{"id":319,"date":"2019-03-11T09:27:38","date_gmt":"2019-03-11T09:27:38","guid":{"rendered":"http:\/\/esp11.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=319"},"modified":"2019-04-25T04:42:50","modified_gmt":"2019-04-25T04:42:50","slug":"structure-and-operation-of-solid-waste-landfill","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/esp11\/chapter\/structure-and-operation-of-solid-waste-landfill\/","title":{"rendered":"Structure and operation of solid waste landfill"},"content":{"raw":"
\"epgp<\/a>\r\n<\/span><\/div>\r\n\r\n
\r\n\r\n \r\n\r\nObjectives:<\/strong>\r\n\r\n \r\n\r\n1.\u00a0\u00a0\u00a0\u00a0\u00a0 To define landfill\r\n\r\n \r\n\r\n2.\u00a0\u00a0\u00a0\u00a0\u00a0 To understand the components of landfill\r\n\r\n \r\n\r\n3.\u00a0\u00a0\u00a0\u00a0\u00a0 To know the different types of lining material and liner system used in landfill\r\n\r\n \r\n\r\n4.\u00a0\u00a0\u00a0\u00a0\u00a0 To discuss the types of waste emplacement within the landfill\r\n\r\n \r\n\r\n5.\u00a0\u00a0\u00a0\u00a0\u00a0 To understand the structure of a landfill capping or cover\r\n\r\n \r\n\r\n6.\u00a0\u00a0\u00a0\u00a0\u00a0 To discuss the process of waste degradation within the landfill\r\n\r\n \r\n\r\n7.\u00a0\u00a0\u00a0\u00a0\u00a0 To know the various factors influencing the waste degradation in landfill\r\n\r\n \r\n\r\nDisposal of solid waste<\/strong>\r\n\r\n \r\n

Solid wastes are any discarded or abandoned materials that is discarded by the human society as it is of no further use. According to the source of generation and type they are classified as urban wastes, agricultural wastes, biomedical wastes, bulky waste, open area waste, radioactive wastes, e wastes and many more. The term refuse is also used for denoting solid wastes. The solid waste must be properly managed to avoid environmental and health hazards. The waste management involves various steps namely waste collection, segregation, transport, processing, treatment and disposal. Disposal is the final step in the waste management. Ultimately all solid waste ends in disposal site either directly or after some processing and treatment it ends in disposal sites. Most of the developing and under developed countries, dispose or dump the solid waste in an open land without any protection or environmental control. Such dumping is not safe and is called as open dumps or open dumping. Solid waste is also disposed off in water bodies eg. Sea, ocean, lake, river etc. Sometimes they are also burned in open areas, the phenomenon termed as open burning. Developed countries are practicing a system of safe or controlled dumping called the landfill. Landfill is an engineered structure where the waste is safely disposed and contained.<\/p>\r\n \r\n\r\nControlled dumping or landfills<\/strong>\r\n\r\n \r\n

Landfills are the largest route of disposal. Landfill is an engineered structure for disposal or containment of solid waste. It is considered to be the safe method of waste disposal. Landfills are designed and operated according to acceptable standards. It is designed in a way to protect the environment and health of people. Landfills are not homogeneous. They are usually made up of cells in which a discrete volume of waste is kept isolated from adjacent waste cells by a suitable barrier. This landfill option of waste disposal is suitable only when the land is available at an affordable price, availability of adequate workforce, availability of technical resources to operate and manage the site.<\/span><\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n \r\n\r\nTypes of landfill<\/strong>\r\n\r\n \r\n\r\nLandfills are of three types. They are\r\n\r\n \r\n

\u2022 Waste landfills for hazardous waste or secured landfill \u2013 This type of landfill is used for containment of hazardous waste that possess great potential in causing health and environmental effects.<\/p>\r\n \r\n

\u2022 Waste landfills for non-hazardous waste or sanitary landfill \u2013 This type of landfill is generally used for municipal solid waste that does not cause dangerous effects on environment and living beings.<\/p>\r\n \r\n

\u2022 Waste landfills for inert waste \u2013 Used mainly for wastes that does not react and remains inert. Eg. Construction and demolition waste.<\/p>\r\n \r\n\r\nStructure of landfill<\/strong>\r\n\r\n \r\n

As mentioned earlier, landfills are engineered structures to contain the waste (Figure 1). This helps in protecting the environment from various effects. The main purpose of designing a landfill is to contain the waste and protect the environment through a geological barrier and liner system at the base, sides and on top named the cap of the system landfill. The requirement and type of the barrier system depends on the nature of waste being loaded in the landfill. The barrier system is selected based on few criteria. They are<\/p>\r\n \r\n\r\n\u2022\u00a0\u00a0\u00a0\u00a0\u00a0 prevent the pollution of soil, groundwater or surface water\r\n\r\n \r\n\r\n\u2022\u00a0\u00a0\u00a0\u00a0\u00a0 ensure efficient collection of the leachate\r\n\r\n<\/div>\r\n \r\n\r\nThe barrier used are both natural and synthetic. Natural or geological barrier used for a particular landfill is selected based on the geological and hydrogeological conditions below the landfill and availability of material in the vicinity of the landfill site.<\/span>\r\n

\r\n\r\n \r\n\r\nThe landfills are composed of three main components. They are\r\n\r\n \r\n\r\n\u2022\u00a0\u00a0\u00a0\u00a0\u00a0 A liner system \u2013 used at the bottom to protect the soil and ground water.\r\n\r\n \r\n\r\n\u2022\u00a0\u00a0\u00a0\u00a0\u00a0 Waste emplacement cells \u2013 pattern by which waste is loaded into the landfill\r\n\r\n \r\n\r\n\u2022\u00a0\u00a0\u00a0\u00a0\u00a0 Cover or capping \u2013 It is the top most protection layer that prevents the entry of water or other animals into the waste pile\r\n\r\n\"\"\r\n

Figure 1 Landfill structure<\/strong><\/p>\r\n \r\n\r\nLiner system:<\/strong>\r\n\r\n \r\n

As discussed earlier, landfill liner is a barrier that is laid at the bottom and sides of the landfill to protect the contaminants from entering into the soil and ground water. In addition to protection they are also designed to collect the leachate and control the accumulation and migration of landfill gas.<\/p>\r\n \r\n

Thus liner system is a combination of many layers. The liner system is made of both natural and artificial or synthetic materials. A liner system consists of the following layers<\/span><\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n \r\n\r\n\u2013\u00a0 natural liner,\r\n\r\n \r\n\r\n\u2013\u00a0 a synthetic liner,\r\n\r\n \r\n\r\n\u2013\u00a0 a leachate collection system and\r\n\r\n \r\n\r\n\u2013\u00a0 geofabric for preventing the entry of solid material into the leachate collection tube\r\n\r\n \r\n

The permeability is one important factor based on which the liner materials are chosen. The materials used should provide sufficient permeability and thickness. Permeability is the ease with which the leachate flows through the liner material. The permeability or hydraulic conductivity of the material is calculated using Darcy\u2019s law that describes the flow of a liquid through a porous material. Table 1 summarizes the hydraulic conductivity of few liner materials.<\/p>\r\n \r\n

Table 1 Hydraulic conductivity of few materials used as liners<\/strong><\/p>\r\n \r\n\r\n\"\"\r\n\r\n<\/div>\r\n

<\/div>\r\n
Liner materials<\/span><\/div>\r\n
<\/div>\r\n
There are a large variety of natural and synthetic mineral materials and synthetic polymeric materials which are used in the construction of landfills (hazardous, non-hazardous and inert waste landfill). The selection of liner material is done based on certain criteria such as<\/span><\/div>\r\n
\r\n\r\n \r\n\r\n\u2013\u00a0 the type of waste\r\n\r\n \r\n\r\n\u2013\u00a0 geological and hydrogeological conditions in the surrounding environment\r\n\r\n \r\n\r\n\u2013\u00a0 the properties of the derived leachate and\r\n\r\n \r\n\r\n\u2013\u00a0 the resistance of the liner to the leachate.\r\n\r\n \r\n

The properties that need to be considered for a good liner system include density, tensile strength, puncture resistance, tear resistance, resistance to ultraviolet (UV) light, ozone and chemical resistance. Resistance of membrane to chemicals is very important since the leachate may contain a range of organic and inorganic acids and alkali and organic hydrocarbons.<\/p>\r\n \r\n\r\nNatural clay<\/strong>\r\n\r\n \r\n

Clays is an unconsolidated rock material that is composed of clay minerals such as montmorillanite, illite and kaolinite ormed during the weathering of rocks. The clay minerals are extremely fine which determines the porosity and permeability of the material. The permeability and porosity should be very low for good liner material. The clay liner possess low permeability. The clay is collected from the nearby areas, homogenized, sieved to remove large rocks and spread on the landfill by bulldozers or scrapers. The large roller vehicles compacts the materials and reduces the void space between the pieces. It also increase the density of the clay.<\/p>\r\n \r\n\r\nBentonite-enhanced soils<\/strong>\r\n\r\n \r\n

Bentonite is a mixture of clay minerals, principally of the montmorillante type. The bentonite-type clay minerals have a high swelling characteristic on absorbing moisture. When the naturally occurring clay soil does not have a high enough level of clay minerals to produce a suitably low permeability, bentonite clay is added to form a bentonite-enhanced soil. The permeability of the bentonite-enhanced soil gets reduced further by swelling under pressure due to mass of waste overlying in the landfill.<\/p>\r\n \r\n

Bentonite exists in two forms namely sodium bentonites and calcium bentonites. Sodium form possess lower permeabilities. Around 5-15% sodium bentonite is added to the original soil.<\/span><\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n \r\n\r\nGeosynthetic clay liner<\/strong>\r\n\r\n \r\n

Geosynethetic clay liners is a mixture of bentonite clay mechanically or chemically adhered to a geotextile fabric. The clay is sandwiched between two layers of the geotextile fabric where the layers are joined by adhesives, needlepunching or stitching. The thickness of these liners were around 1 cm thick. Geosynthetic clay liner are often used as alternatives to natural compacted clay liners.<\/p>\r\n \r\n\r\nFlexible membranes<\/strong>\r\n\r\n \r\n

Synthetic, polymeric plastic materials with extremely low permeabilities are used as Flexible membranes. High-density polyethylene and PVC are commonly used as flexible membranes. The thickness of these membrane range from 0.75mm to 3 mm<\/p>\r\n \r\n\r\nGeotextiles<\/strong>\r\n\r\n \r\n

Geotextiles are fabric materials used as protection for polymeric plastic membranes and filtration material to filter out fine-grained particles from the leachate so that drainage layers do not get blocked. They possess high permeability and are composed of polypropylene or polyester fibres which are manufactured to form a fabric-type material.<\/p>\r\n \r\n\r\nGeonets<\/strong>\r\n\r\n \r\n

They are porous sheets of plastic netting used as drainage layers to carry leachate or landfill gas. They prevent the net from clogging due to particles in the leachate hence always associated with geotextiles. They act as an alternative to gravel in liner system. Geonets are made of polyethylene with a thickness of 5 mm.<\/p>\r\n \r\n\r\nLiner system\r\n\r\n \r\n\r\nFour types are liner system is used in construction of landfills. They are\r\n\r\n \r\n\r\n1.\u00a0\u00a0\u00a0\u00a0\u00a0 Single liner system\r\n\r\n \r\n\r\n2.\u00a0\u00a0\u00a0\u00a0\u00a0 Composite liner system\r\n\r\n \r\n\r\n3.\u00a0\u00a0\u00a0\u00a0\u00a0 Double liner system<\/span>\r\n\r\n \r\n\r\n4.\u00a0\u00a0\u00a0\u00a0\u00a0 Multiple liner system<\/span>\r\n\r\n<\/div>\r\n

\r\n\r\n \r\n\r\nThe liner system is selected based on the following criteria.\r\n\r\n \r\n\r\n\u2013\u00a0 Nature and composition of waste\r\n\r\n \r\n\r\n\u2013\u00a0 Cost\r\n\r\n \r\n\r\n\u2013\u00a0 Geology and hydrogeology of the surrounding area\r\n\r\n \r\n\r\n\u2013\u00a0 Should not allow the ground water to seep into the landfill\r\n\r\n \r\n\r\n\u2013\u00a0 Prevent the escape of leachate and gas from the landfill\r\n\r\n \r\n\r\n\u2013\u00a0 Should be resistant to chemical reactions\r\n\r\n \r\n\r\n\u2013\u00a0 The liner system should have proper stability and good lifetime\r\n\r\n \r\n\r\nSingle liner system<\/strong>\r\n\r\n \r\n

Single liner system is used for low risk waste where the generation of leachate is very negligible. The system comprises of a primary barrier made of clay or\/and bentonite enhanced soil. Above and below the primary barrier is a layer of geotextile. It filters out suspended solids and provides protection. Between the waste and the protection layer would be the leachate collection system which consists of perforated drainage pipes that facilitates collection of leachate. The leachate is then pumped out and treated in municipal wastewater treatment plants. Beneath the liner system there is groundwater collection system which consists of gravel covered by a geonet. This layer is an alternative and not compulsory. Figure 2 depicts the single liner system.<\/p>\r\n \r\n\r\nComposite liner system<\/strong>\r\n\r\n \r\n

In a composite liner system (Figure 3), two different types of liner material is used namely: clay based mineral layer and polymeric membrane layer. The primary barrier here is synthetic polymeric flexible membrane with a separation layer of thin geotextile or polymeric material. The polymeric material can be HDPE, LDPE, PVC and many more. In addition to primary barrier, a secondary barrier made of clay, bentonite enhanced soil or geosynthetic clay is used. Similar to single liner, between the waste\u00a0and the protection layer leachate collection system which consists of drainage pipes is layered. The composite liner system is used for more secure containment of waste.<\/span><\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n \r\n\r\nDouble liner system<\/strong>\r\n\r\n \r\n

Figure 4 depicts the double liner system. Similar to composite liner system the primary barrier is a synthetic polymeric flexible membrane with a separation layer of thin geotextile or polymeric material (HDPE, LDPE, PVC etc). Secondary barrier is composed of clay, bentonite enhanced soil or geosynthetic clay. A leachate collection tubes are layered between the waste and the protection layer.<\/p>\r\n\"\"\r\n

Figure 2 Single liner system<\/strong><\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n\"\"\r\n

Figure 3 Composite liner system<\/strong><\/p>\r\n \r\n

An intermediate high permeability drainage layer is incorporated between primary and secondary barrier. This layer is for the collection of leachate and gas. Every barrier is separated by geotextile fabric.<\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n\"\"\r\n

Figure 4 Double liner system<\/strong><\/p>\r\n \r\n\r\nMultiple liner system<\/strong>\r\n\r\n \r\n

Multiple liner system combines few layers of double and composite liner system. Three barriers are made in this type of system. They are primary, secondary and tertiary barriers. Between these barriers intermediate layer is also attached for leachate and gas collection and maintenance. The primary barrier (synthetic polymer material) is in intimate contact with the secondary barrier (clay, bentonite enhanced soil etc.). This is done to prevent lateral movement of leachate and gas. All other layers are similar to other liner systems.<\/p>\r\n \r\n

Waste emplacement<\/strong><\/p>\r\n\r\n<\/div>\r\n

\r\n\r\n \r\n

Waste is loaded in the landfill is a systematic way. Four methods are used for loading the waste in the landfill. They are<\/p>\r\n\r\n