2.7.4 Acidogenesis
Among all the biochemical reactions in the biogas production, acidogenesis usually
is the fastest reaction. Acidogenic microorganisms which are involved are Streptococcus, Lactobacillus, Bacillus, Escherichia coli and Salmonella which decompose
fatty acids, sugars and amino acids. The fast reaction rate is due to the high growth
rate of the acidogenic bacteria and another important characteristic is that they can
tolerate low pH up to 5. End products of acidogenesis are alcohols, carbon dioxide,
hydrogen, ammonia, and organic acid such as propionic acid, butyric and acetic acid.
Organic acid produced from sugars leads to decrease in pH which is favourable for
the growth of acidogenic and acetogenic bacteria. Amino acids also serve as energy
source for the growth of the facultative fermentative bacteria. Concentrations of
butyric and acetic acid are important in the acidogenesis stage as they are the
precursors of the methane formation.
Fig. 2.8 ABE fermentation pathway by Clostridia (Adapted from Open Source Ecology)
2 Application of Microorganisms for Biofuel Production
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