Simulating the fate and transport of TCE from groundwater to indoor air

This work provides an exploratory analysis on the relative importance of various factors controlling the fate and transport of volatile organic contaminants (in this case, TCE) from a DNAPL source zone located below the water table and into the indoor air. The analysis is conducted using the multi-phase compositional model CompFlow Bio, with the base scenario problem geometry reminiscent of a field experiment conducted by Rivett [Rivett, M.O., (1995), Soil–gas signatures from volatile chlorinated solvents: Borden field experiments. Groundwater, 33(1), 84–98.] at the Borden aquifer where groundwater was observed to transport a contaminant plume a substantial distance without vertical mass transport of the contaminant across the capillary fringe and into the vadose zone. Results for the base scenario model indicate that the structure of the permeability field was largely responsible for deflecting the groundwater plume upward towards the capillary fringe, permitting aqueous phase diffusion to transport the TCE into the vadose zone. Alternative permeability realizations, generated as part of a Monte Carlo simulation process, at times deflected the groundwater plume downwards causing the extended thickness of the saturated zone to insulate the vadose zone from exposure to the TCE by upward diffusive transport. Comparison of attenuation coefficients calculated using the CompFlow Bio and Johnson and Ettinger [Johnson, P.C. and Ettinger, R.A., (1991), Heuristic model for predicting the intrusion rate of contaminant vapors into buildings. Environmental Science and Technology, 25, 1445–1452.] heuristic model exhibited fortuitous agreement for the base scenario problem geometry, with this agreement diverging for the alternative permeability realizations as well as when parameters such as the foundation slab fracture aperture, the indoor air pressure drop, the capillary fringe thickness, and the infiltration rate were varied over typical ranges.     

Visualization and localization of bromotoluene distribution in Hedera helix using NanoSIMS

Some plants are known as indoor air purifiers. A large number of studies report kinetic purification results for an extensive panel of plants, i.e. the pollutant concentration (volatile organic compounds, as known as VOC, most of the time) is continuously monitored by gas chromatography. However, only a few papers describe the mechanisms involved in such processes. This study deals with the use of secondary ion mass spectrometry imaging as an efficient tool to locate atmospheric pollutant as bromotoluene within the Hedera helix plant (leaf, roots) and the substrate on which it was previously grown. Hedera helix plants have been placed in a pollution chamber with control of the exposure parameters. Plant and soil samples excised were transferred into a fixative solution of glutaraldehyde and paraformaldehyde for a few days, were dehydrated using ethanol and were embedded with resin. Cross sections were made from the pale brown solids obtained. Then, a device using a cathodic pulverization device capable of depositing a few nanometers of gold atoms over the sample was used to make the surface electronically conductive for the NanoSIMS. Hence, polluted and unpolluted samples of Hedera helix and substrates were obtained following a careful procedure that allowed for the discrimination between polluted and nonpolluted ones. Nanoscale spatial resolution was an invaluable tool (NanoSIMS) to achieve this, and proved that VOCs, such as bromotoluene, were actually trapped by plants such as Hedera helix.     

Multi-step approach for comparing the local air pollution contributions of conventional and innovative MSW thermo-chemical treatments

In the sector of municipal solid waste management the debate on the performances of conventional and novel thermo-chemical technologies is still relevant. When a plant must be constructed, decision makers often select a technology prior to analyzing the local environmental impact of the available options, as this type of study is generally developed when the design of the plant has been carried out. Additionally, in the literature there is a lack of comparative analyses of the contributions to local air pollution from different technologies. The present study offers a multi-step approach, based on pollutant emission factors and atmospheric dilution coefficients, for a local comparative analysis. With this approach it is possible to check if some assumptions related to the advantages of the novel thermochemical technologies, in terms of local direct impact on air quality, can be applied to municipal solid waste treatment. The selected processes concern combustion, gasification and pyrolysis, alone or in combination. The pollutants considered are both carcinogenic and non-carcinogenic. A case study is presented concerning the location of a plant in an alpine region and its contribution to the local air pollution. Results show that differences among technologies are less than expected. Performances of each technology are discussed in details.     

Octanol–air partition coefficients of polybrominated biphenyls

The octanol–air partition coefficients (K_OA) for PBB15, PBB26, PBB31, PBB49, PBB103 and PBB153 were determined as a function of temperature using a gas chromatographic retention time technique with 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (p,p′-DDT) as a reference substance. The internal energies of phase change from octanol to air (Δ_OAU) were calculated for the six compounds and were in the range from 74 to 116 kJ mol⁻¹. Simple regression equations of log K_OA versus relative retention times (RRTs) on gas chromatography (GC), and log K_OA versus molecular connectivity indexes (MCI) were obtained, for which the correlation coefficients (r²) were greater than 0.985 at 283.15 K and 298.15 K. Thus the K_OA values of the remaining PBBs can be predicted by using their RRTs and MCI according to these relationships.     

Gas/particle partitioning of atmospheric PCDD/Fs in a satellite town in Eastern China

Gas/particle partitioning of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in ambient air was investigated in a satellite town in Eastern China from April 2007 to January 2008 comprehending large temperature variations (from 3 to 34 °C, daily average). Molecular weight, molecular structure and ambient temperatures are the three major factors that govern the gas/particle partitioning of atmospheric PCDD/Fs throughout the year. Generally, good agreements were obtained (except for winter) between measured particulate fractions and theoretical estimates of both the Junge–Pankow adsorption model and Harner Bidleman absorption model using different sets of subcooled liquid vapor pressure and octanol–air partition coefficient (K_oa), respectively. Models utilizing estimates, derived from gas chromatographic retention indices (GC-RIs), are more accurate than that of entropy-based. Moreover, during winter, the K_oa-based model using the GC-RIs approach performs better on lower chlorinated PCDD/Fs than that of -based. Furthermore, possible sources of mismatch between measured and predicted values in winter (3–7 °C) were discussed. Gas adsorption artifact was demonstrated to be of minor importance for the phenomena observed. On the other hand, large deviations of slopes (m_r) and intercepts (b_r) in logK_p vs. plots from theoretical values are observed in the literature data and these are found to be linearly correlated with ambient temperatures (P<0.001) in this study. This indicates that the non-equilibrium partitioning of PCDD/Fs in winter may be significantly influenced by the colder temperatures that may have slowed down the exchange between gaseous and particulate fractions.     

Particle size distribution of airborne Aspergillus fumigatus spores emitted from compost using membrane filtration

Information on the particle size distribution of bioaerosols emitted from open air composting operations is valuable in evaluating potential health impacts and is a requirement for improved dispersion simulation modelling. The membrane filter method was used to study the particle size distribution of Aspergillus fumigatus spores in air 50 m downwind of a green waste compost screening operation at a commercial facility. The highest concentrations (approximately 8 × 10⁴ CFU m⁻³) of culturable spores were found on filters with pore diameters in the range 1–2 μm which suggests that the majority of spores are emitted as single cells. The findings were compared to published data collected using an Andersen sampler. Results were significantly correlated (p < 0.01) indicating that the two methods are directly comparable across all particles sizes for Aspergillus spores.     

Integrated catalytic wet air oxidation and aerobic biological treatment in a municipal WWTP of a high-strength o-cresol wastewater

This study examines the feasibility of coupling a Catalytic Wet Air Oxidation (CWAO), with activated carbon (AC) as catalyst, and an aerobic biological treatment to treat a high-strength o-cresol wastewater. Two goals are pursued: (a) To determine the effect of the main AC/CWAO intermediates on the activated sludge of a municipal WasteWater Treatment Plant (WWTP) and (b) To demonstrate the feasibility of coupling the AC/CWAO effluent as a part of the influent of a municipal WWTP. In a previous study, a high-strength o-cresol wastewater was treated by AC/CWAO aiming to establish the distribution of intermediates and the biodegradability enhancement. In this work, the biodegradability, toxicity and inhibition of the most relevant intermediates detected in the AC/CWAO effluent were determined by respirometry. Also, the results of a pilot scale municipal WWTP study for an integrated AC/CWAO-aerobic biological treatment of this effluent are presented. The biodegradation parameters (i.e. maximum oxygen uptake rate and oxygen consumption) of main AC/CWAO intermediates allowed the classification of the intermediates into readily biodegradable, inert or toxic/inhibitory compounds. This detailed study, allowed to understand the biodegradability enhancement exhibited by an AC/CWAO effluent and to achieve a successful strategy for coupling the AC/CWAO step with an aerobic biological treatment for a high-strength o-cresol wastewater. Using 30%, as COD, of AC/CWAO effluent in the inlet to the pilot scale WWTP, the integrated AC/CWAO-biological treatment achieved a 98% of total COD removal and, particularly, a 91% of AC/CWAO effluent COD removal without any undesirable effect on the biomass.     

催化湿式氧化技术处理山梨酸生产废水的研究

采用催化湿式氧化技术处理生产山梨酸过程中产生的高浓度有机废水,对催化剂组分进行优选.对反应温度、O2分压(Po2)和废水pH等工艺条件进行考察.实验结果表明:采用自制CuO-Cr2O3-La2O3/TiO2为复合催化剂处理该有机废水时表现出较好的催化活性;在190℃、Po2=2.1 MPa、pH=6.1、COD=10 030.0 mg/L时,反应90 min的COD去除率达到98.3%,而在相同条件下未加催化剂的湿式氧化的COD去除率只有60.1%.     

焚烧秸秆对城市空气质量的影响及对策

通过夏收季节农民焚烧秸秆的烟尘，引起对城市环境空气质量变化的分析，结果表明：焚烧秸秆对城市环境空气质量有很大影响，使环境空气质量明显下降，而主要污染物为可吸入颗粒物PM10。有关部门应采取有效措施，禁止焚烧秸秆，同时应积极为农民寻找合理利用秸秆的途径，减少对城市空气的烟尘污染。     

新装饰装修房屋室内空气中的苯系物调查

对新装饰装修房屋室内的一类主要有机苯系污染物进行了调查,调查采用吸附柱采集、GC/MS 和GC-FID测定,检测了321家居室内的苯系物.检出的苯系物有12种,苯平均浓度为0.068 mg/m^3,有86.9%的居室符合《室内空气质量标准》（GB/T18883-2002）规定的限量值,甲苯、二甲苯平均浓度分别为0.14 mg/m^3和0.41 mg/m^3,符合《室内空气质量标准》规定限值的居室分别达85.4%和73.3%.苯系物约占室内空气中TVOC的62%,浓度由低到高分别是苯、甲苯、乙苯和二甲苯,其中二甲苯中的间二甲苯占二甲苯总量的55% .