The International Information Center for Geotechnical Engineers

Biodegradation in Municipal Solid Waste landfills

 

 

Landfills - a brief review

 As over 50% of MSW and many other solid wastes are disposed of in landfills, a basic understanding of the design of a landfill is helpful. In the United States, the design and operation of landfills is regulated by Subtitle D of the Resource Conservation and Recovery Act, the New Source Performance Standards of the Clean Air Act, and related state regulations. Landfills have evolved from open dumps to highly engineered facilities designed to contain waste and separate it from the environment, capture contaminated water that contacts the waste (leachate), and control gas migration. A landfill site is typically excavated and lined with a system that includes layers to (1) minimize the migration of leachate to the groundwater, and (2) collect leachate for treatment. A typical cross section of a landfill is illustrated in Figure 3. 

 Fig4

Fig 4. Typical cross-section of a landfill receiving MSW (Barlaz et al., 2010)

A common system used to restrict leachate migration consists of a 0.67- to 1-m-thick clay layer with a hydraulic conductivity of no more than 10−7 cm/s overlain with a geomembrane (GM). The GM is typically 1.5-mm-thick polyethylene. A drainage layer that contains a high-permeability material such as sand or gravel is placed above the liner to promote leachate collection. This layer has perforated pipes embedded to remove leachate from the landfill. A protective barrier is then installed above the leachate collection system to shield it from the equipment used to place and compact refuse. Waste may then be placed above the protective barrier, and it is covered daily to minimize wind blown refuse, odors, and the attraction of disease vectors. Daily cover alternatives include a 15-cm soil layer, spray-on foams, and synthetic materials that are rolled over the waste at the end of the working day. Once refuse has reached the design elevation, a final cover is applied. The final cover will include, at a minimum, a layer of low-permeability soil designed to minimize stormwater infiltration overlain by a layer of soil that will support vegetative growth. The final cover frequently includes a drainage layer and a GM beneath the vegetative layer. Vegetation serves to minimize erosion of the soil cover and to promote evapotranspiration (Barlaz et al., 2010).

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