What is Landfill Gas (LFG) ?

Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill. Landfill gas is approximately 40% to 60% percent  methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simple hydrocarbons.

Landfill Gas Content

Methane      % 45-70

Carbondioxide      % 30-55

Nitrogen      % 2-5

Oxygen      % 0,1-1

Ammonia      % 0,1-1

Sulphur      % 0-1

Water Vapor      % 1-3

Aerobic Phase

The characteristic feature of this phase is the presence of O2 from the atmosphere at the time the waste is stored. Aerobic bacteria survive until oxygen is depleted. The product of this phase is carbon dioxide and water vapor.
Duration can be expressed in several weeks or hours.

Acid Phase

With the start of the formation of organic acids from the compounds produced in the aerobic phase, more significant amounts of CO2 are produced. The anaerobic decomposition phase begins. The storage area is highly acidic in this phase. Acids dissolve nutrients with moisture.
Duration 1 to 6 months.

Initial Methanogenic Phase

Some of the anaerobic bacteria consume organic acids in this phase. The storage area becomes more neutral thus methane-producing bacteria begin to form themselves. CO2 and N2 amounts are reduced while H2 is completely exhausted.
Duration 3 months to 3 years.

Stable Methanogenic Phase

Decomposition begins when LFG production becomes stable. In this phase, LFG contains
45% - 60% CH4
40-60% CO2
2-9% other gases
This production can last 20 years.
Duration 1 year to 40 years.

LFG Collections:

The typical LFG collection system consists of the following three main components.

  • 1-Horizontal or vertical gas collection wells
  • 2-Condensing and gas treatment systems
  • 3-Blower

In addition, many LFGs are equipped with a Flare unit for use in the combustion of excess gas or downtime in energy recovery plants

GAS COLLECTION SYSTEM - Horizontal Well Structure:

Average channel depth 4 m
Maximum channel depth 10 m
Average channel length 120 m

GAS COLLECTION SYSTEM - Vertical Well Structure:

Maximum well depth -45 m
Diameter of well impact -50 m