2.7.5 Acetogenesis
Acetogenic bacteria are strict anaerobes with an optimum pH of 6. These are slowgrowing bacteria and sensitive to changes in organic load. Acetogenesis is referred
as degradation of lactate, ethanol, propionate, butyrate and higher volatile acids by
obligate hydrogen-producing acetogenic bacteria as these cannot be hydrolysed by
methanogens. Acetogenic bacteria are generally Syntrophomonas wolfeii and
Syntrophobacter wolinii. This step is very important with respect to the production
of biogas. Acetogens make syntrophic association with the methanogens as they
require partial hydrogen pressure for their degradation.
2.7.6 Methanogenesis
In methanogenesis, the methane is produced by two different types of methanogens,
both of which produce methane from different substrates. One group is acetoclastic
methanogens which convert acetic acid to methane. Other groups are hydrogen
utilizing methanogens which convert hydrogen and carbon dioxide to methane.
Methanogenic organisms belong to Archaea. The hydrogenotropic methanogenesis
is the most common metabolic pathway. The hydrogen utliizing methanogens such
as Methannospirillum hungatei, Methanoculles receptaculi are fast growing than the
acetoclastic methanogens, e.g. Methanosarcina thermophile that is the reason hydrogen utilizing methanogens are more common (Merlin Christy et al. 2014; Guo et al.
2015; Bhatia et al. 2017; Srivastava 2020).
The key features of the biogas produced by anaerobic digestion are it does not
deplete fossil fuels, does not contribute to greenhouse emissions, and uses low cost
digesters.
Biogas is composed mainly of methane, carbon dioxide along with small quantities of hydrogen sulphide, carbon monoxide and water vapour. Removal of water
vapour and hydrogen sulphide is important before its use. Biogas finds applications
in heating, fuel cell, dual engines and power systems (Weiland 2010; Klocke et al.
2008; Caruso et al. 2019; Tsavkelova and Netrusov 2012).
2.8 Microbial Production of Butanol
Biomass-derived alcohols such as biobutanol are next most sustainable alternative to
internal combustion engines as it has similar energy density of 30 MJ/L and same
octane number (97–103) as gasoline (energy density of 33 MJ/L, octane number as
90–105). Butanol has four carbon alcohol with the molecular formula
C 4 H 10 O. Biobutanol has been considered as high heating value fuel because of
long chain. Butanol has following benefits over other fuels; energy density is
60
N. Jaiswal et al.
Acetogenic bacteria are strict anaerobes with an optimum pH of 6. These are slowgrowing bacteria and sensitive to changes in organic load. Acetogenesis is referred
as degradation of lactate, ethanol, propionate, butyrate and higher volatile acids by
obligate hydrogen-producing acetogenic bacteria as these cannot be hydrolysed by
methanogens. Acetogenic bacteria are generally Syntrophomonas wolfeii and
Syntrophobacter wolinii. This step is very important with respect to the production
of biogas. Acetogens make syntrophic association with the methanogens as they
require partial hydrogen pressure for their degradation.
2.7.6 Methanogenesis
In methanogenesis, the methane is produced by two different types of methanogens,
both of which produce methane from different substrates. One group is acetoclastic
methanogens which convert acetic acid to methane. Other groups are hydrogen
utilizing methanogens which convert hydrogen and carbon dioxide to methane.
Methanogenic organisms belong to Archaea. The hydrogenotropic methanogenesis
is the most common metabolic pathway. The hydrogen utliizing methanogens such
as Methannospirillum hungatei, Methanoculles receptaculi are fast growing than the
acetoclastic methanogens, e.g. Methanosarcina thermophile that is the reason hydrogen utilizing methanogens are more common (Merlin Christy et al. 2014; Guo et al.
2015; Bhatia et al. 2017; Srivastava 2020).
The key features of the biogas produced by anaerobic digestion are it does not
deplete fossil fuels, does not contribute to greenhouse emissions, and uses low cost
digesters.
Biogas is composed mainly of methane, carbon dioxide along with small quantities of hydrogen sulphide, carbon monoxide and water vapour. Removal of water
vapour and hydrogen sulphide is important before its use. Biogas finds applications
in heating, fuel cell, dual engines and power systems (Weiland 2010; Klocke et al.
2008; Caruso et al. 2019; Tsavkelova and Netrusov 2012).
2.8 Microbial Production of Butanol
Biomass-derived alcohols such as biobutanol are next most sustainable alternative to
internal combustion engines as it has similar energy density of 30 MJ/L and same
octane number (97–103) as gasoline (energy density of 33 MJ/L, octane number as
90–105). Butanol has four carbon alcohol with the molecular formula
C 4 H 10 O. Biobutanol has been considered as high heating value fuel because of
long chain. Butanol has following benefits over other fuels; energy density is
60
N. Jaiswal et al.