Environmental Engineering Reference
In-Depth Information
Table 8.2 Microorganisms involved in methanogenesis Taxon (order and type) with metabolic
substrates and typical habitats
Taxon (Order)
Typical genus
Major meta-
bolic substrate
Typical habitat
Methanobacteriales
Methanobacterium, Methano-
brevibacter, Methanosphaera,
Methanothermobacter,
Methanothermus
H 2 and CO 2 ,
formate,
methanol
Anaerobic digest-
ers, rumen, paddy
soil, decaying woody
tissues, anaerobic
activated sludge etc.
Methanococcales
Methanococcus, Methano-
thermococcus, Methanocal-
dococcus, Methanotorris
H 2 and CO 2 ,
formate
Marine sediments, hot
springs etc.
Methanomicrobiales
Methanomicrobium, Metha-
noculleus, Methanofollis,
Methanogenium, Methanola-
cinia, Methanoplanus, Metha-
nospirillum, Methanocorpusc
ulum,Methanocalculus
H 2 and CO 2 ,
2- propanol,
2-butanol,
2-butanone
Anaerobic digesters,
soil, marine sediments,
hot springs, decay-
ing woody tissues,
anaerobic activated
sludge, etc.
Methanosarcinales
Methanococcoides, Metha-
nohalobium, Methanoha-
lophilus, Methanolobus,
Methanomethylovorans,
Methanimicrococcus, Metha-
nosalsum, Methanosaeta/
Methanosarcina,
H 2 and CO 2 ,
formate,
MeNH 2,
acetate
Hypersaline marine
sediments, anaerobic
digesters, animal gas-
trointestinal tracts, etc.
Methanopyrales
Methanopyrus
H 2 and CO 2
Marine sediments
by enzymes called carbon monoxide dehydrogenase. The second CO 2 + 4H 2
CH 3 COOH + 2H 2 O is called the Wood-Ljungdahl pathway (homoacetogenesis).
4. Methanogenesis: a biological reaction where acetates are converted into methane
and carbon dioxide, while hydrogen is consumed.
To be useful for bioenergy production, a microbial community must have a stable
metabolic function over time, despite the unavoidable perturbations and disturbanc-
es that occur in real world systems. The activity of microorganisms in anaerobic
fermentation processes depends mainly on water content, temperature, pH, redox
potential, and the presence of inhibitory factors. The microorganisms involved in
methanogenesis Taxon (order and type) are shown in Table 8.2 . Five orders of meth-
anogens can be separated into two functional groups: aceticlastic methanogens and
hydrogenotrophic methanogens. Methanosarcina and Methanosaeta can utilize the
acetate to product methane.
The methane fermentation process can be affected by many factors such as the
operational and physiological conditions shown in Fig. 8.10 . Biogas production
and water content of the initial material are interdependent. Below 20 % by weight,
hardly any biogas is produced. With increasing water content biogas production is
enhanced, reaching its optimum at 91-98 % water (by weight). The process of bio-
methane production is also very sensitive to changes in temperature, and the degree
 
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