolescent depression can lead to serious sequelae such as impaired academic performance and social functioning, substance use disorders, poor self-esteem, and increased risk for suicidal ideation and attempts. Literature on adolescent mental health in Vietnam is limited, despite increased international awareness of this critical issue. This study aimed to investigate the prevalence and associations of depressive symptoms in Vietnamese adolescents.MethodsA cross-sectional, self-administered survey was conducted in five provinces of Vietnam among adolescents aged 14 to 24 years. In addition to collecting participants' demographics, a structured questionnaire was developed to examine depressive symptoms, suicidal ideation, loneliness, and cyberbullying victimization. Depressive symptoms and loneliness were assessed via the PHQ-9 and UCLA Loneliness Scale, respectively. Two-tailed Chi-squared, Mann-Whitney, and Kruskal-Wallis tests were performed to examine associations between variables. Multivariate Logistic regression models were conducted to examine the associations between prior-defined variables and positive depressive symptoms.ResultsAmong 1,600 respondents, 31.8% of participants reported having mild-moderate or severe depressive symptoms. Participants within the moderate-severe depressive symptom group had significantly lower community cohesion scores than those of participants in normal and mild depressive symptom groups (p < 0.05). Youths living alone were more likely to have moderate-severe depressive symptoms (OR 2.16; 95% CI: 1.09–4.25). Cyberbullying had significant associations with depressive severity (OR 1.93; 95% CI 1.38–2.70).ConclusionThe findings of this study characterize various risk and protective factors for depression in Vietnamese youths and adolescents. The results highlight the importance of raising awareness and increasing access to educational resources for depression and other mental health illnesses. With the rising prevalence of depression, parents, teachers, and community leaders play a vital role in addressing mental health problems in adolescents.
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