312
P. Prabakaran et al.
fermenter. However, the disadvantages of enzymatic pre-treatment are the enzymatic rate is rather too slow for commercial application (10–14 days) (Agbor et al.
2011) and high enzymes specificity towards different microalgae species (Yuan et al.
2016). The current commercial enzymes are cellulase and amylase, which are used
to hydrolyze cellulose and starch, respectively (Yuan et al. 2016).
Kim et al. (2014) used cellulase and pectinase to saccharify Chlorella vulgaris.
From the results obtained, Chlorella vulgaris cultivated under nitrogen stress condition were able to increase the carbohydrates content within their cells. By using
Aspergillus pectinase enzyme, 79% of carbohydrates were successfully extracted
from the saccharification process. The study also evaluated the activity of immobilized yeast fermentation and attained 89% of conversion. This can be concluded that
immobilized enzymes on support were able to enhance the bioethanol production
yield.
6 Fermentation Process
Free sugars extracted from microalgae biomass can be fermented into bioethanol
through some ethanologen microorganisms (bacteria, filamentous fungi, yeast).
There are two different types of fermentation process: (i) separate hydrolysis and
fermentation (SHF); and (ii) simultaneous saccharification and fermentation (SSF).
The comparison of both SHF and SSF is tabulated in Table 1.
Depending on the microalgae species and cultivation conditions, different hydrolysis and fermentation (SSF and SHF) approaches are introduced for bioethanol
production.
Table 1 Comparison of SHF and SSF process
Fermentation Benefit
Drawback
SHF
• Easier to optimize the hydrolysis and
fermentation operating conditions
• Simpler equipment design
• Shorter residence time
• Using cheaper chemicals
• Higher contamination rates
• Inhibitory effects
SSF
• Higher bioethanol yields
• Higher rates of hydrolysis
• Less inhibitory effects
• Lower operating cost
• Lower contamination rate
• Required less sterile conditions
• Smaller amount of enzyme intake
• Shorter residence time
• Only can performed optimal
operating conditions for either
hydrolysis or fermentation process
• Difficulty in process control
P. Prabakaran et al.
fermenter. However, the disadvantages of enzymatic pre-treatment are the enzymatic rate is rather too slow for commercial application (10–14 days) (Agbor et al.
2011) and high enzymes specificity towards different microalgae species (Yuan et al.
2016). The current commercial enzymes are cellulase and amylase, which are used
to hydrolyze cellulose and starch, respectively (Yuan et al. 2016).
Kim et al. (2014) used cellulase and pectinase to saccharify Chlorella vulgaris.
From the results obtained, Chlorella vulgaris cultivated under nitrogen stress condition were able to increase the carbohydrates content within their cells. By using
Aspergillus pectinase enzyme, 79% of carbohydrates were successfully extracted
from the saccharification process. The study also evaluated the activity of immobilized yeast fermentation and attained 89% of conversion. This can be concluded that
immobilized enzymes on support were able to enhance the bioethanol production
yield.
6 Fermentation Process
Free sugars extracted from microalgae biomass can be fermented into bioethanol
through some ethanologen microorganisms (bacteria, filamentous fungi, yeast).
There are two different types of fermentation process: (i) separate hydrolysis and
fermentation (SHF); and (ii) simultaneous saccharification and fermentation (SSF).
The comparison of both SHF and SSF is tabulated in Table 1.
Depending on the microalgae species and cultivation conditions, different hydrolysis and fermentation (SSF and SHF) approaches are introduced for bioethanol
production.
Table 1 Comparison of SHF and SSF process
Fermentation Benefit
Drawback
SHF
• Easier to optimize the hydrolysis and
fermentation operating conditions
• Simpler equipment design
• Shorter residence time
• Using cheaper chemicals
• Higher contamination rates
• Inhibitory effects
SSF
• Higher bioethanol yields
• Higher rates of hydrolysis
• Less inhibitory effects
• Lower operating cost
• Lower contamination rate
• Required less sterile conditions
• Smaller amount of enzyme intake
• Shorter residence time
• Only can performed optimal
operating conditions for either
hydrolysis or fermentation process
• Difficulty in process control