usually longer (>1 h). This conversion technique is aimed at producing high-energydensity solid fuels from the process of carbon concentration (Mathimani et al. 2018).
8.5.2 Biochemical Conversion
Anaerobic digestion, alcoholic fermentation, and inter-transesterification are the
three main biological processes for the production of biofuels from the microalgal
biomass. Since this conversion technique involves generation of other energy
sources along with various coproducts, it is technically more viable as compared
to the remaining conversion methods (Adeniyi et al. 2018). A renewable feedstock
for biofuel production is produced from this environmentally feasible process. These
biofuels serve as efficient sources of energy that can be utilized at the industrial scale
(Ehimen et al. 2013; Adeniyi et al. 2018).
8.5.2.1 Anaerobic Digestion (AD)
The process comprises of three consecutive steps (Adeniyi et al. 2018): the first step
is hydrolysis where soluble sugars are formed from the breakdown of complex
molecules, the second step is fermentation where these sugars are further converted
by the fermentative bacteria, and the third step is methanogenesis where the fermentation products are then acted upon by the methanogens, and they metabolize them to
provide methane and carbon dioxide as the principal products (Saratale et al. 2018).
Various advantages offered by the AD of microalgal cells for biofuel production
include great amounts of carbon that are fixed by this process owing to the efficient
nutrient extraction from the harvested biomass and followed by their subsequent
transfer back into the cultivation system (Hallenbeck et al. 2016; Adeniyi et al.
2018). Biogas, particularly carbon dioxide and methane, can be produced by the
decomposition of organic matter present in the biomass waste. This biogas can be
further utilized for domestic cooking or power generation (Lee and Lee 2016;
Adeniyi et al. 2018). Energy recovery from sunlight is encouraged by this process
and is achieved through photosynthesis, further leading to the integration of efficiency into the biofuel production process (Adeniyi et al. 2018).
8.5.2.2 Alcoholic Fermentation
This biochemical process relies on the production of alcohol from an organic solvent
through various enzymes (Suganya et al. 2016; Adeniyi et al. 2018). This metabolic
reaction basically results in the formation of bioethanol from starch/alginate/cellular
sugar/laminarin/mannitol stored in the microalgal cells employing the activities of
yeast (Lee and Lee 2016). Acetone and butanol can also be produced from this
process by utilizing acidogenesis and solventogenesis (Trivedi et al. 2015; Adeniyi
et al. 2018). However, this conversion technique is associated with a drawback that
pretreatment processes, such as milling, saccharification, and liquefaction, are
required to achieve an efficient fermentation of the algal biomass (Lee and Lee
2012; Adeniyi et al. 2018). Chlorella vulgaris is effectively used for alcoholic
fermentation and thus ethanol production. The high concentration of starch found
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
221
8.5.2 Biochemical Conversion
Anaerobic digestion, alcoholic fermentation, and inter-transesterification are the
three main biological processes for the production of biofuels from the microalgal
biomass. Since this conversion technique involves generation of other energy
sources along with various coproducts, it is technically more viable as compared
to the remaining conversion methods (Adeniyi et al. 2018). A renewable feedstock
for biofuel production is produced from this environmentally feasible process. These
biofuels serve as efficient sources of energy that can be utilized at the industrial scale
(Ehimen et al. 2013; Adeniyi et al. 2018).
8.5.2.1 Anaerobic Digestion (AD)
The process comprises of three consecutive steps (Adeniyi et al. 2018): the first step
is hydrolysis where soluble sugars are formed from the breakdown of complex
molecules, the second step is fermentation where these sugars are further converted
by the fermentative bacteria, and the third step is methanogenesis where the fermentation products are then acted upon by the methanogens, and they metabolize them to
provide methane and carbon dioxide as the principal products (Saratale et al. 2018).
Various advantages offered by the AD of microalgal cells for biofuel production
include great amounts of carbon that are fixed by this process owing to the efficient
nutrient extraction from the harvested biomass and followed by their subsequent
transfer back into the cultivation system (Hallenbeck et al. 2016; Adeniyi et al.
2018). Biogas, particularly carbon dioxide and methane, can be produced by the
decomposition of organic matter present in the biomass waste. This biogas can be
further utilized for domestic cooking or power generation (Lee and Lee 2016;
Adeniyi et al. 2018). Energy recovery from sunlight is encouraged by this process
and is achieved through photosynthesis, further leading to the integration of efficiency into the biofuel production process (Adeniyi et al. 2018).
8.5.2.2 Alcoholic Fermentation
This biochemical process relies on the production of alcohol from an organic solvent
through various enzymes (Suganya et al. 2016; Adeniyi et al. 2018). This metabolic
reaction basically results in the formation of bioethanol from starch/alginate/cellular
sugar/laminarin/mannitol stored in the microalgal cells employing the activities of
yeast (Lee and Lee 2016). Acetone and butanol can also be produced from this
process by utilizing acidogenesis and solventogenesis (Trivedi et al. 2015; Adeniyi
et al. 2018). However, this conversion technique is associated with a drawback that
pretreatment processes, such as milling, saccharification, and liquefaction, are
required to achieve an efficient fermentation of the algal biomass (Lee and Lee
2012; Adeniyi et al. 2018). Chlorella vulgaris is effectively used for alcoholic
fermentation and thus ethanol production. The high concentration of starch found
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
221