SEAR技术修复土壤和地下水中NAPL污染的研究进展

就SEAR技术修复土壤及地下水中NAPL污染的原理及发展现状进行了综述.SEAR技术可以快速有效地去除土壤和地下水中的NAPL污染源,适于多种污染物.该技术通过增溶和增流2种途径提高NAPL污染物的去除率.表面活性剂的选择和微乳液体系的调配是SEAR技术实施的关键环节.将SEAR技术用于高浓度NAPL污染源的治理,并与生物修复和自然降解相结合,是经济高效的治理方案.     

SEAR技术修复土壤和地下水中NAPL污染的研究进展

就SEAR技术修复土壤及地下水中NAPL污染的原理及发展现状进行了综述.SEAR技术可以快速有效地去除土壤和地下水中的NAPL污染源,适于多种污染物.该技术通过增溶和增流2种途径提高NAPL污染物的去除率.表面活性剂的选择和微乳液体系的调配是SEAR技术实施的关键环节.将SEAR技术用于高浓度NAPL污染源的治理,并与生物修复和自然降解相结合,是经济高效的治理方案.     

江阴某场地土壤及地下水环境风险管控与修复项目工程案例

通过对江阴某地块土壤及地下水环境风险管控与修复项目的工程实施过程介绍,重点针对柔性垂直/水平阻隔技术、水处理高级氧化技术在污染土壤及地下水风险管控项目应用中的技术原理、施工流程进行了分析与探讨,可为后续采用柔性垂直阻隔技术的风险管控项目提供参考。     

水力截获技术研究进展

水力截获技术是地下水污染控制及修复技术的重要措施之一,它是通过一系列合理布置的抽注水井,最大限度地抽取污染地下水,有效控制污染物运移的一种水动力技术,其核心是根据污染场地的水文地质背景条件、污染物性质及其分布特征,应用渗流理论及最优化理论等学科知识,在污染带下游设置治理井来形成水力截获带.目前,水力截获技术在国外已被广...     

地下水中多环芳烃迁移转化研究

吸附和生物降解是受污染地下水中多环芳烃(PAHs)归宿的主要途径.论述了PAHs在含水层中吸附过程的特征、影响因素与研究方法,并比较各种研究方法的优缺点;分析了PAHs在含水层中生物降解过程机制以及研究进展;介绍了PAHs在地下水中迁移、转化数学模型与数值模拟的研究开发状况;指出了PAHs与固相介质的吸附机制和竞争吸附行为、高分子量PAHs的生物降解途径和机制及共存PAHs或与其他污染物在地下水中的迁移、转化、归宿与修复技术是深入研究的方向.     

原位热处理技术修复重质非水相液体污染场地研究进展

重质非水相液体(DNAPLs)是土壤及地下水中广泛存在的有机污染物,原位热处理技术是目前修复受DNAPLs污染土壤及地下水的最具潜力的技术之一。综述了国内外常用原位热处理技术的基本原理及其影响因素,介绍了相关现场应用实例,并展望了该技术未来的应用前景和发展趋势,以期为中国污染土壤及地下水的原位修复提供有益借鉴。     

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。     

基于蒙特卡罗法和层次分析法的污染场地地下水修复技术筛选方法研究

在工业转型发展过程中,出现了大量遗留污染场地,对地下水造成严重污染,并加重水资源短缺,而现阶段缺乏易操作的污染场地地下水修复技术筛选方法。为筛选有效的污染场地地下水修复技术,建立了基于层次分析法(AHP)与蒙特卡罗法(MC)的污染场地地下水修复技术筛选方法。该方法利用AHP构建指标体系,结合MC进行抽样,避免了定性描述和单一数值评价带来的不确定性。将该方法用于某铬渣污染场地地下水修复技术的筛选,发现化学氧化/还原是最适宜的修复技术,筛选结果符合实际。     

多介质渗透反应格栅中氨氮的转化与存在形态

在利用渗透反应格栅技术修复地下水氨氮污染过程中,掌握氨氮在不同介质环境中的转化规律及存在形态对多介质渗透反应格栅中各介质作用及氮转化过程的控制十分重要.针对进水氨氮浓度约10 mg/L的模拟地下水,以天然河沙、释氧材料、斜发沸石及海绵铁为反应介质,设计了一套多介质渗透反应格栅模拟氨氮在各介质环境中的转化及归宿.结果表明,在天然河沙层,氨氮优先被河沙吸附固定,但去除量有限(△C＜1.5 mg/L),氨氮主要以离子态溶于模拟地下水.在好氧沸石层,氨氮经沸石吸附及生物硝化协同作用几乎被完全去除,该层出水氨氮浓度低于0.01 mg/L,且氮主要存在形态为硝酸盐氮(C=10～26.6 mg/L).在铁厌氧层,部分硝酸盐氮经海绵铁化学还原和生物反硝化作用,分别被转化为氨氮(△C=2～9.5 mg/L)和氮气(△C＜8 mg/L),其余硝酸盐氮以离子态继续存留于模拟地下水.     

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.     

空气喷射处理饱和土壤和地下水中有机污染物

空气喷射 (airsparging)被认为是修复由可挥发性有机物污染的饱和土壤和地下水的一种有效新技术。介绍了空气喷射技术的现场应用与研究现状 ,讨论了空气喷射技术的原理和各种影响因素 ,说明了其对于饱和土壤中有氧生物降解的促进作用 ,分析了空气喷射技术的应用前景。     

Modeling of air sparging of VOC-contaminated soil columns

Air sparging is a remediation technology currently being applied for the restoration of sites contaminated with volatile organic compounds (VOCs). Attempts have been made by various researchers to model the fate of VOCs in the gas and liquid phase during air sparging. In this study, a radial diffusion model with an air–water mass transfer boundary condition was developed and applied for the prediction of VOC volatilization from air sparging of contaminated soil columns. The approach taken was to use various parameters such as mass transfer coefficients and tortuosity factors determined previously in separate experiments using a single air channel apparatus and applying these parameters to a complex system with many air channels. Incorporated in the model, is the concept of mass transfer zone (MTZ) where diffusion of VOCs in this zone was impacted by the volatilization of VOCs at the air–water interface but with negligible impact outside the zone. The model predicted fairly well the change in the VOC concentrations in the exhaust air, the final average aqueous VOC concentration, and the total mass removed. The predicted mass removal was within 1% to 20% of the actual experimental mass removed. The results of the model seemed to suggest that air-sparged soil columns may be modeled as a composite of individual air channels surrounded by a MTZ. For a given air flow rate and air saturation, the VOC removal was found to be inversely proportional to the radius of the air channel. The approach taken provided conceptual insights on mass transfer processes during air sparging operations.     

Changes in air saturation and air-water interfacial area during surfactant-enhanced air sparging in saturated sand

Reduction in the surface tension of groundwater, prior to air sparging for removal of volatile organic contaminant from aquifer, can greatly enhance the air content and the extent of influence when air sparging is implemented. However, detailed information on the functional relationship between water saturation, air-water contact area induced by air sparging and the surface tension of water has not been available. In this study, the influence of adding water-soluble anionic surfactant (sodium dodecyl benzene sulfonate) into groundwater before air sparging on the air-water interfacial area and water saturation was investigated using a laboratory-scale sand packed column. It was found that water saturation decreases with decreasing surface tension of water until it reaches a point where this trend is reversed so that water saturation increases with further decrease in the surface tension. The lowest water saturation of 0.58 was achieved at a surface tension of 45.4 dyn/cm, which is considered as the optimum surface tension for maximum de-saturation for the initially water-saturated sand used in this study. The air-water contact area generated in the sand column due to air sparging was measured using a gaseous interfacial tracer, n-decane, and was found to monotonically increase with decreasing water saturation. The results of this study provide useful design information for surfactant-enhanced air sparging removal of volatile contaminants from aquifers.     

Contaminated site remedial investigation and feasibility removal of chlorinated volatile organic compounds from groundwater by activated carbon fiber adsorption

Groundwater contaminated by dense, non-aqueous phase liquids (DNAPLs) such as chlorinated solvents has become a serious problem in some regions of Taiwan. The sources of these contaminants are due to industrial discharges. These chlorinated volatile organic compounds (VOCs) have been proven to be carcinogenic to humans. The groundwater is used for domestic drinking water supply in some cities of Taiwan and the severely contaminated groundwater has to be treated in order to meet the requirement of drinking water standards. This study covers two areas of work. In the first part, polluted groundwater samples were collected from the contaminated site and analytical results indicated measurable concentrations of 12 representative chlorinated VOCs in water samples. The primary VOCs detected included trichloroethene (TCE), tetrachloroethene (PCE), 1,1,2-trichloroethane (1,1,2-TCA), and 1,1-dichloroethene (1,1-DCE). Second, to remove VOCs groundwater was treated using adsorption on activated carbon fiber (ACF). This involved pumping groundwater through vessels containing ACF. Most VOCs, including TCE, PCE, 1,1,2-TCA, and DCE, were readily adsorbed onto ACF and are removed from the water stream. Our study showed that the technology was able to significantly reduce chlorinated VOCs concentrations in groundwater.     

Landfill Gas Effects on Groundwater Samples at a Municipal Solid Waste Facility

A study was performed to determine the source of low concentrations of volatile organic compounds (VOCs) detected in groundwater samples at a solid waste management facility. The affected wells were identified as hydraulically upgradient of an old unlined facility, but downgradient of a new clay-lined landfill. These monitoring wells are close to both sites. Subsurface landfill gas migration was identified after a low permeability cap was installed on the older site. Subsurface gas pressure was monitored to identify horizontal landfill gas migration. Monitoring well headspace gases were evaluated to identify depressed oxygen concentrations and methane because of landfill gas migration into the well. Monitoring well headspace gas VOC concentrations were compared to groundwater VOC concentrations to determine the direction of phase transfer. A ratio above 1.0 of the observed well headspace gas concentration of a VOC to the concentration that would be in equilibrium with the groundwater concentration indicates gas-to-water phase transfer within the well. For the major gas-phase and aqueous-phase VOC, cis-1,2-dichloroethene, gas-to-water phase transfer is clearly indicated from the data for two of the four wells. Fifteen other VOCs were detected in monitoring well headspace gases but not in groundwater samples from the four wells studied. Only one compound in one well was detected in the groundwater sample but not in the headspace gases, and only one compound in one well was detected in both matrices at concentrations that suggested water-to-gas phase transfer. This study suggests that if landfill gas is suspected as the source of detected VOCs, monitoring well construction and stratigraphy are important considerations when attempting to differentiate between groundwater contamination by landfill gas and contamination from other sources.     

土壤、地下水中有机污染物的就地处置

有机化合物对土壤、地下水的污染已引起世界各国的普遍关注.地层介质中的有机物主要以自由态、挥发态、溶解态和固态4种形态存在.有机污染物的自然降解能力较差,如不进行人工清除,在自然环境中它们可能存留长达几十年之久,对土壤、地下水资源构成长期的威胁.传统的开挖处理技术不仅费用昂贵,而且当贮油设施的地表被利用时则无法进行开挖处理(如有建筑物等).近年来,以地下冲洗法、土壤抽水法和地下水曝气法为代表的有机污染物就地处置技术得到了迅速的发展.本文对这3种技术进行概要的介绍,总结指出决定这些技术可能性的主要因素是地层介质的通透能力,有机物的挥发、溶解能力及其可生物降解能力,并列出目前的主要有机污染物挥发、溶解及生物降解能力的相对强弱作为制定具体处置技术的参考指标.     

Pulsed gas injection: A minimum effort approach for enhanced natural attenuation of chlorobenzene in contaminated groundwater

Chlorobenzene-contaminated groundwater was used to assess pulsed gas sparging as a minimum effort aeration strategy to enhance intrinsic natural attenuation. In contrast to existing biosparging operations, oxygen was supplied at minimum rate by reducing the gas injection frequency to 0.33 day^?1. Field tests in a model aquifer were conducted in a 12 m long reactor, filled with indigenous aquifer material and continuously recharged with polluted groundwater over 3 years. The closed arrangement allowed yield balances, cost accounting as well as the investigation of spatial distributions of parameters which are sensitive to the biodegradation process. Depending on the injection frequency and on the gas chosen for injection (pure oxygen or air) oxygen-deficient conditions prevailed in the aquifer. Despite the limiting availability of dissolved oxygen in the groundwater, chlorobenzene degradation under oxygen-deficient conditions proved to be more effective than under conditions with dissolved oxygen being available in high concentrations.     

A land use regression model for predicting ambient volatile organic compound concentrations in Toronto,Canada

More than 25 studies have employed land use regression (LUR) models to estimate nitrogen oxides and to a lesser extent particulate matter indicators, but these methods have been less commonly applied to ambient concentrations of volatile organic compounds (VOCs). Some VOCs have high plausibility as sources of health effects and others are specific indicators of motor vehicle exhaust. We used LUR models to estimate spatial variability of VOCs in Toronto, Canada. Benzene, n-hexane and total hydrocarbons (THC) were measured from July 25 to August 9, 2006 at 50 locations using the TraceAir organic vapor monitors. Nitrogen dioxide (NO₂) was also sampled to assess its spatial pattern agreement with VOC exposures. Buffers for land use, population density, traffic density, physical geography, and remote sensing measures of greenness and surface brightness were also tested. The remote sensing measures have the highest correlations with VOCs and NO₂ levels (i.e., explains >36% of the variance). Our regression models explain 66–68% of the variance in the spatial distribution of VOCs, compared to 81% for the NO₂ model. The ranks of agreement between various VOCs range from 48 to 63% and increases substantially – up to 75% – for the top and bottom quartile groups. Agreements between NO₂ and VOCs are much smaller with an average rank of 36%. Future epidemiologic studies may therefore benefit from using VOCs as potential toxic agents for traffic-related pollutants.     

Biosensor-based diagnostics of contaminated groundwater: assessment and remediation strategy

Shallow groundwater beneath a former airfield site in southern England has been heavily contaminated with a wide range of chlorinated solvents. The feasibility of using bacterial biosensors to complement chemical analysis and enable cost-effective, and focussed sampling has been assessed as part of a site evaluation programme. Five different biosensors, three metabolic (Vibrio fischeri, Pseudomonas fluorescens 10568 and Escherichia coli HB101) and two catabolic (Pseudomonas putida TVA8 and E. coli DH5alpha), were employed to identify areas where the availability and toxicity of pollutants is of most immediate environmental concern. The biosensors used showed different sensitivities to each other and to the groundwater samples tested. There was generally a good agreement with chemical analyses. The potential efficacy of remediation strategies was explored by coupling sample manipulation to biosensor tests. Manipulation involved sparging and charcoal treatment procedures to simulate remediative engineering solutions. Sparging was sufficient at most locations.     

Hydrogeo-chemical impacts of air sparging remediation on a semi-confined aquifer: Evidences from field monitoring and modeling

Air sparging (AS) was explored for remediation of a petroleum contaminated semi-confined groundwater system in NE China. Physical, hydro-chemical and hydraulic behaviors in subsurface environment during AS were investigated with support of modeling to understand the hydrogeo-chemical impacts of AS on the aquifer. The responses of groundwater, dissolved oxygen and temperature indicated that the radius of influence of AS was up to 8–9 m, and a 3D boundary of the zone of influence (ZOI) was accordingly obtained with volume of 362 m³. Water mounding unlike normal observations was featured by continuous up-lift and blocked dissipation. AS induced water displacement was calculated showing no obvious spreading of contaminant plume under this AS condition. Slug tests were employed before and after AS to reveal that the physical perturbation led to sharp increase in permeability and porosity. Modeling indicated that the regional groundwater flow field was not affected by AS except the physical perturbation in ZOI. Hydro-chemically increase of pH and Eh, and reduction of TDS, electrical conductivity and bicarbonate were observed in ZOI during AS. PHREEQC modeling inferred that these chemical phenomena were induced by the inorganic carbon transfer during air mixing.