3.6.1.1.3 Hydrolysis of Lipids
Lipids, commonly present in the form of triglycerides and in digestion process, is
taken as fat, oils, and greases (FOG). The lipids are degraded by the enzyme lipases
(Alves et al. 2009).
3.6.1.2 Acidogenesis or Fermentation
This is the second stage of AD process, where the products of the hydrolysis stage
are used as a substrate by acidogenic bacteria. The substrates such as soluble
monomers are converted to short-chain organic acids (volatile fatty acids – acetic,
butyric, lactic, propionic, and succinic acid). The other products from hydrolysis are
converted to alcohols, ammonia, hydrogen, and carbon dioxide. The formation of
compound depends on the organism present, substrate and environmental conditions
(Bischofsberger et al. 2005).
3.6.1.3 Acetogenesis
The products produced in the acidogenesis are used as substrates for the acetogenic
microorganisms, which are active acetogenes. So the volatile fatty acids (VFA) and
alcohols are oxidized into methanogenic substrates like acetate, hydrogen, and
carbon dioxide. This intermediary translation is crucial for successful biogas production (Bischofsberger et al. 2005).
3.6.1.4 Methanogenesis
The final step in the AD process is methanogenesis. This is critical and also the
slowest step in whole process. The methanogenic bacteria utilize the products of
previous steps as substrate. Two different microbes produce methane by two wellbalanced processes. In the first process, the acetic acid produces methane and carbon
dioxide by acetoclastic microorganisms. In the second process, hydrogen is reduced
to form carbon dioxide and methane by hydrogenophilic methanogens, and based on
thermodynamics, scientists identified a new reaction (Fig. 3.3).
3.7
Biogas Plant
“Biogas plant” is a physical structure which is designed to perform the anaerobic
digestion process. The principal part of the biogas plant is a digester (Fig. 3.4). The
digester is an airtight tank where the bacteria break down the organic waste material
in an anaerobic digestion process (Samah 2016) (Fig. 3.5). During the last century,
different types of digesters were reported. Based on the nature of feeding material
(organic waste), the biogas plant can be divided into several types as mentioned
below.
3 Biogas: An Effective and Common Energy Tool – Part I
77
Lipids, commonly present in the form of triglycerides and in digestion process, is
taken as fat, oils, and greases (FOG). The lipids are degraded by the enzyme lipases
(Alves et al. 2009).
3.6.1.2 Acidogenesis or Fermentation
This is the second stage of AD process, where the products of the hydrolysis stage
are used as a substrate by acidogenic bacteria. The substrates such as soluble
monomers are converted to short-chain organic acids (volatile fatty acids – acetic,
butyric, lactic, propionic, and succinic acid). The other products from hydrolysis are
converted to alcohols, ammonia, hydrogen, and carbon dioxide. The formation of
compound depends on the organism present, substrate and environmental conditions
(Bischofsberger et al. 2005).
3.6.1.3 Acetogenesis
The products produced in the acidogenesis are used as substrates for the acetogenic
microorganisms, which are active acetogenes. So the volatile fatty acids (VFA) and
alcohols are oxidized into methanogenic substrates like acetate, hydrogen, and
carbon dioxide. This intermediary translation is crucial for successful biogas production (Bischofsberger et al. 2005).
3.6.1.4 Methanogenesis
The final step in the AD process is methanogenesis. This is critical and also the
slowest step in whole process. The methanogenic bacteria utilize the products of
previous steps as substrate. Two different microbes produce methane by two wellbalanced processes. In the first process, the acetic acid produces methane and carbon
dioxide by acetoclastic microorganisms. In the second process, hydrogen is reduced
to form carbon dioxide and methane by hydrogenophilic methanogens, and based on
thermodynamics, scientists identified a new reaction (Fig. 3.3).
3.7
Biogas Plant
“Biogas plant” is a physical structure which is designed to perform the anaerobic
digestion process. The principal part of the biogas plant is a digester (Fig. 3.4). The
digester is an airtight tank where the bacteria break down the organic waste material
in an anaerobic digestion process (Samah 2016) (Fig. 3.5). During the last century,
different types of digesters were reported. Based on the nature of feeding material
(organic waste), the biogas plant can be divided into several types as mentioned
below.
3 Biogas: An Effective and Common Energy Tool – Part I
77