Comparison studies of the mechanistic formation of polyhalogentaed dibenzo-p-dioxins and furans from the thermal degradation of 2-bromophenol and 2-chlorophenol

Emissions of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) from hazardous waste incinerators, and many other sources for combustion have been considered environmentally hazardous and a major health threat. Recently, a growing number of materials containing brominated hydrocarbons, commonly used flame retardants, have been disposed in municipal and hazardous waste incinerators. This results in the increased potential for formation of PBDD/Fs and other hazardous combustion by-products. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. In fact, studies have shown that brominated phenols form higher yields of PBDD/Fs than the analogous chlorinated phenols form PCDD/Fs. For this study, the individual homogeneous, gas-phase oxidative and pyrolytic thermal degradations of 2-bromophenol and 2-chlorophenol were studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000°C. In addition, 50:50 mixture of 2-chlorophenol and 2-bromophenol with a combined concentration of 88 ppm was studied under similar conditions. Also in order to compare previous work with 2-chlorophenol, the surface catalyzed gas-phase reactions for 2-bromophenol to form PBDD/Fs are described over a temperature range from 250 to 550°C. The results are compared and contrasted with each other in order to understand the roles oxygen, chlorine and bromine play in the formation of PCDD/Fs and PBDD/Fs. Reaction pathways to PCDD/F and PBDD/F products as well as all other products detected are proposed that are consistent with the experimental data for each condition. The presence of oxygen increases the formation of PBDFs and PCDFs. Presence of bromine increases the concentration of Cl radicals which in turn increases chlorination and formation of 4,6-dichlorodibenzofuran (4,6-DCDF). However the yields of the PCDFs and PBDFs are considerably less with the presence of both bromine and oxygen. The pool of ·OH and concentration of the chlorine atoms is reduced and thus prevents these furans from becoming major products

Pollutant emissions during pyrolysis and combustion of waste printed circuit boards, before and after metal removal

The constant increase in the production of electronic devices implies the need for an appropriate management of a growing number of waste electrical and electronic equipment. Thermal treatments represent an interesting alternative to recycle this kind of waste, but particular attention has to be paid to the potential emissions of toxic by-products. In this study, the emissions from thermal degradation of printed circuit boards (with and without metals) have been studied using a laboratory scale reactor, under oxidizing and inert atmosphere at 600 and 850 °C. Apart from carbon oxides, HBr was the main decomposition product, followed by high amounts of methane, ethylene, propylene, phenol and benzene. The maximum formation of PAHs was found in pyrolysis at 850 °C, naphthalene being the most abundant. High levels of 2-, 4-, 2,4-, 2,6- and 2,4,6-bromophenols were found, especially at 600 °C. Emissions of PCDD/Fs and dioxin-like PCBs were quite low and much lower than that of PBDD/Fs, due to the higher bromine content of the samples. Combustion at 600 °C was the run with the highest PBDD/F formation: the total content of eleven 2,3,7,8-substituted congeners (tetra- through heptaBDD/Fs) was 7240 and 3250 ng WHO2005-TEQ/kg sample, corresponding to the sample with and without metals, respectively.Support for this work was provided by the CTQ2013-41006 project from the Ministry of Education and Science (Spain) and the PROMETEO/2009/043/FEDER project from the Valencian Community Government (Spain)

TEKNIK PENYISIHAN FENOL DARI AIR LIMBAH

Abstrak Senyawa fenolik adalah polutan yang berbahaya dengan tingkat toksisitas yang tinggi bahkan pada konsentrasi yang rendah. Dalam ulasan ini, efisiensi dari metode penanganan konvensional dan modern akan dibahas. Penerapan metode penanganan senyawa fenolik ini akan dibandingkan performanya jika diaplikasikan untuk senyawa turunan yang lain. Penanganan konvensional seperti distilasi, absorpsi, ekstraksi, oksidasi kimiawi, dan oksidasi elektrokimiawi menunjukkan tingkat efisiensi yang tinggi terhadap berbagai senyawa fenolik, sementara penanganan canggih seperti proses Fenton, ozonisasi, wet air oxidation, dan penanganan dengan fotochemical hanya membutuhkan bahan kimia yang sedikit tetapi biaya yang dikeluarkan terkait penyediaan energi sangat tinggi. Dibandingkan dengan penanganan secara kimia fisis, penanganan biologis lebih ramah lingkungan dan hemat energi, tetapi tidak bisa menangani polutan dengan konsentrasi tinggi. Penanganan dengan enzim telah terbukti menjadi cara terbaik untuk menangani berbagai senyawa fenolik dalam kondisi yang ringan dengan enzim yang beragam seperti peroksidase, lakase, dan tirosinase

Exploring the potential of high mass resolution and mass accuracy mass spectrometric techniques to track the environmental metabolism and fate of BFRS: application to the ambient environment

This thesis investigates levels, sources, and transformation products of both legacy BFRs (LBFRs), and several novel BFRs (NBFRs). To accurately target these emerging pollutants in environmental matrices, an analytical method based on liquid chromatography coupled to high resolution mass spectrometry was developed. Sediment samples taken along the River Thames revealed the presence of both legacy and novel compounds, with concentrations of selected NBFRs approaching those of LBFRs. Tentative sources in the industrial area of London were identified, along with the presence of hydroxylated transformation products of polybrominated diphenyl ethers (PBDEs). Further, the employed technique facilitates the precise identification of metabolites and degradation products formed through in vitro and photodegradation studies. This provides valuable insight into the transformation mechanisms of NBFRs, including hydroxylation and debromination reactions. While 2,3,4,5-tetrabromobenzoic acid (TBBA) was the major metabolite of 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (DBE-DBCH) was biotransformed to monohydroxy- DBE-DBCH and monohydroxy-triDBE-DBCH in trout liver microsomes. Photolysis of investigated NBFRs resulted in the formation of lower brominated species through stepwise reductive debromination as a main pathway. In addition, the use of mass defect plots and bromine isotopic pattern assist in the identification of relevant unknown chemicals within complex mixtures of halogenated compounds in dust and sediment samples

Monohydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) and Dihydroxylated Polybrominated Biphenyls (Di-OH-PBBs): Novel Photoproducts of 2,6-Dibromophenol

Hydroxylated polybromodiphenyl ethers (OH-PBDEs) are emerging aquatic pollutants, but their origins in the environment are not fully understood. There is evidence that OH-PBDEs are formed from bromophenols, but the underlying transformation processes remain unknown. Here, we investigate if the photoformation of OH-PBDEs from 2,6-dibromophenol in aqueous solution involves 2,6-bromophenoxyl radicals. After the UV irradiation of an aqueous 2,6-dibromophenol solution, HPLC–LTQ-Orbitrap MS and GC–MS analysis revealed the formation of a OH-PBDE and a dihydroxylated polybrominated biphenyl (di-OH-PBB). Both dimeric photoproducts were tentatively identified as 4′-OH-BDE73 and 4,4′-di-OH-PBB80. In addition, three debromination products (4-OH-BDE34, 4′-OH-BDE27, and 4,4′-di-OH-PBBs) were observed. Electron paramagnetic resonance spectroscopy revealed the presence of a 2,6-dibromophenoxyl radical with a six-line spectrum (a^H (2 <i>meta</i>) = 3.45 G, a^H (1 <i>para</i>) = 1.04 G, <i>g</i> = 2.0046) during irradiation of a 2,6-dibromophenol solution in water. The 2,6-dibromophenoxyl radical had a relatively long half-life (122 ± 5 μs) according to laser flash photolysis experiments. The <i>para–para</i> C–C and O–<i>para</i>-C couplings of these 2,6-dibromophenoxyl radicals are consistent with the observed formation of both dimeric OH-PBDE and di-OH-PBB photoproducts. These findings show that bromophenoxyl radical-mediated phototransformation of bromophenols is a source of OH-PBDEs and di-OH-PBBs in aqueous environments that requires further attention

Oxidation Kinetics of Bromophenols by Nonradical Activation of Peroxydisulfate in the Presence of Carbon Nanotube and Formation of Brominated Polymeric Products

This work demonstrated that bromophenols (BrPs) could be readily oxidized by peroxydisulfate (PDS) activated by a commercial carbon nanotube (CNT), while furfuryl alcohol (a chemical probe for singlet oxygen (¹O₂)) was quite refractory. Results obtained by radical quenching experiments, electron paramagnetic resonance spectroscopy, and Fourier transform infrared spectroscopy further confirmed the involvement of nonradical PDS-CNT complexes rather than ¹O₂. Bicarbonate and chloride ion exhibited negligible impacts on BrPs degradation by the PDS/CNT system, while a significant inhibitory effect was observed for natural organic matter. The oxidation of BrPs was influenced by solution pH with maximum rates occurring at neutral pH. Linear free energy relationships (LFERs) were established between the observed pseudo-first-order oxidation rates of various substituted phenols and the classical descriptor variables (i.e., Hammett constant σ⁺, and half-wave oxidation potential <i>E</i>_1/2). Products analyses by liquid chromatography tandem mass spectrometry clearly showed the formation of hydroxylated polybrominated diphenyl ethers and hydroxylated polybrominated biphenyls on CNT surface. Their formation pathway possibly involved the generation of bromophenoxyl radicals from BrPs one-electron oxidation and their subsequent coupling reactions. These results suggest that the novel nonradical PDS/CNT oxidation technology is a good alternative for selectively eliminating BrPs with alleviating toxic byproducts in treated water effluent

Oxidation of Bromophenols and Formation of Brominated Polymeric Products of Concern during Water Treatment with Potassium Permanganate

The extensive use of bromophenols (BrPs) in industrial products leads to their occurrence in freshwater environments. This study explored the oxidation kinetics of several BrPs (i.e., 2-BrP, 3-BrP, 4-BrP, 2,4-diBrP, and 2,6-diBrP) and potential formation of brominated polymeric products of concern during water treatment with potassium permanganate [Mn­(VII)]. These BrPs exhibited appreciable reactivity toward Mn­(VII) with the maxima of second-order rate constants (<i>k</i>_Mn(VII)) at pH near their p<i>K</i>_a values, producing bell-shaped pH-rate profiles. The unusual pH-dependency of <i>k</i>_Mn(VII) was reasonably explained by a tentative reaction model, where the formation of an intermediate between Mn­(VII) and dissociated BrP was likely involved. A novel and powerful precursor ion scan (PIS) approach was used for selective detection of brominated oxidation products by liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry. Results showed that brominated dimeric products such as hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and hydroxylated polybrominated biphenyls (OH-PBBs) were readily produced. For instance, 2′-OH-BDE-68, one of the most naturally abundant OH-PBDEs, could be formed at a relatively high yield possibly via the coupling between bromophenoxyl radicals generated from the one-electron oxidation of 2,4-diBrP by Mn­(VII). Given the altered or enhanced toxicological effects of these brominated polymeric products compared to the BrP precursors, it is important to better understand their reactivity and fate before Mn­(VII) is applied by water utilities for the oxidative treatment of BrP-containing waters