6.1.1.2 Acidogenesis
Acidogenesis is the next step of anaerobic digestion in which acidogenic
microorganisms further break down the monomer products after hydrolysis. These
fermentative bacteria produce an acidic environment in the digestive tank while
creating volatile fatty acids, carbonic acids, alcohols, as well as trace amounts of
other by-products. While acidogenic bacteria further break down the organic matter,
it is still too large and unusable for the ultimate goal of methane production, so the
biomass must next undergo the process of acetogenesis (Parawira et al. 2004).
6.1.1.3 Acetogenesis
In general, acetogenesis is the creation of acetic acid or acetate, from carbon and
energy sources by acetogens. These microorganisms catabolize many of the products
created in acidogenesis into acetic acid, CO 2 , and H 2 . Acetogens break down the
volatile fatty acids and alcohols to a point at which methanogens can utilize much of
the remaining materials to create methane as a biofuel (Kalia 2007).
6.1.1.4 Methanogenesis
Methanogenesis constitutes the final stage of anaerobic digestion in which
methanogens create methane from the final products of acetogenesis as well as
from some of the intermediate products from hydrolysis and acidogenesis. While
CO 2 can be converted into methane and water through the reaction, the main
mechanism to create methane in methanogenesis is the path involving acetic acid.
This path creates methane and CO 2 , the two main products of anaerobic digestion
(Ziemiński and Frąc 2012; An et al. 2008).
6.1.2 Factors Affecting Biogas Yield
The factors affecting the biogas yield are carbon/nitrogen ratio, temperature, pH,
dilution and consistency of feed, loading rate, hydraulic retention time, toxicity,
agitation, and additives (Mahanta et al. 2005).
6.1.2.1 Carbon/Nitrogen (C/N) Ratio
The relationship between the amount of carbon and nitrogen present in organic
materials is expressed by the carbon/nitrogen (C/N) ratio. A suitable C/N ratio plays
an important role for the proper proliferation of the bacteria for the degradation
process (Augenstein et al. 1976). Depending upon the relative richness in carbon and
nitrogen content, feed material can be classified as nitrogen-rich or carbon-rich. It is
generally found that during digestion, microorganisms utilize carbon 25–30 times
faster than nitrogen, that is, carbon content in feedstock should be 25–30 times of the
nitrogen content (Report No. ETSU B 1118 1986; Barnett et al. 1978; Fry and
Merrill 1973). To meet this requirement, constituents of feedstock are chosen in such
a way to ensure a C/N ratio of 25:1 to 30:1 and concentration of dry matter as
6 Stoichiometric Analysis of Biogas Production from Industrial Residues
143
Acidogenesis is the next step of anaerobic digestion in which acidogenic
microorganisms further break down the monomer products after hydrolysis. These
fermentative bacteria produce an acidic environment in the digestive tank while
creating volatile fatty acids, carbonic acids, alcohols, as well as trace amounts of
other by-products. While acidogenic bacteria further break down the organic matter,
it is still too large and unusable for the ultimate goal of methane production, so the
biomass must next undergo the process of acetogenesis (Parawira et al. 2004).
6.1.1.3 Acetogenesis
In general, acetogenesis is the creation of acetic acid or acetate, from carbon and
energy sources by acetogens. These microorganisms catabolize many of the products
created in acidogenesis into acetic acid, CO 2 , and H 2 . Acetogens break down the
volatile fatty acids and alcohols to a point at which methanogens can utilize much of
the remaining materials to create methane as a biofuel (Kalia 2007).
6.1.1.4 Methanogenesis
Methanogenesis constitutes the final stage of anaerobic digestion in which
methanogens create methane from the final products of acetogenesis as well as
from some of the intermediate products from hydrolysis and acidogenesis. While
CO 2 can be converted into methane and water through the reaction, the main
mechanism to create methane in methanogenesis is the path involving acetic acid.
This path creates methane and CO 2 , the two main products of anaerobic digestion
(Ziemiński and Frąc 2012; An et al. 2008).
6.1.2 Factors Affecting Biogas Yield
The factors affecting the biogas yield are carbon/nitrogen ratio, temperature, pH,
dilution and consistency of feed, loading rate, hydraulic retention time, toxicity,
agitation, and additives (Mahanta et al. 2005).
6.1.2.1 Carbon/Nitrogen (C/N) Ratio
The relationship between the amount of carbon and nitrogen present in organic
materials is expressed by the carbon/nitrogen (C/N) ratio. A suitable C/N ratio plays
an important role for the proper proliferation of the bacteria for the degradation
process (Augenstein et al. 1976). Depending upon the relative richness in carbon and
nitrogen content, feed material can be classified as nitrogen-rich or carbon-rich. It is
generally found that during digestion, microorganisms utilize carbon 25–30 times
faster than nitrogen, that is, carbon content in feedstock should be 25–30 times of the
nitrogen content (Report No. ETSU B 1118 1986; Barnett et al. 1978; Fry and
Merrill 1973). To meet this requirement, constituents of feedstock are chosen in such
a way to ensure a C/N ratio of 25:1 to 30:1 and concentration of dry matter as
6 Stoichiometric Analysis of Biogas Production from Industrial Residues
143