Land Filling | Environmental Engineering - Civil Engineering (CE) PDF Download

LANDFILL

Landfills include any site which is used for more than a year for the temporary storage of waste; and, any internal waste disposal site, that is to say a site where a producer of waste is carrying out its own waste disposal at the place of production. 

Landfills does not include (a) any facility where waste is unloaded in order to permit its preparation for further transport for recovery, treatment or disposal elsewhere; (b) any site where waste is stored as a general rule for a period of less than three years prior to recovery or treatment; or, (c) any site where waste is stored for a period of less than one year prior to disposal.

MSW landfills represent the most widely accepted option for waste disposal in many parts of the world, particularly in underdeveloped and developing countries, due to its economic advantage over other methods. 

Even highly developed countries also largely depend on landfilling. In USA, 54% of the 250 × 106 metric tons of MSW generated was landfilled in 2008, with recycling and composting accounting for about 33% of MSW management . 

WASTE DECOMPOSITION PROCESS IN LANDFILL

• MSW contains a large proportion of organic materials that naturally decompose when landfilled.  
• This decomposition process initially is aerobic where the main byproducts are carbon dioxide, plus contaminated water. However, after the oxygen within the waste profile is consumed, it switches over to anaerobic processes. In the anaerobic process, carbon dioxide and methane are produced as waste decomposes. Liquid byproducts contain a large concentration of various contaminants that naturally move toward the landfill’s base. 
• The decomposition process continues for many years. As this takes place, trace quantities of materials that may have significant impacts upon the environment can be contained in both the landfill gas and in the leachate. These trace materials are generated until the landfill becomes completely stabilized. Although it isn’t known how long this will take, some estimate between 300 and 1,000 years .

LANDFILL GAS RECOVERY 

• The waste deposited in a landfill gets subjected, over a period of time, to anaerobic conditions and its organic fraction gets slowly volatilized and decomposed, leading to production of landfill gas which contains a high percentage of methane (about 50%). 
• Typically, production of landfill gas starts within a few months after disposal of wastes and generally lasts for 10 years or even more depending upon mainly the composition of wastes and availability of moisture. As the gas has a calorific value of around 4500 kcal/m³, it can be used as a source of energy either for direct heating/cooking applications or to generate power through IC engines or turbines . 

Advantages of Landfill Gas Recovery 

• Reduced GHG emissions;  
• Low cost means for waste disposal; and  
• The gas can be utilized for power generation or as domestic fuel.  

Disadvantages of Landfill Gas Recovery 

• Inefficient gas recovery process yielding only 30-40% of the total amount of gas actually generated. Balance gas escapes to the atmosphere (significant source of two major green house gases, carbon-dioxide and methane);  
• Utilization of methane may not be feasible for remote sites;  
• Cost of pre-treatment to upgrade the gas may be high; and 
• Spontaneous ignition/explosions may occur due to possible build up of methane concentrations in atmosphere. 

LANDFILL RECLAMATION 

•  An approach used to expand municipal solid waste (MSW) landfill capacity and avoid the high cost of acquiring additional land. 
• The equipment used for reclamation projects is adapted primarily from technologies already in use in the mining industry, as well as in construction and other solid waste management operations . 

Steps in Landfill Reclamation

(i) Excavation: An excavator removes the contents of the landfill cell. A front-end loader then organizes the excavated materials into manageable stockpiles and separates out bulky material, such as appliances and lengths of steel cable. 

(ii) Soil Separation (Screening): A trommel (i.e., a revolving cylindrical sieve) or vibrating screens separates soil (including the cover material) from solid waste in the excavated material. The size and type of screen used depends on the end use of the recovered material. For example, if the reclaimed soil typically is used as landfill cover, a 2.5-inch screen is used for separation. If, however, the reclaimed soil is sold as construction fill, or for another end use requiring fill material with a high fraction of soil content, a smaller mesh screen is used to remove small pieces of metal, plastic, glass, and paper. Trommel screens are more effective than vibrating screens for basic landfill reclamation. Vibrating screens, however, are smaller, easier to set up, and more mobile . 

Benefits of Landfill Reclamation 

• Extending landfill capacity at the current site 
•  Generating revenues from the sale of recyclable materials
• Lowering operating costs or generating revenues from the sale of reclaimed soil 
• Reducing landfill closure costs and reclaiming land for other uses 
• Retrofitting liners and removing hazardous materials 

Drawbacks of Landfill Reclamation 

• Managing hazardous materials 
• Controlling releases of landfill gases and odors 
• Controlling subsidence or collapse
• Excavation of one landfill area can undermine the integrity of adjacent cells, which can sink or collapse into the excavated area. 
• Increasing wear on excavation and MWC equipment 

MANAGEMENT OF CLOSED LANDFILLS 

Aftercare management of closed landfills typically includes monitoring of emissions (e.g. leachate and gas) and receiving systems (e.g. groundwater, surface water, soil, and air) and maintenance of the cover and leachate and gas collection systems . 

Landfill Gas: Closed landfill sites pose a potential hazard because of their methane production. The greatest risk occurs at sites that are within 250 m of housing and/or industrial estates. Problems become more severe when there are no gas-control measures .  

Landfill leachates: Landfill leachates are defined as the aqueous effluent generated as a consequence of rainwater percolation through wastes, biochemical processes in waste’s cells and the inherent water content of wastes themselves. It contains many organic matters, minerals, heavy metals and has high concentration of ammonia-nitrogen, all these lead to the low biodegradability. The leachate qualities changes according to the landfill climate conditions and hydrology, it also varies according to the qualities of the garbage that has been buried in the landfill . The removal of organic material based on chemical oxygen demand (COD), biological oxygen demand (BOD) and ammonium from leachate is the usual prerequisite before discharging the leachates into natural waters. Conventional landfill leachate treatments can be classified into three major groups :  

(a) leachate transfer: recycling and combined treatment with domestic sewage,  
 (b) biodegradation: aerobic and anaerobic processes and  
 (c) chemical and physical methods: chemical oxidation, adsorption, chemical precipitation, coagulation/flocculation, sedimentation/flotation and air stripping. After the hardening of the standards of rejection, conventional landfill leachate treatment plants are not able to meet the desired standards. Today, the landfill leachate treatment consists of various combined processes such as coagulation and ammonia-nitrogen stripping, UBF anaerobic process and two stages of Anoxic/Oxic process filter, UF and RO deep treatment . 

Landfill mining: Landfill mining could be described as a process for extracting minerals or other solid natural resources from waste materials that previously have been disposed of by burying them in the ground .