Compositing Water Samples for Analysis of Volatile Organic Compounds

Accurate mean concentrations of volatile organic compounds (VOCs) can easily and economically be obtained from a single VOC analysis by using proven methods of collecting representative, discrete water samples and compositing them with a gas-tight syringe. The technique can be used in conjunction with chemical analysis by a conventional laboratory, field-portable equipment, or a mobile laboratory. The type of mean concentration desired depends on the objectives of monitoring. For example, flow-weighted mean VOC concentrations can be used to estimate mass loadings in wastewater and urban storm water, and spatially integrated mean VOC concentrations can be used to assess sources of drinking water (e.g., reservoirs and rivers). The mean error in a discrete sample due to compositing is about 2% for most VOC concentrations greater than 0.1 μg∕L. The total error depends on the number of discrete samples comprising the composite sample and precision of the chemical analysis.     

Biotrickling Filtration for Control of Volatile Organic Compounds from Microelectronics Industry

This study investigated the transient and steady-state performance of a bench-scale biotrickling filter for the removal of an organic mixture (acetone, toluene, and trichloroethylene) typically emitted by the microelectronics industry. The microbial consortium consisting of seven bacterial strains that were fully acclimated prior to inoculation onto activated carbon media. Among the seven strains, the Pseudomonas and Sphingomonas strains appeared to be the major groups degrading toluene (>25?ppmv/h?108 cell) and trichloroethylene (>2.3?ppmv/h?108 cell), while Mycobacteria and Acetobacteriaceae strains were the primary decomposers of acetone (>90?ppmv/h?108 cell). The column performance was evaluated by examining its responses to the fluctuating influent total hydrocarbon concentrations, which varied from 850 to 2,400 ppmv. Excellent steady-state removal efficiencies greater than 95% were consistently observed, and system recovery was typically within two days after a significant increase in the inlet loading was experienced. The overall mass-transfer rate and the biokinetic constants were determined for each organic component. Mathematical simulations based on these parameters demonstrated that the removal of acetone was kinetically limiting, whereas the removals of toluene and trichloroethylene were at least partially mass-transfer limiting.     

土壤中挥发性有机物的GC-MS测定

利用索氏提取-气相色谱-质谱联用技术,对某废弃化工厂原厂区土壤中可能存在的挥发性有机污染物进行定性和定量分析;利用索氏提取进行土样中有机物的提取,用十四烯配制标准曲线,以质谱全扫描方式的数据进行定性,选择离子监测的数据进行外标法定量,提高检测的灵敏度和准确度.依照美国环保局对环境分析的质量保证和质量控制指标对分析结果进行检测,发现方法的检出限为0.024mg·kg-1,回收率为95.84%,结果符合要求.     

Volatile Organic Compounds in New Automobiles: Screening Assessment

Four new vehicles were tested to assess the nature (constituents and concentrations) of volatile organic compounds (VOCs) associated with new vehicle interiors. The total VOC (TVOC) concentration within the interior of one vehicle (minivan) was 7,500 μg∕m3 on the first day of sampling (second day after purchase), approximately two orders of magnitude higher than the outdoor TVOC concentration. The TVOC concentration in the minivan was observed to decay significantly with time, with an approximate 90% reduction in concentration after three weeks of testing. The other three vehicles had TVOC concentrations that ranged from 300 to 600 μg∕m3 on the first day of testing. Over sixty chemicals were identified inside the interiors of the four vehicles. Compounds identified in all four vehicles and their GC∕MS area percent ranges were toluene (2.2–12.6%), ethylbenzene (0.5–2.2%), xylene (2.4–10.7%), and undecane (0.8–7.5%).     

Adsorption and Desorption of Volatile Organic Compounds in Fluidized Bed

A model of adsorption and thermal desorption was built and validated from experiments performed under various operating conditions. The abatement increased with the reduction in the inlet concentration and with the increase of bed height. Particles at the end of adsorption step were saturated although their pores were not completely filled with acetone. Adsorption yielded an increase of the bed temperature at the beginning of the tests, where the separation rate had the maximum value nearly equal to 100%, but the temperature rise of the bed remained much smaller than that obtained in fixed-bed adsorption for similar conditions. Simulations of a process operating with successive cycles of adsorption and thermal desorption was then performed. Desorption appeared to have a reasonable duration compared to adsorption. Calculations proved that a third reactor for transient states from adsorption to desorption or from desorption to adsorption that would achieve the cooling or the heating of particles was not necessary. Results show the feasibility of the adsorption–desorption process of volatile organic compounds in fluidized beds of granular activated carbon.     

关于我国停车场的博弈实证分析

如今,我国停车问题日益尖锐化,主要表现为停车场的建设严重匮乏,现有停车设施不能有效利用,以致影响到交通的畅通,社会的综合收益降低.停车问题产生的一个重要原因是停车场的建设不足,远不能满足有车族的停车需求,本文从3个方面分析我国停车场的发展现状,进而阐述了停车难的原因,从博弈论的角度对几个停车难的典型案例进行分析,说明路边停车拥挤和停车位不足的问题.     

饮用水源中痕量有机物的生物膜降解

生物膜工艺是去除饮用水中痕量有机物的有效方法,共代谢是生物膜工艺中的重要方式。在微污染饮用水源中,自然有机物作为初级基质支持生物膜的生长,痕量有机物作为第二级基质被生物膜降解而被去除。     

Applications of Low-Temperature Regenerative Thermal Oxidizers to Treat Volatile Organic Compounds

A series of plant scale low temperature regenerative thermal oxidizers (LTRTOs) equipped with heating wires were constructed to treat volatile organic compounds (VOCs) laden gas streams. All regenerative beds were packed with gravel (approximate particle size 1.25 cm, specific area 205 m2/m3, and specific heat capacity 840 J/kg?°C) and equipped with K-type thermocouples for measuring gas temperatures. Test gas streams were extracted from manufacturing sections of varnishing, semiconductor packing, and petrochemical plants, representing a variety of gas-phase pollutants, including several commercial solvents. Experimental results indicate that 98% or greater treatment of VOCs with concentrations between 100 and 7,000 ppm as methane. Analysis of gas temperature variation with time at various bed depths confirm that VOC degradation occurs at temperatures ranging from 300 to 440°C, which are much lower than autoignition points of tested compounds. A 1.0 s gas residence time in the oxidation zone of regenerative beds is required for successful LTRTO operation.     

Characterizing Polyurethane Foam as a Sink for or Source of Volatile Organic Compounds in Indoor Air

Polyurethane foam (PUF) is widely used in indoor consumer products. Despite strong potential interactions with volatile organic compounds (VOCs), the effect of PUF on indoor concentrations of VOCs has not been examined. This study determines the behavior of PUF as a potential sink for or source of VOCs in indoor air. A flexible polyether-type foam and eight aromatic VOCs ranging in molecular weight from naphthalene to benzene were studied. Rapid determinations of PUF–air partition coefficient (K) and PUF–phase diffusion coefficient (D) were achieved using a dynamic microbalance procedure. A diffusion model was applied to interpret the experimental data. The PUF sample was assumed to conform to semi-infinite cylindrical geometry with solid-phase diffusion being the rate limiting step. The results indicate that sorption of VOCs by PUF is fully reversible. For the VOCs studied, K can be correlated with vapor pressure and D with molecular free surface area. Humidity appears to reduce the extent of sorption and slow the sorption kinetics. These findings should facilitate the prediction of the source/sink behavior of PUF and the related impact on VOC concentrations in the indoor environment.     

吹扫捕集与色谱—质谱联用分析宝钢水和废水中VOCs

吹扫捕集与色谱—质谱联用技术是一种较为成熟的有机物分析技术,结合实验室仪器条件采用此技术,开发出依据美国环保局(EPA)8260B方法分析水和废水中挥发性有机物(VOCs)的方法,并应用于宝钢实际水样的监测,取得了较好的分析结果。该方法可分析40种(类)挥发性有机物,每种物质分析的线性相关系数都能达到0.99以上,基体加标试剂的回收率为89.5%～102.7%,除四种物质为0.01mg/L外,其余物质的定量下限基本上为0.005mg/L,完全能够满足应用要求。     

Ceria-Modified Clay Supported Palladium Catalysts for Complete Oxidation of Volatile Organic Compounds

Ceria- and alumina-pillared interlayered clays were synthesized in the presence of PEO surfactant by using laponite clay as raw material.And the synthesized pillared clays were used as supports to load palladium catalysts for complete oxidation of benzene.Nitrogen adsorption/desorption experiments reveal that the pillared clays have higher tests show that ceria pillar exhibited promoting effect on the activity of the palladium catalysts, and ceria-pillared clay supported palladium catalyst catalyzed the complete oxidation of benzene at less than 250 ℃.The calcination temperature affects the activity of the catalysts significantly, and it is found that the optimal calcination temperature are 600 and 400 ℃ for ceria- and alumina-pillared clay supported palladium catalysts, respectively.     

Induction of Volatile Organic Compounds in Leaves of Lycopersicon Esculentum by Nd^3＋

The effects of Nd^3＋ on the quality and quantity of volatile organic compounds （VOCs） in the leaves of Lycopersicon esculentum were studied. The results demonstrate that Nd^3＋ can increase the total amount of VOC by 75% after treatment for 120 h, as compared with the control. Phyto-oxylipins, terpenoids and aromatic compounds were increased by 73%, 38% and 21%, respectively. （E）-2-hexenal, the most abundant constituent is increased by 74%, β- phellandrene and α-caryophyllene in terpenoids,     

Modeling of Adsorption and Regeneration of Volatile Organic Compounds on Activated Carbon Fiber Cloth

A mathematical model is developed to predict continuous adsorption-regeneration cycling of volatile organic compounds (VOCs) on activated carbon fiber cloth (ACFC) at the indoor VOC concentration levels. The adsorption-regeneration model incorporates both the adsorption equilibrium and mass transfer fundamentals. It assumes local equilibrium between the gas-phase and the solid-phase, and axially dispersed-flow, film transfer, and intraparticle transport by surface and pore diffusion. Successful agreement between model simulations and experimental data was obtained and the kinetic properties of the adsorption/regeneration cycling on the ACFC were characterized. For the adsorption process, the film transfer is the dominant factor for mass transfer at low flow rates (45–184 L/min), and the intraparticle mass transfer rate controls over the gas-phase rate as the flow rates increase. The regeneration concentration profiles are most sensitive to the adsorption isotherms at the temperatures of interest, especially as desorption is initiated. The surface diffusivity also contributes to the shape of the regeneration profile: the tailing of desorption profile shifts up with the increase of surface diffusivity.     

Effect of Moisture on the Adsorption of Volatile Organic Compounds by Zeolite 13×

The adsorption of volatile methanol, acetone, and benzene onto zeolite 13× was studied in the presence of water vapor. Breakthrough curves for these volatile organic compounds (VOCs) were measured by using a gas-phase Fourier transformation infrared (FT-IR) spectrometer instead of a gas chromatograph (GC) because a gas-phase FT-IR spectrometer provides a more rapid response to the change of gas concentration than that of GC. To observe the influences of humidity (i.e., water vapor) on the performance of zeolite 13× during the VOC adsorption, the adsorption experiments were carried out at three different initial concentrations and two humidity conditions for each VOC. The results showed a significant influence of increased humidity on the breakthrough time, the shapes of breakthrough curves, and the uptake of VOCs. For the case of the benzene and water vapor coadsorption system, the presence of the moisture caused a greater decrease in the VOC uptake as well as the breakthrough time than for the other VOC–water coadsorption systems. A modified Freundlich-type isotherm was introduced in this study to describe the decrease in the uptake of VOCs in the presence of the moisture. This modified empirical equation provided a good fit to experimental results, with an average error of 8%.     

Regional Analysis of Nonmethane Volatile Organic Compounds in the Lower Troposphere of the Southeast United States

Nonmethane organic compounds (NMOCs) along with ozone as well as other trace gas and meteorological parameters were measured at eight rural sites located in the Southeast United States, as part of the Southern Oxidants Study. Fifty-four C2–C10 NMOCs were collected from 1,200–1,300 local time, once every six days from September 1992 through October 1993 and intermittently during 1994. This study was undertaken to characterize the nonmethane hydrocarbons in the rural areas of Southeast United States with respect to their concentrations, reactivities, and relative importance of natural and anthropogenic abundances of NMOCs. Though the sites are well removed from large urban source regions, the observations show a clear anthropogenic influence on the hydrocarbon levels at these rural sites. The data for the sites show similar seasonal patterns for total NMOC with summer maxima (average concentrations of 198 ppbC at the Long Creek, South Carolina, site to 47 ppbC at the Candor, North Carolina site) and fall minima (average concentrations of 73 ppbC at the Long Creek site to 31 ppbC at the Centreville, Alabama site). A secondary maximum is observed during the winter. A seasonal trend was observed in the concentrations of light molecular weight C2–C4 NMOCs (ethane, ethene, acetylene, propane, i-butane, and n-butane) with a winter maximum and a summer minimum. An analysis of changes in C2–C4 hydrocarbon ratios over a period of one year indicates that the variation is most likely due to seasonal changes in OH concentrations. A seasonal trend was also observed for the biogenically emitted NMOC, isoprene, with summer maxima (average concentrations of 37 ppbC at the Long Creek, South Carolina, site to 8.6 ppbC at the Giles County, Tennessee and Metter, Georgia, sites) and winter minima with winter seasonal values below the level of detection. Isoprene was observed to be the most dominant NMOC at most sites during the summer. The ambient concentrations of isoprene measured during the summer were found to be dependent on the ambient temperature. The monoterpenes a-pinene, b-pinene, and d-limonene also peaked during the summer with averages ranging between 3.19 ppbC (Centreville, Alabama) and 6.38 ppbC (Oak Grove, Missouri), and a background concentration of 1.25 to 1.9 ppbC for all the sites during the winter.     

气相色谱质谱法测定饮用水源中60种半挥发性有机物

在碱性、中性和酸性三种条件下,采用二氯甲烷萃取水中半挥发性有机物（SVOCs）,气相色谱质谱法测定饮用水源地水中的60种SVOCs。结果表明,60种SVOCs的回收率为88 %~96 %,相对标准偏差为1.1 %~4.8 %,具有较好的正确度和精密度。目标SVOCs在 0.05~1.00 μg/mL范围内有较好的线性关系,线性相关系数R2>0.99。     

Temporal Moment Analysis for Volatile Organic Compounds in Dual-Porosity Porous Media: Loss Fractions and Effective Parameters

Using transform techniques, analytical expressions for potential losses by volatilization and degradation are developed for several organic compounds in dual porosity porous media. A sensitivity analysis is conducted to study the importance of different physical/chemical processes on volatilization, degradation, and leaching losses. To obtain estimates for overall solute behavior, expressions for effective Péclet numbers and degradation rates for organic contaminants are presented using method of moments. Results indicate that large fractions of many organic compounds are likely to volatilize into the atmosphere for sandy and clayey soils under typical flow conditions. It is found that nondimensional degradation influences both advective and dispersive effects. Thus, the Péclet number from effective-parameter equation tends to be enhanced when the nondimensional degradation is rather high. The simple expressions for moments and effective parameters can be used as screening tools to assess the behavior of volatile compounds in vadoze zone of soils.     

Removal of a Volatile Organic Compound in a Hybrid Rotating Drum Biofilter

A hybrid bioreactor, combining an activated sludge process (ASP) and a rotating drum biofilter (RDB), was developed and evaluated for the treatment of volatile organic compounds (VOCs) in waste gas streams. The effects of the influent VOC concentration and the organic loading rate on the VOC removal efficiency and on the pattern of biomass accumulation were investigated. Toluene was used as the model VOC, the flow rate of the waste gas stream was 0.59 L/s, and the empty-bed retention time (EBRT) in the ASP portion was 46 s with an actual retention time of about 2 s. The EBRT in the RDB portion was 38 s based on the drum volume. When the VOC feed concentration increased from 221 to 884 mg toluene/m3 (from 57.2 to 229 ppm), correspondingly the organic loading rate of the hybrid bioreactor increased from 1.58 to 6.32 kg chemical oxygen demand/m3/day (from 0.505 to 2.02kg?toluene/m3/day) based on the drum volume, both the ASP and RDB decreased, and the overall toluene removal efficiency declined from 99.8 to 74.1%. Biomass accumulation at different medium depths became more even when the organic loading rate was increased. Part of the applied VOC was biodegraded by the ASP, which suggests that this hybrid bioreactor could achieve longer runs between medium cleanings and higher VOC removal efficiencies than a single RDB bioreactor without an ASP portion at the same organic loading rate.     

Sorptive Media Biofiltration for Inorganic Nitrogen Removal from Storm Water

Passive biological filtration for nitrate removal from storm-water drainage is challenged by highly transient mass loadings, the need to adequately supply an electron donor, and potential inhibition by dissolved oxygen (DO). An approach to optimizing nitrate removal is to employ a filter medium containing a mixture of ion exchange and electron donor particles, where the former serve to retain nitrate at high loadings and enable biological denitrification to be more effective. Bench scale filtration experiments were conducted using a 50:50 volume mixture of expanded clay particles (Filtralite P) and elemental sulfur pastille. Nitrate reduction was 98% under steady flowrate operation at 30?min residence time and 2.1?mg/L influent NO3–N. Step increases in flowrate by factors of 5.2, 11, and 25 resulted in maximum effluent NO3–N of 0.93, 1.54, and 1.87?mg/L, respectively. Substantial nitrate breakthrough occurred even when effluent DO remained close to zero. The results suggest methods by which mixed media denitrification filters can be more effectively designed and operated.     

Sediment Monitoring Bias by Automatic Sampler in Comparison with Large Volume Sampling for Parking Lot Runoff

A field study was conducted to assess biases of suspended sediment concentration (SSC) analyses (ASTM Standard D3977-97) performed on discrete samples obtained by automatic sampler in comparison with actual sediment concentrations from large volume sampling. Research results indicate that the biases attributed to the monitoring of sediment event mean concentration (EMC) and median particle size in parking lot runoff by automated samplers (nonisokinetic) were minimal. Large volume samples ( ～ 15,000??L) of the first-flush event runoff were taken from a storm-water sewer system for eighteen storm events over two years. The intent was to obtain a complete portion of a storm to accurately determine EMCs and particle size distributions (PSDs). Concurrently, flow-weighted discrete samples were obtained by automatic samplers for the same portion of the events. Thus, characteristics of sediments from a whole-storm sample were compared with those of subsamples obtained by an automatic sampler using nonisokinetic sampling. SSCs and PSDs were compared for the two respective field sampling methods. The two methods showed a strong correlation for median sediment EMCs (R2 = 0.98, n = 18). Biases to particle size distributions were found to be both for the large particles (>75–150??μm) and smaller fines (<25??μm). Specific sediment size fractions captured by the large volume sampling and automatic sampler were not significantly different (α = 0.05) for D50, which = 58 and 46??μm, respectively.