Abstract
Landfill gas (LFG) consisting of 50-60 % v/v CH4 contributes to global greenhouse gas emissions as well as to local air pollution and nuisance odours; in addition, the uncontrolled subsurface migration of LFG can pose an explosion hazard. LFG is explosive mostly due to its CH4 content. CH4 is explosive at concentrations of 5-15 % in air. Venting of the gas to the atmosphere prevents any explosion risk; however, the concern lies with the lateral migration of CH4 through soil and along cracks and its subsequent accumulation. This highlights the importance of subsurface LFG monitoring. In this study, subsurface LFG generation is measured at a solid waste disposal site situated approximately 20 km west of Johannesburg. The results of three first-order kinetic models (to estimate LFG generation) for the site are compared. The three models are LandGEM, GasSim and the IPCC model contained in the 2006 UNFCCC 2006 National Inventory Guidelines for waste. High LFG concentrations are recorded along the northern boundary of the site (exceeding 60% v/v). Modelled LFG generation simulations are slightly higher from LandGEM whilst the IPCC Waste Model predicts the lowest concentrations.
Highlights
Once the maximum rate of deposition is calculated, landfills are categorised into four sizes namely communal (C), small (S), medium (M) and large (L) (DWAF, 1998)
Landfill gas (LFG) generation was estimated at a landfill in Johannesburg, denoted Landfill B
Subsurface LFG monitored at the site in September 2009 was analysed and CH4 and CO2 fractions in LFG identified
Summary
In South Africa, environmental regulations governing waste disposal are set out in the Minimum Requirements for Waste Disposal, released by Department of Water Affairs and Forestry (DWAF) in 1998 (Morris, 2001) These documents provide a set of standards and criteria for the selection, investigation, design, preparation, operation, closure and monitoring of landfill sites (DWAF, 1998; Morris, 2001). The water balance at the landfill is based on the potential for significant leachate generation to occur at the site and is affected by rainfall, evaporation, moisture content of waste and water infiltrating the waste body (DWAF, 1998) If it is positive for less than one year in five, it is assumed that no significant leachate generation will occur at the site and the site is classified as B- (sporadic leachate generation likely). LFG generation was estimated at a landfill in Johannesburg, denoted Landfill B
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