The effect of waste composition on leachate and gas quality: a study in South Africa

South Africa has a system of graded landfilling standards that takes account of climatic conditions, waste type and the rate of deposition of waste. At present, waste is classified into general, i.e., municipal solid waste and low and high hazard wastes. Many of the hazardous wastes are liquids, and these are codisposed with general wastes at restricted, fully lined and drained sites. The characteristics of the municipal or general wastes differ, depending on the income level of the originating community and the source of the energy they use. The major source of variation lies in the relative proportions of putrescible matter. There is presently no differentiation between general wastes, based on composition. However, it may be possible to relax standards when low putrescible content general waste is landfilled, and this is the issue addressed in this paper. Experiments, using waste from low and middle income communities, are being conducted using small and large field test cells or lysimeters and laboratory lysimeters. Preliminary results indicate significant differences in the quality of leachate from the two waste types. The characteristics for gas generation also differ significantly. It will be necessary to continue long-term monitoring of the test cells and lysimeters to determine differences in the long term analyses of leachate and gas and the long-term total contaminant load of the wastes. The results may influence future landfilling standards, but on present evidence, this will be unlikely.