Evaluation of Landfill Gas Emissions from an Instrumented Bioreactor Landfill Cell

城市固体废物(MSW)填埋场的主要环境影响是将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，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，MSW垃圾填埋场在关闭时，必须用包含土层和土工膜的最终覆盖物覆盖，土工膜是一种厚度约为1至1.5毫米的平坦土工合成产品。液体或气体通过土工膜完整部分的平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，气体或液体可能会通过缺陷(如孔洞、穿孔和不规则焊缝)通过平流泄漏。目前，仅在美国，就有2000多个城市生活垃圾填埋场在运行，随着它们的关闭，这些垃圾填埋场将逐步达到最终封顶。生物反应器垃圾填埋场的运作是为了快速转化和降解有机垃圾，与传统的“干坟墓”城市垃圾填埋场方法在概念上不同。为了将生活垃圾填埋场用作生物反应器，一个关键的操作要求是添加渗滤液或水分以加速垃圾中有机部分的分解，从而加速气体产生。可以使用渗滤液再循环系统或通过允许从垃圾填埋场的最终盖子进行受控渗透来增加水分。然而，在目前的法规下，使用土工膜实际上以渗透的形式消除了通过盖子的湿气通量。此外，土工膜是最终盖子中最昂贵的部件。这项行动是为了量化作为生物反应器运行的生活垃圾填埋场最终盖子的垃圾填埋气排放量，这一行动得到了小额探索性研究补助金(SGER)计划的支持。位于密歇根州的现有野外规模生物反应器的最终盖将配备以下仪器：(1)用于测量无机气体浓度和压力分布的气体探头；(2)用于测量表面无机和有机气体排放的通量室。这些气体排放将通过RCRA包含土工膜的最终帽进行测量。将测量气体排放量，以评估盖子的三种情况：(1)完好无损；(2)在土工膜上打出1厘米2的洞；(3)在土工膜上开一个相对较大的窗口，以模拟土工帽。作为由能源部(DOE)资助并由环境研究与教育基金会(EREF)管理的正在进行的研究项目的一部分，生物反应器单元已经在最终盖下安装了仪器。由于现场规模(约1英亩)生物反应器单元中已经安装了仪器的范围，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、化学和生物输入的气体生成和排放模型。此外，该项目还促进了教学、培训和学习，并扩大了本科生对野外数据收集的参与。

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.