Environmental Engineering Reference
In-Depth Information
IV.
L
ANDFILL
G
AS
(LFG)
This section covers LFG characteristics, composition, LFG production, and gas yield. It
also discusses gas-generation mechanisms and gas-transport mechanisms and factors
affecting both mechanisms.
A. Landfill Gas Characteristics
Landfill gas is typically a combination of methane, carbon dioxide, and non-
methanogenic organic compounds. Table 1 shows characteristics of some of the typical
components of landfill gas.
1. Density and viscosity
The density of LFG depends on the proportion of gas components present. For example, a
mixture of 10 percent hydrogen and 90 percent carbon dioxide, such as might be produced in
the first stage of anaerobic decomposition, will be heavier than air, while a mixture of 60
percent methane and 40 percent carbon dioxide, such as might be produced during the
methanogenic phase of decomposition, will be slightly lighter than air. Some typical values
for density and viscosity at 0
0
C and atmospheric pressure are given in Table 2.
Table 1. Landfill Gas Characteristics
Relative
Specific
Gravity
Concentration in
Landfill Gas
Constituent
Notes
Forms explosive mixture with
methane
Air
1
NA
Explosive; LEL 5% in air; UEL
15% in air
Methane
0.554
40-70%
Carbon Dioxide
1.529
30-60%
Forms weak acid; Asphyxiant
Forms strong acid
Toxic: PEL = 10 STEL = 15
Hydrogen Sulfide
1.19
800 ppm
Forms acids with hydrogen
sulfide and carbon dioxide
Water Vapor
0.62
100% Saturated
Flammable
Toxic: PEL 1.0 ppm STEL 5
ppm
Benzene
2.8
30 ppm
Toxic: PEL 100 ppm STEL 150
ppm
Toluene
3.1
300 ppm
Organic Acids
GT 2
Traces
Odorous
Organosulphur
Compounds
GT 1.5
50 ppm
Odorous
Source: US Army Corps of Engineers (2008)
LEL = lower explosive limit; UEL = upper explosive limit; STEL = short-term-exposure limit; PEL =
permissible exposure limit.
