Environmental Engineering Reference
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hydrolysis of higher molecular mass compounds into compounds suitable for use by
microorganisms as a source of energy and cell carbon, followed by the acidogenesis of the
previous formed compounds to produce lower-molecular mass intermediate compounds, as
typified mainly by acetic acid (CH 3 COOH). Carbon dioxide is the principal gas generated in
this phase. Small amounts of hydrogen gas will also be produced.
Table 1. Typical composition of LFG (Tchobanoglous et al., 1993)
Percent
(dry volume basis)
Percent
(dry volume basis)
Component
Component
Methane
45-60
Sulfides, disulfides,
mercaptans, etc.
0-1,0
Carbon dioxide
40-60
Nitrogen
2-5
Ammonia
0,1-1,0
Oxygen
0,1-1,0
Hydrogen
0-0,2
Carbon monoxide
0-0,2
Trace constituents
0,01-0,6
The microorganisms involved in this conversion, described collectively as
nonmethanogenic, consist of facultative and obligate anaerobic bacteria. In the following
phase - the methane fermentation phase (phase IV) a second group of microorganisms, which
convert the acetic acid and the hydrogen to methane and carbon dioxide, becomes more
predominant. The microorganisms responsible for this phase are strict anaerobes and are
called methanogenic. In this phase both methane and acid formation proceed simultaneously,
although the rate of acid formation is considerably reduced. Finally the last phase - the
maturation phase (phase V) occurs when almost all the readily available biodegradable
organic material has been converted. The rate of LFG generation decreases significantly
because most of the available nutrients have been previously removed and the remaining
substrates are slowly biodegradable.
The duration of the individual phases in the production of LFG will vary depending on
the distribution of the organic components in the landfill, the availability of nutrients, the
moisture content of waste, moisture routing through the landfill and the degree of initial
compaction.
Figure 1. Generalised phases in the generation of LFG (Tchobanoglous et al., 1993).
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