Next phase is the solventogenesis which starts with the completion of the log
phase or the exponential phase of growth of microorganisms and also the acidproducing pathways (acidogenesis) get converted to solvent producing pathways
(solventogenesis).
Important factors which effect the solventogenesis are pH drop, acid products,
temperature, oxygen and nutrient limitation as this is the end of exponential phase.
During the initiation of solventogenesis, acetyl Co-A and butyryl Co-A are
converted to ethanol and butanol by respective dehydrogenases (Amiri and Karimi
2019).
The main limitation of Clostridia sp. during the ABE fermentation and butanol
production is that the growth is repressed by increase in the concentration of butanol
produced during the fermentation.
The second phase of fermentation process is limited by a number of factors such
as inhibition of substrate, toxicity of butanol, slow growth of the microorganisms
and all these factors leading to lower cell density in the medium.
There are certain challenges with respect to the butanol production by Clostridia
sp. which needs to be worked upon which are low yield, cost of substrate, low
productivity of butanol because of inhibition and energy-intensive process for
recovery (Pratto et al. 2020; Cao et al. 2016; da Conceição Gomes et al. 2019;
Bardhan et al. 2019; Tsai et al. 2020).
2.8.9 Applications
Biobutanol is used in the production of fuels for spark ignition engines (internal
combustion engines) along with the gasoline as it is miscible with gasoline. It is
generally used directly as fuel in automobile engines. It is a non-toxic, non-corrosive
and biodegradable fuel which do not pose any environmental impact. The primary
use of biobutanol as fuel is in the spark ignition engines (internal combustion
engines) because of the fact that biobutaol has higher energy that bioethanol because
of the higher number of carbon atoms in butanol which gives higher energy, high
polarity and high combustion values. It is non-hygroscopic in nature which makes it
as safe to store product. Apart from this it can also be used as industrial solvent and
chemical feedstock. Other applications include pharmaceuticals, resins, herbicides,
paints and coatings (Dharmaraja et al. 2020; Patakova et al. 2011; Sindhu et al. 2019;
Tigunova et al. 2020; Verardi et al. 2020).
2.9 Syngas Fermentation
Syngas is mainly composed of carbon dioxide, hydrogen and carbon monoxide. It
can be majorly produced by two ways which are Fischer-Tropsch (FT) synthesis
using metal catalysts and microbiological fermentation. The feedstock which are
preferred are lignocellulosic feedstock, agriculture residue and agriculture
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N. Jaiswal et al.
phase or the exponential phase of growth of microorganisms and also the acidproducing pathways (acidogenesis) get converted to solvent producing pathways
(solventogenesis).
Important factors which effect the solventogenesis are pH drop, acid products,
temperature, oxygen and nutrient limitation as this is the end of exponential phase.
During the initiation of solventogenesis, acetyl Co-A and butyryl Co-A are
converted to ethanol and butanol by respective dehydrogenases (Amiri and Karimi
2019).
The main limitation of Clostridia sp. during the ABE fermentation and butanol
production is that the growth is repressed by increase in the concentration of butanol
produced during the fermentation.
The second phase of fermentation process is limited by a number of factors such
as inhibition of substrate, toxicity of butanol, slow growth of the microorganisms
and all these factors leading to lower cell density in the medium.
There are certain challenges with respect to the butanol production by Clostridia
sp. which needs to be worked upon which are low yield, cost of substrate, low
productivity of butanol because of inhibition and energy-intensive process for
recovery (Pratto et al. 2020; Cao et al. 2016; da Conceição Gomes et al. 2019;
Bardhan et al. 2019; Tsai et al. 2020).
2.8.9 Applications
Biobutanol is used in the production of fuels for spark ignition engines (internal
combustion engines) along with the gasoline as it is miscible with gasoline. It is
generally used directly as fuel in automobile engines. It is a non-toxic, non-corrosive
and biodegradable fuel which do not pose any environmental impact. The primary
use of biobutanol as fuel is in the spark ignition engines (internal combustion
engines) because of the fact that biobutaol has higher energy that bioethanol because
of the higher number of carbon atoms in butanol which gives higher energy, high
polarity and high combustion values. It is non-hygroscopic in nature which makes it
as safe to store product. Apart from this it can also be used as industrial solvent and
chemical feedstock. Other applications include pharmaceuticals, resins, herbicides,
paints and coatings (Dharmaraja et al. 2020; Patakova et al. 2011; Sindhu et al. 2019;
Tigunova et al. 2020; Verardi et al. 2020).
2.9 Syngas Fermentation
Syngas is mainly composed of carbon dioxide, hydrogen and carbon monoxide. It
can be majorly produced by two ways which are Fischer-Tropsch (FT) synthesis
using metal catalysts and microbiological fermentation. The feedstock which are
preferred are lignocellulosic feedstock, agriculture residue and agriculture
64
N. Jaiswal et al.