The estimation of landfill gas emissions in the Durban Metropolitan Area (DMA) using the LANDGEM model.
Landfill gas (LFG) contributes significantly to air pollution. Methane (CH4) and carbon dioxide (CO2) are the major constituents of LFG, and are significant greenhouse gases that play a vital role in causing global warming. Certain air pollutants from landfill sites are carcinogenic (e.g. benzene), while others are odorous (e.g. methyl mercaptan). Due to these potential negative impacts, there is need to forecast the yield and production rate of biogas generated. Limited work has been done on the modelling of LFG emissions for landfill sites in Durban. This study focuses on the estimation of air pollutant emissions from three landfill sites, namely Bisasar Road, Shongweni and Buffelsdraai using the LANDGEM model and comparing the results against the findings of Hofstetter Gas Yield Model which has been utilized before by Durban Solid Waste (DSW) for Bisasar Road landfill. The greenhouse gases of global concern, namely CH4, CO2 and halocarbons were investigated in this study. The LANDGEM model predicted CO2 emissions to be higher than CH4 and other greenhouse gases. The warm, moist climatic conditions suitable for CH4 oxidation may be responsible for the increased generation rates of CO2. The main components of LFG which cause landfill odour problems are sulphur-containing compounds. Methyl mercaptan is the component causing persistent bad odours in the landfills, contrary to popular belief that hydrogen sulphide is the major contributor to odour pollution. Hydrogen sulphide has been predicted by LANDGEM to be the sulphur-containing gas that is produced in greatest quantities. Benzene and vinyl chloride are the most hazardous compounds emitted from landfills, since they are carcinogenic. The emission rates of benzene were found to be higher than those of vinyl chloride in the active landfill sites of Bisasar Road and Shongweni. The LANDGEM model estimated total LFG emissions of 8.371 x 107 m3y-1 at Bisasar Road landfill, compared with a lower emission rate of 3.285 x 107 m3y-1 predicted by the Hofstetter model. The LANDGEM model revealed LFG to peak during the closure of the landfill, and to decline thereafter for a long period of time. The Hofstetter model showed that LFG could reach its maximum within three years of waste deposition. LANDGEM model is a widely used methodology for estimating LFG emissions. It is used in United States as regulatory model to quantify the potential LFG emissions produced from the landfill. This model can be used by landfill owners and operators to evaluate the performance of the landfill and to determine whether the landfill is still subject to regulatory requirements, especially in the countries where emission guidelines have been established. Therefore, in the developing country like South Africa, it is essential to quantify and evaluate the LFG emissions released from landfills despite the fact that no legal LFG emission guidelines are put in place yet.