converted from triglycerides by the transesterification reaction. During the reaction,
oil or fat (containing triglycerides) undergoes a nucleophilic attack by an incoming
alcohol (methanol or ethanol) to give a tetrahedral intermediate, which proceeds to
the transesterified product (biodiesel) and a coproduct (glycerol). The catalyst of
base or acid is typically used to improve formation of biodiesel, but an alkali catalyst
as NaOH is effective to promote biodiesel as well as ultrasonic pretreatment for
biodiesel can completely eliminate the need for chemical catalysts (Warabi et al.
2004). Theoretically, FAME/biodiesel ratio is 1:1 for diesel production; but in
reality, 1 g of FAME results in 0.84 g of biodiesel production (El-Shimi et al.
2013). The quality of biodiesel is considerably affected by the composition of
FAMEs; thus the composition is an important factor for selecting the most adequate
algal species for biofuel production. For most biodiesel industries using algae, the
goal is to improve a specific FAMEs as oleic acid (C18:1:ω9) for high-quality
biodiesel due to oleic acid reasonable balance of fuel properties, including ignition
quality, combustion heat, cold filter plugging point, oxidative stability, viscosity,
and lubricity (Or-Rashid et al. 2008). To improve production of high-quality FAME,
it is important to understand the lipid biosynthesis pathway and its regulators;
however, these pathways have not yet been fully elucidated (Bellou et al. 2014).
One apparent advantage of algae cultivation from wastewater is the potential for high
lipid production compared to freshwater, because wastewater has enough media with
organic carbon and nutrient. Nutritional and environmental factors, CO 2 /light intensity, pH, and specific stress conditions are potential cultivation parameters that affect
FAME quality in microalgae (Ji et al. 2014). For example, a specific stress condition
of N depletion or high salinity during algae cultivation produced large amounts of
unsaturated fatty acids (Bartley et al. 2013; Sharma et al. 2012). Although their
mechanism is not much more to be discovered, current literature supports N and
salinity stress as a lipid-improving and effective high-quality biodiesel production
strategy.
3.3.2 Bio-alcohol (Ethanol and Butanol) Production from Microalgae
Microalgae are considered to be a biofuel (i.e., ethanol) feedstock that is exceedingly
rich in carbohydrates, which can be converted to ethanol by fermentation (Adams
et al. 2009). Based on the different species of microalgae, a maximum 32%,
30–40%, and 50% of bioethanol have been achieved in the treatment of sonication
of Scenedesmus obliquus (Choi et al. 2011), acid hydrolysis of Gelidium amansii
(Kim et al. 2015), and combined pretreatment (sonication and enzymatic hydrolysis)
of Chlamydomonas mexicana (Eldalatony et al. 2016), respectively. In separate
hydrolysis and fermentation (SHF), enzymatic hydrolysis and fermentation are
carried out in two separate steps of hydrolysis and fermentation, which lead to
high bioethanol yield comparing to simultaneous saccharification and fermentation
(SSF) due to the possibility of cell recycling in end product (Roca and Olsson 2003).
In addition, more economic and effective SHF processes should also be developed to
12 Microalgae: An Eco-friendly Tool for the Treatment of Wastewaters for. . .
291
oil or fat (containing triglycerides) undergoes a nucleophilic attack by an incoming
alcohol (methanol or ethanol) to give a tetrahedral intermediate, which proceeds to
the transesterified product (biodiesel) and a coproduct (glycerol). The catalyst of
base or acid is typically used to improve formation of biodiesel, but an alkali catalyst
as NaOH is effective to promote biodiesel as well as ultrasonic pretreatment for
biodiesel can completely eliminate the need for chemical catalysts (Warabi et al.
2004). Theoretically, FAME/biodiesel ratio is 1:1 for diesel production; but in
reality, 1 g of FAME results in 0.84 g of biodiesel production (El-Shimi et al.
2013). The quality of biodiesel is considerably affected by the composition of
FAMEs; thus the composition is an important factor for selecting the most adequate
algal species for biofuel production. For most biodiesel industries using algae, the
goal is to improve a specific FAMEs as oleic acid (C18:1:ω9) for high-quality
biodiesel due to oleic acid reasonable balance of fuel properties, including ignition
quality, combustion heat, cold filter plugging point, oxidative stability, viscosity,
and lubricity (Or-Rashid et al. 2008). To improve production of high-quality FAME,
it is important to understand the lipid biosynthesis pathway and its regulators;
however, these pathways have not yet been fully elucidated (Bellou et al. 2014).
One apparent advantage of algae cultivation from wastewater is the potential for high
lipid production compared to freshwater, because wastewater has enough media with
organic carbon and nutrient. Nutritional and environmental factors, CO 2 /light intensity, pH, and specific stress conditions are potential cultivation parameters that affect
FAME quality in microalgae (Ji et al. 2014). For example, a specific stress condition
of N depletion or high salinity during algae cultivation produced large amounts of
unsaturated fatty acids (Bartley et al. 2013; Sharma et al. 2012). Although their
mechanism is not much more to be discovered, current literature supports N and
salinity stress as a lipid-improving and effective high-quality biodiesel production
strategy.
3.3.2 Bio-alcohol (Ethanol and Butanol) Production from Microalgae
Microalgae are considered to be a biofuel (i.e., ethanol) feedstock that is exceedingly
rich in carbohydrates, which can be converted to ethanol by fermentation (Adams
et al. 2009). Based on the different species of microalgae, a maximum 32%,
30–40%, and 50% of bioethanol have been achieved in the treatment of sonication
of Scenedesmus obliquus (Choi et al. 2011), acid hydrolysis of Gelidium amansii
(Kim et al. 2015), and combined pretreatment (sonication and enzymatic hydrolysis)
of Chlamydomonas mexicana (Eldalatony et al. 2016), respectively. In separate
hydrolysis and fermentation (SHF), enzymatic hydrolysis and fermentation are
carried out in two separate steps of hydrolysis and fermentation, which lead to
high bioethanol yield comparing to simultaneous saccharification and fermentation
(SSF) due to the possibility of cell recycling in end product (Roca and Olsson 2003).
In addition, more economic and effective SHF processes should also be developed to
12 Microalgae: An Eco-friendly Tool for the Treatment of Wastewaters for. . .
291