Methane oxidation through landfill cover soils: An engineering perspective

Landfill gas (LEG) typically contains 500 to 600 mL L-1 CH, and 400 to 500 mL L-1 CO2. Methane is generated by methanogenic bacteria in anaerobic conditions that are present inside landfills. LEG can either be vented to the atmosphere, collected and burned using flares, or used to generate energy. An alternative way to mitigate CH4 emissions to the atmosphere is the oxidation of CH4 as it escapes through landfill cover soils. Considerable research effort has focused on CH4 oxidation in landfill cover soils. Methane emissions from landfills have been reported to vary seven orders of magnitude (from 0.0004-4000 g CH4 m(-2) d(-1)). Soil properties, climate, gas emission rate, and fauna/flora seem to control CH4 oxidation in landfill covers. From an engineering perspective, the challenge is to identify the properties that lead to suitable conditions for growth of methanotrophic bacteria and therefore high oxidation rates of CH4. Such properties are: porosity, organic matter content, water content, compaction, water holding capacity, pH, and vegetation. This paper summarizes previous research on how these properties affect oxidation of CH4 as it travels through landfill covers. This paper also identifies research needs in this area to fill the knowledge gap needed to promote the engineering of landfill cover systems capable of reducing CH4 emissions.