254 Marine Macro- and Microalgae: An Overview
accounts for 40–50% of total sunlight (Akkerman et al. 2002; Suh and Lee 2003). Cyanobacterium
anabaena was studied (Gao et al. 2007) for growth responses under different solar radiation experiments.
It was found that exposure to natural levels of PAR and UV light increased and inhibited cell growth,
respectively (Gao et al. 2007). Another important parameter is the effects of the diurnal cycle (Pulz and
Scheinbenbogan 1998) for outdoor cultivation, which have remarkable effects on the overall efficiency
of solar energy capture. However, this may be limited by available sunlight due to diurnal cycles and
the seasonal variations, thereby limiting the viability of commercial production to areas with high solar
radiation. Both photo-inhibition and low light stress of photosynthesis causes decrease in microalgal
biomass production (Barbosa et al. 2003; Kuda et al. 2005). As a result, up to 42% of biomass produced
during daytime could be lost throughout the subsequent night (Tredici et al. 1991; Jacob et al. 2009). To
address the limitations of natural sunlight growth conditions, artificial light in the form of fluorescent
lamps are usually used for the cultivation of phototrophic microalgae at large scale (Muller et al. 1998),
which allows for continuous production, but at significantly higher energy input. Light limitation due to
high volume to surface ratios may also induce reduced biomass productivity. However, enhanced light
supply is possible by reducing layer thickness, using thin layer photobioreactors with optimised culture
mixing (Pulz 2001; Chisti 2007; Ugwu et al. 2008). More recently, flashing light-emitting diodes (LEDs)
have been proposed as an alternative to fluorescent lamps to illuminate photobioreactors in order to
decrease light attenuation and improve microalgal productivity (Schulze et al. 2014, 2017b).
Carbon dioxide (CO 2 )
Carbon is an essential nutrient for microalgae growth; nearly 50% of the microalgae biomass is made up
of carbon (Becker 1994), as it is a major nutrient for cell growth. Approximately 1.8 Kg of CO 2 are needed
to produce 1 Kg of microalgae biomass (Amaro et al. 2011). Microalgae can be used to mitigate CO 2 from
various sources, such as organic compounds (Lodi et al. 2005), inorganic carbonates (Emma et al. 2000;
Wang et al. 2008), atmosphere (i.e., CO 2 ), as well as flue gas from industrial and power plants (Sydney et
al. 2010). Some microalgae species such as Arthrospira platensis and Chlamydomonas reinhardtii (Chen
et al. 1996) and Arthrospira sp. (Chojnacka and Noworyta 2004) are capable of growing in darkness
and of using organic carbons (such as acetate or glucose) as energy and carbon sources (Ogbonna et al.
2000); however, using organic carbons for microalgal growth is expensive. Thus, a cheap source of CO 2
for photosynthetic production of biofuels is needed (Wang et al. 2008). Mitigation of atmospheric CO 2
is probably the most basic method to mitigate carbon, and relies on the mass transfer from the air to the
microalgae in their aquatic growth environments during photosynthesis (Wang et al. 2008). However,
atmospheric CO 2 (0.03%) is not sufficient to support the microalgal growth rates and productivities
needed for full-scale biofuel production, which makes it economically infeasible (Stepan et al. 2002).
Combustion of fossil fuel is the largest source of CO 2 emissions globally and CO 2 mitigation from flue
gas emissions may be a way to achieve higher biomass productivities due to the higher CO 2 concentration
(Bilanovic et al. 2009; Chiu et al. 2009). Consequently, when CO 2 -enriched air is employed, light usually
becomes the limiting factor.
Temperature
Temperature is another limiting factor for microalgae cultivation, which influences oxygen evolution and
production efficiency (Ras et al. 2013). The optimal growth temperature for most species of microalgae is
between 20 to 25ºC (Ras et al. 2013 and references therein). A few microalgae can tolerate temperatures
below 16ºC, but this will result in reduced production of biomass and slower growth rates. Temperatures
higher than 35ºC are normally harmful (Hanagata et al. 1992; Andersen and Andersen 2006; Graham et
al. 2008). However, some cyanobacteria such as Anabaena variabilis (Fontes et al. 1987) and Arthrospira
sp. (Rafiqul et al. 2003; Vonshak and Tomaselli 2003; Ogbonda et al. 2007) can grow optimally at
temperatures between 30–38ºC. In addition, thermophilic cyanobacteria belonging to the Synechococcus
genus (Murata 1989) can tolerate temperatures as high as 60ºC (Miyairi 1995). The optimum temperature
range required to support microalgae growth is strain dependent (Ras et al. 2013). Temperature has also
accounts for 40–50% of total sunlight (Akkerman et al. 2002; Suh and Lee 2003). Cyanobacterium
anabaena was studied (Gao et al. 2007) for growth responses under different solar radiation experiments.
It was found that exposure to natural levels of PAR and UV light increased and inhibited cell growth,
respectively (Gao et al. 2007). Another important parameter is the effects of the diurnal cycle (Pulz and
Scheinbenbogan 1998) for outdoor cultivation, which have remarkable effects on the overall efficiency
of solar energy capture. However, this may be limited by available sunlight due to diurnal cycles and
the seasonal variations, thereby limiting the viability of commercial production to areas with high solar
radiation. Both photo-inhibition and low light stress of photosynthesis causes decrease in microalgal
biomass production (Barbosa et al. 2003; Kuda et al. 2005). As a result, up to 42% of biomass produced
during daytime could be lost throughout the subsequent night (Tredici et al. 1991; Jacob et al. 2009). To
address the limitations of natural sunlight growth conditions, artificial light in the form of fluorescent
lamps are usually used for the cultivation of phototrophic microalgae at large scale (Muller et al. 1998),
which allows for continuous production, but at significantly higher energy input. Light limitation due to
high volume to surface ratios may also induce reduced biomass productivity. However, enhanced light
supply is possible by reducing layer thickness, using thin layer photobioreactors with optimised culture
mixing (Pulz 2001; Chisti 2007; Ugwu et al. 2008). More recently, flashing light-emitting diodes (LEDs)
have been proposed as an alternative to fluorescent lamps to illuminate photobioreactors in order to
decrease light attenuation and improve microalgal productivity (Schulze et al. 2014, 2017b).
Carbon dioxide (CO 2 )
Carbon is an essential nutrient for microalgae growth; nearly 50% of the microalgae biomass is made up
of carbon (Becker 1994), as it is a major nutrient for cell growth. Approximately 1.8 Kg of CO 2 are needed
to produce 1 Kg of microalgae biomass (Amaro et al. 2011). Microalgae can be used to mitigate CO 2 from
various sources, such as organic compounds (Lodi et al. 2005), inorganic carbonates (Emma et al. 2000;
Wang et al. 2008), atmosphere (i.e., CO 2 ), as well as flue gas from industrial and power plants (Sydney et
al. 2010). Some microalgae species such as Arthrospira platensis and Chlamydomonas reinhardtii (Chen
et al. 1996) and Arthrospira sp. (Chojnacka and Noworyta 2004) are capable of growing in darkness
and of using organic carbons (such as acetate or glucose) as energy and carbon sources (Ogbonna et al.
2000); however, using organic carbons for microalgal growth is expensive. Thus, a cheap source of CO 2
for photosynthetic production of biofuels is needed (Wang et al. 2008). Mitigation of atmospheric CO 2
is probably the most basic method to mitigate carbon, and relies on the mass transfer from the air to the
microalgae in their aquatic growth environments during photosynthesis (Wang et al. 2008). However,
atmospheric CO 2 (0.03%) is not sufficient to support the microalgal growth rates and productivities
needed for full-scale biofuel production, which makes it economically infeasible (Stepan et al. 2002).
Combustion of fossil fuel is the largest source of CO 2 emissions globally and CO 2 mitigation from flue
gas emissions may be a way to achieve higher biomass productivities due to the higher CO 2 concentration
(Bilanovic et al. 2009; Chiu et al. 2009). Consequently, when CO 2 -enriched air is employed, light usually
becomes the limiting factor.
Temperature
Temperature is another limiting factor for microalgae cultivation, which influences oxygen evolution and
production efficiency (Ras et al. 2013). The optimal growth temperature for most species of microalgae is
between 20 to 25ºC (Ras et al. 2013 and references therein). A few microalgae can tolerate temperatures
below 16ºC, but this will result in reduced production of biomass and slower growth rates. Temperatures
higher than 35ºC are normally harmful (Hanagata et al. 1992; Andersen and Andersen 2006; Graham et
al. 2008). However, some cyanobacteria such as Anabaena variabilis (Fontes et al. 1987) and Arthrospira
sp. (Rafiqul et al. 2003; Vonshak and Tomaselli 2003; Ogbonda et al. 2007) can grow optimally at
temperatures between 30–38ºC. In addition, thermophilic cyanobacteria belonging to the Synechococcus
genus (Murata 1989) can tolerate temperatures as high as 60ºC (Miyairi 1995). The optimum temperature
range required to support microalgae growth is strain dependent (Ras et al. 2013). Temperature has also