Evaluation of Landfill Gas Emissions from an Instrumented Bioreactor Landfill Cell

城市固体废物填埋场的主要环境影响是渗滤液成分排放到地下水和地表水中；以及向大气排放垃圾填埋气体，包括甲烷和挥发性有机化合物（VOCs）。州和联邦法规（RCRA副标题D）要求，城市生活垃圾填埋场关闭后，必须加盖一层最终覆盖物，其中包括土层和土工膜——一种厚度约为1至1.5毫米的扁平土工合成产品。液体或气体通过土工膜完整部分的对流通量可以忽略不计。然而，污染物可以通过完整的土工膜扩散，气体或液体可以通过平流通过缺陷，如洞，穿孔和不规则焊缝泄漏。目前，仅在美国，就有2000多个城市生活垃圾填埋场在运行，这些填埋场将在关闭后逐步获得最终限额。生物反应器填埋可以快速转化和降解有机废物，在概念上与传统的“干墓”市政填埋方法不同。为了将垃圾填埋场作为生物反应器运行，一个关键的操作要求是添加渗滤液或水分，以加速废物有机部分的分解，从而加速气体的产生。可以使用渗滤液再循环系统来增加水分，或者允许从垃圾填埋场的最终盖层进行有控制的渗透。然而，根据目前的规定，土工膜的使用实际上消除了以渗透形式通过帽的水分通量。此外，土工膜是最终排放帽中最昂贵的组成部分。这项量化作为生物反应器的城市生活垃圾填埋场最终排放帽的垃圾填埋气体排放的行动得到了探索性研究小额拨款（SGER）计划的支持。位于密歇根州的一个现有的现场规模的生物反应器单元的最终顶盖将配备：(1)气体探针，用于测量无机气体浓度和压力分布；(2)通量室测量地表无机和有机气体排放。这些气体排放将通过含有土工膜的RCRA最终帽来测量。气体排放量将通过测量来评估帽的三种情况：(1)完好状态；(2)在土工膜上打1 cm 2的孔；(3)在土工膜上开一个相对大尺寸的窗口，以模拟土盖。生物反应器细胞已在最终盖下进行仪器测量，这是美国能源部（DOE）资助的一项正在进行的研究项目的一部分，并由环境研究与教育基金会（EREF）管理。由于已经安装在现场规模（约1英亩）生物反应器细胞中的仪器的范围，收集的气体排放数据将是全面和独特的。这样一个全面的数据集将用于测试需要综合物理、化学和生物输入的天然气生成和气体排放模型。此外，该项目促进了教学、培训和学习，并扩大了本科生对实地数据收集的参与。

The key environmental impacts from a municipal solid waste (MSW) landfill are the discharge of leachate constituents into ground water and surface water; and emissions of landfill gases including methane and volatile organic compounds (VOCs) into the atmosphere. State and federal regulations (RCRA Subtitle D) require that a MSW landfill, upon closure, be capped with a final cover containing soil layers and a geomembrane - a flat geosynthetic product about 1 to 1.5 mm thick. Advective flux of liquid or gas through an intact portion of a geomembrane is negligible. However, contaminants can diffuse through an intact geomembrane, and gases or liquids can leak via advection through defects such as holes, punctures, and irregular welds. Currently, in the U.S. alone, there are over 2,000 MSW landfills in operation, and these will receive final caps progressively as they close.A bioreactor landfill operates to rapidly transform and degrade organic waste, and differs in concept from the traditional "dry tomb" municipal landfill approach. In order to operate a MSW landfill as a bioreactor, a key operational requirement is the addition of leachate or moisture to accelerates the decomposition of the organic fraction of waste, and hence accelerate gas generation. Moisture can be added using a leachate recirculation system, or by allowing controlled infiltration from the final cap of the landfill. However, under current regulations, use of a geomembrane virtually eliminates the moisture flux through the cap in the form of infiltration. In addition, the geomembrane is the most expensive component of the final cap.This action, to quantify landfill gas emissions from the final cap of a MSW landfill operated as a bioreactor, is supported under the Small Grants for Exploratory Research (SGER) program. The final cap of an existing field-scale bioreactor cell located in Michigan will be instrumented with: (1) gas probes to measure inorganic gas concentrations and pressure profile; and (2) flux chamber to measure inorganic and organic gas emissions from the surface. These gas emissions will be measured through a RCRA final cap containing a geomembrane. The gas emissions will be measured to evaluate these three scenarios of the cap: (1) intact condition; (2) 1 cm 2 hole made in the geomembrane; and (3) a relatively large size window cut in the geomembrane to simulate an earthen cap. The bioreactor cell has been instrumented below the final cap as part of an ongoing research project funded by the Department of Energy (DOE), and administered through Environmental Research & Education Foundation (EREF).The gas emissions data collected will be comprehensive and unique due to the extent of the instrumentation already installed in the field-scale (~1 acre) bioreactor cell. Such a comprehensive dataset will be used to test gas generation and gas emission models requiring comprehensive physical, chemical, and biological input. In addition, the project promotes teaching, training, and learning, and broadens the participation of undergraduate students in field data collection.