Humic acid enhanced remediation of an emplaced diesel source in groundwater. 1. Laboratory-based pilot scale test

The enhanced solubility of petroleum-derived compounds in humic acid solutions is the basis for a new groundwater remediation technology. In this unique pilot-scale test, a stationary contaminant source consisting of diesel fuel was placed below the water table in a model sand aquifer (1.2 x 5.5 x 1.8-m deep) and flushed with water at a flow rate of 2 cm/h over 5 years. At 51 days, laboratory grade humic acid was added to the water and maintained at a level of approximately 0.8 g/l. The addition of humic acid had only a small impact on the aqueous transport of the BTEX components, which were rapidly dissolved from the diesel, but had a large effect on the flushing of PAHs, including methylated naphthalenes (MNs). Binding to aqueous humic acid enhanced the solubilization of MNs two- to tenfold. During aqueous transport, biodegradation of the BTEX and PAHs occurred, limiting the lateral and longitudinal extent of the diesel contaminant plume in the model aquifer. It appears that through enhanced solubilization, the overall biodegradation rate of the MNs was increased. As the various MNs were depleted from the diesel source, the MN plume shrank and then disappeared.     

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.     

地下水曝气修复技术现场试验与应用研究进展

结合近年来国内外地下水曝气修复现场工程实践,对原位曝气的设计、操作和监测技术进行了全面的综述。对原位设计中的相关参数进行了整理分析,给出了合理取值范围,并探讨了不同场地条件下的应对方法。发展新的监测技术(如示踪技术、新型传感器等)能使曝气系统的工作性能得到更有效的监测,对于曝气修复工程现场监测新技术进行了系统的归纳和总结。此外,对现场曝气修复效果影响因素如污染物类型、曝气方式、曝气井数量、最大生物降解速率、土体孔隙率和含水层有机碳含量等进行了分析,以利于实际操作工艺的优化。最后对未来地下水曝气修复现场试验研究需开展的工作进行了展望。     

柴油机与柴油汽车烟度标准的发展及应用

研究了中国柴油机与柴油汽车烟度排放标准的发展和现状,分析了现行标准应用中应注意的问题,指出柴油机和柴油汽车烟度排放标准不统一,在烟度限值、试验方法、试验规程、试验仪器等方面存在较大差异.强调了自1993年以来,中国对柴油汽车的烟度排放要求并没有提高,以及出台更为严格的强制性标准和法规对在用柴油车排放监控的重要性,旨在有...     

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.     

东莞地下水邻苯二甲酸酯分布特征及来源探讨

在广东东莞地区采集了59组地下水水样和9组地表水水样,采用气相色谱-质谱联用技术进行测定,结果表明,地下水中邻苯二甲酸酯(PAEs)的检出率为39.0％,6种PAEs的质量浓度在未检出～6.70 μg/L.其中,邻苯二甲酸双(2-乙基己基)酯(DEHP)检出率最高,为22.O％,最大值为6.20 μg/L;邻苯二甲酸二...     

地下水修复系统中释氧材料的改进及pH调控

在采用释氧材料的地下水污染修复系统中,释氧材料提供溶解氧的同时,往往造成体系pH的升高。针对这一问题,将过氧化钙(CaO2)、水泥、河沙、膨润土和KH2PO4按一定比例混合在一起制作了3种释氧材料,并在柱实验中观测了不同释氧材料对水体溶解氧(DO)及pH值的影响。实验数据表明,水泥对释氧材料的缓释作用明显,有助于保证释氧速率平稳,避免由于释氧材料反应过快所带来的高pH问题;在释氧材料中添加一定量KH2PO4(质量分数小于10%),可以起到缓冲体系pH值的作用,并且不会造成修复系统磷污染;电气石具有降低溶液高pH值的作用,以粒径为1～2 mm的电气石作缓冲介质可以将体系pH值由11.3降至10.2。     

A remediation performance model for enhanced metabolic reductive dechlorination of chloroethenes in fractured clay till

A numerical model of metabolic reductive dechlorination is used to describe the performance of enhanced bioremediation in fractured clay till. The model is developed to simulate field observations of a full scale bioremediation scheme in a fractured clay till and thereby to assess remediation efficiency and timeframe. A relatively simple approach is used to link the fermentation of the electron donor soybean oil to the sequential dechlorination of trichloroethene (TCE) while considering redox conditions and the heterogeneous clay till system (clay till matrix, fractures and sand stringers). The model is tested on lab batch experiments and applied to describe sediment core samples from a TCE-contaminated site. Model simulations compare favorably to field observations and demonstrate that dechlorination may be limited to narrow bioactive zones in the clay matrix around fractures and sand stringers. Field scale simulations show that the injected donor is expected to be depleted after 5 years, and that without donor re-injection contaminant rebound will occur in the high permeability zones and the mass removal will stall at 18%. Long remediation timeframes, if dechlorination is limited to narrow bioactive zones, and the need for additional donor injections to maintain dechlorination activity may limit the efficiency of ERD in low-permeability media. Future work should address the dynamics of the bioactive zones, which is essential to understand for predictions of long term mass removal.     

Fe2+活化过硫酸钠原位修复氯苯污染地下水

通过建立土槽模型模拟实际污染场地,并采用Na2S2O8为氧化剂、柠檬酸螯合Fe2+为活化剂,研究了氯苯在地下水中的迁移分布规律、原位修复及其对地下水环境的影响。结果表明,氯苯在含水层水平纵向上的迁移作用大于横向迁移;随着时间的增加,地下水中氯苯浓度变化总趋势为先增加后减少并最终趋于稳定;随着迁移距离的增加,氯苯的浓度逐渐降低。柠檬酸螯合Fe2+活化Na2S2O8能够有效修复受氯苯污染的地下水和土壤;持续氧化36 h后,地下水和土壤中氯苯的去除率分别达到82.4%和80.3%。进一步研究发现,氧化处理后,出水的pH值基本稳定在3.5、SO42-浓度为88.7 mg/L,满足地下水Ⅱ类水质标准。     

中国台湾地区土壤及地下水污染整治管理与经验

中国台湾地区土壤及地下水污染整治基金管理会自2001年成立以来,不断完善管理架构和管理体系,发布相关领域的法律法规、行政规则和公告,有效运行污染整治基金的财务筹措和使用等经济管理机制。开展了一系列行之有效的预防、监测、调查、评估等管理工作,为污染场地的识别和筛选奠定了坚实的基础。对于污染场地的整治工作,采用标准和风险评估相结合的验收方式,推行场地可持续利用的绿色修复技术。重点研究台湾地区土壤及地下水污染整治工作的管理政策、模式和措施,总结相关经验,为中国土壤及地下水污染防治工作提供借鉴和参考。     

SDBS在土壤中的吸附及对淋洗柴油效果的影响

为考察污染土壤淋洗修复过程中表面活性剂的动态吸附解吸过程及其对淋洗效果影响,以北京潮土为例,采用土柱淋洗实验,对4种浓度（600、1 800、3 000和4 200 mg·L-1）的阴离子表面活性剂十二烷基苯磺酸钠（SDBS）淋洗柴油污染土壤的过程进行模拟。结果表明,土柱淋洗过程中北京潮土对 SDBS 的吸附过程可分3个阶段：快吸附阶段、慢吸附阶段及动态平衡阶段。吸附动力学较好地符合颗粒内扩散方程。SDBS淋洗柴油污染潮土时,初期由于表面活性剂在土壤中的吸附未达到平衡而无法在溶液中形成胶束,导致淋洗液中柴油浓度很低。此后SDBS在土壤中的吸附逐渐达到平衡状态,溶液中SDBS的浓度超过临界胶束浓度（CMC）开始形成胶束,土壤中残留的柴油开始大量解吸。淋洗液中柴油浓度总体呈先升到峰值,而后呈锯齿状波动下降的变化规律。淋洗到400 h时,4种浓度SDBS溶液对柴油的去除率分别为1.06%、1.52%、25.55%和27.99%,柴油去除率与表面活性剂浓度呈正相关。但表面活性剂浓度过高时,会降低土柱中土壤渗透系数,导致淋洗流量显著降低,采用SDBS淋洗柴油污染潮土时,表面活性剂浓度在3 000~4 200 mg·L-1较佳。     

酒石酸强化重金属复合污染模拟土壤电动修复过程及机理分析

为提高电动修复重金属复合污染土壤的效率,通过配制重金属复合污染模拟土壤,构建电动修复实验装置,利用2因素完全随机实验设计研究了酒石酸浓度和时间对重金属去除效果的影响;采用BCR法对土壤金属赋存形态进行了分析表征。结果表明：与对照相比,以酒石酸为电解液显著提高了重金属的去除率;重金属去除率受酒石酸浓度和修复时间影响显著;以0.05 mol·L⁻¹酒石酸为电解液修复120 h后,重金属去除效果最好,重金属总去除率为86.15%,Cu²⁺、Mn²⁺、Cd²⁺、Pb²⁺、Zn²⁺的去除率分别为75.67%、98.11%、85.1%、70.75%和90.9%。BCR分析表明,酒石酸有助于提高土壤中弱酸提取态重金属含量,提高了重金属的迁移性能,从而有利于电动修复过程。     

The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater

Data from long-term groundwater sampling, limited coring, and associated studies are synthesised to assess the variability and intrinsic remediation/natural attenuation of a dissolved hydrocarbon plume in sulphate-rich anaerobic groundwater. Fine vertical scale (0.25- and 0.5-m depth intervals) and horizontal plume-scale (>400 m) characteristics of the plume were mapped over a 5-year period from 1991 to 1996. The plume of dissolved BTEX (benzene, toluene, ethylbenzene, xylene) and other organic compounds originated from leakage of gasoline from a subsurface fuel storage tank. The plume was up to 420 m long, less than 50 m wide and 3 m thick. In the first few years of monitoring, BTEX concentrations near the point of leakage were in approximate equilibrium with non-aqueous phase liquid (NAPL) gasoline. NAPL composition of core material and long-term trends in ratios of BTEX concentrations in groundwater indicated significant depletion (water washing, volatilisation and possibly biodegradation) of benzene from residual NAPL after 1992. Large fluctuations in BTEX concentrations in individual boreholes were shown to be largely attributable to seasonal groundwater flow variations. A combination of temporal and spatial groundwater quality data was required to adequately assess the stationarity of plumes, so as to allow inference of intrinsic remediation. Contoured concentration data for the period 1991 to 1996 indicated that plumes of toluene and o-xylene were, at best, only partially steady state (pseudo-steady state) due to seasonal groundwater flow changes. From this analysis, it was inferred that significant remediation by natural biodegradation was occurring for BTEX component plumes such as toluene and o-xylene, but provided no conclusive evidence of benzene biodegradation. Issues associated with field quantification of intrinsic remediation from groundwater sampling are highlighted. Preferential intrinsic biodegradation of selected organic compounds within the BTEX plume was shown to be occurring, in parallel with sulphate reduction and bicarbonate production. Ratios of average hydrocarbon concentrations to benzene for the period 1991 to 1992 were used to estimate degradation rates (half-lives) at various distances along the plume. The estimates varied with distance, the narrowest range being, for toluene, 110 to 260 days. These estimates were comparable to rates determined previously from an in situ tracer test and from plume-scale modelling.     

An integrated anaerobic/aerobic bioprocess for the remediation of chlorinated phenol-contaminated soil and groundwater.

An investigation of biodegradation of chlorinated phenol in an anaerobic/aerobic bioprocess environment was made. The reactor configuration used consisted of linked anaerobic and aerobic reactors, which served as a model for a proposed bioremediation strategy. The proposed strategy was studied in two reactors before linkage. In the anaerobic compartment, the transformation of the model contaminant, 2,4,6-trichlorophenol (2,4,6-TCP), to lesser-chlorinated metabolites was shown to occur during reductive dechlorination under sulfate-reducing conditions. The consortium was also shown to desorb and mobilize 2,4,6-TCP in soils. This was followed, in the aerobic compartment, by biodegradation of the pollutant and metabolites, 2,4-dichlorophenol, 4-chlorophenol, and phenol, by immobilized white-rot fungi. The integrated process achieved elimination of the compound by more than 99% through fungal degradation of metabolites produced in the dechlorination stage. pH correction to the anaerobic reactor was found to be necessary because acidic effluent from the fungal reactor inhibited sulfate reduction and dechlorination.     

基于模糊权物元理论的地下水水质评价模型构建及应用

在物元分析的基础上,结合模糊权重理论与层次分析方法,构建用于评价地下水水质的模糊权物元分析模型。应用此模型对徐州市的重要水源地——张集水源地的地下水水质进行了综合评价。选取数据较为完整的20个监测井的监测数据进行评价。结果表明,研究区的20个采样点水质为Ⅱ、Ⅲ级的占95%,绝大多数地下水水质较好,符合饮用水的要求。与投影寻踪法和模糊概率法的评价结果比较发现,得出的评价结果与以上2种评价结果基本一致。     

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.     

Design of aquifer remediation systems: (2) estimating site-specific performance and benefits of partial source removal

A Lagrangian stochastic model is proposed as a tool that can be utilized in forecasting remedial performance and estimating the benefits (in terms of flux and mass reduction) derived from a source zone remedial effort. The stochastic functional relationships that describe the hydraulic "structure" and non-aqueous phase liquid (NAPL) "architecture" have been described in a companion paper (Enfield, C.G., Wood, A.L., Espinoza, F.P., Brooks, M.C., Annable, M., Rao, P.S.C., this issue. Design of aquifer remediation systems: (1) describing hydraulic structure and NAPL architecture using tracers. J. Contam. Hydrol.). The previously defined functions were used along with the properties of the remedial fluids to describe remedial performance. There are two objectives for this paper. First, is to show that a simple analytic element model can be used to give a reasonable estimate of system performance. This is accomplished by comparing forecast performance to observed performance. The second objective is to display the model output in terms of change in mass flux and mass removal as a function of pore volumes of remedial fluid injected. The modelling results suggest that short term benefits are obtained and related to mass reduction at the sites where the model was tested.     

Surfactant enhanced recovery of tetrachloroethylene from a porous medium containing low permeability lenses. 2. Numerical simulation

A numerical model of surfactant enhanced solubilization was developed and applied to the simulation of nonaqueous phase liquid recovery in two-dimensional heterogeneous laboratory sand tank systems. Model parameters were derived from independent, small-scale, batch and column experiments. These parameters included viscosity, density, solubilization capacity, surfactant sorption, interfacial tension, permeability, capillary retention functions, and interphase mass transfer correlations. Model predictive capability was assessed for the evaluation of the micellar solubilization of tetrachloroethylene (PCE) in the two-dimensional systems. Predicted effluent concentrations and mass recovery agreed reasonably well with measured values. Accurate prediction of enhanced solubilization behavior in the sand tanks was found to require the incorporation of pore-scale, system-dependent, interphase mass transfer limitations, including an explicit representation of specific interfacial contact area. Predicted effluent concentrations and mass recovery were also found to depend strongly upon the initial NAPL entrapment configuration. Numerical results collectively indicate that enhanced solubilization processes in heterogeneous, laboratory sand tank systems can be successfully simulated using independently measured soil parameters and column-measured mass transfer coefficients, provided that permeability and NAPL distributions are accurately known. This implies that the accuracy of model predictions at the field scale will be constrained by our ability to quantify soil heterogeneity and NAPL distribution.     

Solar photodegradation of dichloroacetic acid and 2,4-dichlorophenol using an enhanced photo-Fenton process

The photo-Fenton process using potassium ferrioxalate as a mediator was investigated for the photodegradation of dichloracetic acid (DCA) and 2,4-dichlorophenol (DCP) in aqueous medium using solar light as source of irradiation. The influence of the solution depth, the light intensity and the effect of stirring the solution during irradiation process were evaluated using DCA as a model compound. A negligible influence of stirring the solution was observed when the concentration of ferrioxalate (FeOx) was 0.8 mM and solution depth was 4.5 or 14 cm. The optimum FeOx concentration determined for solution depths between 4.5 and 14 cm was 0.8 mM considering total organic carbon (TOC) removal during DCA irradiation. The high efficiency of the photo-Fenton process was demonstrated on summer days, when only 10 min of exposition (around noon) were sufficient to completely destroy the organic carbon of a 1.0 mM DCA solution in the presence of 0.8 mM FeOx and 6.0 mM H2O2 using a solution depth of 4.5 cm. It was observed that the photodegradation efficiency increases linearly with the solar light intensity up to values around 15 Wm(-2) but this linear relationship does not hold above this value showing a square root dependence. The photodegradation of a solution of DCP/FeOx showed a lower TOC removal rate than that observed for DCA/FeOx, achieving approximately 90% after 35 min irradiation under 19 W m(-2), while under this light intensity, the same TOC removal of DCA/FeOx was achieved in only 10 min irradiation.