Introduction to disposal part 2 engineering barriers in landfill

Dr. Rehab O. Abdel RahmanAssociate Professor, AEAE

[email protected]

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.