Typical landfill site

Figure 9.7 A sketch of a typical landfill site, showing leachate and landfill gas management options and cellular filling practices. Based on References 7, 53, 54 and 55.

This process is an extension of the anaerobic treatment of waste diseussed in Chapter 2, and is also similar to the natural process operating in landfill sites, which evolves methane. By treatment of biomass with bacteria in the absence of air a gas rich in methane can be produced a typical digester may produce over 300 m of gas containing over 50% methane per tonne of dry biomass. The economics of biogas generation for use as a fuel are currently unfavourable. The plants that do exist have been built because of the need to treat waste such as sewage sludge. 

Table 16.1 Typical compositions of leachates (g/m3) from landfill sites... 

At a landfill site in Oregon, the cost of installing an Ecolotree cap was approximately 10,000 per acre. In contrast, the plastic liners that are typically nsed to cap landfills cost approximately 100,000 per acre (D20764H, p. 2). 

The dumping of wastes at landfill sites is a widespread practice. Indeed, many old sites can be regarded as ecological time bombs. Hazardous substances in landfills are typically mixed with... 

Typical sites that may contain significant quantities of asbestos debris or ground contamination generally include railway land, depots, sidings, shipbuilders yards, dockyards, heavy engineering or industrial sites and waste disposal/landfill sites. 

The Fukuota University study has charted the corrosion rate and mercury leaching potential from batteries buried in typical landfill conditions. The findings showed that after 9.5 years, the maximum loss of mercury from the battery containing test sites was... 

Foundry sand (FS) - In typical foundry processes, sand from collapsed molds or cores can be reclaimed and reused - Little information is available regarding the amount of FS that is used for purposes other than in-plant reclamation, but spent FS has been used as a fine aggregate substitute in construction applications and as kiln feed in the manufacture of Portland cement - Most of the spent FS from green sand operations is land filled, sometimes being used as a supplemental cover material at landfill sites 81-87... 

Because gas migration cannot be easily prevented, removal of the landfill gas, to reduce the driving force for gas movement is often the preferred option. This is normally undertaken by the use of within waste vents (wells) through which the gas can be extracted either actively or passively, or by the use of stone-filled vent trenches, often placed around the periphery of landfill sites. The design of a typical gas vent system is shown in Figure 9. 

A typical landfill will have an impermeable plastic liner and a thick clay barrier. The site must be monitored for leakage and emissions. Monitoring should be intensive during the disposal process. With continuing good results, it can later be reduced to a normal program, but it must continue even after the landfill is sealed. 

Table 11.2. Typical leachate composition from landfill sites (Christianson et al. 1994)...

Figure 3. Typical example of the application of hand-held monitoring technique for the soil gas emission of a landfill site (depth of exploration of the drilling points 1.50 1.80 m visualisation by using SURFER software)...

Leachates generated from municipal landfills are complex effluents that contain high concentrations of organic pollutants, ammonium, chloride, and many other soluble compounds. Table 1 lists the typical concentrations found in the leachate of a mature landfill site [1, 2], With regard to the value of BOD5/COD, this leachate may be classified as a poorly biodegradable wastewater. 

At the worst extreme a very high generation rate can be taken as 10 m per tonne of waste per year or higher, which is the typical gas generation rate of a new landfill site (Nastev, 1998 (see Chapter 4)). At the opposite end of the spectrum very low generation rates mean negligible volumes of gas are being produced that are at least 10 or 100 times lower than the peak rate from a new landfill site. Carbon dioxide can be produced by natural soils at very low rates... 

There are numerous man-made or natural sources of groxmd gas including landfill sites. Gas can also be trapped in material such as coal and be released when excavations for mines take place (or in peat and released when activities such as piling occur). The level of risk associated with differing sources varies according to how much gas can potentially be generated. The various sources and typical level of risk associated are given in this chapter. 

In landfill gas generated from landfill sites there are several hundred trace volatile hydrocarbon gases that can be present, for example volatile organic compounds (VOCs). Their total presence is typically about 1% of the total volume of landfill gas. There are many household chemical products that will... 

Gases emanating from landfill sites are typically composed of approximately 45% each of methane and carbon dioxide, a few percent of nitrogen, and lesser amounts of H2S and other objectionable trace components. The volumes in question are such that it is now deemed profitable to recover the metimne... 

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