我国城市垃圾填埋场岩土工程研究的现状与展望

本文从垃圾填埋场的场地选择,城市垃圾的成分及其工程性质、覆盖粘性土层工程性质,垃圾填埋场的结构优化设计,渗滤液的运移模型的研究等方面介绍我国城市垃圾填埋场岩土工程研究现状。     

垃圾渗漏液在包气带及含水层中的联合运移模拟

近年来,全国各地新建了大量的垃圾填埋场,其中多有不符合垃圾处理处置场地建设规范的,垃圾填埋场渗滤液对地下水的污染风险也逐年凸显,这就要求对后续垃圾填埋场建设时,在环评阶段做好垃圾填埋场渗滤液对地下水的污染风险预测,为垃圾填埋场地下水污染预防设施的设计与建设提供指导。本文探索了垃圾渗滤液在包气带和含水层中的联合运移模拟,首先利用Hydrus建立包气带模型,模拟垃圾渗滤液中氨氮在包气带中的迁移转化,在此基础上用Visual Modflow软件建立地下含水层模型,对比渗滤液经过包气带过滤和没经过包气带过滤两种情景下的污染范围和程度。模拟结果显示,包气带和含水层联合运移模拟渗滤液泄漏后的运移途径和路线,更接近渗滤液进入含水层的实际情况。     

阜新城市垃圾填埋场对地下水污染的研究

随着我国城市化的发展,城市生活垃圾产量剧增,垃圾渗滤液对地下水的污染问题已成为当前主要的水环境污染问题。通过对阜新市城市垃圾填埋场地理、地质和气候特征的调查,结合阜新市城市发展现状,分析了阜新市城市垃圾填埋场垃圾成分,渗滤液产生量及渗滤液中污染物的浓度,得出了阜新市城市垃圾填埋场渗滤液中各种污染物污染地下水的源强度。采用数值模拟的方法,对垃圾渗滤液污染地下水的情况进行模拟分析,验证了模拟方法的正确性,并对今后的污染情况进行了预测分析。     

不同龄期垃圾渗滤液对浅层地下水污染的实验研究

为了深入了解垃圾渗滤液对浅层地下水污染的机理,揭示不同龄期垃圾渗滤液在浅层地下水中多组分运移规律,文章以阜新市垃圾填埋场为研究对象,通过室内土柱对比实验,研究了不同龄期垃圾渗滤液在浅层地下水中多组分运移的机理和规律。结果表明不同龄期垃圾渗滤液在入渗过程中都会引起地下水不同程度的污染,且新鲜垃圾渗滤液较老龄垃圾渗滤液更易污染地下水,其污染机理主要为吸附、解析、溶解、沉淀和离子交换等水岩作用。研究结果为今后垃圾填埋场的治理和地下水的修复提供理论依据。     

垃圾渗滤液在含水层中的污染规律研究——以阜新市垃圾填埋场为例

垃圾的堆存和填埋会产生大量的渗滤液。渗滤液对垃圾填埋场周围环境能够造成严重污染,尤其使地下水质污染而丧失利用价值。通过阜新市垃圾填埋场现场采集新鲜渗滤液水样、垃圾堆体附近土样的实验研究,获得了新鲜渗滤液的各组分浓度和垃圾堆体附近土壤的性质。结合当地地理气候等情况揭示了垃圾渗滤液中污染溶质在地下水系统中的迁移转化的动态过程,定量化预测了污染范围及时空分布,为研究该地区地下水污染控制、管理和评价提供了可靠依据。     

垃圾填埋场对周边地质环境影响与防治对策

垃圾填埋场对周边地质环境的污染越来越受到研究人员的重视,其影响因素复杂,不仅与MSW的性质有关,还与垃圾填埋场的类型及其所处地质环境有密切关系。为分析垃圾填埋场中的渗滤液、重金属以及其他有害物质对周边地质环境(地下水环境、土壤环境)的影响规律,对大量相关文献和实验资料进行研究分析。研究结果表明:渗滤液是垃圾填埋场影响周围地质环境最为重要的因素,对渗滤液污染地表水及地下水情况和防治方法进行了探讨;同样渗滤液也是重金属污染土壤的载体,重金属在土壤剖面中的滞留量一般随深度的增加而逐渐减少;重金属对土壤的污染具有积累性和滞后性特点,随着填埋时间的延长污染加重。最后,根据其污染途径和污染规律,提出了相应具体防治对策。     

垃圾破碎和垃圾压实在厌氧渗滤液循环中的作用

通过3个对比反应柱研究了厌氧渗滤液循环中垃圾的破碎和压实对垃圾降解的影响。实验结果显示：在填埋垃圾量和渗滤液循环量相同的条件下，经过60d的厌氧渗滤液循环，对比垃圾柱的出水CODcr浓度为1333．2mg／L，而破碎垃圾柱和压实垃圾柱出水的CODcr浓度分别为582．4mg／L和2112．4mg／L。在厌氧渗滤液循环中，对垃圾进行破碎处理能够加速垃圾的降解，降低垃圾填埋场对地下水的危害；而对垃圾填埋体的压实不利于垃圾的降解，从而增加了垃圾填埋场污染地下水的风险。     

不同降雨模式下山谷型垃圾填埋场水分运移及其稳定性研究

近10年的运营经验表明,国内南方地区第1批建造的山谷型垃圾填埋场中的渗滤液水位一般较高。同时,现有研究表明,降雨入渗引起渗滤液水位过高是垃圾填埋场失稳的主要诱因之一。因此,研究强降雨条件下山谷型垃圾填埋场的水分运移规律及其稳定性,具有重要的现实意义。基于七子山填埋场浅层、中层和深层垃圾土的土-水特征曲线和Brooks-Corey公式,利用非线性拟合技术得到垃圾土的渗透性函数;运用饱和-非饱和渗流理论,对递减型、中心型、增强型和平均型4种降雨模式下七子山填埋场的水分运移进行了数值计算;利用极限平衡理论,对不同降雨模式下七子山填埋场的稳定性进行了分析。结果表明,降雨模式对山谷型垃圾填埋场内的水分运移规律和填埋场的稳定性有显著的影响,递减型降雨模式下填埋场内孔隙水压的变化最大,同时填埋场稳定系数也下降最为明显,为最不利降雨模式;经历7 d 746 mm的极端强降雨后,七子山填埋场具有极大的失稳隐患。     

二妃山垃圾填埋场污染地下水的可能性分析

在对武汉市敦茨口、流芳和金口垃圾场多调研的基础上，对武汉市拟建的二妃山垃圾填埋场地下水环境的影响因素进行了分析，并对填埋场的设计和管理进行了探讨。分析结果表明：（1）垃圾渗滤液对地下水环境存在巨大的潜在危险性；（2）垃圾渗滤液潜在污染危害年限长；（3）场内渗滤液水力梯度和场底防渗层渗透系数的设计管理有很大关系。     

多级膜组合工艺处理不同时期城市生活垃圾渗滤液工程实例

通过对广西若干城市垃圾填埋场渗滤液处理系统的调查,采用"生化处理+多级膜组合"工艺能很好适应不同时期垃圾渗滤液的水质波动变化,出水可稳定达到GB16889-2008《生活垃圾填埋场污染控制标准》的要求。该工艺处理效率高、运行成本低、占地小,对于未来在中小城镇垃圾渗滤液处理领域具有很好的推广应用价值。     

岩溶地区垃圾填埋场的选址评价探讨

岩溶地区的垃圾填埋选址较为困难,现行的垃圾填埋场选址评价方法又存在较大局限。笔者等依据垃圾填埋场的建设宗旨和选址基本原则,结合岩溶地区的环境地质特点,探讨提出一套适用于岩溶地区的垃圾填埋场选址评价方法。通过实例应用表明,该方法可在现行较难选出垃圾填埋场的岩溶地区,优选出适宜性较好的未来垃圾填埋场,能够担当起解决岩溶地区的垃圾无害化、减量化填埋处置的难题和重任。     

淮南垃圾填埋场固液气热特性

已关闭的淮南大通垃圾填埋场建场24 a,最大堆填高度为15 m,垃圾最大填埋龄期达24 a。通过钻孔获取不同深度的6个垃圾样,土工试验结果表明:填埋场内垃圾最小孔隙比为1.18,最大孔隙比为2.53,塑料和纸张类含量对试样孔隙比影响较大;经过24 a的扩散,渗滤液透过了10 m厚的天然致密粘土层而对地下水体产生了污染;实测填埋场垃圾体内气体中CH₄的最高体积分数达2.8654%,CH₄/CO₂比值在0.773～1.79;填埋体内最高温度大约发生在垃圾进场40 d后,达到56℃。针对垃圾填埋场固液气热特性,提出了填埋场治理措施的建议。      

Relationships between electrochemical properties of leachate and resistivity of strata in the landfill site consisting mainly of combustion residuals

There are many landfill sites consisting mainly of combustion residuals in Japan. The disposed materials are chemically unstable. Therefore, temporal changes of waste deposit conditions must be monitored for environmental management of landfill sites. Electrochemical properties of leachate and the relationships between the leachate properties and the resistivities of strata were studied in such landfill sites. In addition, incineration ashes immersed in distilled water were prepared and the temporal changes of electrochemical properties of the solution were examined. In composition, the ashes used in the experiment are similar to those disposed in the above sites. From the above results, the electrochemical properties of waste deposits consisting mainly of combustion residuals have been studied and the efficiency for managing landfill sites by resistivity measurements has been established.     

钻孔灌注桩施工过程中垃圾渗滤液对地下水的污染分析

采用大直径钻孔灌注桩时,施工时会破坏现有垃圾填埋场的防渗体系,且渗滤液将对地下水造成一定程度的污染。通过对基桩施工过程中渗滤液污染传输过程以及特征进行分析,提出了包括全护筒支护、膨润土泥浆护壁以及减少钻孔成孔至灌注混凝土的间隔时间等控制污染的主要措施,建立了基桩施工过程中钻孔泥浆浆液的损失模型以及渗滤液传输到地水下中的污染物质浓度的计算模型。根据某一具体施工条件进行估算,预测了地下水中污染物质浓度以及污染程度。最后,提出了垃圾填埋场内钻孔灌注桩的施工工艺以及施工注意事项。     

Can stable isotopes be used to monitor landfill leachate impact on surface waters?

Bacterially mediated methanogenesis in municipal solid waste landfills has been shown to cause an enrichment of carbon stable isotope ratios of dissolved inorganic carbon and hydrogen stable isotope ratios of water in landfill leachate. In the present study, we investigate the universality of this enrichment in leachate obtained from four diverse landfill sites in New Zealand. At each site, surface water samples upstream and downstream of landfills were analysed to examine the applicability of stable isotope ratios as a tool for monitoring leachate contamination in landfill-associated streams. The design of leachate collection systems, operational history, and landfill location appeared to strongly influence leachate isotopic values and the effectiveness of isotope ratios as an environmental monitoring tool for surface water.     

Electrical geophysical and hydrogeological investigations of groundwater aquifers in Ruseifa municipal landfill, Jordan

The effect of the Ruseifa municipal landfill on the shallow groundwater aquifers in the area was investigated in two separate sites. The first one was not used since 1994, whereas the other is still being used for dumping. Fourteen electrical resistivity soundings were performed to detect the leachate and its effect on the quality of the groundwater. Results indicated that the solid waste thickness of the landfill was ranged from 3 to 20 m with resistivity value less than 10 Ω m. Based on the resistivity decreases of values less than 5 Ω m, the leachate was detected in the landfill sites at depths ranged from 10 to 50 m. However, the flow direction of the leachate at depth ranging 10–20 m in the terminated site was toward north, whereas the flow direction of the leachate in the site still used for dumping was toward east–northeast which causes the major source of groundwater pollution.     

天然与改性膨润土组合处理难生物降解垃圾渗滤液的实验研究

以北京市阿苏卫垃圾填埋场中晚期渗滤液为研究对象,通过正交实验的方法分析了改性土、原土、明矾、改性土加明矾等的用量及搅拌速度、搅拌时间、静置时间等因素对垃圾渗滤液CODcr去除率的影响。通过对改性土、原土、明矾处理垃圾渗滤液的机理进行分析后,将改性土、原土分别用来处理垃圾渗滤液中可溶性物质中的疏水性物质和亲水性物质,并结合明矾的絮凝作用组合处理垃圾渗滤液。处理后垃圾渗滤液CODcr值从4700mg/L明显下降到839mg/L,CODcr去除率为82.15%,BOD5从700mg/L下降到263mg/L,BOD5去除率为62.43%。有机改性膨润土、明矾、原土组合处理是一种有效的处理垃圾渗滤液方法。     

Removal of contaminants from landfill leachates by filtration through glauconitic greensands

Passing landfill leachate through glauconitic greensand filters reduces the heavy metal cation content, lessens the unpleasant odor, and diminishes the murkiness of the leachate. The capability of the greensand to trap metal cations is increased by prolonging the contact time between the leachate and the greensand. Flushing the charged greensand filter with water does not cause significant release of cations back into solution, suggesting that polluted greensand might be disposed of at landfill sites without endangering the quality of either ground or surface water.     

Containment landfills: the myth of sustainability

A number of major problems associated with the containment approach to landfill management are highlighted. The fundamental flaw in the strategy is that dry entombment of waste inhibits its degradation, so prolonging the activity of the waste and delaying, possibly for several decades, its stabilisation to an inert state. This, coupled with uncertainties as to the long-term durability of synthetic lining systems, increases the potential, for liner failure at some stage in the future whilst the waste is still active, leading to groundwater pollution by landfill leachate. Clay liners also pose problems as the smectite components of bentonite liners are subject to chemical interaction with landfill leachate, leading to a reduction in their swelling capacity and increase in hydraulic conductivity. Thus, their ability to perform a containment role diminishes with time. More critically, if diffusion rather than advection is the dominant contaminant migration mechanism, then no liner will be completely impermeable to pollutants and the containment strategy becomes untenable.

There are other less obvious problems with the containment strategy. One is the tendency to place total reliance on artificial lining systems and pay little attention to local geological/hydrogeological conditions during selection of landfill sites. Based on the attitude that any site can be engineered for landfilling and that complete protection of groundwater can be effected by lining systems, negative geological characteristics of sites are being ignored. Furthermore, excessive costs in construction and operation of containment landfills necessitate that they are large scale operations (superdumps), with associated transfer facilities and transport costs, all of which add to overall waste management costs. Taken together with unpredictable post-closure maintenance and monitoring costs, possibly over several decades, the economics of the containment strategy becomes unsustainable. Such a high-cost, high-technology approach to landfill leachate management is generally beyond the financial and technological resources of the less wealthy nations, and places severe burdens on their economies. For instance, in third world countries with limited water resources, the need to preserve groundwater quality is paramount, so expensive containment strategies are adopted in the belief that they offer greatest protection to groundwater. A final indictment of the containment strategy is that in delaying degradation of waste, the present generations waste problems will be left for future generations to deal with.

More cost-effective landfill management strategies take advantage of the natural hydrogeological characteristics and attenuation properties of the subsurface. The ‘dilute and disperse’ strategy employs the natural sorption and ion exchange properties of clay minerals, and it has been shown that in appropriate situations it is effective in attenuating landfill leachate and preventing pollution of water resources. Operated at sites with thick clay overburden sequences, using a permeable cap to maximise rainfall infiltration and a leachate collection system to control leachate migration, ‘dilute and disperse’ is a viable leachate management strategy. Hydraulic traps are relatively common hydrogeological situations where groundwater flow is towards the landfill, so effectively suppressing outwards advective flow of leachate. This approach is also best employed with a clay liner, taking advantage of the attenuation properties of clays to combat diffusive flow of contaminants. These strategies are likely to guarantee greater protection of groundwater in the long term.     

Composite landfill liner design with Ankara clay, Turkey

This study presents an overview of the geotechnical properties of the clayey soils, referred to as Ankara clay, at two sites of the Ankara region in an attempt to design a landfill profile composed of a high density polyethylene (HDPE) geomembrane/clay composite liner through the Hydrologic Evaluation of Landfill Performance (HELP) model and the Water Balance Method. The geotechnical properties of the landfill layers along with the water balance factors (i.e., evapotranspiration, precipitation, temperature, etc.) were assessed to determine the height of the water-saturated zone in the refuse above the composite liner for landfill design. The cumulative expected leakage rates through the composite liner constructed with compacted Ankara clay were related quantitatively to the cumulative average leachate head. The results of this investigation show that the leakage rates through the composite liner are within tolerable limits.