and sulfurized compounds, with chains that can contain up to 10 carbon atoms
(Muñoz et al. 2004; Fink 2007; Sun et al. 2012).
Many studies of commercial interest have been conducted to identify VOCs
produced by microalgae and cyanobacteria and point out their potential uses.
Compounds such as b-cyclocyclal, 2-methyl-1-butanol, and 3-methyl-1-butanol
were excreted in the extracellular fraction of Microcystis aeruginosa (Hasegawa
et al. 2012). A wide variety of compounds, such as b-ionone, hexanol, hexanal,
propanol, butanol, among others, were produced by Phormidium autumnale
(Santos et al. 2016). In a study by Eroglu and Melis (2010), the microalgae
Botryococcus braunii synthesized long-chain hydrocarbons, which can be commercially exploited for the synthesis of chemicals and biofuels feedstock. Schirmer
et al. (2010) found in different cyanobacteria alkanes, such as heptadecane, pentadecane, and methyl heptadecane, besides alkenes, that have desirable properties
for combustion. All these compounds have great potential as biofuels.
Most research on microalgae VOCs is focused on their use as industrial
chemicals. Meantime, there are few studies demonstrating the feasibility of
applying these compounds as fuels. Recently, Jacob-Lopes et al. (2017) developed
a bioprocess in an attempt to make feasible the VOCs production in photobioreactors for use as gaseous fuels. A total of 17 compounds of different chemical
structures were produced by microalgae Scenedesmus obliquus and released from
photobioreactor exhaust gases (Fig. 3), which can potentially be used as energy
source in combustion systems. Therefore, assuming that the estimated energy
potential of these compounds is approximately 86.30 MJ/kg, and comparing them
quantitatively with other conventional fuels, VOCs total energy content is superior
to the value of natural gas (47.00 MJ/kg) and diesel oil (43.40 MJ/kg), for example.
The several VOCs generated in photobioreactors could, therefore, be used for the
gaseous fuels production, representing an important step in the consolidation of
strategies to reduce dependence on fossil fuels and the expansion of renewable
energy sources.
6 Photobioreactors Design
A photobioreactor can be defined as a lighted system designed for the development
of photosynthetic reactions. In order for the CO 2 bioconversion in photosynthetic
products to occur efficiently, it is necessary to consider some basic requirements,
such as adequate light energy and CO 2 , dissolved oxygen concentration, efficient
mixing system, temperature control, nutrient availability, and scale-up (Wang et al.
2012).
A wide variety of cultivation systems have been reported for microalgae-based
processes. Photobioreactors are generally classified into two designs: open or closed
systems (Borowitzka 1999). Open systems are most commonly used in large-scale
processes and are based on circular ponds and raceway tanks. They are simple to
operate, cheap, and easy to expand. However, performance is poor, since the culture
282
I. Aguiar Severo et al.
(Muñoz et al. 2004; Fink 2007; Sun et al. 2012).
Many studies of commercial interest have been conducted to identify VOCs
produced by microalgae and cyanobacteria and point out their potential uses.
Compounds such as b-cyclocyclal, 2-methyl-1-butanol, and 3-methyl-1-butanol
were excreted in the extracellular fraction of Microcystis aeruginosa (Hasegawa
et al. 2012). A wide variety of compounds, such as b-ionone, hexanol, hexanal,
propanol, butanol, among others, were produced by Phormidium autumnale
(Santos et al. 2016). In a study by Eroglu and Melis (2010), the microalgae
Botryococcus braunii synthesized long-chain hydrocarbons, which can be commercially exploited for the synthesis of chemicals and biofuels feedstock. Schirmer
et al. (2010) found in different cyanobacteria alkanes, such as heptadecane, pentadecane, and methyl heptadecane, besides alkenes, that have desirable properties
for combustion. All these compounds have great potential as biofuels.
Most research on microalgae VOCs is focused on their use as industrial
chemicals. Meantime, there are few studies demonstrating the feasibility of
applying these compounds as fuels. Recently, Jacob-Lopes et al. (2017) developed
a bioprocess in an attempt to make feasible the VOCs production in photobioreactors for use as gaseous fuels. A total of 17 compounds of different chemical
structures were produced by microalgae Scenedesmus obliquus and released from
photobioreactor exhaust gases (Fig. 3), which can potentially be used as energy
source in combustion systems. Therefore, assuming that the estimated energy
potential of these compounds is approximately 86.30 MJ/kg, and comparing them
quantitatively with other conventional fuels, VOCs total energy content is superior
to the value of natural gas (47.00 MJ/kg) and diesel oil (43.40 MJ/kg), for example.
The several VOCs generated in photobioreactors could, therefore, be used for the
gaseous fuels production, representing an important step in the consolidation of
strategies to reduce dependence on fossil fuels and the expansion of renewable
energy sources.
6 Photobioreactors Design
A photobioreactor can be defined as a lighted system designed for the development
of photosynthetic reactions. In order for the CO 2 bioconversion in photosynthetic
products to occur efficiently, it is necessary to consider some basic requirements,
such as adequate light energy and CO 2 , dissolved oxygen concentration, efficient
mixing system, temperature control, nutrient availability, and scale-up (Wang et al.
2012).
A wide variety of cultivation systems have been reported for microalgae-based
processes. Photobioreactors are generally classified into two designs: open or closed
systems (Borowitzka 1999). Open systems are most commonly used in large-scale
processes and are based on circular ponds and raceway tanks. They are simple to
operate, cheap, and easy to expand. However, performance is poor, since the culture
282
I. Aguiar Severo et al.