Performance of multicomponent GCLs in high salinity impoundment applications

The interface transmissivity (θ) of two multicomponent geosynthetic clay liners (GCLs) is investigated upon hydration and permeation with a highly saline solution (TDS ≈ 260,000 mg/l; Na⁺ ~ 95,000 mg/l; K⁺~12,000 mg/l) at two stress levels (10 kPa and 150 kPa). One GCL had a smooth 0.2 mm-thick coating whereas the second GCL had a textured 1 mm-thick coating. For both GCLs, the interface transmissivity after 2-weeks is shown to be higher than at steady-state. The lower the geomembrane's (GMB) stiffness, the lower interface transmissivity. However, the effect is generally diminished at steady state and higher stress. The effect of GMB stiffness at 10 kPa is shown to be 1.6-times that at 150 kPa. Similarly, the 2-week and steady state interface transmissivity for the textured GMB was higher at 10 kPa than at 150 kPa. Coating texture and coating orientation are shown to have a significant effect on GMB/multicomponent GCL interface transmissivity. A hole in the coating aligned with GMB hole creates an additional flow path at the coating/GCL interface (θ_Geofilm/GCL), however most of the flow occurs at the coating/GMB interface (θ_Geofilm/GMB).     

Effect of prehydration,permeant, and desiccation on GCL/Geomembrane interface transmissivity

A laboratory investigation was conducted on two different conventional GCLs (one with fine granular and another one with powdered bentonite) to explore the effect of prehydration and permeant fluid; GCL desiccation on the interface transmissivity, θ, between the interfaces of a 1.5 mm-thick high-density polyethylene (HDPE) geomembrane (GMB) and a GCL. The study also aimed to assess the self-healing capacity of desiccated GCLs for three different permeant solutions under a range of applied stresses (10–150 kPa). It was found that at stresses less than 70 kPa, θ was dominated by variability in the initial contact condition between the GMB-GCL interfaces. The effect of other factors was largely masked by the contact variability. At 100–150 kPa, the effects of initial variability were largely eliminated, but there was no notable effect of other factors on θ in the absence of desiccation. GCL desiccation increased θ by up to three orders of magnitude than an intact specimen at 10–100 kPa. Even at 150 kPa, desiccated specimens had a θ ≤ 8.0 × 10⁻⁹ m²/s for all specimens tested. The chemical composition of the permeant solutions, crack width, and nature of bentonite could play an important role in healing the cracks of desiccated GCLs.     

The effect of thickness reduction on the hydraulic transmissivity of geonet drains using rigid and non-rigid flow boundaries

In this paper, relationships between in-plane flow capacity reduction and thickness reduction are presented in tri-planar and bi-planar geonets for rigid and non-rigid flow boundaries. Using these equations, the long-term flow capacity of geonets can be determined using creep test results. To validate these relationships, geonet thickness was measured under different conditions and the theoretical values of the transmissivity reduction ratios were calculated by substituting the results in the equations. Transmissivity tests were then performed under the same conditions to obtain experimental values of the reduction ratios. A comparison showed that the theoretical and experimental values of the transmissivity reduction ratios were in agreement, and the relationships provide a useful tool to predict the drainage capacity of both tri-planar and bi-planar geonets influenced by loading pressure. However, special precautions must be taken when applying the equations to investigate the hydraulic capacity of other types of geosynthetic drains as well as when the geonet is covered by geotextile material acting as a filter between the geonet and adjacent soil, is overlain by geosynthetic clay liner material where the swelling potential of the bentonite in the geonet exists, is placed in inclined positions or is subjected to complex combinations of load.     

Impact of a synthetic leachate on permittivity of GCLs measured by filter press and oedopermeameter tests

Geosynthetic clay liners (GCLs) are used in landfill liner applications due primarily to their low hydraulic conductivity to water. The low hydraulic conductivity of GCLs comes from the structure of the clay in the bentonite. However, the interaction between clay and aggressive liquids may alter the structure of the clay and, thus, result in an increase in the hydraulic conductivity of the GCL. This paper presents the results of a project aimed at evaluating the impact of a synthetic leachate on the structure of four different bentonites used in the manufacturing of GCLs. The preparation of bentonite dispersions increased the interaction between the bentonites and the various liquids. The hydraulic properties of the dispersions also were tested using filter press tests to obtain flow curves. Results of these tests were correlated with the cationic concentration, electrical conductivity and pH of the dispersions, swell indexes of the bentonite extracted from the GCLs, and permittivities of the intact GCLs determined in oedopermeameter tests. The results showed that one bentonite was more sensitive to the synthetic leachate than the other bentonites. For example, the permittivities of the more sensitive bentonite based on the oedopermeameter tests and filter press tests were respectively 2.11 × 10⁻⁸ s⁻¹ and 5.6 × 10⁻⁸ s⁻¹, whereas the permittivities for other bentonites, including a natural sodium bentonite and two sodium-activated calcium bentonites, were respectively 5.7 to 6.5 × 10⁻⁹ s⁻¹ and 3.2 to 3.5 × 10⁻⁸ s⁻¹. The filter press test served as a quick and easy-to-use test to compare the performance of the various bentonites in containing a given liquid. However, the oedopermeameter test or direct permeation test is preferable to filter press tests or fluid loss tests for evaluating the long-term impact of a liquid on a bentonite.     

UASB+A/O+MBR+两级RO处理垃圾焚烧发电厂渗滤液

垃圾焚烧发电厂产生的渗滤液具有污染物成分复杂、水质水量波动大、有机物和氨氮浓度高、处理难度大的特点,以国内某垃圾焚烧发电厂450 m³/d的渗滤液处理项目为例,针对垃圾焚烧发电厂渗滤液的特点,采用UASB+A/O+MBR+两级RO组合处理工艺,确保处理后出水稳定达到《生活垃圾填埋场污染控制标准》(GB 16889—2008)。RO浓缩液采用高压管网式反渗透(STRO)减量化处理后回喷焚烧炉。近两年的工程运行结果表明,该组合工艺具有耐冲击负荷能力强、处理出水稳定达标、占地省等优点,对COD、BOD5、NH3-N、TN的平均去除率分别为99.8%、99.9%、99.0%、98.7%,渗滤液处理系统运行成本为47.05元/m³。     

MBR/RO工艺处理垃圾渗滤液

采用外置式膜生物反应器(MBR)/反渗透(RO)工艺对成都长安垃圾填埋场的渗滤液进行处理,设计处理规模为1300m3/d,出水水质满足《生活垃圾填埋场污染控制标准》(GB16889—2008)中一般地区对渗滤液出水水质的要求。     

Effect of ammonium on the hydraulic conductivity of geosynthetic clay liners

Hydraulic conductivity and swell index tests were conducted on a conventional geosynthetic clay liner (GCL) containing sodium-bentonite (Na-B) using 5, 50, 100, 500, and 1000 mM ammonium acetate (NH₄OAc) solutions to investigate how NH₄⁺ accumulation in leachates in bioreactor and recirculation landfills may affect GCLs. Control tests were conducted with deionized (DI) water. Swell index of the Na-B was 27.7 mL/2 g in 5 mM NH₄⁺ solution and decreased to 5.0 mL/2 g in 1000 mM NH₄⁺ solution, whereas the swell index of Na-B in DI water was 28.0 mL/2 g. Hydraulic conductivity of the Na-B GCL to 5, 50, and 100 mM NH₄⁺ was low, ranging from 1.6–5.9 × 10^?11 m/s, which is comparable to the hydraulic conductivity to DI water (2.1 × 10^?11 m/s). Hydraulic conductivities of the Na-B GCL permeated with 500 and 1000 mM NH₄⁺ solutions were much higher (e.g., 1.6–5.2 × 10^?6 m/s) due to suppression of osmotic swelling. NH₄⁺ replaced native Na⁺, K⁺, Ca²⁺, and Mg²⁺ in the exchange complex of the Na-B during permeation with all NH₄⁺ solutions, with the NH₄⁺ fraction in the exchange complex increasing from 0.24 to 0.83 as the NH₄⁺ concentration increased from 5 to 1000 mM. A Na-B GCL specimen permeated with 1000 mM NH₄⁺ solution to chemical equilibrium was subsequently permeated with DI water. Permeation with the NH₄⁺ converted the Na-B to “NH₄-bentonite” with more than 80% of the exchange complex occupied by NH₄⁺. Hydraulic conductivity of this GCL specimen decreased from 5.9 × 10^?6 m/s to 2.9 × 10^?11 m/s during permeation with DI water, indicating that “NH₄-bentonite” can swell and have low hydraulic conductivity, and that the impact of more concentrated NH₄⁺ solutions on swelling and hydraulic conductivity is reversible.     

废水浸没燃烧蒸发技术的发展及应用

介绍了浸没燃烧蒸发(SCE)技术的发展及其在废水处理中的应用现状。以在垃圾填埋场渗滤液处理中的应用为例对SCE工艺进行了详细介绍。指出在解决了其燃料来源的基础上,废水SCE技术的应用前景广阔,尤其适用于垃圾渗滤液的处理。     

MBR/NF工艺处理垃圾渗滤液工程设计与运行

采用MBR/NF工艺处理垃圾渗滤液,运行结果表明该工艺设计合理,保证了渗滤液出水水质达到《生活垃圾填埋场污染控制标准》(GB 16889—2008)。介绍了渗滤液处理站的主要工艺设计参数、实际运行情况、运行成本等,可供参考。     

A~2/O与混凝沉淀法处理垃圾渗滤液研究

采用厌氧—缺氧—好氧—混凝沉淀工艺处理垃圾填埋场渗滤液。当进水COD为2 0 0 0mg/L左右时 ,好氧出水COD可降至 90 0mg/L ,混凝沉淀出水COD可降至 80mg/L ;当进水氨氮浓度为 130 0mg/L左右时 ,好氧出水氨氮 <10mg/L。生物处理系统对总氮的去除率较低 ,仅为2 0 %～ 30 % ,因而提高总氮的去除率应是今后研究的方向之一。     

垃圾卫生填埋场渗滤液组合处理工艺设计与调试

针对垃圾渗滤液水质变化较大的特点,采用铁床、铁床沉淀池、超声脱氨氮、UASB反应塔、PSB（光合细菌）反应池、水解酸化池、SBR反应塔、沉淀滤池工艺处理垃圾渗滤液,运行结果表明,该工艺对水质变化具有很强的适应能力,出水水质优于〈生活垃圾填埋污染控制标准〉（GB 16889-1997）的二级排放标准.介绍了该渗滤液处理系统的组成、重要构筑物及其设计参数、工程调试运行和经济分析等情况,总结了该工艺的设计特点.     

TW-JM1混凝土界面处理剂研制与应用

本文通过配方及性能试验,研制了TW-JM1混凝土界面处理剂。并将其应用于工程实际。应用结果表明：TW—JM1混凝土界面处理剂是一种性能优良的混凝土界面处理材料,能同时用于水泥混凝土和加气混凝土界面处理。具有良好的应用前景。     

微滤/反渗透处理、回用循环冷却排水

考察了利用双膜(MF—RO)技术回收循环冷却排水的可行性。结果表明,将微滤作为反渗透的预处理工艺能够保证反渗透对进水水质的要求,反渗透出水(电导率<40μS/cm)回送到冷却系统后可降低冷却水的腐蚀性,提高了冷却水的浓缩倍率。     

垃圾填埋场边坡稳定安全监测指标及警戒值

随着垃圾的产量和填埋量迅速增加,垃圾堆体的稳定问题日益突出,填埋场运行中安全监测显得十分重要。针对某大型垃圾填埋场失稳事件,对该填埋场堆体边坡开展了近2年的监测,获得了各种气象条件下渗滤液水位、地表水平位移、竖向位移、深层侧向变形等监测数据,特别是2008年6月强降雨期间垃圾堆体边坡局部失稳和2009年2月污泥坑周边堆体滑移过程中完整、全面的监测数据。基于监测数据,并结合实际降雨条件、填埋场运行状况,对填埋场失稳的内在因素进行详细的分析,得出渗滤液水位过高是导致堆体边坡失稳的主要内因,水平位移速率是填埋场边坡稳定状态最为敏感的指标。最后 根据监测数据 进行统计分析 ,提出垃圾填埋场稳定安全监测关键指标及警戒值, 为今后垃圾填埋场的现场监测工作提供重要依据 。     

淹没式固定床/物化/反渗透处理二级出水并回用

北方某大型化工企业以城市污水厂二级出水为原水建设了中水回用工程,采用了淹没式固定床／物化／反渗透深度处理组合工艺,介绍了该工艺的设计特点及参数。运行结果表明,处理系统的出水水质达到了企业对中水回用的水质要求,取得了良好的社会效益和经济效益。     

Effect of geotextile ageing and geomembrane surface roughness on the geomembrane-geotextile interfaces for heap leaching applications

A series of large scale direct shear experiments is used to investigate the effect of the geomembrane (GMB) surface roughness, geotextile (GTX) properties, and GTX ageing, on the GMB-GTX interface shear behaviour. Interfaces involving smooth, coextruded textured, and structured surface GMBs underlying four different nonwoven needle-punched staple fibres (GTXs) with mass per unit areas between 200 and 2400 g/m², and a geocomposite drain (GCD) are examined at normal stresses between 250 and 1000 kPa. The results showed that the interlocking between the GMB and GTX increased with increasing the GMB asperity height and/or decreasing the mass per unit area of the GTX. For the interfaces that involved GTXs preaged prior to the shear box experiments for up to 2 years at 85 °C, it was found that the 2400 g/m² heat bonded two-layered GTX exhibited internal shear failure at low shear displacements. However, all the highly aged single layered GTXs showed an increase in the peak interface friction angles with the increase in their ageing. For these single layered GTX, the results suggest that assessing the interface friction angles using unaged GTXs for the stability analysis is conservative as long as the GTX remains intact in the field.     

Effect of water chemistry on the hydro-mechanical behaviour of compacted mixtures of claystone and Na/Ca-bentonites for deep geological repositories

In the French deep geological disposal for radioactive wastes, compacted bentonite/claystone mixtures have been considered as possible sealing materials. After emplacement in place, such mixtures are hydrated by the site solution as well as the cement solution produced by the degradation of concrete. In this study, the effects of synthetic site solution and cement solution on the hydro-mechanical behaviour of compacted mixtures of claystone and two types of bentonites (MX80 Na-bentonite and Sardinia Ca-bentonite) were investigated by carrying out a series of swelling pressure, hydraulic conductivity and mercury intrusion porosimetry (MIP) tests. It was found that for the MX80 bentonite/claystone mixture hydrated with synthetic site solution, the swelling capacity was reduced compared to the case with deionised water owing to the transformation of Na-montmorillonite to multi-cation dominant montmorillonite by cation exchanges. For the Sardinia bentonite/claystone mixture, the similar increasing rate of swelling pressure was observed during the crystalline swelling process for different solutions, suggesting insignificant cation exchanges. Additionally, the cations in the synthetic site solution could reduce the thickness of diffuse double layer and the osmotic swelling for both MX80 bentonite/claystone and Sardinia bentonite/claystone mixtures. The large-pore volume increased consequently and enhanced water flow. In the cement solution, the hydroxide could also dissolve the montmorillonite, reducing the swelling pressure, and increase the large-pore volume, facilitating the water flow. Furthermore, the decrease of swelling pressure and the increase of hydraulic conductivity were more significant in the case of low dry density because of more intensive interaction between montmorillonite and hydroxide due to the high permeability.     

国际大厦常规冷却与海水冷却方案比较

结合一个濒海工程实例，具体地分析了常规冷却与海水冷却方案在设备投资，运行费用和占用面积等方面的差异，得出了就该工程而言，海水冷却方案明显优于常规冷地方案的结论，同时指出有前者的实施过程中必须注意的几个问题。     

Influence of uncertainty in geosynthetic stiffness on deterministic and probabilistic analyses using analytical solutions for three reinforced soil problems

The paper examines the quantitative influence of uncertainty in the estimate of geosynthetic reinforcement stiffness on numerical outcomes using analytical solutions for a) the maximum outward facing deformation in mechanically stabilized earth (MSE) walls, b) maximum reinforcement tensile loads and strain in MSE walls under operational conditions, and c) the mobilized reinforcement stiffness in a geosynthetic layer used to reinforce a fill over a void. The stiffness of the reinforcement is modelled using an isochronous two-parameter hyperbolic load-strain model. A linear relationship between isochronous stiffness and the ultimate tensile strength of the reinforcement is used to estimate reinforcement stiffness when product-specific creep data are not available at time of design. Solution outcomes are presented deterministically and probabilistically. The quantitative link between nominal factor of safety used in deterministic working stress design practice and reliability index is provided. The latter is preferred in modern performance-based design to quantify margins of safety within a probabilistic framework. Finally, the paper highlights the practical benefit of using product-specific isochronous secant stiffness data when available, rather than estimates of isochronous stiffness values based on reinforcement type or pooled data.