Stabilization of solid waste through leachate recycling
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One characteristic which landfills Have in common is the long stabilization times they require. Stabilization implies that conditions within the fill have achieved a state of relative physical, biological and chemical immutability (Zison 1974). Some investigators have claimed that stabilization requires as little as four years (APWA, 1966), while other authorities hold the view that stabilization may require considerably longer. There have been instances, for example, where wastes in landfills over fifty years old have yielded readable newspapers (Zison 1974). The concept of stabilization has been studied more in depth (Stanforth et al. 1979; Todd & Ham 1982; Kelly 1987; Pohland etal. 1983; Pohland etal. 1987). The causes of the extended periods of time required for the organic fraction of the waste to stabilize are not well known. However, there are several possibilities, including: 1. Excessively high carbon to nitrogen ratios in the range 120:1 may inhibit bacterial activity within the fills. 2. Anaerobic decomposition is inherently slower and less complete than aerobic. (Stabilization in modern, engineered landfills is almost exclusively an anaerobic process). 3. Substances in the initial waste or products of the stabilization process may be toxic to decomposition. Biochemical feedback mechanisms may be responsible for a decreased rate of waste decomposition due to the resultant inhibition of enzyme synthesis or transport systems. 4. Certain components of waste, such as cellulose may be slow to decompose due to their molecular structure. 5. As decomposition slowly progresses, changes in pH may inhibit the metabolism or reproduction of microorganisms. Methane forming anaerobics, for example, are known to be very sensitive to pH changes. 2. Laboratory experimentation procedure The research work undertaken involved setting up in the laboratory four simulated landfill lysimeters. Although the four lysimeters, each containing 30 kg of waste, were the same in physical construction, they were loaded and operated differently. Details of the refuse loaded into each lysimeter and the Mode of operation of each are summarized in Table 1, while a typical lysimeter is shown in Fig. 1. Small scale laboratory experiments were carried out because they permitted a wider range of Parameters to be studied than would have been possible in actual landfills. It is.