A dynamic two‐phase flow model for air sparging

Air sparging (AS) is an in situ soil/groundwater remediation technology, which involves the injection of pressurized air/oxygen through an air sparging well below the zone of contamination. Characterizing the mechanisms governing movement of air through saturated porous media is critical for the design of an effective cleanup treatment system. In this research, micromechanical investigation was performed to understand the physics of air migration and subsequent spatial distribution of air at pore scale during air sparging. The void space in the porous medium was first characterized by pore network consisting of connected pore bodies and bonds. The biconical abscissa asymmetric concentric bond was used to describe the connection between two adjacent pore bodies. Then a rule‐based dynamic two‐phase flow model was developed and applied to the pore network model. A forward integration of time was performed using the Euler scheme. For each time step, the effective viscosity of the fluid was calculated based on fractions of two phases in each bond, and capillary pressures across the menisci was considered to compute the pressure field. The developed dynamic model was used to study the rate‐dependent drainage during air sparging. The effect of the capillary number and geometrical properties of the network on the dynamic flow properties of two‐phase flow including residual saturation, spatial distribution of air and water, dynamic phase transitions, and relative permeability‐capillary pressure curves were systematically investigated. Results showed that all the above information for describing the air water two‐phase flow are not intrinsic properties of the porous medium but are affected by the two‐phase flow dynamics and spatial distribution of each phase, providing new insight to air sparging. Copyright © 2012 John Wiley & Sons, Ltd.     

地下水有机污染治理技术现状及发展前景

概述了现有的几种地下水有机污染治理方法：抽出处理、注气－抽取土壤气、内在生物净化、流线控制、多技术结合法、生物治理、吸附、原位反应墙等工作原理和治理效果;简要分析了地下水有机污染治理技术存在的问题和发展前景。     

Remediation of saturated Shanghai sandy silt contaminated with p-xylene using air sparging

Air sparging is an effective technique for the remediation of soil and groundwater polluted by volatile organic compounds. In this paper, this technique was investigated by conducting air-sparging test in the laboratory on the Shanghai sandy silt that was artificially contaminated with p-xylene. A test tank was designed for this purpose. During the air-sparging process, aqueous p-xylene solutions were extracted from the observation holes, and their concentrations were quantified by the spectrophotometric detection method. The mechanism of mass transfer process of p-xylene in the vicinity of sparging well and the remediation of the contaminated groundwater by air sparging were explored. The results showed that the removal zone of the p-xylene was mainly located within a radius of about 20?cm around the air injection well, with 90?% p-xylene removed after 20-day air sparging. Within the initial 5-day sparging, the concentration of p-xylene decreased rapidly in the mass transfer zone. By contrast, in the area far from the injection well, the p-xylene concentration decreased evenly and slowly. Thus, the remediation of contaminated soil and groundwater by air sparging is space?Ctime dependent. For further analysis, the adsorption of silt was taken into account, and the distribution coefficient, K _d , was introduced to the modified Shackleford??s mass transfer model. The comparison between the simulated and measured results indicates that the modified model can satisfactorily describe the p-xylene mass transfer observed in this study.     

地下水曝气工程技术研究——以德州胜利油田地下水石油污染治理为例

为了研究地下水石油污染现场曝气治理效果,在胜利油田石油开采区进行了地下水现场曝气治理技术研究。采用溶解氧浓度法研究了曝气操作条件(曝气深度、曝气压力和曝气流量)对地下水石油污染曝气治理技术的影响。实验结果表明:在相同曝气压力和流量下,曝气深度越大,影响半径越大,但影响区内的气流分布越稀疏;相反,曝气深度越小,则曝气影响半径越小,但在影响区内空气流线分布越密。气流分布密度和曝气影响半径随曝气压力和流量增大而增大,但存在一个最佳限值;现场曝气存在气流分布不对称现象,是由于土壤介质的渗透性不均匀所致。地下水曝气技术对地下水石油污染治理效果显著,但曝气操作条件对该技术影响较大,需根据地质条件通过现场曝气试验确定。     

地下水有机污染控制及就地恢复技术研究进展（一）

本文是关于地下水有机污染控制及其就地恢复技术研究进展的第一篇文章，文中介绍抽出－处理系统、水力隔离系统、生物通风及曝气技术的研究进展。     

Effect of sediment size on area of influence during groundwater remediation by air sparging: a laboratory approach

 Air sparging is a groundwater remediation technique, in which organic contaminants volatilize into air as it rises from the saturated to vadose zone. An unknown has been the relationship between sediment size and area affected by air. Laboratory experiments were performed on sediments to determine the area affected by air as a function of grain size. For average grain sizes of 1.1 and 1.3-mm diameter, air flow occurs in discrete meandering channels, with a maximum area of sediment column affected of 13%/m² for 1.1-mm and 14%/m² for 1.3-mm sediments. For average grain sizes of 1.84, 2.61 and 4.38-mm diameter, air flow is pervasive, forming a symmetrical cone of influence around the injection point. Maximum areas affected are15%/m² for 1.84-mm, 25%/m² for 2.61-mm, and 9%/m² for 4.38-mm sediments. Optimal sites for air sparging, may be those with grain diameters between about 2–3 mm. Received: 26 June 1998 · Accepted: 27 July 1998     

TECHNICAL NOTE An experimental investigation of air flow patterns in saturated soils during air sparging

Air sparging is an emerging method used to remediate saturated soils and groundwater that have been contaminated with volatile organic compounds (VOCs). During air sparging, air is injected into the subsurface below the lowest known depth of contamination. Due to buoyancy, the injected air will rise through the zone of contamination. Through a variety of mechanisms, including volatilization and biodegradation, the air will serve to remove or help degrade the contaminants. The contaminant-laden air will continue to rise towards the ground surface, eventually reaching the vadose zone, where the vapours are collected and treated using a soil vapour extraction (SVE) system.Air sparging performance and ultimately contaminant removal efficiency is highly dependent on the pattern and type of subsurface air flow. This paper presents the results of a laboratory experimental study which investigated the injected air flow pattern development within an aquifer simulation apparatus. The test apparatus consisted of a tank measuring 61 cm long by 25.4 cm wide by 38.1 cm high. The apparatus was equipped with one air injection well and two vapour extracton wells. Three different soils were used to simulate different aquifer conditions, including a sand, a fine gravel and a medium gravel. Experiments were performed with different injected air pressures combined with different vacuum and groundwater flow conditions. Experiments were also conducted by injecting air into simulated shallow aquifers with different thicknesses. The air flow patterns observed were found to depend significantly on the soil type, groundwater flow conditions and system controls, including injected air pressure, flow rate and applied vacuum. © Rapid Science Ltd. 1998     

含水介质对地下水污染曝气修复的影响

为进一步研究地下水曝气原位修复技术的影响因素,采用室内实验的方法系统地研究了含水介质对原位曝气技术修复地下水污染的影响。研究结果表明:大量水相中的柴油在曝气的开始阶段被去除,随着时间的延长,污染物去除率不断增加,但增加的幅度逐渐减小。污染物去除率与时间关系曲线符合对数曲线规律,相关方程为y=alnx+b,R2=0.802 4～0.907 1,相关性较好。含水介质的渗透系数对地下水污染修复的影响较大,渗透系数与污染物的去除率基本呈正相关关系,渗透系数越大,污染物的去除率越大;含水介质密度与污染物去除率基本呈负相关关系,含水介质密度越大,污染物的去除率越小。     

地下水VOCs污染修复技术探讨

污染物事故性排放、工矿企业搬迁后遗留的污染场地修复面临各种问题,给地下水资源的使用带来严重威胁。地下水VOCs污染,具有易扩散迁移、毒性高、风险大的特点,修复难度较高。本文结合典型深层地下水修复案例,充分分析场地地质背景、水文地质条件等,根据污染物的特性、污染范围和分布特征,探讨各种修复技术的修复机理、修复对象和技术特点,针对VOCs污染修复进行性能比较及适用性分析。同时通过两个阶段的试验综合研究,原位和异位技术相结合,为开展类似地下水VOCs污染修复实践和管理提供了依据和思路。     

空气扰动技术对地下水中氯苯污染晕的控制及去除效果

原位空气扰动技术(air sparging,AS)是去除饱和土壤和地下水中挥发性有机物的最有效方法之一。首先利用二维砂槽研究曝气量与空气饱和度、影响半径的关系。结果表明:提高曝气量可以增大地下水中的空气饱和度以及曝气影响半径,但二者的增幅与曝气量的增幅不成比例,随着曝气量的增加,二者增幅减缓。又利用砂槽研究了在水力梯度一定的情况下,不同曝气量对氯苯迁移和去除效果的影响。空气的注入降低了影响区域的渗透系数,减缓了地下水的流动,有效地控制了污染物的迁移。未曝气时,130 h以后,氯苯随地下水流迁移出砂箱的比例为19.7%,而曝气量为0.1、0.2 m³/h时,此比例仅为3.6%和0.9%;与此同时,AS对氯苯的去除率分别为68.2%和78.6%。这说明AS可以有效控制污染物的迁移和去除,曝气量较大时效果更为明显。     

纳米零价铁地下水修复技术的最新研究进展

纳米零价铁（NZVI）是粒径在1～100nm之间的铁颗粒,它的比表面积和反应活性远远大于普通铁屑和铁粉,可以直接注入到含水层的重污染区,形成一个高效的原位反应带,灵活、高效、低成本地治理地下水污染。NZVI不仅可以降解各种卤代烃,还可以降解部分不含卤族元素的有机污染物,吸附或降解地下水中的重金属离子和多种无机阴离子。NZVI地下水修复技术在发达国家已经得到工程应用并正在迅速推广,原位场地因素对NZVI地下水修复效果的影响是今后该领域重要发展方向。NZVI在含水层中的有效分散和运移是今后NZVI用于地下水修复的主要突破点。     

重庆涪陵页岩气勘查开发区环境地质调查进展

紧密结合国家非常规能源勘探开发的重大战略,聚焦重庆涪陵页岩气勘查开发区环境地质调查工作,总结了研究区岩溶发育特征与分布规律,评价了涪陵页岩气开发区区域水资源量和地下水质量。在此基础上,收集分析国内外资料,梳理了页岩气勘查开发所引发的6类环境(地质)问题及勘查、钻井、压裂、开采、闭井等5个阶段需关注的地质环境问题或风险等,其中涪陵页岩气勘查开发区主要诱发水土污染、地质灾害和大气污染等环境(地质)问题; 基本识别了2种地下水污染模式、3种污染类型及可能的地下水污染风险途径; 初步确定了涪陵页岩气勘查开发区污染指示性特征因子,并形成了页岩气勘查开发区地质环境影响评价指标体系,可指导页岩气勘查开发的环境地质调查。该研究为页岩气国家新型清洁能源的绿色开发和开发区生态文明建设提供支撑。     

重庆涪陵页岩气勘查开发区环境地质调查进展

紧密结合国家非常规能源勘探开发的重大战略,聚焦重庆涪陵页岩气勘查开发区环境地质调查工作,总结了研究区岩溶发育特征与分布规律,评价了涪陵页岩气开发区区域水资源量和地下水质量。在此基础上,收集分析国内外资料,梳理了页岩气勘查开发所引发的6类环境(地质)问题及勘查、钻井、压裂、开采、闭井等5个阶段需关注的地质环境问题或风险等,其中涪陵页岩气勘查开发区主要诱发水土污染、地质灾害和大气污染等环境(地质)问题; 基本识别了2种地下水污染模式、3种污染类型及可能的地下水污染风险途径; 初步确定了涪陵页岩气勘查开发区污染指示性特征因子,并形成了页岩气勘查开发区地质环境影响评价指标体系,可指导页岩气勘查开发的环境地质调查。该研究为页岩气国家新型清洁能源的绿色开发和开发区生态文明建设提供支撑。     

Influence Factors on the In-situ Remediation of Halogenated Organic Compounds by Nanoscale Zerovalent Iron

The pollution of soil and groundwater by halogenated organic compounds (HOCs) is more and more severe. HOCs are of strong toxicity and difficult to be biodegraded. Due to its unique advantages, nanoscale zerovalent iron (NZVI) has become a hot research topic in the field of in situ remediation around the world. In this paper, basic reaction theories and kinetics of HOCs degradation by NZVI are briefly summarized. The influence factors on the in situ remediation of HOCs by NZVI are comprehensively discussed. The influence factors include the intrinsic properties of NZVI due to its different preparation and modification methods, and environment factors, such as pH, dissolved oxygen, ionic species, metals, nonreactive hydrophobic and natural organic compounds, concentrations and components of HOCs, microorganisms and subsurface heterogeneity. The effects of all these factors on NZVI stability, deliverability, targeting ability, and reactivity during in situ remediation are emphasized. Finally, the practical application of this technology are summarized and prospected.     

岩溶地下工程地质环境影响区范围划定初步研究

在大量建设城市地下轨道交通及城市更新工程的背景之下,我国城市岩溶地质灾害日趋严重。文章以深圳市3个岩溶地面塌陷事件为例,开展岩溶地下工程地质环境影响区的划定研究。首先运用高频岩溶地下水气压力监测技术对工程影响实际范围进行监测分析,然后结合工程施工参数、岩溶塌陷主要影响因素与水文地质试验参数,采用定性分析和量化计算的综合研究方法,推导出岩溶地下工程地质环境影响范围理论计算经验公式。结果表明:岩溶地下工程影响范围主要与渗透系数、工程深度成正比,与土层厚度成反比,推导的半定量理论公式适用于岩溶承压水条件下,可快速为缺乏地下水监测资料的岩溶地区地下工程安全建设及城市防灾减灾工作提供依据。      

某氨氮污染地下水体抽出 -处理系统优化模拟研究

抽出 -处理系统设计多侧重于考虑修复初期的效率,在修复后期通常效率低下,产生拖尾现象,其优化的关键在于布设的井群系统能否高效抽出受污染的地下水体。利用溶质运移数值模拟可为井群布设和抽水方案优化提供依据。本研究旨在优化我国北方某化肥厂高浓度氨氮污染的地下水体的抽出 -处理修复系统,节约时间和成本。在水文地质调查及氨氮浓度监测的基础上,综合考虑井数、抽水天数和总抽水量三个变量,采用中轴线法与三角形法结合的布井方法,利用GMS软件反复试算,筛选出三种较优抽水方案并进一步模拟优化,最终从中选出最优抽水方案。结果,相比最初方案（方案1）,最优方案（方案3）将修复周期缩短了23个月,抽水总量减少了约31.9×104 m3,而抽水井数量仅增加了1口。该模型进行了稳定流水位拟合验证和4期非稳定流实测溶质浓度验证,较符合实际。结果表明,针对抽水井数量不足引起的拖尾问题,关键因素在于合理的井位布设与分阶段的抽水模式。在修复过程中,及时对地下水中污染物进行监测,并随着污染羽变化过程及时调整抽水方案,保证高浓度区一直有抽水井进行较大流量抽水,可有效提高修复效率并缩短修复周期。     

Fluids’ dynamics in transient air sparging of a heterogeneous unconfined aquifer

Water table dynamics, dissolved oxygen (DO) content, electrical resistivity (ER) in monitoring wells and air pressure in the vadose zone are monitored in air sparging (AS) accompanied by soil vapor extraction (SVE) at a hydrocarbon-contaminated groundwater site in Oman, where a diesel spillover affected a heterogeneous unconfined aquifer. The formation of a groundwater mound at the early stage of air injection and potential lateral migration of contaminants from the mound apex called for an additional hydrodynamic barrier constructed as a pair of pump-and-treat (P&T) wells whose recirculation zone encompassed the AS and SVE wells. In all monitored piezometers the phreatic surface showed a rapid and distinct peak, which is attributed to the time of air breakthrough from the injection point to the vadose zone and a relatively mild recession limb interpreted as a decay of the mound. Tracer tests showed a layer of a relatively low hydraulic conductivity at an intermediate depth of the screened interval of the wells. Increased levels of DO and borehole air pressure that have been observed (as far as 50 m away) are likely mitigated by SVE and P&T. Radius of influence can be indirectly inferred from ER and DO changes in the AS operation zone. Salt tracer tests have shown that groundwater velocity within the AS zone decreases with the increase of air injection rate.     

Mathematical model for hydraulically aided electrokinetic remediation of aquifer and removal of nonanionic copper

One of the most cost-effective in situ technologies for soil and groundwater (i.e., aquifer) remediation is electrokinetic remediation. In electrokinetic remediation, electromigration due to electric field is combined with hydromigration due to hydraulic flow by purge water to remove pollutants from aquifers through the pore water. This study aims at investigating theoretically the role of electromigration (as active movement) of pollutants and the role of hydromigration (as passive movement) of pollutants in electrokinetic remediation, and making it clear that the control variables for electrokinetic remediation are the applied voltage and the hydraulic flow rate. These aims are pursued by construction of a mathematical model based on physico-chemical considerations and by model simulations of the electrokinetic remediation applied to the virtual aquifer polluted by heavy metals of copper sulfate. According to numerical simulations with the model: (1) heavy metal (nonanionic copper) is removed from the upstream anode region and accumulated in the downstream cathode region; (2) to carry away the heavy metal outside the aquifer (global removal), hydromigration by purge water flow is essential; and (3) electromigration contributes mainly to the redistribution of heavy metals within the aquifer (local removal and local accumulation).     

高放废物深地质处置地下水流数值模拟方法研究进展

地下水流数值模型不仅是认识深部水动力场形成演化机制的有效工具,也是建立核素迁移数值模型的基础,因而是高放废物处置场选址和安全评价中重要的技术手段。高放废物深地质处置地下水流数值模拟方法较多,如何选择适当的方法也是值得关注的问题。针对高放废物深地质处置地下水流数值模拟技术展开研究,通过阅读大量国内外文献,文章系统阐述了目前常用的4 类地下水流数值模拟方法的研究进展、适用条件和实例应用;综述了深地质处置中常用的模型不确定性分析方法及研究成果,列表给出了适用于放射性废物地质处置的地下水流数值模拟软件及其在废物处置选择和安全评价中的应用。研究结果表明:等效连续介质模型适用于大区域、长序列、裂隙发育程度较高或较均匀的地区,该类模型方法成熟、所需的数据和参数易于获得,但是不能精确刻画裂隙介质中地下水的流动特征。离散裂隙网络模型适合解决处置场地、储罐尺度等需要精细刻画的地下水流问题,但由于需要大量裂隙及其连通性数据、相关参数等,该方法存在着工作量大、耗时多的缺点。双重介质模型主要用于解决区域尺度裂隙水流问题,但并不能表现出裂隙介质的各向异性、不连续性等特征,因而适用范围存在一定的限制。等效-离散耦合模型可以通过区域分解法对裂隙密度大的区域采用等效连续介质模型,对于裂隙密度较小的地区采用离散裂隙网络模型,从而更符合一般地质条件下裂隙渗流的特征,但也存在交换量难以确定、模型耦合技术问题。通过灵敏度分析,将不同敏感因子对模型敏感指标的影响程度进行排序,提高模型精度、减少参数不确定性分析的工作量。蒙特卡罗法是目前常用的一种模型不确定性方法,原理简单、易于实现。文章展望了数值模型在仿真性、不确定性分析、预测和多介质耦合等方面的研究前景。     

PRB技术在地下水污染修复中的研究进展

在综合分析可渗透反应墙（PRB）修复污染技术基础上,提出了存在问题及发展趋势,进而理出需通过深入研究,提高修复系统性能及其可行途径。预计在不远的将来,PRB处理工艺的持续性也同样会有大幅度改进和发展。