垃圾填埋场衬垫温度效应下开裂及可挥发性有机污染物运移

In China, up to 90% of the municipal solid waste (MSW) is disposed by land-based filling. However, the landfill leachate is characterized by hazardous organic contaminants, large amount of which are unlikely to be bio-decomposed but with biologically accumulation, cancer-producing, mutagenic and teratogen, as well as a variety of heavy metals. Therefore, a properly designed basal liner is essential to avoid its pollution to the surrounding environment. The desiccation crack of liner and breakthrough of volatile organic contaminants through geomembrane layer by the mechanism of diffusion have been observed in field or experimentally. This project aims to investigate the interaction between desiccation crack of basal liner and migration of both inorganic and volatile organic contaminants by theoretical analysis, numerical simulation and laboratory experiments. The non-isothermal moisture transport theory, the advection-dispersion-equations (ADEs) for multi-phase contaminants migration will be applied. Based on the coupled 'thermal-hydro-mechanical-chemical' model, the understanding of effects of geomembrane defection, temperature gradient and variation of groundwater level on the transport of leachate will be improved. The research results will provide guidelines and technical supports in the design, management and maintain of MSW landfill and ensure an effective long-term performance of the basal liner. The ultimate object is to significantly protect the groundwater and soil from pollution due to the landfill leachate.

我国城市垃圾处理量的90%以上采用填埋技术。垃圾填埋过程中产生的大量渗滤液富含生物难降解性、生物累积性和三致效应的有毒有机污染物和重金属离子，对地下水和土壤造成巨大危害。做好衬底防渗处理就成为建造填埋场的关键。针对填埋场运行过程中所观测到的底部防渗垫层在温度梯度下开裂失效和挥发性有机物能够穿透土工膜的事实，本项目采用理论分析、数值计算和室内试验相结合的研究方法，建立"热量-流体-力学-化学"耦合计算模型，利用可变形土中水分非等温条件下非饱和渗流、挥发性有机污染物多相态运移的对流-扩散理论，预测垫层脱水开裂和污染物的迁移之间的相互作用，阐明土工膜破损、温度梯度和地下水位变化对污染物传输的影响。本项目的研究成果可为我国垃圾填埋场防渗设计、管理和维护提供可靠的科学依据和有效预测工具，对保证填埋场衬垫的耐久性、防止其周围地下水及土壤污染具有重要的理论和工程应用价值。

垃圾填埋是目前我国和世界各国处理城市垃圾的主要方式。填埋场运营中，渗滤液中的可挥发性有机污染物能够穿透土工膜以至于威胁填埋场周边环境。本项目采用理论分析、数值计算和室内试验相结合的方法研究可挥发性污染物在非饱和多孔介质内的传输。试验发现对黏土基衬垫通过有机改性的方式增强对有机污染物吸附性能时需要谨防其渗透性能不能达标；提出使用膨润土-砂混合作为衬垫材料，在垃圾自重荷载下可基本预防开裂，并首次提出在衬垫中引入气泡或氧气泡以达到阻隔和固有降解污染物，且围绕新方法建立了理论和数值模型。同时，针对生物反应器填埋场生化稳定加速问题，结合“以废治废”的理念，提出使用废旧轮胎绑扎成为空间加筋网络，利用轮胎-垃圾界面裂隙流提高渗滤液回灌效率、促进其分布均匀性，因而营造适合生化反应环境且改善填埋过程中的边坡稳定性，并基于此概念建立了双渗透-力学耦合计算模型。本项目的研究成果对保证填埋场衬垫的防渗效果、防止其周围地下水及土壤污染，以及生物反应器填埋场的高效运行具有重要的理论和工程应用价值。