Removal Of Semi-volatile Organic Compounds Research Articles

Photocatalytic membrane for in situ enhanced removal of semi-volatile organic compounds in membrane distillation under visible light

Membrane distillation (MD) is emerging as a promising technology for wastewater reclamation to relieve the shortage of freshwater. However, due to the contamination of semi-volatile organic compounds (s-VOCs), part of s-VOCs would transfer the membrane and impact the permeate quality during the MD process. Herein, an innovative AgCl/MIL-100(Fe)/PTFE photocatalytic membrane (AM/PTFE) was rationally synthesized in view of the increasing s-VOCs rejection. The AM/PTFE membrane was applied in the photocatalytic direct contact membrane distillation (DCMD) system and nitrobenzene (NB) was selected as the model contamination for evaluating removal performance of s-VOCs under visible light. Compared with the MD process, NB removal rate increased from 63.44% to 87.84% in the photocatalytic MD system. Moreover, stable performance was maintained over five NB removal cycles experiment with s-VOCs rejection higher than 84.84% in the end. The enhanced rejection of s-VOCs could be attributed to the combination of adsorption and photocatalytic. The volatile NB molecules were adsorbed on the surface of photocatalytic membranes, and the photo-electrons (e-) generated by immobilized nanomaterials could effectively remove pollutants under visible light irradiation. This photocatalytic MD system provides an attractive avenue for the water reclamation from s-VOCs contaminated wastewater in the practical applications.

Assessing decontamination and laundering processes for the removal of polycyclic aromatic hydrocarbons and flame retardants from firefighting uniforms

Firefighter uniforms protect firefighters from exposure to potentially harmful chemicals including a range of semi-volatile organic compounds (SVOCs). Contaminated uniforms can become a secondary source of firefighters' exposure to these chemicals. There is inconsistency on the removal efficiency of SVOCs during the cleaning, laundering and field decontamination of firefighting uniforms. Therefore, this study aims to assess how effective decontamination and laundering processes are in reducing firefighter uniforms as a vector for transport and exposure to SVOCs. Firefighters who had attended a controlled house fire and simulated container burns had their uniforms sampled pre- and post-laundering. Clean station wear was laundered with contaminated uniforms and after a load of contaminated uniforms to assess inter and intra load contamination. Surface wipes were collected from uniforms across 12 fire stations, after they had returned from a laundering provider. Concentrations of 13 polycyclic aromatic hydrocarbons (PAHs), six organophosphate flame retardants (OPFRs) and seven polybrominated diphenyl ethers (PBDEs) were measured in the collected samples. The concentrations of ∑13 PAHs in firefighters uniforms ranged between 0.063 and 43 μg g−1, while concentration of ∑6 OPFRs were between 0.061 and 90 μg g−1 with ∑7 PBDEs concentrations being measured between 0.00054 and 0.97 μg g−1.The highest concentrations of ∑13 PAHs were measured on the outer layers of gloves at an average of 19 μg g−1, with the highest ∑6 OPFRs concentrations being measured in the middle layers of gloves at an average of 31 μg g−1. The highest ∑7 PBDEs concentrations were measured on the shell layers of turnout jackets at 0.42 μg g−1. The significant reduction in ∑13 PAHs after laundering or decontamination was only found in 3 of the 16 sampled areas from firefighting uniforms. No significant differences were found in the between pre- and post-laundering concentrations of ∑6 OPFRs or ∑7 PBDEs in firefighting uniforms. The current laundering techniques do not appear to effectively remove PAHs, OPFRs and PBDEs at the measured concentrations from firefighters’ uniforms. Further research is required to assess if chemical exposure though firefighting uniforms poses a health risk to firefighters and to develop methods for the removal of SVOCs from firefighting uniforms.

Catalytic oxidation of dimethyl phthalate over titania-supported noble metal catalysts

Semi-volatile organic compounds (SVOCs) are organic compounds with the boiling point ranging between 240/260 ℃ and 380/400 ℃. Detailed knowledge regarding catalytic removal of SVOCs from indoor environment is very limited as it remains challenge to explore such reaction due to the viscosity nature of target contaminants. Here, we established a facile methodology to explore the heterogeneous catalytic oxidation reaction of dimethyl phthalate (DMP), a model SVOC, over the surface of supported catalyst. DMP was found to be gradually oxidized over the surface of titania supported catalysts including palladium (Pd), platinum and ruthenium with increasing temperature. The cleavage of side chain of DMP occurs at 75 ℃ over the surface of Pd/TiO2, which is significantly lower than that of the other two catalysts. Carbon dioxide was observed as the main product of the catalytic oxidation reaction. However, aromatic products and small molecule products were still observed as side-product in different temperature range. Density functional theory calculations further show that DMP can react with reactive oxygen species to form phthalic acid. While the cleavage of the DMP side chain occurs to form products such as methyl benzoate. This work thus provides basic knowledge about indoor SVOCs catalytic oxidation removal.

Exposure Assessment For Air-To-Skin Uptake of Semivolatile Organic Compounds (SVOCs) Indoors.

Semivolatile organic compounds (SVOCs) are ubiquitous in the indoor environment and a priority for exposure assessment because of the environmental health concerns that they pose. Direct air-to-skin dermal uptake has been shown to be comparable to the inhalation intake for compounds with certain chemical properties. In this study, we aim to further understand the transport of these types of chemicals through the skin, specifically through the stratum corneum (SC). Our assessment is based on collecting three sequential forehead skin wipes, each hypothesized to remove pollutants from successively deeper skin layers, and using these wipe analyses to determine the skin concentration profiles. The removal of SVOCs with repeated wipes reveals the concentration profiles with depth and provides a way to characterize penetration efficiency and potential transfer to blood circulation. We used a diffusion model applied to surface skin to simulate concentration profiles of SVOCs and compared them with the measured values. We found that two phthalates, dimethyl and diethyl phthalates, penetrate deeper into skin with similar exposure compared to other phthalates and targeted SVOCs, an observation supported by the model results as well. We also report the presence of statistically significant declining patterns with skin depth for most SVOCs, indicating that their diffusion through the SC is relevant and eventually can reach the blood vessels in the vascularized dermis. Finally, using a nontarget approach, we identified skin oxidation products, linked to respiratory irritation symptoms, formed from the reaction between ozone and squalene.

CONCENTRATIONS and WET DEPOSITION FLUXES of POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) in a SUBURBAN LOCATION of ESKİŞEHiR

Wet-only precipitation samples were collected using a collection plate between June 2007 and April 2008, in Eskisehir, Turkey. Polycyclic aromatic hydrocarbons (PAHs) were analyzed in precipitation samples by gas chromatography-mass spectrometry (GC-MS). PAH concentrations in the sampling location in atmospheric gas and particle phase samples were also determined. Significant difference in atmospheric concentrations and precipitation samples were observed. Annual PAH flux was found comparable with other cities in Turkey and calculated around 177.2±120.4 μg m -2 day -1 . Wet deposition was noticed an important mechanism on removal of semi-volatile organic compounds from atmosphere.

Reactivity of Semivolatile Organic Compounds with Hydroxyl Radicals, Nitrate Radicals, and Ozone in Indoor Air

Indoor semivolatile organic compounds (SVOCs) originate from indoor and outdoor sources. These SVOCs partition among different phases and available surfaces, which increases their residence time indoors to several years. SVOCs may also react with indoor oxidants, such as hydroxyl radicals (OH), nitrate radicals (NO3), and ozone. In the present study, the second-order reaction rate constants of 72 SVOCs in indoor air (gas and particle phases) at room temperature and ambient air pressure were retrieved from the literature. The pseudo–first-order reaction rate constants of these SVOCs were calculated for the indoor concentration ranges of OH, NO3, and ozone. Then, the extent to which the chemical reaction had a meaningful impact on the removal of SVOCs from the indoor environment was quantitatively analyzed. The orders of magnitude of the second-order rate constant ranged between 10−15 and 10−10 cm3/(molecule·s) for OH/SVOC reactions, 10−17 and 10−12 cm3/(molecule·s) for NO3/SVOC reactions, and 10−20 and 10−16 cm3/(molecule·s) for ozone/SVOC reactions in indoor air. Assuming that the highest indoor reactant concentrations were 1.8 × 106 molecules/cm3 (7.3 × 10−5 ppb) for OH, 2.5 × 108 molecules/cm3 (10−2 ppb) for NO3, and 1.4 × 1012 molecules/cm3 (58 ppb) for ozone, the highest pseudo–first-order rate constants in the gas phase for the studied reactions of OH/SVOCs (n = 72), NO3/SVOCs (n = 3), and ozone/SVOCs (n = 14) reached 1.5 h−1 (OH/benzo[a]pyrene), 0.41 h−1 (NO3/acenaphthene), and 1.0 h−1 (ozone/aldrin and ozone/heptachlor), respectively. The pseudo–first-order rate constants in the particle phase for the studied reactions of OH/SVOCs (n = 13), NO3/SVOCs (n = 6), and ozone/SVOCs (n = 14) at the high indoor reactant concentrations reached 0.09 h−1 (OH/DEHP), 5.8 h−1 (NO3/pyrene), and 11 h−1 (ozone/benzo[a]pyrene), respectively. These results indicate that the chemical reactions of some SVOCs in indoor air have a meaningful impact compared to the air exchange rate, which should be considered in future studies on indoor air quality modeling.

The characterisation of diesel exhaust particles - composition, size distribution and partitioning.

A number of major research questions remain concerning the sources and properties of road traffic generated particulate matter. A full understanding of the composition of primary vehicle exhaust aerosol and its contribution to secondary organic aerosol (SOA) formation still remains elusive, and many uncertainties exist relating to the semi-volatile component of the particles. Semi-Volatile Organic Compounds (SVOCs) are compounds which partition directly between the gas and aerosol phases under ambient conditions. The SVOCs in engine exhaust are typically hydrocarbons in the C15-C35 range, and are largely uncharacterised because they are unresolved by traditional gas chromatography, forming a large hump in the chromatogram referred to as Unresolved Complex Mixture (UCM). In this study, thermal desorption coupled to comprehensive Two Dimensional Gas-Chromatography Time-of-Flight Mass-Spectrometry (TD-GC × GC-ToF-MS) was exploited to characterise and quantify the composition of SVOCs from the exhaust emission. Samples were collected from the exhaust of a diesel engine, sampling before and after a diesel oxidation catalyst (DOC), while testing at steady state conditions. Engine exhaust was diluted with air and collected using both filter and impaction (nano-MOUDI), to resolve total mass and size resolved mass respectively. Adsorption tubes were utilised to collect SVOCs in the gas phase and they were then analysed using thermal desorption, while particle size distribution was evaluated by sampling with a DMS500. The SVOCs were observed to contain predominantly n-alkanes, branched alkanes, alkyl-cycloalkanes, alkyl-benzenes, PAHs and various cyclic aromatics. Particle phase compounds identified were similar to those observed in engine lubricants, while vapour phase constituents were similar to those measured in fuels. Preliminary results are presented illustrating differences in the particle size distribution and SVOCs composition when collecting samples with and without a DOC. The results indicate that the DOC tested is of very limited efficiency, under the studied engine operating conditions, for removal of SVOCs, especially at the upper end of the molecular weight range.

Low-Temperature Thermal Treatment of Contaminated Soils: Simple Mathematical Models

Abstract Mathematical models for low-temperature thermal treatment of contaminated soils for the removal of semivolatile organic compounds (SVOCs) by batch and continuous flow units are described. In one set of models the SVOC is assumed to obey a linear adsorption isotherm on the soil; in the second set the SVOC is assumed to be present as nonaqueous phase liquid (NAPL) blobs dispersed within the porous soil. The soil is represented by porous spheres of specified radius through which the escaping SVOC must diffuse. Results of calculations with both models for continuous flow units are presented, and the dependence of the results on the model parameters is discussed.