地下水浅埋区某加油站特征污染物空间分布简

加油站渗漏污染地下水已经是一个世界性的问题。由于浅埋区加油站储罐与地下水密切接触，更加剧储罐的腐蚀。为揭示加油站渗漏的典型污染物石油烃（TPH）、苯系物（BTEX）、萘和甲基叔丁基醚（MTBE）在该水文地质条件下的迁移变化，在浅埋区某加油站开展了平、枯、丰水期的地下水监测工作。在水平分布上，TPH、BTEX、萘基本相似，均在加油岛附近形成高浓度区，而MTBE则更易随地下水流动而迁移，呈现出不同的污染晕。在垂直分布上，地下水的水位变动是污染物浓度分布的主要影响因素。     

地下水中BTEX的原位生物修复研究进展

BTEX是苯、甲苯、乙苯和二甲苯的统称,存在于原油和石油产品中,其作为化工原料,广泛应用于农药、塑料及合成纤维等制造业.BTEX已成为地下水中普遍存在的污染物,自然衰减或生物修复工程已成功应用于地下水中BTEX的去除.自然衰减受BTEX污染的地下水具有良好的效果,但相比之下,生物修复工程更快、更有效.综述了在好氧和厌氧条件下,地下水中BTEX原位生物修复过程的微生物降解机制.     

颗粒活性炭去除水中甲基叔丁基醚的可行性研究

随着甲基叔丁基醚（MTBE）作为汽油添加剂被持续大量使用，其已成为一种地下水中常见的有机污染物。本文通过纯净水、自来水和地下水中MTBE的平衡吸附容量和微型快速穿透实验（MCRB），比较了5种不同种类活性炭对MTBE的吸附性能。结果显示，苯酚值可准确预测活性炭样品对MTBE的平衡吸附容量大小次序，而丹宁酸值则可大致估计活性炭在实际处理应用时的吸附速度和吸附容量利用率。水样中共存的有机成分降低了活性炭对纯净水中MTBE的吸附容量，在背景TOC较低的去离子水中，活性炭对于MTBE的吸附性能反而比在地下水中降低得更多。穿透实验数据显示双柱串联的处理方式是高效应用活性炭吸附水中MTBE的优选工艺。使用环境友好的竹质活性炭去除地下水中MTBE具有良好的可行性和较高的性价比。     

地下水环境中甲基叔丁基醚运移过程的动力学模型

建立了地下水环境中甲基叔丁基醚(MTBE)运移过程的变系数动力学模型,并对模型进行了验证和参数灵敏度分析.模拟结果表明,地下水流速和阻滞系数对于MTBE的运移过程影响最为显著,而水动力弥散系数的影响较小,忽略其变化不会对预测地下水环境中污染物运移的环境动力学行为造成太大误差.由此得到的结论可定量研究MTBE在地下水环境中的对流.扩散特征,还可为MTBE污染地下水的预测预报、修复治理等研究提供科学依据.     

强化生物通风修复过程中柴油衰减规律及其影响因素研究

强化生物通风技术对于修复因地下储油罐泄漏引起的土壤污染具有很大的应用前景。通过室内土柱模拟柴油泄漏污染土壤，从土柱中总石油烃（total petroleum hydrocarbon，TPH）剖面分布随时间的变化及降解模式角度，分析了其自然衰减和强化生物通风过程。结果表明：初始柴油浓度直接影响着各柱在自然衰减和强化生物通风过程中柱内的残余TPH平衡分布曲线的形状和浓度峰值位置；在前期自然衰减过程中（约1个月），当土壤中的柴油浓度为5 000～40 000 mg油/kg土时，整个柱内TPH变化的主要原因是重力扩散迁移的结果；当土壤中的柴油浓度≤5 000 mg油/kg土时，其TPH的变化不仅是重力扩散迁移作用的结果，生物降解作用也存在；通风约2个月后，抽提作用对于保持土柱上部柴油浓度稳定变化的意义较为突出。     

地下水环境管理与污染防治技术

归纳了造成地下水污染的主要污染源，分析了污染物入渗的主要途径，探讨了污染物在土壤及地下水中迁移转化过程，提出了加强污染源管理，保护地下水环境的技术措施。     

生物可渗透性反应墙修复石油烃污染地下水的效果及微生物多样性研究

采用可渗透性反应墙(PRB)协同微生物作用对石油烃污染地下水进行室内模拟修复.研究结果表明,生物PRB对石油烃污染地下水具有较好的处理效果.反应器运行200 d后,生物PRB前端介质总石油烃(TPH)含量高,15个取样点的TPH质量浓度为0.74～5.42 mg/L,后端介质TPH含量较低且分布较均匀,10个取样点中TPH均低于0.29 mg/L,生物PRB出水中未检出TPH.采用聚合酶链式反应(PCR)-变性梯度凝胶电泳(DGGE)技术对生物PRB内的微生物群落结构进行分析,结果显示,生物PRB中微生物群落结构的相似性随着横向距离的增大而降低,其中B2与B5取样点微生物相似度最高,达83.1％.在生物PRB前端TPH浓度高的部位,微生物群落较为稳定,多样性较低,而后端TPH浓度低的部位,微生物群落不稳定,多样性较高.     

MTBE的生物降解技术

汽油添加剂甲基叔丁基醚(MTBE)的污染在国外已引起重视。概述了目前MTBE生物降解的研究现状，着重介绍了国外对MTBE污染地下水的异位和原位生物处理方法。随着汽车的逐步普及和MTBE用量的增加，我国正在或将面临MTBE的污染。指出了开展相关研究的重要性和迫切性，初步提出了这一新课题的研究思路，为我国环境保护领域从事该项研究的人员提供参考。     

电动与渗透反应格栅联合修复镉污染地下水实验

通过实验方法研究了地下水中镉污染的电动力学修复效果，并分析其迁移变化特征。实验结果表明，电动修复中由于阴阳两极的氧化还原反应造成电极附近pH值产生明显变化，其中阳极附近的pH值由开始时的7.0逐渐变小到6.8，而阴极附近则相反，由开始时6.9逐渐增大到9.1，表明土壤的酸碱条件变化明显。Cd浓度变化反映在自然渗透条件下含水层中重金属污染物的迁移能力较弱，阳极附近地下水中Cd的去除率仅8.4%，而在电场作用下地下水中重金属的浓度发生明显变化，使得重金属污染物能在电极附近富集而被去除，当实验电场强度为0.5 V/cm时，Cd在阴极的累积使得阳极附近地下水中去除率为72.9%，说明电动修复重金属Cd污染地下水的效果明显好于自然渗透状态。     

煤矸石淋溶污染物对高速公路沿线土壤水环境污染的仿真研究

利用淋容试验,模拟自然降雨,分析了煤矸石对高速公路沿线地下水造成的污染,获得了大量真实可靠的数据,得出了煤矸石淋溶液中无机盐是造成高速公路沿线地下水污染的主要原因.并基于多孔介质流体力学和溶质运移动力学建立了描述微量元素在土壤-水环境系统中迁移的数学模型,利用该模型对煤矸石淋溶微量元素在道路沿线土壤-水环境中的迁移规律进行了模拟分析,进一步预测了污染物浓度变化规律及分布特征,可为公路沿线土壤-水环境污染提供分析依据.     

Treatment of groundwater contaminated with gasoline components by an ozone/UV process

In this paper, the treatment of real groundwater samples contaminated with gasoline components, such as benzene, toluene, ethylbenzene, and xylene (BTEX), methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), and other gasoline constituents in terms of total petroleum hydrocarbons as gasoline (TPHg) by an ozone/UV process was investigated. The treatment was conducted in a semi-batch reactor under different experimental conditions by varying ozone gas dosage and incident UV light intensity. The groundwater samples contained BTEX compounds, MTBE, TBA, and TPHg in the ranges of 5-10000, 3000-5500, 80-1400, and 2400-20000mugl(-1), respectively. The ozone/UV process was very effective compared to ozonation in the removal of the gasoline components from the groundwater samples. For the various gasoline constituents, more than 99% removal efficiency was achieved for the ozone/UV process and the removal efficiency for ozonation was as low as 27%. The net ozone consumed per mol of organic carbon (from BTEX, MTBE, and TBA) oxidized varied in the range of 5-60 for different types of groundwater samples treated by the ozone/UV process. In ozonation experiments, it was observed that the presence of sufficient amount of iron in groundwater samples improved the removal of BTEX, MTBE, TBA, and TPHg.     

Using the Gasoline Additive MTBE in Forensic Environmental Investigations

A variety of additives are used in gasoline, and they can sometimes be used to help identify the source, timing, or number of gasoline spills at a site. The physicochemical characteristics of the additive MTBE, and its historical use pattern in the United States since 1979, make it a key compound to study when conducting forensic investigations of gasoline spills. MTBE's low octanol: water distribution coefficient and high solubility cause it to dissolve into groundwater more readily than other gasoline components. Thus, the initial appearance of MTBE in the groundwater is often a good indicator of a recent gasoline spill. MTBE's very low retardation and minimal biodegradation in groundwater can be used with transport rate calculations to establish relatively accurate estimates of spill timing. Because MTBE moves faster in groundwater than BTEX compounds, if a gasoline spill site has a BTEX plume that is longer than the MTBE plume, it is certain that at least two distinctly different gasoline releases have occurred. This allows for the identification of new gasoline spills, even when substantial subsurface petroleum contamination already exists. An example application is reviewed to demonstrate the use of MTBE data in forensic investigations.     

Using the Gasoline Additive MTBE in Forensic Environmental Investigations

A variety of additives are used in gasoline, and they can sometimes be used to help identify the source, timing, or number of gasoline spills at a site. The physicochemical characteristics of the additive MTBE, and its historical use pattern in the United States since 1979, make it a key compound to study when conducting forensic investigations of gasoline spills. MTBE's low octanol : water distribution coefficient and high solubility cause it to dissolve into groundwater more readily than other gasoline components. Thus, the initial appearance of MTBE in the groundwater is often a good indicator of a recent gasoline spill. MTBE's very low retardation and minimal biodegradation in groundwater can be used with transport rate calculations to establish relatively accurate estimates of spill timing. Because MTBE moves faster in groundwater than BTEX compounds, if a gasoline spill site has a BTEX plume that is longer than the MTBE plume, it is certain that at least two distinctly different gasoline releases have occurred. This allows for the identification of new gasoline spills, even when substantial subsurface petroleum contamination already exists. An example application is reviewed to demonstrate the use of MTBE data in forensic investigations.     

Biofiltration of gasoline vapor by compost media

Gasoline vapor was treated using a compost biofilter operated in upflow mode over 4 months. The gas velocity was 6 m/h, yielding an empty bed retention time (EBRT) of 10 min. Benzene, toluene, ethylbenzene and xylene (BTEX) and total petroleum hydrocarbon (TPH) removal efficiencies remained fairly stable approximately 15 days after biofilter start-up. The average removal efficiencies of TPH and BTEX were 80 and 85%, respectively, during 4 months of stable operation. Biodegradation portions of the treated TPH and BTEX were 60 and 64%, respectively. When the influent concentration of TPH was less than 7800 mg TPH/m3, approximately 50% of TPH in the gas stream was removed in the lower half of the biofilter. When the influent concentration of BTEX was less than 720 mg BTEX/m3, over 75% of BTEX in the gas stream was removed in the lower half of the biofilter. Benzene removal efficiency was the lowest among BTEX. A pressure drop could not be detected over a 1-m bed height at a gas velocity of 6 m/h after approximately 4 months of operation. Results demonstrated that BTEX in gasoline vapor could be treated effectively using a compost biofilter.     

Hydrochemical and isotopic effects associated with petroleum fuel biodegradation pathways in a chalk aquifer

Hydrochemical data, compound specific carbon isotope analysis and isotopic enrichment trends in dissolved hydrocarbons and residual electron acceptors have been used to deduce BTEX and MTBE degradation pathways in a fractured chalk aquifer. BTEX compounds are mineralised sequentially within specific redox environments, with changes in electron acceptor utilisation being defined by the exhaustion of specific BTEX components. A zone of oxygen and nitrate exhaustion extends approximately 100 m downstream from the plume source, with residual sulphate, toluene, ethylbenzene and xylene. Within this zone complete removal of the TEX components occurs by bacterial sulphate reduction, with sulphur and oxygen isotopic enrichment of residual sulphate (epsilon(s) = -14.4 per thousand to -16.0 per thousand). Towards the plume margins and at greater distance along the plume flow path nitrate concentrations increase with delta15N values of up to +40 per thousand indicating extensive denitrification. Benzene and MTBE persist into the denitrification zone, with carbon isotope enrichment of benzene indicating biodegradation along the flow path. A Rayleigh kinetic isotope enrichment model for 13C-enrichment of residual benzene gives an apparent epsilon value of -0.66 per thousand. MTBE shows no significant isotopic enrichment (delta13C = -29.3 per thousand to -30.7 per thousand) and is isotopically similar to a refinery sample (delta13C = -30.1 per thousand). No significant isotopic variation in dissolved MTBE implies that either the magnitude of any biodegradation-induced isotopic fractionation is small, or that relatively little degradation has taken place in the presence of BTEX hydrocarbons. It is possible, however, that MTBE degradation occurs under aerobic conditions in the absence of BTEX since no groundwater samples were taken with co-existing MTBE and oxygen. Low benzene delta13C values are correlated with high sulphate delta34S, indicating that little benzene degradation has occurred in the sulphate reduction zone. Benzene degradation may be associated with denitrification since increased benzene delta13C is associated with increased delta15N in residual nitrate. Re-supply of electron acceptors by diffusion from the matrix into fractures and dispersive mixing is an important constraint on degradation rates and natural attenuation capacity in this dual-porosity aquifer.     

Determination of MTBE in a recreational harbor using solid-phase microextraction

Discovery of the fuel additive methyl tert-butyl ether (MTBE) in groundwater, surface water, and stormwater has prompted studies of its sources, transport and fate. More limited data, however, is available on the extent of contamination of coastal waters, as well as the persistence of MTBE in the marine environment. We apply here the combination of solid phase microextraction and gas chromatography-mass spectrometry to the detection of sub-to-low microgram/l concentrations of MTBE in seawater samples. Analysis of samples collected at the Marina del Rey harbor, a shallow recreational harbor near Los Angeles, CA, show MTBE contamination in the low microgram/l level. MTBE measurements were made at different depths, from the surface to the bottom, at five sites within the harbor during months showing no measurable precipitation. The highest concentration of MTBE (18 microgram/l) was found at the boat launching ramp, and the lowest (0.2 microgram/l) near the harbor entrance, approximately 2.3 km from the ramp. The levels of MTBE measured, as well as their variation over the study period, are fully consistent with recreational boating as the primary source of contamination. No evidence for MTBE contamination from the adjacent stormwater control channel was noted.     

Determination of Henry's law constant for methyl tert-butyl ether (MTBE) at groundwater temperatures

The dimensionless Henry's law constant was determined for methyl tert-butyl ether (MTBE) at six temperatures (3, 5, 10, 15, 20 and 25 degrees C) by using a thermostatted flask (430 ml) containing an aqueous MTBE solution. The ratio between the gas phase and the water phase in the flask was approximately 1.7:1. The aim of this study was to acquire data needed to model the behaviour of MTBE at groundwater conditions. The dimensionless Henry's law constant at 10 degrees C is approximately 0.01 but is 0.03 at 25 degrees C. This is important for modelling MTBE because the variation of vaporization cannot be disregarded at groundwater temperatures. In a second experiment the water solubility of MTBE was determined to be 62.1 g/l at 5 degrees C and 35.5 g/l at 20 degrees C). The high solubility at low temperatures could cause MTBE plumes from spills (fuel accidents etc.) to spread rapidly.     

Laboratory evidence of MTBE biodegradation in Borden aquifer material

Mainly due to intrinsic biodegradation, monitored natural attenuation can be an effective and inexpensive remediation strategy at petroleum release sites. However, gasoline additives such as methyl tert-butyl ether (MTBE) can jeopardize this strategy because these compounds often degrade, if at all, at a slower rate than the collectively benzene, toluene, ethylbenzene and the xylene (BTEX) compounds. Investigation of whether a compound degrades under certain conditions, and at what rate, is therefore important to the assessment of the intrinsic remediation potential of aquifers. A natural gradient experiment with dissolved MTBE-containing gasoline in the shallow, aerobic sand aquifer at Canadian Forces Base (CFB) Borden (Ontario, Canada) from 1988 to 1996 suggested that biodegradation was the main cause of attenuation for MTBE within the aquifer. This laboratory study demonstrates biologically catalyzed MTBE degradation in Borden aquifer-like environments, and so supports the idea that attenuation due to biodegradation may have occurred in the natural gradient experiment. In an experiment with batch microcosms of aquifer material, three of the microcosms ultimately degraded MTBE to below detection, although this required more than 189 days (or >300 days in one case). Failure to detect the daughter product tert-butyl alcohol (TBA) in the field and the batch experiments could be because TBA was more readily degradable than MTBE under Borden conditions.