DESIGN OF TOP COVERS SUPPORTING AEROBIC IN SITU STABILISATION OF OLD LANDFILLS - AN EXPERIMENTAL SIMULATION IN LYSIMETERS

摘要

Landfills and old waste deposits are regarded as a major source of anthropogenic methane (CH4) emissions worldwide since considerable proportion of municipal solid waste (MSW) has been deposited without pre-treatment over the last decades. In-situ aeration by means of low pressure air injection has become one of the most promising tools to reduce the emission potential of old landfill sites through accelerating organic matter degradation and biological stabilisation. Landfill cover systems (such as biocovers or evapotranspiration caps) could be applied as a complementary strategy to force in-situ aeration mitigating residual CH4 emissions as well as controlling water infiltration into the landfill body. Landfill covers which are able to enhance methane oxidation could serve as an alternative to gas extraction systems and biofilters for off-gas treatment usually needed in traditional in-situ aeration concepts, particularly in the later stagtf of an in-situ aeration treatment or at very small sites. Consequently, in-situ aeration combined with biologically active covers could be an even more efficient and cost-effective remediation method for sites, where parallel gas extraction is not feasible or necessary anymore. In general, a suitable landfill cover has to fulfil different requirements regarding optimal moisture content, nutrient level, organic matter content and physical properties such as permeability and particle size. On the one hand, a cover system has to be "tight" enough to support a lateral spread of injected air in the landfill body, and on the other hand, it should provide sufficient porosity and gas permeability enabling microbial methane oxidation. Moreover, a top cover should allow water infiltration necessary to enhance waste decomposition processes during aeration measures, but also minimise leachate generation and water saturation of the landfill body.