2.2.1 First-Generation Biofuel
Bioethanol is derived from the fermentation of carbohydrates such as starch obtained
from wheat, barley, corn, rice grain, potato, or disaccharide sugar, acquired from the
sugarcane industry. Biobutanol is the second most valuable product; it can be
produced by the same process as bioethanol but with different fermenting microbes
(Kriger et al. 2020; Lee et al. 2015). Biodiesel is also a well-known first-generation
biofuel. It can be obtained from various crops such as soybean, coconut, palm,
sunflower, recycled used cooking oils, fat obtained from animals, etc. (Bhatia and
Johri 2015). The Brazil government has made the addition of 2% biodiesel to
conventional diesel compulsory in 2008; later, this increased up to 5% in 2013. To
meet this increasing demand of biodiesel, production capacity has been increased.
Agricultural crops cultivated for biomass production need arable agricultural land.
Crops cultivated for biofuel production vary based on the climatic condition of
different geographical areas. Excessive commercial production of first-generation
biofuels through agricultural crops results in low availability of fertile lands being
used to cultivate food and fodders for human and animals (Singh et al. 2018). Hence,
this category of biofuel is based on economically and environmentally safe. All these
issues compelled bio-scientists to focus on second-generation biofuels.
2.2.2 Second-Generation Biofuel
The biofuels that exist in this category are mostly produced from non-food crops like
jatropha, cassava, or miscanthus (Robak and Balcerek 2018). Second-generation
biofuels are produced through several chemical, physical, and biological biomass
conversion processes of lignocellulosic materials from agricultural non-edible crops
or their residues (Nigam and Singh 2014). Fuels produced biochemically are called
biochemical fuels, such as ethanol and biobutanol. Besides these both fuels, other
second-generation fuels are produced from thermochemical method and are known
as thermochemical energy source. Some examples are methanol, ethanol, and ether.
The Fischer-Tropsch liquid is also produced in the thermochemical reaction which is
synthesized from the catalytic reaction of CO and H 2 ; thus, it can be produced from
any biomass that can be made to produce CO and H 2 (Buaban et al. 2010).
Unrefined oils produced thermochemically require extra processing to make them
useful for engines (Larson 2008). There are high interests to produce such fuels
which have high cetane number and very little or no sulfur or aromatic compounds.
It can reduce vehicular exhaust pollution. The entire use of above-ground biomass
and cheaper feeding material and judicious use of non-edible crops boost scientists
to look forward in the research and production of second-generation biofuel. But the
commercial production of second-generation biofuels is not profitable because it
requires expensive and sophisticated technologies (Alam et al. 2015). Researchers
2 Microbiological Aspects of Bioenergy Production: Recent Update and Future. . .
33
Bioethanol is derived from the fermentation of carbohydrates such as starch obtained
from wheat, barley, corn, rice grain, potato, or disaccharide sugar, acquired from the
sugarcane industry. Biobutanol is the second most valuable product; it can be
produced by the same process as bioethanol but with different fermenting microbes
(Kriger et al. 2020; Lee et al. 2015). Biodiesel is also a well-known first-generation
biofuel. It can be obtained from various crops such as soybean, coconut, palm,
sunflower, recycled used cooking oils, fat obtained from animals, etc. (Bhatia and
Johri 2015). The Brazil government has made the addition of 2% biodiesel to
conventional diesel compulsory in 2008; later, this increased up to 5% in 2013. To
meet this increasing demand of biodiesel, production capacity has been increased.
Agricultural crops cultivated for biomass production need arable agricultural land.
Crops cultivated for biofuel production vary based on the climatic condition of
different geographical areas. Excessive commercial production of first-generation
biofuels through agricultural crops results in low availability of fertile lands being
used to cultivate food and fodders for human and animals (Singh et al. 2018). Hence,
this category of biofuel is based on economically and environmentally safe. All these
issues compelled bio-scientists to focus on second-generation biofuels.
2.2.2 Second-Generation Biofuel
The biofuels that exist in this category are mostly produced from non-food crops like
jatropha, cassava, or miscanthus (Robak and Balcerek 2018). Second-generation
biofuels are produced through several chemical, physical, and biological biomass
conversion processes of lignocellulosic materials from agricultural non-edible crops
or their residues (Nigam and Singh 2014). Fuels produced biochemically are called
biochemical fuels, such as ethanol and biobutanol. Besides these both fuels, other
second-generation fuels are produced from thermochemical method and are known
as thermochemical energy source. Some examples are methanol, ethanol, and ether.
The Fischer-Tropsch liquid is also produced in the thermochemical reaction which is
synthesized from the catalytic reaction of CO and H 2 ; thus, it can be produced from
any biomass that can be made to produce CO and H 2 (Buaban et al. 2010).
Unrefined oils produced thermochemically require extra processing to make them
useful for engines (Larson 2008). There are high interests to produce such fuels
which have high cetane number and very little or no sulfur or aromatic compounds.
It can reduce vehicular exhaust pollution. The entire use of above-ground biomass
and cheaper feeding material and judicious use of non-edible crops boost scientists
to look forward in the research and production of second-generation biofuel. But the
commercial production of second-generation biofuels is not profitable because it
requires expensive and sophisticated technologies (Alam et al. 2015). Researchers
2 Microbiological Aspects of Bioenergy Production: Recent Update and Future. . .
33