oxidized to carbon dioxide, hydrogen, and acetic acid by metabolic action of
acetogens. Volatile fatty acids and alcohols are then transformed by acetogenic
bacteria into acetic acid, hydrogen, and carbon dioxide. During acidogenesis,
Desulfovibrio, Lactobacillus, Butyrivibrio, Bacillus, Desulfuromonas, Pelobacter,
Sarcina, Staphylococcus, Selenomonas, Pseudomonas, Streptococcus, Clostridium,
Eubacterium, Desulfobacter, Veillonella, etc. are seen. In the stage of acetogenesis,
Syntrophomonas
buswelii,
Clostridium,
Methanobacillus
omelionskii,
Syntrophomonas wolfei, Syntrophomonas wolinii, etc. are involved.
Methanogenesis leads to the formation of CH 4 . Seventy percent of methane
produced is from acetic acid by acetoclastic methanogenic bacteria. During
methanogenesis, Methanosarcina and Methanosaeta were generally observed.
Hydrogenophilic methanogens such as Methanoplanus, Methanobacterium,
Methanospirillium, Methanobrevibacter, etc. are also seen (Wheatley 1991;
Stronach et al. 1986). Methanogenic bacteria then use acetic acid or hydrogen and
carbon dioxide to generate methane. Yang et al. (2004) have reported that the yield
of biomethane is never greater than 60% of theoretical yield. The possible reason for
this decrease is the presence of other compounds which do not undergo degradation
and are resistant such as lignin, cellulose, or some complex proteins in the waste:
4CH 3 COOH ! 4CH 4 + 4CO 2
CO 2 + 4H 2 ! CH 4 + 2H 2 O
4CH 3 OH ! 3CH 4 + CO2 + 2H 2 O
CH 3 OH + H 2 ! CH 4 + H 2 O
8.4 Microorganisms in Anaerobic Digestion
Different groups of bacteria such as Methanoculleus bourgensis, Peptoniphilus sp.,
Ruminiclostridium cellulosi, Herbinix hemicellulosilytica, Clostridium bornimense,
and Clostridium ultunense participate in various anaerobic digestion stages
(Mauset al. 2014, 2016; Hahnke et al. 2014; Koeck et al. 2015; Tomazetto et al.
2016; Manzoor et al. 2013; Sun and Schnürer 2016). Methanoculleus species are
known to be one of the most biologically involved organisms in methanogenesis
(Nettmann et al. 2010; Wirth et al. 2012; Maset al. 2014). M. bourgensis is an
important microbial species in the process. Certain genes involved in
methanogenesis and osmolytes production were found in the M. bourgensis
MS2T, and much of the genetic information commonly seen in methanogenesis in
biogas plants was found in its genome (Maus et al. 2016). Hahnke et al. (2015) used
the Illumina MiSeq system to sequence the anaerobic Porphyromonadaceae bacterium, which was isolated from an anaerobic digestion plant. They suggested that the
bacterium may play a role in both hydrolysis and acidogenesis stages, as its genome
showed the presence of genes which can produce proteins capable of breakdown of
complex carbohydrates and production of fatty acids (VFAs). Koeck et al. (2014)
sequenced Ruminiclostridium cellulosi DG5, a thermophilic, anaerobic, and cellulolytic bacterium which was responsible for lignocellulose degradation. The
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acetogens. Volatile fatty acids and alcohols are then transformed by acetogenic
bacteria into acetic acid, hydrogen, and carbon dioxide. During acidogenesis,
Desulfovibrio, Lactobacillus, Butyrivibrio, Bacillus, Desulfuromonas, Pelobacter,
Sarcina, Staphylococcus, Selenomonas, Pseudomonas, Streptococcus, Clostridium,
Eubacterium, Desulfobacter, Veillonella, etc. are seen. In the stage of acetogenesis,
Syntrophomonas
buswelii,
Clostridium,
Methanobacillus
omelionskii,
Syntrophomonas wolfei, Syntrophomonas wolinii, etc. are involved.
Methanogenesis leads to the formation of CH 4 . Seventy percent of methane
produced is from acetic acid by acetoclastic methanogenic bacteria. During
methanogenesis, Methanosarcina and Methanosaeta were generally observed.
Hydrogenophilic methanogens such as Methanoplanus, Methanobacterium,
Methanospirillium, Methanobrevibacter, etc. are also seen (Wheatley 1991;
Stronach et al. 1986). Methanogenic bacteria then use acetic acid or hydrogen and
carbon dioxide to generate methane. Yang et al. (2004) have reported that the yield
of biomethane is never greater than 60% of theoretical yield. The possible reason for
this decrease is the presence of other compounds which do not undergo degradation
and are resistant such as lignin, cellulose, or some complex proteins in the waste:
4CH 3 COOH ! 4CH 4 + 4CO 2
CO 2 + 4H 2 ! CH 4 + 2H 2 O
4CH 3 OH ! 3CH 4 + CO2 + 2H 2 O
CH 3 OH + H 2 ! CH 4 + H 2 O
8.4 Microorganisms in Anaerobic Digestion
Different groups of bacteria such as Methanoculleus bourgensis, Peptoniphilus sp.,
Ruminiclostridium cellulosi, Herbinix hemicellulosilytica, Clostridium bornimense,
and Clostridium ultunense participate in various anaerobic digestion stages
(Mauset al. 2014, 2016; Hahnke et al. 2014; Koeck et al. 2015; Tomazetto et al.
2016; Manzoor et al. 2013; Sun and Schnürer 2016). Methanoculleus species are
known to be one of the most biologically involved organisms in methanogenesis
(Nettmann et al. 2010; Wirth et al. 2012; Maset al. 2014). M. bourgensis is an
important microbial species in the process. Certain genes involved in
methanogenesis and osmolytes production were found in the M. bourgensis
MS2T, and much of the genetic information commonly seen in methanogenesis in
biogas plants was found in its genome (Maus et al. 2016). Hahnke et al. (2015) used
the Illumina MiSeq system to sequence the anaerobic Porphyromonadaceae bacterium, which was isolated from an anaerobic digestion plant. They suggested that the
bacterium may play a role in both hydrolysis and acidogenesis stages, as its genome
showed the presence of genes which can produce proteins capable of breakdown of
complex carbohydrates and production of fatty acids (VFAs). Koeck et al. (2014)
sequenced Ruminiclostridium cellulosi DG5, a thermophilic, anaerobic, and cellulolytic bacterium which was responsible for lignocellulose degradation. The
232
R. Kumar et al.