The oil for biodiesel production can be extracted from various feedstocks which
are widely available. The first-generation biodiesel is obtained from various edible
seed oils, like rapeseed, soybean, palm and sunflower which are used commonly;
however, peanut, linseed, safflower, etc. and animal fats can also be used for
extraction. Because of the increasing cost, non-edible vegetable oils and other
economically important plants with the advantage of rapid growth and high seed
productivity are used such as tung, cotton, castor oil, jojoba and jatropha. This is the
second-generation biofuel produced from herbs, woody plants, waste cooking
oils, etc.
The production cost of biodiesel is high because of raw materials that are used for
its production. Apart from this, the catalyst needed during the trans-esterification
reaction also contributes to its increased cost. In order to achieve high efficiency and
lower down the cost, homogeneous catalysts, for example, sodium hydroxide,
sulphuric acid, etc. are commonly used for commercial production of biodiesel but
their recovery and reuse is very difficult and costly too. This can be overcome by the
use of heterogeneous catalyst, but with a disadvantage of difficulty in preparation,
and unstable activity (Atabani et al. 2012).
2.4.1 Microbial Production of Biodiesel
Currently, the use of microorganisms (e.g. microalgae, bacteria, fungi and yeast) is
considered a promising alternative for the biodiesel production because they are able
to accumulate huge amounts of lipids with increased yield and they also use a
smaller proportion of arable land. Among various microorganisms’ storing oils,
only those microorganisms are available for biodiesel production which are oleaginous, i.e. those that can accumulate lipids named single cell oil (SCO) to up to 20%
or above of their total cellular dry weight. Thus, the oils extracted from fast stable
growing microbes are then trans-esterified through simple-chain alcohols, and producing a value quality biodiesel. Various factors determine the yield (oil content)
and composition including types of organism, selection of substrate, culture condition (such as nitrogen, pH, agitation rate, temperature and length of incubation, etc.).
Also, the amount of lipid accumulation in microorganism is regulated by their
genetic composition, as the accumulation of lipid can differ extensively among
species and individual strains (Akinsemolu 2018; Huang et al. 2010; Pandey et al.
2019).
2.4.1.1 Microalgae
Microalgae, prokaryotic or eukaryotic photosynthesizing microorganisms, characterized by rapid growth, are potentially the most favourable crude material to supply
a high percentage of lipids. Microalgae could be grown in photobioreactors and can
be harvested within days of cultivation, thereby leading to the efficient production of
40
N. Jaiswal et al.
are widely available. The first-generation biodiesel is obtained from various edible
seed oils, like rapeseed, soybean, palm and sunflower which are used commonly;
however, peanut, linseed, safflower, etc. and animal fats can also be used for
extraction. Because of the increasing cost, non-edible vegetable oils and other
economically important plants with the advantage of rapid growth and high seed
productivity are used such as tung, cotton, castor oil, jojoba and jatropha. This is the
second-generation biofuel produced from herbs, woody plants, waste cooking
oils, etc.
The production cost of biodiesel is high because of raw materials that are used for
its production. Apart from this, the catalyst needed during the trans-esterification
reaction also contributes to its increased cost. In order to achieve high efficiency and
lower down the cost, homogeneous catalysts, for example, sodium hydroxide,
sulphuric acid, etc. are commonly used for commercial production of biodiesel but
their recovery and reuse is very difficult and costly too. This can be overcome by the
use of heterogeneous catalyst, but with a disadvantage of difficulty in preparation,
and unstable activity (Atabani et al. 2012).
2.4.1 Microbial Production of Biodiesel
Currently, the use of microorganisms (e.g. microalgae, bacteria, fungi and yeast) is
considered a promising alternative for the biodiesel production because they are able
to accumulate huge amounts of lipids with increased yield and they also use a
smaller proportion of arable land. Among various microorganisms’ storing oils,
only those microorganisms are available for biodiesel production which are oleaginous, i.e. those that can accumulate lipids named single cell oil (SCO) to up to 20%
or above of their total cellular dry weight. Thus, the oils extracted from fast stable
growing microbes are then trans-esterified through simple-chain alcohols, and producing a value quality biodiesel. Various factors determine the yield (oil content)
and composition including types of organism, selection of substrate, culture condition (such as nitrogen, pH, agitation rate, temperature and length of incubation, etc.).
Also, the amount of lipid accumulation in microorganism is regulated by their
genetic composition, as the accumulation of lipid can differ extensively among
species and individual strains (Akinsemolu 2018; Huang et al. 2010; Pandey et al.
2019).
2.4.1.1 Microalgae
Microalgae, prokaryotic or eukaryotic photosynthesizing microorganisms, characterized by rapid growth, are potentially the most favourable crude material to supply
a high percentage of lipids. Microalgae could be grown in photobioreactors and can
be harvested within days of cultivation, thereby leading to the efficient production of
40
N. Jaiswal et al.