Deponigas - Mätmetoder för utsläpp och passiva gashanteringssystem. Med fältstudie på tre äldre nedlagda deponier
Sammanfattning: Landfill gas is produced in all landfills containing organic material. Landfill gas consists of mainly methane and carbon dioxide. Methane is a potent greenhouse gas which can be explosive and inflammable. Landfill gas can be collected and used as fuel, for instant for heating. In Sweden and globally there is a large number of landfills where too little gas is produced to enable active gas collection. On these landfills, the control of the landfill gas is often limited. The purpose of this master thesis has been to investigate how methane gas is released through the cap of landfills to the atmosphere and how these emissions can be mitigated and reduced. The project includes both literature and field studies. Several factors influence the emissions of landfill gas. Meteorological factors such as changes in atmospheric pressure, precipitation and temperature are important as well as the type of cap on the landfill. Often, a lion share of the methane emissions occur from a limited number of smaller locations at the landfill surface, so called hot spots. Passive landfill gas mitigation systems are designed to optimize the microbial methane oxidation which will oxidize the unwanted methane. Examples of passive mitigation systems are biocovers, biowindows and biofilters. Passive mitigation systems are suitable for landfills with low landfill gas flows or low methane content. These systems have a permeable surface, which reduce the risk of horizontal migration of gas compared to an impermeable cap. Field studies have been undertaken at three older landfills in southern Sweden. The method used included measurements with flux box on the landfill surface and with gas probes one meter below the landfill surface. The results show that landfill gas is present, but indicate that surface emissions are small. Since measurements have only been done twice at each landfill, it cannot be excluded that larger emissions occur under other circumstances. The method used has shortcomings, but can provide valuable results when performing risk assessments and when designing passive landfill gas mitigation systems.
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