Modeling of air stripping from volatile organic compounds in biological treatment processes

The removal of volatile organic compounds from biological treatment processes occurs through several mechanisms. These include biodegradation, adsorption onto solids, and air stripping or volatilization to the atmosphere. Volatilization results in fugitive emissions to the atmosphere, which is largely uncontrolled. Recent regulations have called for increased evaluation and control of inadvertent volatile organic compounds emissions from treatment processes. The use oxygen as a parallel volatile compound is extremely useful for prediction of volatile organic compounds removal by air stripping. In this study, the simultaneous biodegradation and air stripping of volatile organic compounds, based on steady state mass balance are examined and a general approach to estimating the dominant removal mechanism is developed. A Monte Carlo simulation technique was used to estimate air stripping over a wide range of operating conditions. Several volatile organic compounds were selected for this study. The results showed the values drived from the model correspond with the experimental data for benzene, toluene, methylene chloride, trichloroethylene, and methyl isobutyl ketone.     

Distribution of volatile organic compounds around a polluted river

The objectives of this study were to investigate the species and the concentration distribution of volatile organic compounds around a heavily polluted river. Air samples were collected seasonally at different locations near the polluted river. Samples were then analyzed by gas chromatography (electron capture detector for chlorinated organic compounds and flame ionization detector for ordinary hydrocarbons). The data was then analyzed by the statistical product and service solutions software. The results showed that total of 26 species of volatile organic compounds were identified. Each individual had its own concentration distribution pattern at different seasons and aliphatic volatile organic compounds displayed much higher concentrations than most benzenoic volatile organic compounds. In aliphatic volatile organic compounds, 1,2-dibromo-3-chloropropane, hexachlorobutadiene and 1,2-dibromoetane had much higher concentrations at the nearby environment of the river and they have been claimed to be carcinogenic to some experimental animals and possibly to human. Therefore, It is in doubt that for a long term, the volatile organic compounds evaporating out of the stream may threat the health of the residents living very close to the river. The concentrations of tetrachloroethene, 1,1,2,2-tetrachloroethane, hexachlorobutadiene, dibromoetane, dichlorobenzene and sec-butylbenzene appeared at the nearby environment of the river had significant correlations (P < 0.05) with those of each other or many other volatile organic compounds.     

Geochemistry of volatile organic compounds in seawater: Mesocosm experiments with 14C-model compounds

A series of ten radiotracer experiments were conducted in controlled experimental ecosystems (mesocosms) to investigate the behavior of volatile organic compounds (VOC) in seawater. Time-series measurements of the redistribution of ¹⁴C-activity within several major pools—dissolved, particulate, intermediate metabolite, and CO₂—in the ecosystem made possible an evaluation of the rates of processes—volatilization, biodegradation, Sorption and sedimentation—acting to remove VOC from seawater in summer. The behavior of the model ¹⁴C-VOC fell into three categories. Aromatic hydrocarbons (benzene, toluene, naphthalene) were subject to both volatilization and biodegradation, with mineralization dominating in summer. Chlorinated C₂-hydrocarbons (tetrachloroethylene) and chlorinated benzenes (chlorobenzene, 1,4-dichlorobenzene, and 1,2,4-trichlorobenzene) were affected only by volatilization and were relatively resistant to biodegradation. Of all the model VOC studied, only aliphatic hydrocarbons (decane and octadecane) were sorbed onto suspended paniculate matter; however, the primary route of loss from the water column appeared to be biodegradation rather than sedimentation. The mesocosm-derived removal rate constants were then applied to estimate summer VOC residence times in Narragansett Bay, Rhode Island of about 1 day for aromatic hydrocarbons, 1 week for the chlorinated VOC and about 1 day for aliphatic hydrocarbons. Residence times in winter might be on the order of 1 week for all VOC.     

Development of low-cost passive sampler from cow bone char for sampling of volatile organic compounds

A simple and low-cost passive sampler for collection of volatile organic compounds, specifically benzene, toluene, ethylbenzene and xylene (BTEX), from the ambient air has been developed by using cow bone char (CBC) as an adsorbent with desorption by solvent extraction prior to analysis by gas chromatography–mass spectrometry (GC–MS). The laboratory-made CBC was prepared by calcination process in a partially oxidative atmosphere. The developed passive sampler was tested for a suitable amount of CBC used, diffusion tube type and size, and sampling duration, in a closed chamber saturated with each of the BTEX vapors. With the optimum amount of 250 mg CBC packed in a glass bottle (82.6 mm height × 11.1 mm i.d.) and the exposure time of 168 h, detection limits (µg/m³) for BTEX determination using this developed sampler together with GC–MS were 0.28 (benzene), 0.79 (toluene), 0.58 (ethylbenzene), 0.28 (p-xylene) and 0.54 (o-xylene). The proposed method was applied to sampling BTEX from selected petrol stations, traffic congestion areas and a rural area in Chiang Mai Province, Thailand. The BTEX concentrations detected were well correlated with their sources as they were the highest at the petrol station sites, lower at the traffic congestion area sites and the lowest at the rural area site. The laboratory-made passive sampler containing CBC has thus opened up a possibility of having a simple and effective device for sampling of BTEX in the ambient air.     

岩溶地区垃圾渗透液中36种挥发性有机物的测定

应用吹扫捕集-气相色谱-质谱法测定岩溶地区垃圾渗透液中36种挥发性有机物（VOCs）的含量。获取样品溶液5 mL于吹扫瓶中,利用TELEDYNE TEKMAR型吹扫捕集直接进样,经DB-VRX毛细管色谱柱分离、电子轰击电离（EI）全扫描检测,选择特征离子,再用外标法进行定量测定。结果表明:36种挥发性有机物的质量浓度在1～100 μg·L-1 范围内,与其峰面积呈线性关系,方法检出限在0.03～0.27 μg·L-1 之间,加标回收率在88%～110%之间,相对标准偏差（n=7）在2.32%～6.51%之间。      

Occurrence of selected volatile organic compounds in a bra cup manufacturing facility

This article presents a review of the types and levels of volatile organic compounds (VOC) detected in a bra cup manufacturing facility (considering the past 4 years) while conducting a human health risk assessment to selected VOCs. Most of the tested VOCs were undetected, except in the flocking section in 2014. However, from time to time dichloromethane and toluene were detected in the facility. Dichloromethane levels showed an increase with time in the laminating section (except during 2014) with drastically higher levels in 2015. SWIFT VS1 6016/5A (an adhesive) as per the material safety data sheet (MSDS) was the dichloromethane source. However, none of the MSDS revealed the occurrence of carcinogenic benzene (which was detected in 2014 in the flocking section) and 1,4-dichlorobenzene (which was detected in 2013 in the laminating and injection molding sections) and non-carcinogenic toluene indicating that MSDS do not accurately provide the identity of chemicals. Hazard Indices (HI) for non-carcinogenic VOCs and the total lifetime cancer risks (LCRs) and occupational exposure indices (E _i ) for carcinogenic VOCs varied during the different time periods. Toluene in many cases accounted for 100 % of the HI. LCRs and E _i of dichloromethane accounted for 100 % of the total LCR and total E _i , respectively (except in the flocking section in 2014). LCR and E _i of the individual VOCs (even the total LCR and E _i values) were simultaneously high whenever the levels of the individual VOCs had exceeded the regulatory limits posing a health risk. Some measures needed to prevent exposure to VOCs are discussed in this article.     

Chlorinated volatile organic compounds found near the water surface of heavily polluted rivers

The objectives of this study were to identify the chlorinated volatile organic compounds near the water surface of two heavily polluted rivers in the south of Taiwan and compare their concentration distributions. Air samples were collected seasonally at the upstream, midstream and downstream water surfaces of each river and the chlorinated volatile organic compounds were analyzed qualitatively and quantitatively by gas chromatography and electron capture detector. Totally, twelve kinds of chlorinated volatile organic compounds were found at the water surfaces of both rivers and many of them were reported to be carcinogenic or probably carcinogenic to human. The results showed that each chlorinated volatile organic compound had its own distribution pattern and no good correlation of chlorinated volatile organic compounds between both rivers was obtained. The chlorinated volatile organic compounds identified at the river water surface of Fong Shan Stream showed much higher concentration than those of Chuen-Tsen River. Several chlorinated volatile organic compounds, including chlorodibromomethane, hexachlorobutadiene, 1,1,2,2-tetrachloroethene and 1,2-dibromo-3-chloropropane were found with much higher concentration (mean concentrations of 124.5 μg/m³, 334.5 μg/m³, 92.2 μg/m³, 268.4 μg/m³, respectively) at the water surface of Fong Shan Stream in some seasons (especially spring and summer, summer and winter, spring and winter, spring and summer, respectively) and they were reported to be possibly carcinogenic to human. Therefore, it may be concluded that the people living close to Fong Shan Stream possibly had higher health risks due to the release of volatile organic compounds from the heavily polluted river.     

Aromatic volatile organic compounds and their role in ground-level ozone formation in Russia

This paper reports proton mass spectrometry data on aromatic volatile organic compounds (VOCs) (benzene, toluene, phenol, styrene, xylene, and propylbenzene) obtained in different Russian regions along the Trans-Siberian Railway from Moscow to Vladivostok, based on expedition data retrieved using the TRO-ICA-12 mobile laboratory in the summer of 2008. The contribution of aromatic VOCs to ozone formation in the cities and regions along the measurement route has been estimated quantitatively. The greatest contribution of aromatic VOCs to ozone formation is characteristic of large cities along the Trans-Siberian Railway (up to 7.5 ppbv O₃) specified by the highest concentrations of aromatic VOCs (1–1.7 ppbv) and nitrogen oxides (>20 ppbv). The results obtained are indicative of a considerable contribution (30–50%) of anthropogenic emissions of VOCs to photochemical ozone generation in the large cities along the Trans-Siberian Railway in hot and dry weather against the background of a powerful natural factor such as isoprene emissions controlling the regional balance of ground-level ozone in warm seasons.

     

某石油化工场地土层挥发性有机物的污染特征

在调查华北平原一个污染年限超过35年的石油化工场地时,采用便携式仪器土层测气方法,快速、准确地测定了场地内40多个钻孔不同深度土层中挥发性有机物(VOCs)的浓度。基于对场地地质水文地质条件的认识,以及通过对大量数据的分析对比和应用空间变异分析方法,得出了对场地土层介质中VOCs污染特征的如下认识:(1)土层VOCs浓度的垂向变化可概括为污染源淋滤型、包气带扩散污染型、地下水波动带污染型和混合污染型四种污染类型;(2)在包气带砂土层和粉土层中,VOCs的扩散规律可近似用指数模型描述;(3)包气带土层中VOCs优先积聚在渗透性强的砂性土层中,砂土层中VOCs浓度是粉土层中VOCs浓度的1.5～12倍,平均3.76倍;(4)土层VOCs浓度的水平变异性表现为包气带土层的变异性要比地下水波动带土层大,且水平变异性能在25m尺度内得到充分显示;而土层VOCs浓度的垂向变异性随地而异,变化复杂,很难用统一的一个量化尺度来表征。本文对这一典型污染场地的剖析,有助于从事污染场地调查人员认识我国华北平原石油化工类场地的污染特征,并为调查与治理类似污染场地提供技术依据。     

Comparison of volatile organic compounds in stormwater and groundwater in Seoul metropolitan city,South Korea

Volatile organic compounds (VOCs) detected in stormwater were compared with VOCs present in emission sources, air, groundwater, and influent to sewage treatment plants in Seoul to understand their fate and transport in the urban hydrological system. Stormwater is a carrier of non-point source pollutants and contains VOCs from land surfaces and air. Samples of stormwater and influent to sewage treatment plants were collected and analyzed for 61 VOCs, while the VOCs in emission sources, air and groundwater were investigated through literature reviews for comparison. The results showed that the most frequently detected VOCs in stormwater were similar to those in air. However, the atmospheric concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary-butyl ether (MTBE) were too low to explain their frequent detection and high concentrations in stormwater. As a result, land surfaces seem to be a primary source of these VOCs in stormwater. Comparison of the VOCs in stormwater and groundwater showed that toluene and MTBE were frequently detected in both media, but more often and at higher concentrations in stormwater. This finding indicates that stormwater recharge is a source of toluene and MTBE in groundwater. Regarding groundwater, land surfaces seem to be a primary source of toluene, while urban air is the primary source in the case of MTBE. Specifically, the MTBE values in air were sufficiently high to explain its levels in groundwater, which had continually increased and remained low afterward. Furthermore, the high ratios of TEX (toluene, ethylbenzene, and xylenes) to benzene and MTBE in stormwater indicated that TEX had additional sources other than vehicles, most likely hydrocarbon solvents. These solvents seem to be a primary source of TEX and other frequently detected VOCs in stormwater. However, trichloroethylene (TCE), tetrachloroethylene (PCE) and their dechlorination intermediates were far more frequently detected and at higher concentrations in groundwater than in stormwater. Additionally, their concentrations frequently exceeded the water-quality criteria. It seems that halogenated solvents had produced contamination plumes of these chlorinated VOCs in the Seoul aquifer. Based on VOCs detected in Seoul, stormwater was mixed with groundwater in combined sewers and flowed into sewage treatment plants. The results imply that organic solvents should be handled with extreme care to protect groundwater quality.     

基于多相流数值模拟的某石油污染场地地下水中VOCs自然衰减过程识别及能力评估

监测自然衰减(monitoring natural attenuation,MNA)技术是目前普遍认可的去除地下水中挥发性有机污染物(volatile organic compounds,VOCs)的技术。但受其修复周期长、监测费用昂贵等因素的影响,实地开展MNA技术修复污染场地具有一定的局限性。基于此,本研究运用多相流数值模拟手段识别了某石油污染场地内典型VOCs污染物(苯、甲苯、萘)在地下水中的自然衰减过程并评估了其自然衰减能力。结果表明:采用TMVOC所建立的多相流数值模拟模型能较好地预测和识别VOCs在地下水中的衰减规律;在研究区中,苯、甲苯和萘由于理化性质差异,在地下水中的污染羽分布特征不同,其自然衰减过程受挥发、吸附和生物降解作用的影响程度也不同;挥发和生物降解作用对VOCs自然衰减的影响程度均为苯>甲苯>萘,而吸附作用对VOCs自然衰减的影响程度为萘>甲苯>苯;在污染源被阻断的前提下,苯、甲苯和萘分别在泄漏发生7.0、6.5和6.0年后通过自然衰减达到理想去除效果。本文研究成果可以为水文地质条件类似的VOCs污染场地MNA修复方案的制定和修复效果评估提供理论支撑。     

Fate and transport of volatile organic compounds in glacial till and groundwater at an industrial site in Northern Ireland

Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel Monkstown industrial site, Belfast, Northern Ireland. The objectives of this study were to (1) investigate the characteristics of the geological material and its influences on contaminated groundwater flow across the site using borehole logs and hydrological evaluations, and (2) identify the contaminants and examine their distribution in the subsurface geological material and groundwater using chemical analysis. This report focuses on the eastern car park (ECP) which was a former storage area associated with trichloroethene (TCE) degreasing operations. This is where the greatest amount of volatile organic compounds (VOCs), particularly TCE, were detected. The study site is on a complex deposit of clayey glacial till with discontinuous coarser grained lenses, mainly silts, sands and gravel, which occur at 0.45–7.82 m below ground level (bgl). The lenses overall form an elongated formation that acts as a small unconfined shallow aquifer. There is a continuous low permeable stiff clayey till layer beneath the lenses that performs as an aquitard to the groundwater. Highest concentrations of VOCs, mainly TCE, in the geological material and groundwater are in these coarser lenses at ∼4.5–7 m bgl. Highest TCE measurements at 390,000 μg L⁻¹ for groundwater and at 39,000 μg kg⁻¹ at 5.7 m for geological material were in borehole GA19 in the coarse lens zone. It is assumed that TCE gained entrance to the subsurface near this borehole where the clayey till was thin to absent above coarse lenses which provided little retardation to the vertical migration of this dense non-aqueous phase liquid (DNAPL) into the groundwater. However, TCE is present in low concentrations in the geological material overlying the coarse lens zone. Additionally, VOCs appear to be associated with poorly drained layers and in peat <3.0 m bgl in the ECP. Some indication of natural attenuation as VOCs degradation products vinyl chloride (VC) and dichloromethane (DCM) also occur on the site.     

Methods for evaluating in-stream attenuation of trace organic compounds

Wastewater treatment plants are often the most substantial contributor of trace organic compounds including pharmaceuticals, steroidal hormones, and surfactants to surface waters. Studying stream reaches below wastewater treatment plants provide valuable information on the environmental persistence of these compounds. Three methods for conducting field investigations to evaluate in-stream attenuation of trace organic compounds are presented: (1) using intrinsic tracers in wastewater, (2) environmental sampling coupled with dye studies to assess travel times between sample locations, and (3) Lagrangian sampling. Advantages and limitations of each method are discussed, along with key findings from several investigations.     

Thermodynamic properties of organic iodine compounds

A critical evaluation has been made of the thermodynamic properties reported in the literature for 43 organic iodine compounds in the solid, liquid, or ideal gas state. These compounds include aliphatic, cyclic and aromatic iodides, iodophenols, iodocarboxylic acids, and acetyl and benzoyl iodides. The evaluation has been made on the basis of carbon number systematics and group additivity relations, which also allowed to provide estimates of the thermodynamic properties of those compounds for which no experimental data were available. Standard molal thermodynamic properties at 25 °C and 1 bar and heat capacity coefficients are reported for 13 crystalline, 29 liquid, and 39 ideal gas organic iodine compounds, which can be used to calculate the corresponding properties as a function of temperature and pressure. Values derived for the standard molal Gibbs energy of formation at 25 °C and 1 bar of these crystalline, liquid, and ideal gas organic iodine compounds have subsequently been combined with either solubility measurements or gas/water partition coefficients to obtain values for the standard partial molal Gibbs energies of formation at 25 °C and 1 bar of 32 aqueous organic iodine compounds. The thermodynamic properties of organic iodine compounds calculated in the present study can be used together with those for aqueous inorganic iodine species to predict the organic/inorganic speciation of iodine in marine sediments and petroleum systems, or in the near- and far-field of nuclear waste repositories.     

Effects of land use on the spatial distribution of trace metals and volatile organic compounds in urban groundwater, Seoul, Korea

To investigate the urban groundwater contamination by eight trace metals and 69 volatile organic compounds (VOCs) in relation to land use in Seoul, a total of 57 groundwater samples collected from wells were examined using a non-parametric statistical analysis. Land use was classified into five categories: less-developed, residential, agricultural, traffic, and industrial. A comparison of analyzed data with US EPA and Korean standards for drinking water showed that some metals and VOCs exceeded the standards in a few localities, such as Fe (N=5), Mn (N=6), Cu (N=1), TCE (N=6), PCE (N=8), 1,2-DCA (N=1), and 1,2-dichloropropane (N=1). Among the 69 investigated VOCs, 19 compounds such as some gasoline-related compounds (e.g., toluene) and chlorinated compounds (e.g., chloroform, PCE, TCE) were detected in groundwater. Non-parametric statistical analysis showed that the concentrations of most trace metals (Fe, Mn, As, Cr, Pb, Cd) and some VOCs (especially, TCE, PCE, chloroform; toluene, carbon tetrachloride, bromodichloromethane, CFC113) are significantly higher in the industrial, residential, and traffic areas (P<0.05), indicating that anthropogenic contamination of urban groundwater by those chemicals is growing. Those chemicals can be used as effective indicators of anthropogenic contamination of groundwater in urban areas and therefore a special attention is warranted for a safe water supply in those areas. The results of this study suggest that urban groundwater quality in urban areas is closely related with land use.     

水资源中氯代烃污染物的去除方法

随着工业化的发展。氯代有机溶剂使用越来越广泛。并且难于去除。在20世纪90年代初期，人们就已认识到用Fe^0恢复污染的地下水的潜力。国外正在研究帮使用扔几种还原挥发性氯代烃的还原反应介质，尤其要提高的是双金属反应系统，反应速度快，而且脱Cl中国难解产物少，目前国也只停留在实验室研究阶段，个别做了地上反应器的验证实验，它的脱Cl机理、介质钝化和完全脱Cl问题还有待于进一步研究。     

Exploration for concealed orebodies by the analysis of volatile organic compounds contained in surface rocks: Trèves Zn-Pb deposit (Gard, France)

A previous study (Disnar et al., 1986a) indicated significant volatile hydrocarbon compounds (nC₁ to C₅) in mineralized carbonate rocks of the Trèves Pb-Zn deposit (Gard Dept., France) as well as an accumulation of methane, ethylene and ethane in the hanging wall of the deposit. The present study analyzed rock samples taken from outcrops vertically above and at a distance from the deposit and identified three anomalous zones indicating the presence of concealed mineralization. The first zone is due to methane (radius about 3 km), the second, to alkenes (about 2 km) and the third, to alkanes, higher homologues of methane (about 1 km). These anomalies are interpreted as resulting from migration of these compounds through the sedimentary cover from the deposit where they could have been generated during mineralizing events, or during subsequent diagenesis. Their specific signature with regard to that given by samples taken at a distance from the orebodies can be attributed to the hydrothermal and biological processes responsible for the deposition of the ore.     

Enhanced CE-QUAL-W2 model to predict the fate and transport of volatile organic compounds in water body: Gheshlagh reservoir as case study

Intentional and/or accidental volatile organic compound (VOC) spill into water bodies may lead to severe contamination and health problems in water infrastructures. The importance and widespread use of petroleum products and the threats posed by these products on surface water resources in Iran necessitates the access to numerical hydrodynamic and water quality simulation models with appropriate capabilities. Simulation the fate and transport of VOC in both flowing and standing water bodies is a fairly complex problem. In this research, CE-QUAL-W2 model is modified to simulate the fate and transport of VOC [i.e., Methyl tert-butyl ether (MTBE), benzene] in standing and flowing water bodies. The performance of the modified CE-QUAL-W2 model is evaluated in a MTBE pollution spill at Khalife-Tarkhan river along the headwaters of Gheshlagh reservoir, Kordestan, Iran. The results show the modified CE-QUAL-W2 model’s capability to depict the spatial and temporal variation of MTBE in comparison with recorded data from MTBE spill event of Gheshlagh reservoir. Based on the simulation results of modified CE-QUAL-W2 model, reservoir cleanup time in different meteorological and hydrological scenarios is evaluated. The results show Gheshlagh reservoir cleanup time reduced in scenarios that included air temperature reduction, wind speed increasing, and high inflow condition.     

Composite dust grains: Modeling of infrared absorption bands

We investigate the influence of small-scale asphericity of the surfaces of dust grains on the characteristics of the two deepest absorption bands observed in the spectra of protostellar objects and stars (the 3.1 μm water-ice and 9.7 μm silicate bands). The model used has composite particles in the form of radially inhomogeneous spheres with intermediate layers in which the index of refraction changes. The observed band widths and the ratios of the optical depths at the band centers can be explained if the grains are composed of small particles consisting of silicate cores with thin ice mantles and rough surfaces. The grain surface roughness considerably broadens the profile of the silicate band.     

An analytical model for vapor‐phase volatile organic compound diffusion through landfill composite covers

One‐dimensional mathematical models for vapor‐phase volatile organic compound (VOC) diffusion through composite cover barriers are presented. An analytical solution to the model was obtained by the method of separation of variables. The results obtained by the proposed solution agree well with those obtained by a numerical analysis. Based on the proposed analytical model, the VOC breakthrough curves of five different composite covers are compared. The effects of degree of saturation of geosynthetic clay liner (GCL) or compacted clay liner (CCL) on VOC migration in the composite covers are then presented. Results show that the composite cover barriers provide much better diffusion barriers for VOC than the single CCL. The top surface steady‐state flux for a composite barrier, consisting of a 1.5 mm geomembrane (GM) and a 20 cm CCL, can be 8.3 times lower than that for a 30 cm CCL. The surface steady‐state flux for the case with (1.5 mm GM + 6 mm GCL) was found to be 2.3 times lower than that for the case with (1.5 mm GM + 20 cm CCL). The degree of saturation S_r of the CCL has a great influence on VOC migration in composite covers when S_r is larger than 0.5. The steady‐state flux at the surface of GM for the case with S_r = 0.7 can be 1.8 times lower than that for the case with S_r = 0.2. The proposed analytical model is relatively simple and can be used for verification of complicated numerical models, analysis of experimental data and performance assessment of composite cover barriers. Copyright © 2016 John Wiley & Sons, Ltd.