【作者】 关驰；

【导师】 楼章华； 谢海建；

【作者基本信息】 浙江大学 ， 水工结构工程， 2013， 博士

【摘要】 垃圾填埋场产生的有毒性渗滤液和填埋气对填埋场底部、填埋场周边土壤和大气环境造成了很大的威胁。国内外研究成果表明即使填埋场建造了标准的防渗系统,仍有相当多的场地对地下水、周围土体和大气环境造成了污染。本文在国家自然科学基金面上项目“垃圾填埋场覆盖屏障气体运移特性与长期服役性能评价方法”和国家自然科学基金青年基金项目“垃圾填埋场复合衬垫在高应力和高水头作用下的防污性能研究”、973计划“填埋场服役性能模拟、灾害评价及可持续防控”、国家自然科学基金重大国际合作项目“城市垃圾填埋场水气产生、运移及系统化工程控制”和浙江省公益性技术应用研究计划项目“垃圾填埋场复合衬垫长期性能的离心模型试验与污染防控技术”的基础上研究了填埋场屏障系统服役性能的评价方法。本文首先对国内外填埋场渗滤液和填埋气污染物迁移机理及影响因素进行了汇总和分析。在此基础上通过提出的解析方法和数值方法分析了填埋场饱和与非饱和衬垫系统和覆盖层系统中渗滤液及填埋气的运移问题。探讨了不同类型衬垫系统和覆盖层系统的有效性。最后在国内外对填埋场现场试验研究的成果上,针对淮南填埋场进行了现场试验研究并给出填埋场现场分析的定量方法。本文所做工作及相应的研究成果如下：(1)分别比较了国内外对填埋场底部衬垫系统及顶部覆盖层系统的组成差别及设计标准。对国内外填埋场渗滤液和填埋气的性质及国内外文献报道的渗滤液和填埋气主要污染物在填埋场土层中的环境土工参数进行了汇总和统计分析,给出了这些参数的设计取值范围;(2)由于固体垃圾中很大部分都是有机污染物,有机污染物的降解作用很重要。结合一阶降解理论,并在此基础上针对国内衬垫系统中土工聚合粘土垫(GCL)+衰减层(AL)复合衬垫系统,首次给出了考虑降解作用下污染物在GCL+AL复合衬垫系统的一维解析解。研究结果表明,如果GCL半衰期小于1年,在预测GCL+AL系统中有机污染物迁移时可以忽略GCL中有机物的降解作用；(3)结合非饱和单层土中含水量线性分布,得到了污染物在非饱和衬垫土层中的一维扩散解析解。该解析解简单方便,并能考虑含水量线性变化时污染物的扩散问题,同时指出非饱和问题对污染物浓度变化的影响；(4)分析了国内外填埋场设计中用于控制填埋气释放的覆盖层系统组成。建立了饱和覆盖层中填埋气的一维扩散模型,模型考虑了随时间变化的气体浓度边界。基于菲克定律及线性方程的叠加原理,得到了气体污染物通过饱和复合覆盖层的一维扩散解析解,在此基础上比较了国内不同类型覆盖层系统对填埋气控制性能的有效性,可以有效地应用于基于性能的填埋场复合覆盖层系统的初步设计；(5)对于国内覆盖层系统类型,饱和情况下GM+GCL、CCL、GM+CCL对气体扩散的控制性能依次减弱。对于GM/GCL,GCL含水饱和度从0.85增加到1时,覆盖层顶部通量减小了82.5%。饱和时GM/GCL系统顶部气体达到稳态的时间是非饱和情况下的约100倍。对于GM/CCL, CCL含水饱和度从0.1增加到0.85时,覆盖层顶部通量减小了近1个数量级；(6)针对垃圾填埋场内部生物降解产生的气体(以甲烷为主)和氧气等在非饱和覆盖层中的运移问题,建立了气体在成层非饱和覆盖层中的一维扩散模型。模型考虑了覆盖层含水量瞬态变化和气体扩散的耦合作用。对于lm厚的覆盖层,气体运移20d到100d时,祸合含水量瞬态变化时得到的气体相对浓度较含水量稳态变化时得到的浓度小近8倍。并总结了非饱和土中气体扩散系数变化的经验公式,比较得到不同气体扩散系数形式对祸合结果有较大影响;(7)根据国外对覆盖层顶部大气压强实测数据的基础上,拟合得到压强的变化规律,并提出了大气压强对填埋气运移作用明显时压强波动幅度的取值范围,对实际填埋场区域压强波动对气体控制的研究有很好的参考作用；(8)最后借助于对填埋场污染物的研究理论和分析方法研究了国内淮南某垃圾填埋场污染物的现场运移特性,给出了在成层粘土层中污染物运移及预测的分析方法。现场试验表明17年后,Cl-在填埋场底土中的运移深度已经达到了底土下部的老粘土层;COD的运移深度则在3m左右。将一维对流扩散理论与实测结果的比较可知对流弥散作用对于污染物的运移较为重要；以地表面为接触面得到拟合结果不能很好地表示实际污染物的运移,参考前人研究成果研究了有效接触面问题。最佳的拟合结果得到的有效接触面为地表面之上50cm。将一维对流-弥散解析解与实测数据的拟合比较则可得到粘土层相关运移参数的取值范围,可为污染物进一步运移提供依据。更多还原

【Abstract】 The high concentration and high toxicity leachate and landfill gas generated in landfills have become a great threat to the bottom of landfill, surrounding soil and the atmosphere environment. Though the standard seepage control systems have been constructed for many landfills to impede leachate contaminants, the groundwater, surrounding soils and the atmosphere do have been contaminated due to landfilling.The research works in this thesis are funded by the National Science Foundation of China ’Evaluation of characteristics for gas migration in landfill covers and long-term service performance’and’Study on antifouling performance of landfill composite liner systems under effect of high stress and head’, International (Regional) cooperation and exchange project of NSFC’Water gas generation, migration and systematic engineering controls of municipal solid waste landfill’and973Plan project’Simulation, evaluation and sustainable control on service performance of landfills’. The migration mechanism and transport parameters for leachate and landfill gas from the landfills of China and the foreign countries were summarized and analyzed in the present thesis. Using the proposed analytical methods and numerical methods, the mechanism of leachate and landfill gas migration through saturated and unsaturated landfill liner systems and cover systems was investigated. The performance of different landfill liners and cover systems was evaluated. A field investigation on contaminant transport in Huainan landfill was carried out and analyzed using the mathematical models. The main conclusions are as follows:(1) The composition of landfill bottom liners landfill and top cover systems was studied and compared respectively. The transport parameters for leachate and landfill gas in landfill soils were summarized and suggested on the basis of the reported research on landfill contaminants from China and the foreign countries;(2) The effect of degradation is important due to the large amount of organic contaminants in solid wastes. Considering the effect of degradation as a first-order process, this thesis presented an analytical solution to organic contaminant advection and dispersion in a composite liner consisting of a geosynthetic clay liner (GCL) and an attenuation layer (AL). Results show that if the half-life of GCL is larger than1year, the degradation in GCLcan be neglected when predicting organic contaminant transport in GCL/AL;(3) An analytical solution of contaminant diffusion through unsaturated liner soil is presented based on simplified linear profile of moisture. The diffusion of contaminant through the unsaturated liner soils can be well studied by the proposed solution. The presented analytical solution is relatively simple to apply and can be used for evaluating the influence of unsaturated condition on contaminant migration in landfill bottom liners and soils;(4) The principle goal of landfill cover systems is to control the emissions of landfill gas into the atmosphere. The composition and types of landfill cover systems was discussed. A one dimensional model of gas diffusion through saturated landfill cover was developed. The model takes into account the time-dependent concentration variation boundary conditions. Based on Fick’s law and the superposition principle of linear equations, an analytical solution has been derived for one dimensional landfill gas diffusion in composite cover systems. The performance of the different landfill cover systems was then studied using the proposed analytical solutions. The obtained solutions can be useful for the preliminary design of landfill cover systems;(5) The results showed that the effectiveness of landfill cover systems for controlling the landfill gas emission is in the following order:GM+GCL>CCL> GM+CCL. For GM/GCL, when the degree of water saturation increases from0.85to1, the gas flux at the top of the cover system decreases by82.5%, and the time for the gas flux at the top of the system to reach the steady state for saturated cases is100times longer than the time for the test of unsaturated cases. For GM/CCL, the flux through the top of GM/CCL decreases by about an order of magnitude when the water saturation degree of CCL increases from0.1to0.85;(6) A one-dimensional model is developed to investigate landfill gas diffusion in the unsaturated layered cover systems. Coupled processes of gas diffusion in the unsaturated cover soils and transient water transport in the media were considered. For the1-meter-thcikness unsaturated cover soil, the relative gas concentrations for the case assuming coupled transport can be approximately8times smaller than those assuming steady state water distributions at the time range of20d to100d. The empirical formulas for determining gas diffusion coefficient were summarized and compared for cases of gas migration in unsaturated soils;(7) According to the measured atmospheric pressure on the top of cover system of landfills from foreign countries, the variation formula of atmospheric pressure was fitted. The range of the pressure fluctuations was obtained when the effect of atmospheric pressure on gas emission is significant. This study will be useful for the cases with large pressure fluctuations;(8) The field investigation of Huainan landfill indicate the maximum depth of migration of chloride was beyond the depths of the old clay layer, while the migration distance of COD varied around3m for17years of landfill operation period. It is indicated that advection transport and mechanism dispersion is important in contaminant transport. The range of the transport parameters of the contaminant were obtained by comparing the field data with the theory of one-dimensional contaminant transport. A better fit is obtained by employing an effective interface about50cm above the ground surface. The range of contaminant transport parameters can be used for the further investigation on the field studies of landfills.更多还原