2.1 Introduction
Biofuel research is aimed to the production of eco-friendly and cost-effective fuels
which have the ability to replace the need of fossil fuels (Jang et al. 2012; Hjersted
and Henson 2009; Sharma et al. 2020). Nowadays, conventional fuels such as
petroleum products like petrol, diesel, kerosene, and LPG are the major energy
sources. The limited sources of fossil fuels are available on the Earth, and these
sources may be finished in the future. Therefore, the alternative of these fossil fuels is
an urgent requirement for the energy sector (Singh et al. 2020a). Few demerits of the
fossil fuels are also reported; these fuels generate a large number of toxic agents
which increase the environmental pollution load (Clomburg and Gonzalez 2010;
Vanholme et al. 2010). Carbon monoxide (CO), sulfur dioxide, nitrogen dioxide
(NO 2 ), nitric oxide (N 2 O), carbon dioxide (CO 2 ), and hydrocarbons are produced
during the consumption of fossil fuels. These gases are responsible for air pollution
as well as greenhouse effect. Greenhouse gases play an important role in maintaining
the Earth temperature and provide favorable environment to the living organisms.
The level of these gases at above the certain limit causes the increased temperature of
Earth known as global warming. Global warming affects the distribution of biodiversity and is also responsible for some other dangerous changes like the increased
sea level and melting of glaciers (Singh et al. 2020a; Schmidt et al. 2010). Hence,
developing an alternative option of fossil fuels is extremely important for the
continuation of fulfilling the need of energy source in the future.
Biofuels are considered as suitable energy sources and may take the place of
conventional fuels in the future. They are energy-enriched energy sources derived
from eco-friendly green sources such as dead biomaterials of plants, bacteria, and
microalgae (Allakhverdiev et al. 2009; Razzak et al. 2013; Voloshin et al. 2015;
Dragone et al. 2010). They can be classified into several generations such as first,
second, third, and fourth generations (Singh et al. 2020b). First-generation biofuels
are derived from starch-rich biomass like wheat, corn, potato, and sugarcane.
Mustard, soybean, and fats are considered as good sources for biodiesel production
(Aro 2016). Second-generation biofuels like bioethanol and biomethanol are produced from several plant species such as jatropha, miscanthus, as well as wood
(Hirani et al. 2018). Third-generation fuels are derived from several species of
microbes and microalgae (Gajraj et al. 2018). The fourth-generation category of
fuels is considered as the advanced type of biofuels. In this generation, biofuels are
produced from the genetically modified organism. Biofuels from this category are
derived from microalgae and microbes same as the third-generation biofuels
(Abdullah et al. 2019). Fourth-generation biofuels is the more developing field for
research as well as biofuel industries, and requirement of more study in this area
(Anemaet et al. 2010).
Various production methods are used in biofuel production. Biomasses need to
convert simple biomaterials using various biomass conversion processes. There are
several microorganisms that produce enzymes which have an important role in the
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V. Singh et al.
Biofuel research is aimed to the production of eco-friendly and cost-effective fuels
which have the ability to replace the need of fossil fuels (Jang et al. 2012; Hjersted
and Henson 2009; Sharma et al. 2020). Nowadays, conventional fuels such as
petroleum products like petrol, diesel, kerosene, and LPG are the major energy
sources. The limited sources of fossil fuels are available on the Earth, and these
sources may be finished in the future. Therefore, the alternative of these fossil fuels is
an urgent requirement for the energy sector (Singh et al. 2020a). Few demerits of the
fossil fuels are also reported; these fuels generate a large number of toxic agents
which increase the environmental pollution load (Clomburg and Gonzalez 2010;
Vanholme et al. 2010). Carbon monoxide (CO), sulfur dioxide, nitrogen dioxide
(NO 2 ), nitric oxide (N 2 O), carbon dioxide (CO 2 ), and hydrocarbons are produced
during the consumption of fossil fuels. These gases are responsible for air pollution
as well as greenhouse effect. Greenhouse gases play an important role in maintaining
the Earth temperature and provide favorable environment to the living organisms.
The level of these gases at above the certain limit causes the increased temperature of
Earth known as global warming. Global warming affects the distribution of biodiversity and is also responsible for some other dangerous changes like the increased
sea level and melting of glaciers (Singh et al. 2020a; Schmidt et al. 2010). Hence,
developing an alternative option of fossil fuels is extremely important for the
continuation of fulfilling the need of energy source in the future.
Biofuels are considered as suitable energy sources and may take the place of
conventional fuels in the future. They are energy-enriched energy sources derived
from eco-friendly green sources such as dead biomaterials of plants, bacteria, and
microalgae (Allakhverdiev et al. 2009; Razzak et al. 2013; Voloshin et al. 2015;
Dragone et al. 2010). They can be classified into several generations such as first,
second, third, and fourth generations (Singh et al. 2020b). First-generation biofuels
are derived from starch-rich biomass like wheat, corn, potato, and sugarcane.
Mustard, soybean, and fats are considered as good sources for biodiesel production
(Aro 2016). Second-generation biofuels like bioethanol and biomethanol are produced from several plant species such as jatropha, miscanthus, as well as wood
(Hirani et al. 2018). Third-generation fuels are derived from several species of
microbes and microalgae (Gajraj et al. 2018). The fourth-generation category of
fuels is considered as the advanced type of biofuels. In this generation, biofuels are
produced from the genetically modified organism. Biofuels from this category are
derived from microalgae and microbes same as the third-generation biofuels
(Abdullah et al. 2019). Fourth-generation biofuels is the more developing field for
research as well as biofuel industries, and requirement of more study in this area
(Anemaet et al. 2010).
Various production methods are used in biofuel production. Biomasses need to
convert simple biomaterials using various biomass conversion processes. There are
several microorganisms that produce enzymes which have an important role in the
30
V. Singh et al.