挥发性气体通过填埋场复合覆盖层的一维扩散解析解

为了评价填埋场覆盖层对挥发性气体的防渗性能,建立了挥发性气体在复合覆盖层中的扩散运移模型并采用分离变量法获得了模型解析解。解析解的计算结果与数值解结果吻合得较好。分析结果表明,对于土工膜/土工复合膨润土垫（GM/GCL）与土工膜/压实黏土（GM/CCL）组成的覆盖层,覆盖层顶部气体扩散达到稳态的时间比较接近,约为1.6 a;对于压实黏土（CCL）系统达到稳定状态的时间为0.5 a;稳态时通量依次为6.0×10⁵,1.0×10⁶和7.4×10⁵ mg/ha/a。在这3个覆盖层系统中,GM/CCL对气体扩散的控制性能最差。对于GM/GCL,GCL含水饱和度从0.85增加到1时,覆盖层顶部通量减小了82.5%。饱和时GM/GCL系统顶部气体达到稳态的时间是非饱和情况下的约100倍。对于GM/CCL,CCL含水饱和度从0.1增加到0.85时,覆盖层顶部通量减小了近1个数量级。含水饱和度的变化可导致覆盖层顶部挥发性气体稳态时通量发生数量级的变化。     

气体压力和孔隙对垃圾土体气体渗透系数影响的研究

垃圾土的非饱和气体渗透系数是填埋场气体运移分析和抽气井设计的重要参数,孔隙比、有机物含量、饱和度等是影响垃圾土渗透特性的主要因素。通过研制的垃圾土非饱和渗透试验仪,进行了不同影响因素下的非饱和垃圾土气体渗透试验,发现渗透系数随渗透压力呈现非线性特性,可以用Forchheimer非达西渗流方程较好地拟合。孔隙比增加,渗透系数增大,非达西系数Ba逐渐减小,分界点的气体压力减小;有机物含量越高,渗透系数越小,分界点气体压力越大;片状分布有机物使有效连通的渗透路径减少是垃圾体气体渗透特性降低的原因;饱和度越高,垃圾土的渗透系数越小,分界点气体压力越大;在试验的有效孔隙范围内,渗透系数、分界点气体压力与有效孔隙呈现较好的相关关系、非达西系数变化不大。     

三轴应力条件下原状黄土的渗气特性

用改装的三轴渗气仪,在三轴应力条件下对不同含水率原状黄土进行渗气试验,分析了平均应力、偏应力及含水率变化对渗气系数与饱和度关系的影响,提出了考虑三者影响的渗气函数。研究结果表明:偏应力、平均应力及含水率对渗气系数与饱和度关系皆有较大的影响。平均应力(应力比相同)或偏应力(平均应力相同)作用引起饱和度增大时,渗气系数线性减小,且减小程度与含水率的大小有关;含水率增大时渗气系数随饱和度增大而减小的速率比应力增大时的小。不同应力状态下,相对渗气系数与饱和度关系,渗气系数与修正气体饱和度关系皆可归一,且可分别用以总饱和度为参量的P-v G-M模型及本文提出的修正气体饱和度幂函数(MAPL)模型描述,但相比较而言,MAPL模型参数较少,更便于实际工程应用。MAPL模型对渗气系数的预测结果与试验结果吻合较好。     

Identification of volatile organic contaminants in Washington, D.C. municipal water

A method is described by which trace quantities of volatile organic compounds can be recovered from water by purging the water with a counter-current flow of helium gas. The recovered organic mixture is separated on a suitable gas chromatographic column and eluted components are identified by means of a mass spectrometer. Compounds can be identified at concentrations in the ppt range. Nineteen volatile organic compounds have been identified in District of Columbia drinking water at concentrations below 5 ppb: 13 additional compounds were detected, but with concentrations too low for identification. Possible sources of the major contaminants are discussed.     

Mass transfer mechanisms in a heterotrophic biofilm

The diffusion coefficients of three different chemical species in naturally grown, heterotrophic biofilms have been measured and a simple model of mass transfer in a biofilm matrix is developed. The mechanical structure of the biofilm matrix reduces the molecular diffusion to about 50–80% of the value in pure water. Depending on the roughness of the biofilm surface and the flow conditions eddy diffusion increased the mass transfer into the biofilm near the surface.The influence of the diffusion potential and the donnan potential on ions have been evaluated by comparing the diffusion coefficients of a positively and a negatively charged ion and a neutral molecule in experiments with different background electrolyte concentrations. Mass transfer effects by electrostatic forces are negligible at the ionic strength of waste water and tap water.     

溶气水饱和度对气浮净水溶气效率的影响

对气浮净水系统中溶气水饱和度进行了理论分析 ,认为液相传质系数、气液交换界面系数、溶气时间及溶气温度是影响溶气效率的主要因素 .提出气体静态溶解和动态溶解的概念 ,并推导出溶气水相对饱和度的计算式 .认为在溶气和释气过程连续进行时 ,静态溶气时溶气水达到饱和需时较长 ,因此 ,溶气水中溶气量的高低主要取决于动态溶气效果     

Estimation of the Air Permeability Coefficient and the Radius of Vacuum Influence for Contaminated Soil and Groundwater Remediation

The air permeability coefficient and the radius of vacuum influence are important parameters in the design of soil vapor extraction systems for removing volatile organic chemicals, but procedures for obtaining these parameters have not yet been established. We developed procedures using previously derived analytical equations for the relationship between air discharge rates from an extraction well and the air pressure head generated in the neighborhood of the extraction well in soil with a uniform degree of water saturation in order to obtain these parameters in soil with varying degrees of water saturation. We verified that these procedures could be used to obtain these parameters by using air permeability test data from five sites. In addition, we demonstrated that these procedures could also be applied to gravel soil with fast air flow.     

Growth-Phase-Related Production of Potential Volatile-Organic Tracer Compounds by Moulds on Wood

Abstract The growth-dependent production of known and new potential tracer compounds for moulds of the genus Penicillium on pine wood is shown. The analytical method used involves diffusive sampling by an adsorbent tube (Tenax-TA), thermal desorption, gas chromatography and a mass selective detector. Mass spectra of identified and unidentified potential tracer compounds are presented. Identified compounds are l-Octene-3-ol, 2-Heptanone, 4-Allylanisole and 3-Methyl-l-butanol. In addition, several other compounds were tentatively identified or recognized in different samples by their retention time and mass spectra. The microbiologically produced volatile organic compounds (MVOC) are produced during different time periods of the mould growth cycle. The impact of these results on screening measurements for houses with mould problems is discussed together with the applicability and need for new and more tracer compounds for mould growth in buildings.     

Determining diffusion and partition coefficients of VOCs in cement using one FLEC

The diffusion and partition coefficients of eight volatile organic compounds (VOCs) in cement slabs were experimentally determined using a field and laboratory emission cell (FLEC) system based on the method developed in a previous study on the water vapor diffusion. A cement slab planted with a mixture of eight VOCs was placed in an one-FLEC system to undergo the mass diffusion in the slab and the emission to air flowing through the FLEC. The concentration of each VOC in the air flowing out of the FLEC was measured according to the EPA Method TO-17 using sorbent tube-automatic thermal desorption (ATD) and the gas chromatography-mass spectrum detector (GC-MSD) system. The diffusion and partition coefficients were then obtained by solving the inverse problem of the one-dimensional unsteady mass diffusion equations in the cement slab. And, the partition coefficient was also obtained from the total mass transfer estimated from the VOC concentration measurements and air flowrate, which was equivalent to the headspace concentration-weighting method.     

确定非饱和土渗透特性的一种新方法

用水–气运动联合测试仪对一定湿密状态下的黄土做了大量的试验,结果表明,一定含水量、不同干密度的土样浸水后,渗气系数随时间的变化趋势具有相似的规律,即具有在起初浸水后的短时间内减小,然后逐渐增大,最后趋于稳定的过程。另外,土的渗水和渗气系数随干密度的增大而降低,且干密度越大,降低的幅度也越大。在高饱和度时增湿路径对非饱和土的渗透系数影响不大,而在低饱和度时增湿路径对渗透系数影响较显著。     

石膏板中挥发性有机化合物的测定

本文采用热解析一气：阳色谱质谱联用法对石膏板中的挥发性有机化合物进行测定。本方法以质谱定性,外标法定量,最低检出限为0．001mg／kg,相对标准偏差小于5％。该方法本底低,操作简单,快捷,灵敏度高。     

不同饱和度砂岩渗透率、孔隙度随应力变化规律研究

 制备含水饱和度为0%～70%的砂岩岩样,利用低渗透岩石气体渗透测试装置,对不同含水饱和度的砂岩岩样进行气渗试验,测量其在不同围压和渗压下的渗透率以及对应围压下的孔隙度,分析和讨论不同含水饱和度低渗透砂岩渗透率、孔隙度与应力三者之间的关系。得到以下结论：含水饱和度低于50%的低渗透砂岩,其气测渗透率随孔隙压力的增大而减小,含水饱和度高于50%的低渗透砂岩,其气测渗透率的变化规律相反;气测渗透率与孔隙压力符合指数函数关系;随着含水饱和度的增大,气测渗透率对孔隙压力变化的敏感性减少,且气测渗透率对孔隙压力变化的敏感性随着孔隙压力的增大而增大;绝对渗透率、孔隙度与围压均呈指数函数关系;随着含水饱和度的增大,绝对渗透率对围压变化的敏感性增大,对孔隙度变化的敏感性减小,且绝对渗透率和孔隙度对围压变化的敏感性均是随着围压增大而减小;低渗透砂岩的孔隙度与其绝对渗透率的变化成正相关,孔隙度的少量降低即能引起其绝对渗透率的大幅度下降;绝对渗透率与孔隙度成指数函数关系;随着含水饱和度增大,绝对渗透率对孔隙度变化的敏感性增强,且随着孔隙度的增大,绝对渗透率对孔隙度变化的敏感性也逐渐增强。     

吹扫捕集-气相色谱在线测定饮用水VOCs方法研究

建立了吹扫捕集-气相色谱法在线测定饮用水中19种挥发性有机物的方法,方法集自动进样、吹扫捕集浓缩、气相色谱分离检测于一体,水质监测数据可实时上传,在优化的仪器吹扫和色谱条件下,在0. 005～0. 03 mg/L的浓度范围内有较好的线性,相关系数R为0. 995 0～0. 999 8,相对标准偏差为4. 4%～15. 0%(n=7),加标回收率为70. 1%～122%。应用案例表明,优化建立的方法能有效地分离、检测饮用水中的19种挥发性有机物,操作简单,适于饮用水中挥发性有机物的实时、自动和连续监测。     

不同含水饱和度低渗透岩石气体滑脱效应研究

低渗透岩石气体滑脱效应的研究是油气开采与存储领域十分重要的内容,但目前关于低渗透岩石气体滑脱效应的研究大多是在气体单相流下进行的,对于气–液两相流时,液体对气体滑脱效应的影响,所做的研究不足。因此,利用研发的低渗透岩石惰性气体渗透性测试系统,对含水饱和度为0~70%的低渗透砂岩,进行了不同含水饱和度的低渗透岩石气体滑脱效应及有效渗透率变化规律的研究,试验结果表明:(1)二次公式k_g=k_∞(1+b/q-a/p~2)可以较为准确的解释低渗透岩石的气体滑脱效应,准确性明显高于Klinkenberg公式。(2)含水饱和度对低渗透岩石的气体滑脱效应有明显影响,气体滑脱效应随着含水饱和度增大而减少,在含水饱和度超过50%时,气体滑脱效应几乎完全被限制。(3)由于水的作用,含水的低渗透岩石随着围压增大,气体滑脱效应减少,这与克氏理论的结论相反。(4)含水饱和度对低渗透岩石的有效渗透率影响显著,随含水饱和度的增大有效渗透率减少,且围压越大,低渗透岩石的有效渗透率对含水饱和度变化越敏感。(5)低渗透岩石的有效渗透率与含水饱和度符合幂函数关系,即k_∞=k_0(1-S_w)~c。     

Production of lipophilic volatile organohalogen materials during laboratory chlorination of some waste water and polluted river water samples from Yugoslavia

Water chlorination leads to the generation of various halogenated products of natural and waste water organic mater. In natural surface water humic matter usually makes the greatest part of the total organic matter. However, in the river water polluted with various organic wastes, other organic matter is also present in significant concentrations. The investigation of the relationship between the concentration of organic matter in the samples of waste water and heavily polluted river waters in Yugoslavia on one side, and the production of the lipophilic volatile organohalogen materials during the process of their chlorination on the other side is described. The production of the halomethanes and other ECD response materials during the chlorination of water samples in laboratory conditions is compared with the concentrations of organic materials in water samples. From the obtained linear correlation coefficients, possibilities of predicting amounts of organohalides during the chlorination process by using several very simple methods for the organic materials estimation in the investigated water samples are discussed and compared.     

The determination of gas phase dry deposition fluxes and mass transfer coefficients (MTCs) of polychlorinated biphenyls (PCBs) using a modified water surface sampler (WSS)

Gas phase PCB dry deposition and concentration samples were collected simultaneously between July 2004 and May 2005 at a suburban site in Bursa, Turkey. A modified water surface sampler (WSS) was employed to collect gas phase fluxes while a high-volume air sampler (HVAS) was used for concentration samples. The WSS was able to collect both particle and gas phase PCB deposition samples. The collected PCBs on water surface were captured by a filter and an XAD-2 resin column during water cycle. The average of gas phase PCB deposition flux, determined by analyzing the XAD-2 resin column, was 79.3+/-40.5 ng m(-2) d(-1) and its percentage in total (gas+particle) PCB flux was about 60. The average of gas phase PCB concentration measured concurrently with flux samples was 224.4+/-160.2 pg m(-3) and its ratio to the total (gas+particle) PCB concentration was 85%. This difference was likely due to the different deposition characteristics of gases and particulates. Dominant PCB homolog groups were 3-4 chlorobiphenyls (CBs) for both ambient air and gas phase deposition samples. Mass transfer coefficients (MTC, K(g)) for air-side were determined using gas phase flux and ambient air concentration values. The average overall K(g) ranged between 0.21 and 0.96 cm s(-1) with an average of 0.60+/-0.19 cm s(-1).     

Modeling the formation and growth of organic films on indoor surfaces

Emission, transport, and fate of semi‐volatile organic compounds (SVOCs), which include plasticizers, flame retardants, pesticides, biocides, and oxidation products of volatile organic compounds, are influenced in part by their tendency to sorb to indoor surfaces. A thin organic film enhances this effect, because it acts as both an SVOC sink and a source, thus potentially prolonging human exposure. Unfortunately, our ability to describe the initial formation and subsequent growth of organic films on indoor surfaces is limited. To overcome this gap, we propose a mass transfer model accounting for adsorption, condensation, and absorption of multiple gas‐phase SVOCs on impervious, vertical indoor surfaces. Further model development and experimental research are needed including more realistic scenarios accounting for surface heterogeneity, non‐ideal organic mixtures, and particle deposition.     

Oxygen transfer in membrane bioreactors treating synthetic greywater

Mass transfer coefficients (k_La) were studied in two pilot scale membrane bioreactors (MBR) with different setup configurations treating 200 L/h of synthetic greywater with mixed liquor suspended solids' (MLSS) concentrations ranging from 4.7 to 19.5 g/L. Besides the MLSS concentration, mixed liquor volatile suspended solids (MLVSS), total solids (TS), volatile solids (VS), chemical oxygen demand (COD) and anionic surfactants of the sludge were measured. Although the pilot plants differed essentially in their configurations and aeration systems, similar α-factors at the same MLSS concentration could be determined. A comparison of the results to the published values of other authors showed that not the MLSS concentration but rather the MLVSS concentration seems to be the decisive parameter which influences the oxygen transfer in activated sludge systems operating at a high sludge retention time (SRT).     

环境科学中的渗流力学问题

针对环境科学研究中的渗流力学问题,从环境科学理论和渗流力学理论出发,探讨了挥发性有机污染物在土壤中的迁移机制和规律、地下水多组分反应溶质的迁移模型和规律;分析了垃圾填埋场气体迁移和二次污染问题。在此基础上,提出了挥发性有机物的迁移过程及控制机制的不确定性的两个方面和多组分水化学模型与水动力迁移模型的耦合模型建立的必要性。文中分析对环境科学与渗流力学交叉研究问题的深层次认识具有重要的理论价值和实际意义。     

等向应力条件下非饱和原状黄土增湿渗水特性试验研究

渗水系数是非饱和土固结分析的关键参数之一。用自制的非饱和土三轴剪切渗透仪,在无应力及不同等向应力下分别对不同和相同孔隙比的原状黄土进行了直接向试样分级注水使吸力逐渐减小的增湿渗透试验,分析了孔隙比,应力与饱和度及吸力对增湿渗水系数的影响,对比分析了无应力与应力作用下的渗水特性,提出了可以考虑应力与饱和度或吸力影响的非饱和原状黄土增湿渗水的渗透性函数。研究结果表明:孔隙比和应力对渗水系数与饱和度关系及渗水系数与吸力关系皆有影响,吸力较大时对后者几乎没有影响,可近似归一。无应力及不同应力条件下,只要孔隙比相同,则渗水系数与饱和度或吸力关系相同;相对渗水系数与吸力的关系不能归一,同一吸力对应的相对渗水系数随孔隙比的减小或应力的增大而增大,而相对渗水系数与饱和度及吸力比(吸力与脱气值之比)关系皆可以归一。v G-M模型不适用于描述常孔隙比下原状黄土的渗水系数;提出的渗透函数可以预测一定等向应力作用下增湿过程中饱和度增大及吸力减小时原状黄土的渗水系数,预测结果与试验结果吻合较好。