Methane Oxidation and Degradation of Halocarbons in Landfill Soil Covers

摘要

Waste deposited in a landfill will undergo anaerobic decomposition resulting in generation of landfill gas, which is transported through soil top covers causing emission of gas into the atmosphere. Besides methane and carbon dioxide, landfill gas also contains halocarbons originating from insulation foams, chemical waste etc. Both the methane and the halocarbons contribute to global warming while some of the other halocarbons also contribute to the depletion of the ozone layer. In landfill top covers methane and oxygen counter-gradients may appear due to emission of methane from the waste and diffusion of oxygen from ambient air. Oxidation of methane by methanotrophic bacteria in landfill top cover soil has been shown to reduce the amount of methane emitted to the atmosphere. A defining characteristic of the methanotrophic bacteria is the enzyme methane monooxygenase (MMO) which catalyzes the oxidation of methane. MMO has very broad substrate specificity and is known to co-metabolize a variety of aliphatic compounds including some halogenated hydrocarbons (Hanson & Hanson, 1996). The objective of this study was to investigate the potential of natural oxidation of methane and halocarbons in soil exposed to landfill gas. The investigations have been carried out through laboratory experiments using a column set-up. The chosen trace components included four halocarbons (trichlorofluoromethane' (CFC-11), dichlorodifluoromethane (CFC-12), dichlorofluoromethane (HCFC-21) and chlorodifluoromethane (HCFC-22)).