cultivation as they can be grown in brackish water, near coastal areas, floating on
sea water, or in salt marshes. This also comes with some problems like effects on
natural marine flora; premature rupture of microalgae cells due to high salinity of
water and requirement of pretreatment of marine water, which adversely affects the
economic feasibility. Overall, there is a need of deeper insight on the cultivation
source and production approaches to be used for microalgae including the possible
use of wastewater for microalgae cultivation which leads to solving of both the
issues, that is, treatment of wastewater and cultivation source.
1.2.1 Lipid Content in Microalgae
Higher level of lipid content is an important parameter for utilization of microalgae.
Few microalgae like Botryococcus braunii and Chlorella emersonii are naturally
capable to produce up to 75% of lipid content (g lipids/dry weight). Chlorella vulgaris and Dunaliella sp. can reach up to 50% productivity under normal conditions.
Lipid content in most of the microalgae species is generally between 20 and 50%.
Profile of fatty acids also has a positive impact on biodiesel production (Priyadarshani
and Rath 2012). Lipid profile is typically species-specific. Process improvement
approaches can be efficiently applied to maintain desired specific conditions for
microalgal growth (Patel et al. 2016). Growth parameters like nutrient availability,
environmental factors, and cultivation type have a significant effect on microalgae
lipid content. It has been reported that lipid production can be induced by
nutrient-specific stress, for example, nitrogen starvation causes higher lipid production (Rodolfi et al. 2009). Similarly, phosphate content also has an effect on lipid
productivity though it gives stronger increase in biomass content instead of lipid
content (Xin et al. 2010). Salt stress can also have an impact on the production of
lipids in microalgae as reported by Takagi et al. (2006). The microalgae grown in
water with higher concentration of salts, that is, >1 M NaCl concentration were
reported to have high lipid productivity as compared to those grown in 0.5 M NaCl
solution. To get higher content of lipid is the main target which can be achieved with
help of process optimization of required parameters. In the above cases, process
improvement approaches can be helpful in identifying the desired conditions for
microalgae growth and can increase the overall yield of lipids. The application of
ultrasound as a process intensification approach can also enhance the growth of
microalgae and increase the lipid production. In the study carried out by Han et al.
(2016), it was reported that exposing the microalgae to different powers of ultrasound
increased the overall yield and lipid content by 1.86 and 1.46 times, respectively.
2 Cultivation of Microalgae
Microalgae are cultivated using two main approaches based on the open pond
system (raceway ponds, natural ponds, circular ponds, and inclined systems) and
closed system (PBR-photobioreactor). Since 1950s, the open pond system has been
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S. Joshi and P. Gogate
sea water, or in salt marshes. This also comes with some problems like effects on
natural marine flora; premature rupture of microalgae cells due to high salinity of
water and requirement of pretreatment of marine water, which adversely affects the
economic feasibility. Overall, there is a need of deeper insight on the cultivation
source and production approaches to be used for microalgae including the possible
use of wastewater for microalgae cultivation which leads to solving of both the
issues, that is, treatment of wastewater and cultivation source.
1.2.1 Lipid Content in Microalgae
Higher level of lipid content is an important parameter for utilization of microalgae.
Few microalgae like Botryococcus braunii and Chlorella emersonii are naturally
capable to produce up to 75% of lipid content (g lipids/dry weight). Chlorella vulgaris and Dunaliella sp. can reach up to 50% productivity under normal conditions.
Lipid content in most of the microalgae species is generally between 20 and 50%.
Profile of fatty acids also has a positive impact on biodiesel production (Priyadarshani
and Rath 2012). Lipid profile is typically species-specific. Process improvement
approaches can be efficiently applied to maintain desired specific conditions for
microalgal growth (Patel et al. 2016). Growth parameters like nutrient availability,
environmental factors, and cultivation type have a significant effect on microalgae
lipid content. It has been reported that lipid production can be induced by
nutrient-specific stress, for example, nitrogen starvation causes higher lipid production (Rodolfi et al. 2009). Similarly, phosphate content also has an effect on lipid
productivity though it gives stronger increase in biomass content instead of lipid
content (Xin et al. 2010). Salt stress can also have an impact on the production of
lipids in microalgae as reported by Takagi et al. (2006). The microalgae grown in
water with higher concentration of salts, that is, >1 M NaCl concentration were
reported to have high lipid productivity as compared to those grown in 0.5 M NaCl
solution. To get higher content of lipid is the main target which can be achieved with
help of process optimization of required parameters. In the above cases, process
improvement approaches can be helpful in identifying the desired conditions for
microalgae growth and can increase the overall yield of lipids. The application of
ultrasound as a process intensification approach can also enhance the growth of
microalgae and increase the lipid production. In the study carried out by Han et al.
(2016), it was reported that exposing the microalgae to different powers of ultrasound
increased the overall yield and lipid content by 1.86 and 1.46 times, respectively.
2 Cultivation of Microalgae
Microalgae are cultivated using two main approaches based on the open pond
system (raceway ponds, natural ponds, circular ponds, and inclined systems) and
closed system (PBR-photobioreactor). Since 1950s, the open pond system has been
62
S. Joshi and P. Gogate