hydrolysis, and in each individual stage, various types of faculty or compulsory
anaerobic microorganisms are included as demonstrated in Fig. 4.1 (Merlin Christy
et al. 2014; Chasnyk et al. 2015; Abdeshahian et al. 2016).
4.4.1 Steps Involved in Biogas Production Process
4.4.1.1 Hydrolysis
Hydrolysis is the first phase in biogas manufacturing in which the main elements or
complicated organic molecules of scrap natural matter/biomass (carbohydrates,
lipids, and proteins) break down into lower units (monomer sugars, amino acids,
alcohols, and fatty acids) by cellulolytic, lipolytic, and proteolytic organisms,
respectively. Most commonly bacteria of genera Megasphaera, Sporobacterium,
Sphingomonas,
Bifidobacterium,
Bacteroides,
Lactobacillus,
and
Propionibacterium are found to be involved in hydrolysis including both facultative
and obligatory anaerobes. The rate of hydrolysis is typically represented by using
first-order kinetics (Sharma 2008).
4.4.1.2 Acidogenesis or Acid Production
After hydrolysis of organic matter present in biomass, acidogenic bacteria convert
the products of hydrolysis into short-chain organic acids like volatile fatty acids, i.e.,
propionic, lactic and butyric acids, NH 3 , H 2 S, and H 2 . Carbon dioxide (CO 2 ) and
alcohols, for instance, ethanol, are also formed through this method. Various obligate and facultative anaerobic fermentative bacteria, viz., Desulfovibrio spp., Corynebacterium spp., Clostridium spp., Bifidobacterium spp., Peptostreptococcus
anaerobius, Escherichia coli, Lactobacillus spp., and Staphylococcus spp., were
found to be involved in the process (Sharma 2008; Metcalf and Eddy 2004).
4.4.1.3 Acetogenesis or Acetic Acid Production
In this step volatile fatty acids and ethanol produced by acidogenic microbes are
converted into acetic acid (CH 3 COOH)/acetate (CH 3 COO
À ), H 2 , and CO 2 by
acetogenic bacteria. Acetogenic bacteria like Syntrobacter wolinii and
Syntrophomonas wolfei change alcohol and fatty acids into carbon dioxide, acetate,
and hydrogen.
Fig. 4.1 Degradation process taking place during AD, i.e., hydrolysis, acidogenesis, acetogenesis,
and methanogenesis. (Source: Merlin Christy et al. 2014; Chasnyk et al. 2015; Abdeshahian et al.
2016)
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G. Monika et al.
anaerobic microorganisms are included as demonstrated in Fig. 4.1 (Merlin Christy
et al. 2014; Chasnyk et al. 2015; Abdeshahian et al. 2016).
4.4.1 Steps Involved in Biogas Production Process
4.4.1.1 Hydrolysis
Hydrolysis is the first phase in biogas manufacturing in which the main elements or
complicated organic molecules of scrap natural matter/biomass (carbohydrates,
lipids, and proteins) break down into lower units (monomer sugars, amino acids,
alcohols, and fatty acids) by cellulolytic, lipolytic, and proteolytic organisms,
respectively. Most commonly bacteria of genera Megasphaera, Sporobacterium,
Sphingomonas,
Bifidobacterium,
Bacteroides,
Lactobacillus,
and
Propionibacterium are found to be involved in hydrolysis including both facultative
and obligatory anaerobes. The rate of hydrolysis is typically represented by using
first-order kinetics (Sharma 2008).
4.4.1.2 Acidogenesis or Acid Production
After hydrolysis of organic matter present in biomass, acidogenic bacteria convert
the products of hydrolysis into short-chain organic acids like volatile fatty acids, i.e.,
propionic, lactic and butyric acids, NH 3 , H 2 S, and H 2 . Carbon dioxide (CO 2 ) and
alcohols, for instance, ethanol, are also formed through this method. Various obligate and facultative anaerobic fermentative bacteria, viz., Desulfovibrio spp., Corynebacterium spp., Clostridium spp., Bifidobacterium spp., Peptostreptococcus
anaerobius, Escherichia coli, Lactobacillus spp., and Staphylococcus spp., were
found to be involved in the process (Sharma 2008; Metcalf and Eddy 2004).
4.4.1.3 Acetogenesis or Acetic Acid Production
In this step volatile fatty acids and ethanol produced by acidogenic microbes are
converted into acetic acid (CH 3 COOH)/acetate (CH 3 COO
À ), H 2 , and CO 2 by
acetogenic bacteria. Acetogenic bacteria like Syntrobacter wolinii and
Syntrophomonas wolfei change alcohol and fatty acids into carbon dioxide, acetate,
and hydrogen.
Fig. 4.1 Degradation process taking place during AD, i.e., hydrolysis, acidogenesis, acetogenesis,
and methanogenesis. (Source: Merlin Christy et al. 2014; Chasnyk et al. 2015; Abdeshahian et al.
2016)
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G. Monika et al.