Introduction to disposal part 2 engineering barriers in landfill
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Transcript of Introduction to disposal part 2 engineering barriers in landfill
Liner selection
Leachate collection system
Gas collection system
Monitoring
Closure and post closure plan
Design Objectives
Low hydraulic conductivity to minimize leakage (K ≤ 10-7 cm/sec)
Adequate shear strength to maintain liner stability under landfill weight and loads from vehicular movement
Minimal shrinkage potential to minimize desiccation cracking
Chemical stability for reactions with the waste or leachate
Materials Soils, such as benotnite, compacted clay Admixes such as asphalte concrete, asphalte
membrane, soil cement Polymer such as geotextile, geomembrane Organic and inorganic bases and hydrocarbon
pollutant will eliminate some polymer and soil asphalt
Limited Budget use soil or soil cement or asphalt liner, some polymer
Membrane (asphalte, polymer ) are medium cost
Clay advantage Low cost High cation exchange capacity Resist leachate migration Low Ks, due to ◦ Small size◦ Compact soil fabric
Good geomechnical properties, i.e. Toughness, Dilatancy, Plactiticty
Disadvantage clay Dissolution may occur due to the
acidity of leachate
Types of liner
Single
Single composite
Double composite
Located at the bottom of the landfill above liner
1) Drainage layer
Highly permeable layer to ease lateral drainage of leachate
Its thickness > 30 cm
Permeability 0.001 cm/sec
2) Sloped terrace
To increase the potential to lateral migration of leachate(2% slope)
3) Perforated pipes
To collect and drain the leachate 10 cm D HDPE or PVC pipes with perforation of 1 cm in the upper three quarters
4) Filter layer
An inverted filter used to prevent clogging of pipes due to sand ingression from drainage layer
5) Sump well
Used to pump out the leachate collected at the bottom of the landfill
After collection, leachate is treated using
Biological treatment (aerobic- anaerobic)
Physical and chemical treatment (flocculation –sedimentation-filtration- sorption)
Leachate leakage may occur from the bases or sides of landfill due to
1) Joint failure or puncture of geo-membrane liner 2) Cracks in the clay liner3) Excessive pressure build up in the landfill How to calculate leachate flow in disposalUse darcy law Q=KiA1) Q amount of leachate (m3/d)2) K hydraulic conductivity (m/d)3) i hydraulic gradient (h1-h2)/l4) A area of landfill (m2)
Gases generated in landfill ◦ Methane
◦ Carbon dioxide
◦ Nitrogen
◦ oxygen
◦ Hydrogen
◦ Hydrogen sulfide
◦ Carbon monoxide
Potential environmental impact of landfill gases◦ Explosion
◦ Asphyxiation,
◦ Vegetation damage
◦ Water pollution
◦ Corrosion
◦ Nuisance
Methane is lighter than air
Carbon dioxide is heavier than air
Factors affect gas generation
Moisture content
Waste type
Nutrient content
Specific weight
Ph
Temperature
Particle size
to prevent migration of gas to the nearby areas
it as an energy resource,
Components of Gas Collection System
Gas wells placed within the wastes
Header system to connect the well to the gas Pumping unit
Gas purification system
Energy recovery Plant
Double liner System-at the base and sides of the landfill
to prevent migration of leachate to the surroundings
Leachate Collection and Treatment Facility-to collect leachate from the base of the landfill for treatment to meet regulatory standards
Gas Collection and Treatment Facility-to collect gas emanating from the landfill and to treat
Final Cover-at the top of landfill to prevent infiltration of water into the landfill and to support vegetation.
Surface drainage System-to collect and
divert all surface runoff from the landfill
Environmental Monitoring Plan-for periodic monitoring of environmental quality of air, surface water, groundwater, vadoze zone.
Closure and Post-closure Plan details of activities to be undertaken to close a landfill site once the filling operation has been completed and for monitoring and maintenance of the completed landfill.
