Landfill design and operation

Landfills, designing,Principle, methods, advantages, disadvantages

1. Landfill: Design and Operation Arushe Tickoo M. Tech

2. A landfill is an engineered method for land disposal of solid and hazardous waste. Landfilling is the term used to describe the process by which solid waste is placed in the landfill. Landfills for individual waste constituents such as combustion ash, asbestos and other similar wastes are known as monofill s . Landfills for the disposal of hazardous wastes are called secure landfills. Landfill

3. Principle The purpose of landfilling is to bury/ alter the chemical composition of the waste so that they do not pose any threat to environment/public health. Landfills are usually made up of cells in which a discrete volume of waste is kept isolated from adjacent waste cells by a suitable barrier. The term cell is used to describe the volume of material placed in a landfill during one operating period. Requirements For a Landfill There are four minimum requirements 1) Full/ partial hydrological isolation 2) Formal engineering preparation 3 ) Permanent control 4 ) Planned waste placement and covering

4. Types of Solid Waste Municipal Solid Waste (MSW) Industrial Hazardous Waste Bio Medical Waste(from Hospital) E- Waste (Electronic Waste) Landfill operation : Aerobic landfill Anaerobic landfill Semi – aerobic landfill Consists of : Household waste (From Kitchen & household Rubbish) Construction and demolition debris Commercial waste (from shops-offices) Petrochemical industries Metallurgical industries Pharmaceutical industries Fertilizer industries

5. Landfill operation The gases found in land fills include air, ammonia Carbon-monoxide, hydrogen, sulfide, methane, nitrogen . Carbon monoxide and methane are the principle gases produced from anaerobic decomposition . It involves three steps. Enzyme mediated transformation Bacterial conversion for intermediate compounds . Bacterial conversion of intermediate compounds to low molecular weight compounds .

6. LANDFILL DESIGN

7. Methods of landfill The area method is used when the terrain is unsuitable for excavation. The filling operation usually is started by building an earthen levee against which wastes are compacted and placed in thin layers . At the end of each days operation a 150-300 mm of layer of cover material is placed over the completed landfill. A completed lift, including the cover material is called a cell Area method

8. The trench method is ideally suited where there is adequate amount of cover material available and the groundwater level is well below the surface. Where artificial or natural depressions exist, those can be effectively used for trench method. Canyons ,ravines, dry borrow pits and quarries can be used for this purpose. Trench method

9. Technique involves placement and compaction of SW in canyon/ depression. It differs with geometry of site, characteristics of available cover material, hydrology, geology of the site. Control of surface drainage is often a critical factor in this method. Filling starts at the headed of canyon and ends at mouth, to prevent accumulation of water behind the landfill. Canyon/depression method

10. Landfill Design & Operation Geometry of cell Support material Leachate collection LFG collection Final closure Liners Design Considerations Leachate availability Leachate recirculation methods

11. Site selection process The suitability of a landfill site is determined by Its size/area/volume Technical and environmental factors Climate and hydrological conditions. It requires a development of a working plan, description of site location, operation, engineering work and site restoration. People are reluctant to allow construction of new landfill, thus siting approval authority is important.

12. Construction A specific method of filling will depend on the characteristics of the site, Such as the amount of available cover material , topography , and the local hydrology . During construction of landfill the following must be determined Access roads. Equipment shelters. Scales if used. Topsoil stockpiles sites.

13. Leachate collection system Leachate may be defined as the liquid that has percolated through solidwaste and has extracted dissolved or suspended materials from it. The rate of seepage of leachate from the bottom of a landfill is estimated by Darcys law. The use of clay has favored in reducing the leachate percolation .

14. Landfill gas In most of the cases as the anaerobic decomposition of the wastes predominates the decomposition process the gases obtain are Carbon dioxide and methane . Carbon dioxide as result of its density will move towards the groundwater which can lower the pH of the groundwater and increases the hardness and mineral content in the ground water .

15. The lateral movement of gases produced in a landfill Can be controlled by installing vents made of materials that are more permeable than surrounding soil. The spacing of vents depends on width of waste cells but usually varies from 18 to 60 m . Gas venting system

16. Barrier or well vents also can be used to control the lateral movement of gases. Well vents also can be used to control the lateral movement of gases. The movement of landfill gases through adjacent soil formations can be controlled by constructions of Barriers that are more impermeable than soil Eg ; bentonites , butyl rubber , illites etc ; Outlet for Gas venting system

17. Liner systems Single liner Double liner Composite liner Sand Gravel Geonet Example

18. Final cover and post closure The final cover must be 36” thick layer of clay. Boundaries must be well protected. Long term usage of landfill i.e. reusage of landfill. Once the landfill reaches design height, a final cap is placed to minimize infiltration of rainwater. Facilitate long term maintenance of the landfill . The final cover shall have a barrier soil layer. On the top of barrier soil layer, there shall be drainage layer of 15 cm . On the top of the drainage there shall be a vegetative layer of 45 cm to support natural plant growth and to minimize erosion.

19. A cap consists of from top to bottom Vegetation and supporting soil (6 inches) Filter and drainage layer – protective material (18-36 inches) drainage material (12 inches) A hydraulic barrier– clay layer (24 inches), LDPE barrier Foundation for hydraulic barrier– gravel layer ( 6 inch) sand bedding for LDPE (4 inch) Final cap Specification Mulch is a layer of material applied to the surface of soil, for conservation of soil moisture, improving fertility and health of the soil

20. Landfill Settling Process 1. Primary consolidation Substantial amount of settling occurs at this stage. It is caused by weight of the waste layers, truck movements, bulldozers , mechanical compactors. After this stage aerobic degradation of waste occurs. 2. Secondary compression Rate of settling is much lower than first stage. Settling occurs through compression 3. Decomposition It is the degradation process. Organic material is converted to gas and leachate. Settling rate increases as compare to secondary stage, but with the passage of time it gradually decreases. It continues till the organic matter is degraded.

21. Biological process is most important aspect in landfilling which determines the quantity and quality of leachate and gas. After the disposal, large part of waste becomes anaerobic(due to absence of oxygen). Microbial activity degrade the solid organic carbon and produces methane and carbon dioxide . In an anaerobic process solid and dissolved organic compounds are hydrolyzed and fermented to volatile fatty acids, alcohols, hydrogen and carbon dioxide. The methanogenic bacteria convert acetic acid to methane and carbon dioxide. Hydrogenophilic bacteria convert hydrogen and carbon dioxide to methane. Microbial Degradation Process

22. Composition Of Landfill Gas

23. Factors Affecting The Landfill Gas And Leachate Generation 1. Nature of waste – amount of gas depends on the content of biodegradable matter in the waste. 2. Moisture content – microorganisms require minimum 12% moisture for growth, thus it is important factor in determining gas production. 3. pH – methanogens grow only at low pH around neutrality. % of gas depends on pH. 4. Particle size and density – particle size affects density achieved by compaction that affects surface area and hence volume. This affects the moisture absorption and thus the biological degradation. 5. Temperature – Increase in temperature tends to increase in gas production. It affects microbial activity.

24. In addition to provide an option for waste management, it also serves to improve/ reclaim poor quality land. It raises the ground elevation/surface grade of the site. Completed landfills have been converted to municipal parks, playgrounds, golf courses, community land use projects. It is the most economical alternative for SW disposal which accounts for its frequent application. Other disposal methods are not entirely safe and efficient throughout the year. Incineration is a costly process, residue requires ultimate disposal on land . Composting is a seasonal option . It is not possible to reclaim and recycle all SW material. Advantages of Landfilling

25. Difficult to find suitable site within economically feasible distance. It is not possible to build a completely safe and secure SW landfill. Some of the pollutants may escape in the environment in the form of leachate. Potential harm to public health due to air, soil, water and noise pollution Damage to local ecosystem. Hydrology (GW flow) and geology (Rock type, soil permeability) of the site has a direct influence on the possibility of water pollution (GW pollution). Disadvantages

26. 1. Laying of Geo-Textile 2. Laying of sand layer over gravels bed 3. Laying of gravels at the bottom Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Made from polypropylene or polyester , geotextile fabrics come in three basic forms: woven (resembling mail bag sacking), needle punched or heat bonded (resembling ironed felt)

27. 7. Lateral Leachate pipes 6. Laying of clay layer over HDPE sheets 5. Marking of detected leakages 4. Laying of HDPE sheets

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