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.     

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。     

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。     

地下水曝气理论模型研究进展

地下水曝气(Air Sparging,AS)是修复饱和土壤及地下水有机污染的有效技术.AS多相流动过程中气液流动以及污染物传质过程的模型研究是AS技术的关键因素,详细介绍了近年来AS系统的理论模型方法及研究进展,并对其效果进行评价.     

土壤及地下水有机污染的化学与生物修复

本文综述了土壤及地下水有机污染的化学与生物修复技术研究的最新进展。比较详细地介绍了土壤及地下水有机污染的化学修复、生物修复、化学与生物相结合修复的具体方法、治理效率及其影响因素。     

铬渣污染场地污染状况研究与修复技术分析

选取某一化工厂铬渣堆放场地作为典型铬渣污染场地,对其钻孔并采集不同深度土壤和地下水样品进行分析。研究发现，该铬渣污染场地存在很严重的土壤和地下水污染。污染物地表扩散较小，剖面扩散很严重，污染深度达6 m，不同特性土壤对六价铬的截留作用不同。在此基础上，归纳总结了国外常用铬渣污染场地修复治理技术的优缺点，并提出具体污染场地修复技术的选取应该根据勘探情况选择合适的某些技术组合。     

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...     

电阻加热修复佳乐麝香污染土壤的工艺优化

佳乐麝香(Galaxolide,HHCB)是土壤中的一种新兴的半挥发性有机污染物,具有较高的毒性,需修复治理.电阻加热技术(electrical resistance heating,ERH)因加热均匀、效果好,逐渐被应用于有机污染土壤修复工程.采用自主研制的电阻加热装置,研究了加热过程中电场强度、土壤含水率和土壤粒径...     

场地污染土壤和地下水修复中受监控的自然修复/恢复技术的应用与研究进展

场地污染土壤和地下水的修复可以分为两个阶段,第1阶段是以消除对人体可能产生的健康风险为主要目标的工程修复,第2阶段是以消除对生态环境的影响为主要目标的自然修复/恢复.受监控的自然修复/恢复技术和强化自然修复/恢复技术具有成本低廉、修复作用持续等优点,在场地污染土壤和地下水的修复中具有广泛的应用潜力,其在消除生态影响和规避修复工程风险方面的作用是工程修复无法取代的.介绍了受监控的自然修复/恢复技术的4种主要途径及其在欧美国家污染土壤和地下水修复中的应用情况,提出了受监控的自然修复/恢复技术的方法步骤,以及这项技术在中国污染土壤和地下水修复中的应用潜力,以期为中国在受监控的自然修复/恢复技术上的科学研究和修复实践提供参考.     

包气带土壤对石油烃的截留作用研究

包气带土壤对地表污染物的截留作用是地下水免受污染的一道天然屏障.土壤截留污染物的能力对地下水石油烃污染的治理起着关键作用,在对实际污染场地进行调查研究的基础上,采用土柱淋滤、吸附/解吸、石油挥发等室内模拟实验,研究包气带土壤对石油烃的截留作用及其影响因素.结果表明,细砂、中砂和粗砂3种土壤对石油烃的截留率分别为81.0...     

A compositional simulator for modeling surfactant enhanced aquifer remediation, 1 formulation

We describe a three-dimensional, multicomponent, multiphase compositional finite-difference simulator for application to the analysis of contaminant transport and surfactant enhanced aquifer remediation (SEAR) of nonaqueous-phase liquid (NAPL) pollutants. Mixtures of surfactant, water and NAPL can form many types of micellar and microemulsion phases with a complex and important dependence on many variables of which the dilute aqueous solution typically assumed in SEAR models is just one example. The phase behavior model is central to our approach and allows for the full range of the commonly observed micellar and microemulsion behavior pertinent to SEAR. The other surfactant related properties such as adsorption, interfacial tension, capillary pressure, capillary number and microemulsion viscosity are all dependent on an accurate phase behavior model. This has proven to be a highly successful approach for surfactant enhanced oil recovery modeling, so it was adapted to SEAR modeling. However, there are many significant differences between petroleum and environmental applications of surfactants, so many new features have been added to model contaminant transport and remediation and these are described and illustrated for the first time here.     

Effect of nonionic surfactant partitioning on the dissolution kinetics of residual perchloroethylene in a model porous medium

At concentrations above the critical micelle concentration, surfactants can significantly enhance the solubilization of residual nonaqueous phase liquids (NAPL) and, for this reason, are the focus of research on surfactant-enhanced aquifer remediation (SEAR). As a consequence of their amphiphilic nature, surfactants may also partition to various extents between the organic and aqueous phases, thereby affecting SEAR performance. We report here on the observation and analysis of the effect of surfactant partitioning on the dissolution kinetics of residual perchloroethylene (PCE) by aqueous solutions (1000 mg/L) of the non-ionic surfactant Triton X-100 in a model porous medium. For this fluid system, batch equilibration experiments showed that the surfactant partitions strongly into the NAPL (NAPL-water partition coefficient equal to 12.5). Dynamic interfacial tension (IFT) measurements were employed to study surfactant diffusion and interfacial adsorption. The dynamic IFT measurements were consistent with partitioning of the surfactant between the two liquid phases. PCE dissolution experiments, conducted in a transparent glass micromodel using an aqueous surfactant solution, were contrasted to experiments using clean water. Surfactant partitioning was observed to delay significantly the onset of micellar solubilization of PCE, an observation reproduced by a numerical model. This effect is attributed to the reduction of surfactant concentration in the immediate vicinity of the NAPL-water interface, which accompanies transport of the surfactant into the NAPL. Accordingly, it is suggested that both the rate and the extent of diffusion of the surfactant into the NAPL affect the onset of and the driving force for micellar solubilization. While many surfactants do not readily partition in NAPL, this possibility must be considered when selecting non-ionic surfactants for the enhanced solubilization of residual chlorinated solvents in porous media.     

The effects of surfactant formulation on nonequilibrium NAPL solubilization

Surfactant-enhanced aquifer remediation (SEAR) involves the injection of surfactant solutions into aquifers contaminated with nonaqueous phase liquids (NAPL). Batch and column experiments were used to assess the effect of surfactant formulation on the rate of NAPL solubilization. The experimental variables were surfactant type, surfactant concentration, electrolyte concentration, and cosolvent concentration. Model equations were proposed and solved to describe solubilization under the conditions of each type of experiment. Using these models, a solubilization rate constant, kappa(b), and an overall mass transfer rate coefficient, kappa, were estimated from the batch and column experiments, respectively. The solubilization rate constant was consistently sensitive to surfactant type, surfactant concentration, and electrolyte concentration. The estimated solubilization rate constants varied over two orders of magnitude. The results of the column experiments also were sensitive to the surfactant formulation. Variations in the fitted mass transfer rate coefficient parameter, beta(0), were related to variations in the surfactant formulations. A comparison between the results of the batch and column experiments yields an apparent relationship between beta(0) and kappa(b). This relationship suggests that the mass transfer rate coefficient is directly related to the formulation of the surfactant solution.     

Effects of source zone heterogeneity on surfactant-enhanced NAPL dissolution and resulting remediation end-points

The effectiveness of removal of nonaqueous phase liquids (NAPLs) from the entrapment source zone of the subsurface has been limited by soil heterogeneity and the inability to locate all entrapped sources. The goal of this study was to demonstrate the uncertainty of degree of source removal associated with aquifer heterogeneity. In this demonstration, source zone NAPL removal using surfactant-enhanced dissolution was considered. Model components that simulate the processes of natural dissolution in aqueous phase and surfactant-enhanced dissolution were incorporated into an existing code of contaminant transport. The dissolution modules of the simulator used previously developed Gilland-Sherwood type phenomenological models of NAPL dissolution to estimate mass transfer coefficients that are upscaleable to multidimensional flow conditions found at field sites. The model was used to simulate the mass removal from 10 NAPL entrapment zone configurations based on previously conducted two-dimensional tank experiments. These entrapment zones represent the NAPL distribution in spatially correlated random fields of aquifer hydraulic conductivity. The numerical simulations representing two-dimensional conditions show that effectiveness of mass removal depends on the aquifer heterogeneity that controls the NAPL entrapment and delivery of the surfactant to the locations of entrapped NAPLs. Flow bypassing resulting from heterogeneity and the reduction of relative permeability due to NAPL entrapment reduces the delivery efficiency of the surfactant, thus prolonging the remediation time to achieve desired end-point NAPL saturations and downstream dissolved concentrations. In some extreme cases, the injected surfactant completely bypassed the NAPL source zones. It was also found that mass depletion rates for different NAPL source configurations vary significantly. The study shows that heterogeneity result in uncertainties in the mass removal and achievable end-points that are directly related to dissolved contaminant plume development downstream of the NAPL entrapment zone.     

Wettability hysteresis and its implications for DNAPL source zone distribution

Subsurface heterogeneity at sites contaminated with nonaqueous phase liquids (NAPLs) reduces the effectiveness of traditional remediation measures. One cause may be the increased proportion of NAPL that is hydraulically isolated due to capillary trapping in heterogeneously-wetted materials. This study examines the wettability of ten materials, ranging from minerals, such as calcite and dolomite, to carbonaceous materials, such shale and coal, in air and water, NAPL and air, and NAPL and water systems. The wettability differed depending on which phase the solid material was initially immersed in: the less crystalline solids, if initially contacted by water were water-wet, but if initially contacted by NAPL were NAPL-wet. This difference, termed here wettability hysteresis, was observed for a suite of halogenated NAPLs and was independent of equilibration time. The degree of wettability hysteresis was greatest in the NAPL and water systems, with the magnitude of the difference increasing with the carbonaceous materials. Since the degree of capillary trapping in subsurface materials is related to wettability, the phenomenon of wettability hysteresis suggests that system history is a factor that may increase the heterogeneity of NAPL source zones.     

A multi-objective optimization framework for surfactant-enhanced remediation of DNAPL contaminations

The occurrence of Dense Non-Aqueous Phase Liquid (DNAPL) contaminations in the subsurface is a threat for drinkwater resources in the western world. Surfactant-Enhanced Aquifer Remediation (SEAR) is widely considered as one of the most promising techniques to remediate DNAPL contaminations in-situ, be it with considerable additional costs compared to classical pump-and-treat remediations. A cost-effective design of the remediation set-up is therefore essential. In this work, a pilot SEAR test is executed at a DNAPL contaminated site in Belgium in order to collect data for the calibration of a multi-phase multi-component model. The calibrated model is used to assess a series of scenario-analyses for the full-scale remediation of the site. The remediation variables that were varied were the injection and extraction rate, the injection and extraction duration, and the surfactant injection concentrations. A constrained multi-objective optimization of the model was applied to obtain a Pareto set of optimal remediation strategies with different weights for the two objectives of the remediation: (i) the maximal removal of DNAPL and (ii) a total minimal cost. These Pareto curves can help decision makers to select an optimal remediation strategy in terms of cost and remediation efficiency. The Pareto front shows a considerable trade-off between the total remediation cost and the removed DNAPL mass.     

Investigation of surfactant-enhanced mass removal and flux reduction in 3D correlated permeability fields using magnetic resonance imaging

Magnetic resonance imaging (MRI) was used to visualize the NAPL source zone architecture before and after surfactant-enhanced NAPL dissolution in three-dimensional (3D) heterogeneously packed flowcells characterized by different longitudinal correlation lengths: 2.1 cm (aquifer 1) and 1.1 cm (aquifer 2). Surfactant flowpaths were determined by imaging the breakthrough of a paramagnetic tracer (MnCl(2)) analyzed by the method of moments. In both experimental aquifers, preferential flow occurred in high permeability materials with low NAPL saturations, and NAPL was preferentially removed from the top of the aquifers with low saturation. Alternate flushing with water and two surfactant pulses (5-6 pore volumes each) resulted in approximately 63% of NAPL mass removal from both aquifers. However, overall reduction in mass flux (Mass Flux 1) exiting the flowcell was lower in aquifer 2 (68%) than in aquifer 1 (81%), and local effluent concentrations were found to increase by as high as 120 times at local sampling ports from aquifer 2 after surfactant flushing. 3D MRI images of NAPL revealed that NAPL migrated downward and created additional NAPL source zones in previously uncontaminated areas at the bottom of the aquifers. The additional NAPL source zones were created in the direction transverse to flow in aquifer 2, which explains the higher mass flux relative to aquifer 1. Analysis using a total trapping number indicates that mobilization of NAPL trapped in the two coarsest sand fractions is possible when saturation is below 0.5 and 0.4, respectively. Results from this study highlight the potential impacts of porous media heterogeneity and NAPL source zone architecture on advanced in-situ flushing technologies.     

Modelling of iron cycling and its impact on the electron balance at a petroleum hydrocarbon contaminated site in Hnevice, Czech Republic

Over a period of several decades multiple leaks of large volumes from storage facilities located near Hnevice (Czech Republic) have caused the underlying Quaternary aquifer to be severely contaminated with nonaqueous phase liquid (NAPL) petroleum hydrocarbons. Beginning in the late 1980's the NAPL plume started to shrink as a consequence of NAPL dissolution exceeding replenishment and due to active remediation. The subsurface was classified geochemically into four different zones, (i) a contaminant-free zone never occupied by NAPL or dissolved contaminants, (ii) a re-oxidation zone formerly occupied by NAPL, (iii) a zone currently occupied by NAPL, and (iv) a lower fringe zone between the overlying NAPL and the deeper underlying contaminant-free zone. The study investigated the spatial and temporal variability of the redox zonation at the Hnevice site and quantified the influence of iron-cycling on the overall electron balance. As a first step inverse geochemical modelling was carried out to identify possible reaction models and mass transfer processes. In a subsequent step, two-dimensional (forward) multi-component reactive transport modelling was performed to evaluate and quantify the major processes that control the geochemical evolution at the site. The study explains the observed enrichment of the lower fringe zone with ferrihydrite as a result of the re-oxidation of ferrous iron. It suggests that once the NAPL zone started to shrink the dissolution of previously formed siderite and FeS by oxygen and nitrate consumed a significant part of the oxidation capacity for a considerable time period and therefore limited the penetration of electron acceptors into the NAPL contaminated zone.     

DNAPL source depletion: linking architecture and flux response

The relationship between dense non-aqueous phase liquid (DNAPL) mass reduction and contaminant mass flux was investigated experimentally in four model source zones. The flow cell design for the experiments featured a segmented extraction well that allowed for analysis of spatially resolved flux information. This flux information was coupled with image analysis of the NAPL spatial distribution to investigate the relationship between flux and the up-gradient NAPL architecture. Results indicate that in the systems studied, the relationship between DNAPL mass reduction and contaminant mass flux was primarily controlled by the NAPL architecture. A specific definition of NAPL architecture was employed where the source zone is resolved into a collection of streamtubes with spatial variability in NAPL saturation along each streamtube integrated and transformed into an effective NAPL content for each streamtube. The distribution of NAPL contents among the streamtubes (NAPL architecture) controlled dissolution dynamics. Two simplified models, a streamtube model and an effective Damkohler number model, were investigated for their ability to simulate dissolution dynamics.     

Kinetic constraints on theIn-situ remediation of soils contaminated with organic chemicals

Cleanup of contaminated soils to comply with soil quality limits currently receives much interest.In-situ remediation of contaminated soils relies on the ability of the techniques employed to enhance the rate of release of contaminants from the soil-sorbed and nonaqueous phase liquid (NAPL) phases into the aqueous or gaseous phases from which they can be more readily removed and treated. Contaminant concentrations in these “environmentally mobile” forms usually decline over time so that the economic efficiency and the overall success of remediation technologies are subject to the “law of diminishing returns”. In this paper we consider the “state of the art” in our understanding of NAPL dissolution and transport, desorption of soilsorbed contaminants and fluid flow in porous media. The extent to which these processes may constrain the success of bioremediation, pump-and-treat remediation and soil venting in relation to established soil quality limits is addressed. Finally, we suggest directions for future research and comment on legislative considerations.