Biofilters for mitigation of landfill methane emissions

英国和欧洲有一个大型的封闭垃圾填埋场遗产，大约有20,000个封闭的垃圾填埋场。垃圾填埋场产生的甲烷是一种比二氧化碳强25倍的温室气体，因此防止其逃逸到大气中是垃圾填埋场行业的首要任务，需要严格的操作条件来最大限度地减少排放和对环境的风险。诺维奇附近的Strumpshaw垃圾填埋场是一个15公顷的废弃采石场，里面装满了约1,000,000立方米的生活和商业废物。废气被送入现场的斯特林发动机，通过燃烧和发电来管理垃圾填埋气体。现场的迁移线含有15%的甲烷，难以燃烧，因此需要处理以控制场外迁移。由Charles Wright领导的诺福克郡议会（NCC）封闭垃圾填埋场小组已经在Strumpshaw成功地试验了垃圾填埋气的生物氧化，使用了一个58m3的生物过滤器，该过滤器由堆肥、木屑、膨胀粘土和coir组成，埋在垃圾填埋场的土壤中，内衬有不渗透的气体屏障。甲烷的生物氧化是通过将空气和垃圾填埋气体泵入生物过滤器来完成的。天然存在于土壤中的好氧甲烷氧化细菌（甲烷氧化菌）通过将甲烷转化为水和二氧化碳来去除甲烷。这种生物过滤技术专门针对旧的封闭垃圾填埋场，这些填埋场产生的气体低于发电变得困难的水平。这个多学科项目的一个关键目标是评估生物氧化作为一种气体管理技术对含有5-20%甲烷的垃圾填埋气体的有效性。为了实现这一目标，必须了解生物过滤器有效性的生物学基础，并为填埋场甲烷生物过滤器的未来设计和长期管理创建一个强大的框架。关键问题：氧化甲烷菌的数量和活动如何随深度变化，哪些在生物过滤器中最有效地消耗甲烷？回答这些问题将导致基于输入气体的生物过滤器设计的最佳深度。生物滤池的理化参数是否最适合甲烷氧化菌？它们是否有所需的营养物质（CH4, O2， N， P, Cu, Fe）？这为生物过滤器的设计提供了信息，以创造理想的基质，使气体和营养物质能够渗透，并使甲烷氧化菌茁壮成长。水分含量是否正确，做季节差异要紧；温度重要吗？如果生物过滤器可以在不带盖子/不绝缘/不加热的情况下运行，这些问题将得到解答。方法：物理化学参数包括水分含量，温度，基质渗透率，微量元素有效性和垃圾填埋气组成将被测量。现场分析技术将包括地面排放测试设备（FID， TDL）和井下监测，实验室分析将用于收集样品进行基质和微量气体成分分析。生物过滤器样品的甲烷氧化电位将用气相色谱法测定。通过分析16S rRNA基因和关键酶甲烷单加氧酶（pmoA, mmoX）靶向基因，确定生物滤池中甲烷氧化菌的分布和多样性。生物过滤器样品中存在的关键活性甲烷氧化菌将通过使用13CH4的稳定同位素探测来识别，这是Murrell实验室首创的一项技术，随后在生理和分子水平上进行分离和表征。

The UK and Europe has a large closed landfill legacy with approximately 20,000 closed landfill sites. Methane generated in landfill is 25x more potent a greenhouse gas than CO2 so prevention of its escape to the atmosphere is a priority for the landfill industry and requires stringent operating conditions to minimise emissions and the risks to the environment. Strumpshaw landfill site near Norwich is a disused quarry of 15 ha filled with ~1,000,000 mcubed of domestic and commercial waste. Waste gas is fed into on- site Stirling engines which manage the landfill gas through combustion and generate electricity. The migration line on site contains 15% methane which is difficult to combust and so needs to be treated to control off-site migration. The Norfolk County Council (NCC) Closed Landfill Team, led by Charles Wright, has been trialling successfully at Strumpshaw the bioxidation of landfill gas using a 58m3 biofilter composed of compost, wood chip, expanded clay and coir, buried in landfill soil, lined with an impermeable gas barrier. Bioxidation of the methane is done by pumping air and landfill gas through the biofilter. Aerobic methane oxidising bacteria (methanotrophs) naturally occurring in soils remove methane by converting it to water and CO2. This biofilter technology is specifically aimed at older closed landfills that are generating gas below the level where electricity generation becomes difficult. A key objective in this multidisciplinary Project is to assess the effectiveness of bio-oxidation as a gas management technique for landfill gas containing 5-20% methane. To achieve this, it is imperative to understand the biology underpinning the effectiveness of the biofilter and to create a robust framework for future design and long term management of landfill methane biofilters.Key questions:How do methanotroph populations and activities change with depth and which are the most effective in consuming methane in the biofilter? Answering these questions would lead to an optimal depth for the biofilter design based on the input gas.Are physico-chemical parameters in the biofilter optimum for methanotrophs. Do they have the nutrients they need (CH4, O2, N, P, Cu, Fe)? This informs biofilter design, to create the ideal matrix to allow gas and nutrients to percolate through and for methanotrophs to thrive.Is moisture content correct, do seasonal differences matter; is temperature important? These questions would answer if the biofilter can be run uncovered/uninsulated/unheated.Methodology:Physico-chemical parameters including moisture content, temperature, matrix permeability, trace element availability and landfill gas composition will be measured. Field analytical techniques used will include surface emissions testing equipment (FID, TDL) and downhole monitoring, and laboratory analysis will be used for collected samples for matrix and trace gas composition analysis.Methane oxidation potential of biofilter samples will be determined using gas chromatography. Distribution and diversity of methanotrophs in the biofilter will be determined by analysis of 16S rRNA genes and genes targeting the key enzyme methane monooxygenase (pmoA, mmoX). Key active methanotrophs present in biofilter samples will be identified by stable isotope probing using 13CH4, a technique pioneered in Murrell's lab and subsequently isolated and characterised at the physiological and molecular level.