Surfactant enhanced recovery of tetrachloroethylene from a porous medium containing low permeability lenses. 1. Experimental studies

A matrix of batch, column and two-dimensional (2-D) box experiments was conducted to investigate the coupled effects of rate-limited solubilization and layering on the entrapment and subsequent recovery of a representative dense NAPL, tetrachloroethylene (PCE), during surfactant flushing. Batch experiments were performed to determine the equilibrium solubilization capacity of the surfactant, polyoxyethylene (20) sorbitan monooleate (Tween 80), and to measure fluid viscosity, density and interfacial tension. Results of one-dimensional column studies indicated that micellar solubilization of residual PCE was rate-limited at Darcy velocities ranging from 0.8 to 8.2 cm/h and during periods of flow interruption. Effluent concentration data were used to develop effective mass transfer coefficient (Ke) expressions that were dependent upon the Darcy velocity and duration of flow interruption. To simulate subsurface heterogeneity, 2-D boxes were packed with layers of F-70 Ottawa sand and Wurtsmith aquifer material within 20-30 mesh Ottawa sand. A 4% Tween 80 solution was then flushed through PCE-contaminated boxes at several flow velocities, with periods of flow interruption. Effluent concentration data and visual observations indicated that both rate-limited solubilization and pooling of PCE above the fine layers reduced PCE recovery to levels below those anticipated from batch and column measurements. These experimental results demonstrate the potential impact of both mass transfer limitations and subsurface layering on the recovery of PCE during surfactant enhanced aquifer remediation.     

表面活性剂冲洗法治理非水卡流体污染多相流研究进展

表面活性剂冲洗法是一种治理土壤与地下水非水相流体（NAPLs）污染的有效技术。在简要介绍表面活性剂冲洗法去除作用机理的基础上，总结了近些年来与表面活性剂冲洗法多相流相关的国内外试验研究和模型研究成果，主要包括表面活性剂作用所引起的混溶驱替和不混溶驱替多相流问题，并指出目前研究中存在的问题和进一步探讨的方向。     

In-situ surfactant/surfactant-nutrient mix-enhanced bioremediation of NAPL (fuel)-contaminated sandy soil aquifers

SCOPE AND BACKGROUND: Contamination of soils, aquifers and groundwater by nonaqueous phase liquid (NAPL) pollutants constitutes a major environmental issue of concern, worldwide. The residual (biodegradation-resistant) hydrophobic fuel hydrocarbons entrapped in the soil porous matrix, possess a particular bioremediation challenge due to their becoming virtually immobile, nor desorbable, or water dispersible. Consequently, they are not available as substrates to the micro-organism-based biodegradation. MATERIALS AND METHODS: Our research involves the development of economically feasible, surfactant/surfactant-nutrient mix (SSNM)-enhanced bioremediation methodologies for sustainable, in situ bioremediation of fuel-contaminated aquifers. This requires, methodologically, (a) the optimization, via in vitro 'flow' (columns) lab experiments and screening processes, of an effective mixture for the intended SSNM-enhanced bioremediation; and (b) the study of the combined effect of the optimized SSNM on the solubilization/mobilization and biodegradation of NAPL (fuel) in in vitro site/aquifer-simulated bioremediation. RESULTS AND DISCUSSION: The essence of our findings: (1) kerosene's maximum enhanced mobilization - f = 3.6, compared with that of deionized water, was achieved with an SSNM having the composition of linear alkylbenzene sulfonate (LABS): coco-amphodiacetate (containing N): surfactant-nutrient X (containing both N and P) = 0.15: 0.15: 0.05 g/L, respectively; (2) 62-64% of the initial amount of kerosene in the initially saturated soil matrix, 'packed' in a column, has been eluted from it during approximately 30 days, compared with 68% of kerosene biodegradation in 'vessel' settings, in 21 days. CONCLUSIONS: (1) The indigenous microorganisms present in th vadose zones of fuel-contaminated sandy soil aquifers are potentially capable of unassisted removal of approximately 80% of the initially contained fuel (kerosene), during a period of about 42 days; (2) the major effects of the SSNM addition are (a) enhanced mobilization of the bulky NAPL; and (b) enhanced desorbtion/ solubilization/dispersion of the entrapped NAPL which, in turn, facilitate their enhanced biodegradation. RECOMMENDATIONS AND PERSPECTIVE: Our findings suggest that pre-optimized, biodegradable SSNM is essential for surfactants-based bioremediation of NAPL-contaminated aquifers, in order to make this in-situ methodology both technologically and economically feasible.     

Effect of the water–oil ratio on brine/surfactant/alcohol/oil systems optimized for soil remediation

The optimum middle-phase microemulsion used for remediation of oily contaminated soils is often obtained by mixing a certain amount of a surfactant/alcohol mixture with oil and adjusting the salinity concentrations at a constant water–oil ratio. Upon introduction to the subsurface, however, the system may not be in the optimum state throughout the remediation process owing to the change in the water–oil ratio. This research has attempted to investigate the effect of the water–oil ratio on the phase behavior of systems containing brine, anionic surfactant, alcohols, and different oils. By systematically changing the water–oil ratio, while keeping the others variables constant, the systems exhibited different phase behavior. The results revealed that the effect of the water–oil ratio on system behavior was significant, and analogous to that of salinity. Increasing the water–oil ratio led the system change from winsor I → winsor III → winsor II. The greater the water–oil ratio the lower the salinity required to produce the middle-phase microemulsion, but the narrower the salinity range of the three-phase region. An empirical correlation has been developed in order to predict the changes in phase behavior with the changes in water–oil ratio. This provides a useful tool for designing optimum formulations suitable for soil remediation. Received: October 5, 1999 / Accepted: March 27, 2000     

甲苯在典型土壤中的迁移性能

采用一维土柱装置模拟非水相液体(NAPLs)在我国两种典型土壤(北京潮土与湖南红壤)中的垂向迁移过程,以甲苯为例研究了其在两种土壤中的迁移性能;采用XRD技术测定土壤的矿物组成。实验结果表明,当潮土和红壤孔隙率均为45%时,甲苯在潮土中的迁移速率和最终迁移距离均显著高于在红壤中。甲苯在潮土中的阻滞系数(Rf=18.9)小于在红壤中(Rf=26.5),表明红壤对甲苯的吸附阻滞作用强于潮土。XRD表征结果显示,红壤中粒径小的黏粒含量较高,具有较多的黏土矿物,对甲苯具有更强的吸附阻滞能力,致使甲苯在红壤中垂向迁移速率小,最终迁移距离较短。     

NAPLs污染物垂向指流迁移分形表征中图像处理的影响研究

染色示踪技术是研究多孔介质中指流形态的主要手段之一,而如何更精确地对所采集的图像数据进行分析,是该研究工作中非常重要的组成部分.分形理论在染色示踪影像的基础上对指流形态进行定量描述,以质量分形维数(D m)表征渗流面积,以界面分形维数(D s)表征渗流驱替边界长度,对于识别和预测指流形态有一定的实际意义.而分形维数的计算基于二值化图像完成,因此明确图像二值化过程对分形维数表征的影响对分形维数的应用有重要意义.本研究以4种非水相流体在二维砂箱中迁移的130幅染色图像为目标影像,详细比较了图像预处理过程中不同饱和度(红色)阈值、不同亮度(灰度)阈值以及图形中"湖"的填充3个因素分别对D m和D s的影响.结果表明,在砂箱实验中,与田间实验相比由于染色污染物与石英砂颜色对比度较大,红色阈值调整对两种分形维数影响相对较小;随着灰度阈值的提高D m平均降低0.02,D s平均增加0.05;图形中"湖"的填充对D m几乎没有影响,而使D s平均降低0.10.研究发现与D s相比,D m在图像处理过程中受各种因素影响较小,建议在进一步研究中以D m为指流形态指示指标以避免图形处理过程中主观因素的影响.     

4种NAPLs污染物在二维砂箱中的指进锋面形态特征研究

为明确介质和流体性质等因素对非水相液体(NAPLs)在多孔介质中入渗迁移的影响,利用数码图像分析技术对甲苯、柴油、1,2-二氯乙烷和四氯乙烯这4种NAPLs在4种不同粒径多孔介质中的非饱和入渗特性进行了实验研究.结果表明,数码图像分析技术能够动态、全过程记录NAPLs的迁移锋面;NAPLs在驱替气体过程中会出现指进形式的不稳定流;指进生长过程中出现分叉、合并和屏蔽等现象;NAPLs的迁移特性受介质性质和流体特性的共同影响,入渗过程中垂向上的迁移速率和污染面积增长率与介质粒径大小呈正相关,与流体密度呈正相关(甲苯除外),入渗过程中形成的指进与介质和流体本身性质也密切相关.相同时间内,DNAPL相较于LNAPL入渗的距离更深,造成的污染面积更大,其环境风险明显大于LNAPL.     

非水液相混合有机污染物的过冷液体溶解度间接测量

存在于混合物中的有机污染物是现代生活环境中常见的危害性较高的污染物。有机物过冷液体溶解度不仅是环境科学研究领域的重要概念,也是环境监测、环境质量评价、制定污染治理方案所需要的重要参数。由于过冷液体溶解度无法通过常规的实验方法进行测量,只能借助热力学计算取得。但是已有的热力学参数欠缺、精度不够,很多有机物的过冷液体溶解度或者无法准确计算,或者差异巨大。针对非水液相混合有机污染物中过冷液体溶解度取值问题,本文提出了一种测量过冷液体溶解度的实验方法,即采用批处理实验在不同摩尔分数点取得该点的平衡浓度,根据实验结果将不同摩尔分数点的平衡浓度外推(依线性或者非线性规律)至摩尔分数为一时,得到值为过冷液体溶解度。本文对对几种多环芳香烃进行了实验研究,并将实验结果的与其它方法得到的数值进行比较。结果与已经发表数值吻合,证实该方法的准确性和可靠性。同时也点评了该方法的局限性及应用前景。     

表面活性剂冲洗法治理非水相流体污染多相流研究进展

表面活性剂冲洗法是一种治理土壤与地下水非水相流体(NAPLs)污染的有效技术.在简要介绍表面活性剂冲洗法去除作用机理的基础上,总结了近些年来与表面活性剂冲洗法多相流相关的国内外试验研究和模型研究成果,主要包括表面活性剂作用所引起的混溶驱替和不混溶驱替多相流问题,并指出目前研究中存在的问题和进一步探讨的方向.     

土壤含水层NAPLs污染修复技术的研究进展＊

文章介绍了非水相流体(NAPLs)的性质,综述了地下土壤含水层NAPLs污染治理的六种主要技术,分析了各种技术的原理、特点、治理效果及其研究进展,提出了修复技术存在的问题及今后要做的工作。