Composite liner

Composite Liners Clay versus Synthetic Components. 1118... 

The U.S. EPA guidance6 discusses three types of liners FMLs, compacted clay liners (CCLs), and composite liner systems (an FML overlying a compacted low-permeability soil layer). Material specifications in the guidance for FMLs and CCLs are briefly reviewed below, along with regulations regarding all three liner systems. 

U.S. EPA also determined the total quantity of liquids entering the two bottom liner systems over a 10-year time span with a constant top liner leak rate of 50 gallons/acre/day. A composite bottom liner with an intact FML accumulates around 70 gal/acre, primarily through water vapor transmission. Even with a 10-ft tear, which would constitute a worst-case leakage scenario, a composite liner system will allow 47,000-50,000 gallons/acre to enter that bottom liner over a 10-year time span. Compacted soil liners meeting the 10-7 cm/s permeability standard will allow significant quantities of liquids into the bottom liner, and potentially out of the unit over time, on the order of hundreds of thousands of gal/acre.5... 

The numerical results indicate superior performance of composite liner systems over CCLs in preventing hazardous constituent migration out of the unit and maximizing leachate collection and removal. Consequently, owners of new units subject to the double-liner requirement of FISWA are now installing composite bottom liners or double composite liner systems.3... 

The guidance16 recommends a three-layer cap design consisting of a vegetative top cover, a middle drainage layer, and a composite liner system composed of an FML over compacted low-permeability soil. The final cover is to be placed over each cell as it is completed. 

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. 

Understanding the basic hydraulic mechanisms for synthetic liners and clay liners is very important in appreciating the advantages of a composite liner. Clay liners are controlled by Darcy s law (Q = kiA). In clay liners, the factors that most influence liner performance are hydraulic head and soil permeability. Clay liners have a higher hydraulic conductivity and thickness than do synthetic liners. Additionally, leachate leaking through a clay liner will undergo chemical reactions that reduce the concentration of contaminants in the leachate. 

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. 

Yang X, Lo IMC (2004) Flow of gasoline through composite liners. J Environ Eng 130 886-890... 

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,... 

Early tests of the SCWO reactors (discussed below) indicated significant corrosion and plugging. Plugging problems were solved by procedural modifications that include periodic flushing with clean water at slightly subcritical conditions. The corrosion is mitigated by inserting various composite liners that resist the corrosivity of the different feed streams. 

A double or triple composite liner system provides maximum protection. 

Figure 4. Sulfur composite used as a lining for an earthen irrigation canal. (left) Weed-choked canal before it was lined with sulfur composite. (right) Same canal in use with the sulfur composite liner.

Figure 7. Spill containment basin lined with sulfur composite. (top) The basin surrounded a petroleum storage tank. (bottom) The sulfur composite liner was applied to the earthen berm and the basin bottom.

Kevlar 29 and versions thereof (K 129 and Kl j.) are also used extensively in lightweight body armor as well as composite liners (with vinylester, polyester or epoxy as the matrix). A quick look at the properties of different Kevlar aramid fibers in Table 4.2 shows why K29 is better than K49 for lightweight body armor applications. K29 has a higher strain to failure than K49. That means that the total work of fracture, i.e. the area under the stress-strain curve, is larger for K29 than K49. Hence, the energy absorbed in the fracture process is higher for K29... 

A liner which is typically a composite liner (chapter S), the function of which is to prevent leachate escape to the surrounding environment... 

At least a single composite liner of permealMlity equivalent to, or less than, lO m.s should be provided... 

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. 

Figure 10. Composite liner and leachate collection system design in unapproved...

PRIMARY COMPOSITE LINER LEACHATE COLLECTION/REMOVAL... 

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. 

The primary objective of a liner, or barrier layer, is to prevent or reduce the migration of potentially harmful chemicals, or contaminants, into the strrrotmding environment. With respect to this objective, several different types of liners are ttsed for the containment of waste. As outlined in Table V, the different types of liners may be separated into three broad classifications (1) earthen (soil) liners, (2) geosynthetic (polymer) liners, and (3) composite liners. Earthen liners may be further divided into natirrally occtrrring low-permeability soil liners and manmade liners (e.g., compacted or mechanically stabilized low-permeability soils). 

Composite liners are combinations of soil liners and/or geosynthetic materials. The properties of composite liners are essentially the same as the component materials for the composite liner. However, animpoitant aspect for the effective use of composite liners is that the composite materials must be in intimate contact (i.e., without separation between materials). In reality, the type of GCL shown in Fig. 9c is a manufactured composite liner. Composite liner systems typically are used in conjunction with municipal and hazardous solid waste disposal. 

---