Landfill composite liner

After a landfill site has been chosen and a basin has been excavated, the basin is lined with one or more layers of water-retaining material (liners) that form a leachate bathtub. The contained leachate is pumped out through a network of pipes and collector layers. Liners may be constructed of synthetic polymer sheets or of clay. U.S. EPA s MTG3A7 relies on a composite liner that utilizes the advantages obtained from combining both liner systems. 

An alternate system, one based on gravity, requires penetration of both the FML and clay components of the secondary composite liner system. It also requires a monitoring and collection manhole on the opposite side of the landfill cell. The manhole and connecting pipe, however, become an underground storage tank that needs its own secondary containment and LDSs. 

Composite interfaces, ceramic—matrix composites, 5 558-561 Composite liner, in landfills, 25 877 Composite material coatings, 14 105 Composite materials, 13 533 26 750-785. See also Composites advanced materials in, 1 693 classification by geometry, 26 752-755 classification by matrix material,... 

The key points (above) are not exhaustive but show the similarities between the two sets of controls, where, for example, composite liners, leachate collection and treatment, gas collection, and groundwater monitoring are common. The proposals for the European Landfill Directive have not been ratified, and at the time of writing, the future of the Directive remains uncertain. However, irrespective of the fate of the Directive, many of the requirements are already being implemented in many European countries. 

An alternative bioreactor concept - the fermentationAeaching wet cell (F/L wet-cell) has been developed by Lee and Jones-Lee (1993). This concept also aims to effectively stabilise the waste and leach the soluble potentially polluting components. The design requires that the waste is shredded prior to emplacement to try to ensure contact of the liquid with all waste components. According to Lee and Jones-Lee (1993) who cite Ham (1975), this will also eliminate the need for daily cover, and has the potential to increase the capacity of landfill by about 20%. The other key feature of F/L wet-cell is the use of a clean water system beneath the clay of the composite liner to maintain movement of water up through the clay, thus preventing any leachate leakages to escape from the containment system. 

Construction and Demolition (C D) waste typically consists of concrete, bricks, asphalt, wood, glass, masonry, roofing, siding and plaster, alone or in combinations. Intermediate C D landfills must have a 3-foot-thick clay liner and a leachate collection system. The diameter of leachate collection pipes must be at least six inches. Engineered landfills for municipal and industrial waste are constructed with a base liner and a leachate collection system. The primary purpose of the liner is to prevent grormdwater pollution. The liner may consist of clay only or be a combination of geomembrane and clay (known as a composite liner). The liner is constructed with at least a 2% slope towards perforated leachate collection piping to direct leachate to a collection system. 

The minimum thickness of a clay liner is five feet except in intermediate C D landfills where three feet is allowed. In a composite liner, a 60-mil or thicker geomembrane is placed directly over a 4-foot-thick clay liner. Composite liners are required for all new mimicipal waste landfills. The maximum allowable slope of inside walls of a landfill is three horizontal to one vertical. In clay-lined landfills, leachate transfer lines may penetrate die liner horizontally at the perimeter berm. An antiseep collar is placed around the transfer line penetrating the liner to minimize the escape of leachate. In composite-lined landfills, on the other hand, leachate is pumped from the landfill s leachate collection system inside a sideslope riser - a large-diameter pipe that extends from a sump at the base of the landfill to the top of the berm. 

Additional Protection. If leachate is expected to be extremely hazardous, or if the landfill is located in an environmentally sensitive area, then either a double composite liner with backup... 

HDPE geomembranes can be combined with various other components (leak monitoring system, geosynthetic clay liners of high durability, polymer amended sand-bentonite-mixtures, capillary barriers) to form alternative composite liners as reliable and cost effective capping systems (Simon and Muller 2004). Such alternative capping systems are tested and increasingly applied for landfills and for the containment of contaminated sites. 

The permeation rate for the difihision of a pollutant through the composite liner is thus determined according to Eqs. 7.35 and 7.36 at specified thicknesses (for example. di = 2.5 mm and J2 = 0.75 m and/or 1.50 m for municipal waste landfill and/or the hazardous waste landfill) by diffusion coefficients Di and Do, partition coefficient cTo,i and as well as by the parameters of the porous mineral material 0 and 77 While the parameters Di and Do as well as 0 and /"vary only by one or two orders of magnitude for different pollutants and mineral materials, the partition coefficients partition coefficient between plastic geomembrane and leachate which characterises the permeation rate of the composite liner for different pollutant classes. The partition coefficient for cations and anions is in practice zero, since they cannot be dissolved in the non-polar medium polyethylene. For the diffusive mass transport therefore only undissociated organic and inorganic molecules have to be taken into consideration. 

Bimdesanstalt fiir Materialforschung und -priifung (BAM), 1994. Guidelines for the Certification of Geomembranes as a Component of Composite Liners for Municipal and Hazardous Waste Landfills and for Lining Contaminated Land (Berlin). 

The minimum thickness specification for an FML top liner covered with a layer of soil is 0.75 mm for an FML without a soil cover layer, the specification is 1.14 mm. An FML in a composite bottom liner system must be at least 0.75 mm thick. Even though these FML thicknesses meet U.S. EPA specifications, 0.75mm is not a suitable thickness for all FML materials. In fact, most FML materials installed at landfills are in the range of 1.50-2.50 mm in thickness. Other key factors affecting the selection of FML materials include chemical compatibility with waste leachate, aging and durability characteristics, stress and strain characteristics, ease of installation, and water vapor/ chemical permeation. 

Figure 26.3 compares theoretical leachate collection efficiencies for landfills having compacted soil bottom liners with those having composite bottom liners. Leachate collection efficiency... 

FIGURE 26.3 Comparison of leachate collection efficiencies for compacted soil and composite bottom liners. (Adapted from U.S. EPA, Requirements for Hazardous Waste Landfill Design, Construction, and Closure, EPA/625/4-89/022, U.S. Environmental Protection Agency, Cincinnati, OH, August 1989.)... 

Clay liners, synthetic liners, or combinations of both are required in landfills. Figure 26.1 depicted the synthetic/composite double-liner system that appears in U.S. EPA s MTG. As explained... 

As described earlier, concerns around water and air pollution have transformed landfill technology. Figure 17.4 is an illustration of a modem lined landfill with a gas recovery system, leachate collection and treatment, a cap to prevent rain water entry, and ground water monitoring to confirm the integrity of the liner. The composition of landfills have been characterized by various garbologists and... 

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