Characterisation and management of landfill emissions under a sub- tropical climate using full-scale landfill cells.
It is now widely understood that landfills, compnslng municipal solid wastes, typically undergo biological degradation processes in what are referred to as Bio-Reactor Landfills. These microbiological processes cause the release of gaseous and liquid emissions, which are commonly called landfill gas (LFG) and landfillleachate respectively. They are formed through mass transfer and biodegradation processes, which occur between percolating water and the solid waste matrix. Such emissions, if not correctly managed, may pose a threat to the natural environment surrounding landfills, and, specifically, landfill leachate may cause significant pollution of the ground water regime. The changes that landfilled wastes undergo to achieve a relatively stable, methanogenic state of decompQsition are now well understood, however little is known on the rate at which biodegradation processes take place, and particularly the timescale over which degradation of waste materials is completed. This dissertation presents research work demonstrating the behaviour of landfill emissions under specific climatic conditions encountered in South Africa in three containment landfill cells situated within the Bisasar Road and Mariannhill Landfill Sites. The containment cells, which are equipped with leachate extraction systems, proved to be ideal full-scale 'pilot plants' where changes in leachate and biogas emissions could be monitored. The characterisation of the landfill emissions allowed for the qualitative determination of the time-scales involved in reaching methanogenic conditions under a sub-tropical climate. Using this information, two landfill gas production models (adapted for the prevalent climatic conditions) were applied to two containment cells in order to predict the volume and duration of gas emissions. The results of the emissions characterisation show that the management of landfill developments in the form of small cells within the larger landfill footprint ('cellular' landfilling) can enhance waste degradation processes, and hence achieve desired levels of stabilised waste conditions relatively quickly. The results of the landfill gas models show that relatively large volumes of gas are emitted early in the lifetime of a landfill cell, and that the maximum emissions will be produced within a relatively short period of time (six to twelve months) after the last deposition of waste. This would allow for the extraction and treatment of landfill gas almost immediately after the closure of a cell, thereby shortening the time span over which potentially harmful emissions can occur.