Ecofriendly Approach for Bioethanol Production …
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6.1 Separate Hydrolysis and Fermentation (SHF)
During SHF, both of the enzymatic hydrolysis pre-treated biomass and fermentation
process take place in two different units of reactors. Hence, optimizations of operating
conditions for each stage are able to be performed. However, the inhibitory effect
from the accumulation of hydrolysis products (especially glucose and cellobiose),
will suppress the activity of cellolases and resulted to slower hydrolysis rate (Balat
et al. 2008).
6.2 Simultaneous Saccharification and Fermentation (SSF)
In SSF, enzymatic hydrolysis and fermentation take place in a single reactor. Therefore, the hydrolysis products (glucose and cellobiose) is consumed by the yeast in
fermentation process, which could greatly reduce the inhibitory effects (El-Dalatony
et al. 2016). In addition, higher concentration of bioethanol resulted to lower degree
of contamination, due to the lower solids contents yields (>15% dry weight basis)
(Harun et al. 2011). After all, since both of the enzymatic hydrolysis and fermentation are operated under the same conditions, it would be difficult to attain an optimal
temperature for SSF operation.
7 Microorganism for Fermentation of Microalgae Biomass
The performance features of fermentation process include: temperature, pH, microorganism growth rate, bioethanol productivity and yield, alcohol tolerance, osmotic
tolerance, inhibitor tolerance, and genetic stability (Balat et al. 2008). It is well known
that Saccharomyces cerevisiae is the most efficient yeast in fermentative bioethanol.
It has shown a good alcohol and inhibitor tolerances associated with high bioethanol
productivity Saccharomyces cerevisiae was utilized to produce bioethanol via SHF
and SSF processes (El-Dalatony et al. 2016). The yeast was able to maximize the
sugars consumption efficiency (91–98%) and achieving 0.5 g/g or an equivalent of
88.2% (theoretical) of bioethanol yield from SSF. However, energy recovery was
higher in SHF mode (85.96%) than SSF (70%).
Other than that, others microorganism such as bacteria are also used in microalgae
biomass fermentation process. These bacteria include Bacillus stearothermophilus,
Clostridium thermohydrosulfuricum, Clostridium thermocellum, Escherichia coli,
Klebsiella oxytoca, Thermoanaerobacterium thermosaccharolyticum, Thermoanaerobacter ethnolicus, and Zymomonas mobilis (Simas-Rodrigues et al. 2015). Recently,
Z. mobilis was reported to be an efficient bacterium in sugars fermentation, in which
the sugars (e.g. glucose and fructose) uptake rate was increased, high tolerance to
ethanol content (~11% v/v) and able to withstand high osmotic pressure caused by
313
6.1 Separate Hydrolysis and Fermentation (SHF)
During SHF, both of the enzymatic hydrolysis pre-treated biomass and fermentation
process take place in two different units of reactors. Hence, optimizations of operating
conditions for each stage are able to be performed. However, the inhibitory effect
from the accumulation of hydrolysis products (especially glucose and cellobiose),
will suppress the activity of cellolases and resulted to slower hydrolysis rate (Balat
et al. 2008).
6.2 Simultaneous Saccharification and Fermentation (SSF)
In SSF, enzymatic hydrolysis and fermentation take place in a single reactor. Therefore, the hydrolysis products (glucose and cellobiose) is consumed by the yeast in
fermentation process, which could greatly reduce the inhibitory effects (El-Dalatony
et al. 2016). In addition, higher concentration of bioethanol resulted to lower degree
of contamination, due to the lower solids contents yields (>15% dry weight basis)
(Harun et al. 2011). After all, since both of the enzymatic hydrolysis and fermentation are operated under the same conditions, it would be difficult to attain an optimal
temperature for SSF operation.
7 Microorganism for Fermentation of Microalgae Biomass
The performance features of fermentation process include: temperature, pH, microorganism growth rate, bioethanol productivity and yield, alcohol tolerance, osmotic
tolerance, inhibitor tolerance, and genetic stability (Balat et al. 2008). It is well known
that Saccharomyces cerevisiae is the most efficient yeast in fermentative bioethanol.
It has shown a good alcohol and inhibitor tolerances associated with high bioethanol
productivity Saccharomyces cerevisiae was utilized to produce bioethanol via SHF
and SSF processes (El-Dalatony et al. 2016). The yeast was able to maximize the
sugars consumption efficiency (91–98%) and achieving 0.5 g/g or an equivalent of
88.2% (theoretical) of bioethanol yield from SSF. However, energy recovery was
higher in SHF mode (85.96%) than SSF (70%).
Other than that, others microorganism such as bacteria are also used in microalgae
biomass fermentation process. These bacteria include Bacillus stearothermophilus,
Clostridium thermohydrosulfuricum, Clostridium thermocellum, Escherichia coli,
Klebsiella oxytoca, Thermoanaerobacterium thermosaccharolyticum, Thermoanaerobacter ethnolicus, and Zymomonas mobilis (Simas-Rodrigues et al. 2015). Recently,
Z. mobilis was reported to be an efficient bacterium in sugars fermentation, in which
the sugars (e.g. glucose and fructose) uptake rate was increased, high tolerance to
ethanol content (~11% v/v) and able to withstand high osmotic pressure caused by