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University of the Witwatersrand (1996)

Effects of waste composition on landfill processes under semi-arid climatic conditions

Morris JWF

Titre : Effects of waste composition on landfill processes under semi-arid climatic conditions

Auteur : Morris JWF

Université de soutenance : University of the Witwatersrand

Grade : Doctor of Philosophy PhD (Civ Eng) 1996

The main objectives of this research study were to investigate the effects of waste composition on degradation processes and to ascertain whether the findings could be used to further the affordability of waste disposal in an environmentally acceptable manner through incorporation into the regulatory framework governing waste disposal in South Africa, the Minimum Requirements documents produced by the Department of Water Affairs and Forestry. In addition, the study set out to further investigate the premise accepted by the Minimum Requirements that water deficient landfills sited in semi-arid regions possess limited environmental pollution potentials due to their low levels of degradation activity and leachate production. The long term liabilities associated with preservation of the pollution potential of waste in a ’dry tomb’ landfill are considerable, and this study also set out to determine what measures could be taken to improve rates of bio degradation in landfills while still maintaining some control over the level of leachate emissions. The most promising and cost-effective of these measures was identified as the addition of some proportion of ash-rich waste from poor, coal burning communities to the typical municipal solid waste produced by rich communities (rich waste). Experimental set-ups and monitoring programmes across a wide range of scales were established. The main findings of the study were that there would be little to be gained from attempting to incorporate a waste composition classification into the Minimum Requirements. Although there is evidence that landfilling of ash-rich poor waste presents a lower risk to the surrounding environment than rich waste, the differences in the pollution potential of the two waste types are not significant enough to warrant such an inclusion. There is strong evidence, however, that a number of improvements to the behaviour and properties of rich waste can be brought about by mixing it with ash-rich poor waste such that ash comprises at least 10 % of the total wet mass. These include more rapid and stable onset of methanogenic conditions and improved hydraulic properties such as increased moisture retention capacity and a reduction in the presence of preferential flow paths for macro-pore flow of moisture. This results in increases in the proportion of infiltrating rainwater that can be stored in the waste and lost through evapotranspiration. Such losses can account for almost all infiltration into semi-arid landfills with the results that these landfills never need produce leachate. This property could be further exploited in the landfill design and operation practices set out in the Minimum Requirements.

Présentation (NRF)

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