258
M. M. Maroneze et al.
The company Algatechnologies Ltd. (Ketura, Israel) established tubular photobioreactors in two stages for astaxanthin production from Haematococcus pluvialis
(Ayalon 2014), and similar systems are widely employed in other companies around
the world, as was showed in Table 11.1 (Maeda et al. 2018).
Tubular photobioreactors consist of an array of straight transparent tubes that
are usually made of plastic or glass and have a diameter of 0.1 m or less, in
which the culture is circulated by pumps or air streams (airlift) (Acién et al. 2017;
Maroneze and Queiroz 2018). These transparent tubes can be arranged in different
patterns, including horizontal/serpentine (Chaumont et al. 1988; Molina Grima et al.
2001), vertical (Chen et al. 2016), near-horizontal (Tredici and Zittelli 1998), conical
(Watanabe and Hall 1996), and inclined (Ugwu et al. 2002, 2008).
This distribution of the tubes in the solar collector, together with the tube diameter,
will determine the amount of solar radiation that the culture will be able to capture,
which will directly reflect on the productivity in biomass and photosynthetic bioproducts. Besides, the choice of the diameter of the tube will affect the temperature of
the culture, the oxygen concentration in the culture, and the length of the tubes. It is
already well established that smaller diameters favor the performance of the system
since it will reflect in a higher surface-volume ratio (S/V) (Torzillo and Zitelli 2015).
Generally, tubes lower than 0.1 m required, but it must be considered that although it
can increase the kinetic performance of the process, the use of very small diameters
leads to a significant increase in energy consumption; therefore, minimum values of
0.03 m are recommended (Molina Grima et al. 2001).
As for the length, it must be dimensioned so that there is no accumulation of
excess oxygen in the PBR loop. Photosynthesis is a well-established biochemical
reaction, where to produce one ton of microalgal biomass, it generates 1.9 tons of
oxygen. Which needs to be efficiently removed as its excess presence has a toxic
effect on cells. In this sense, it is recommended that the maximum length is in the
range of 100 to 400 m, depending on the configuration (Torzillo and Zitelli 2015).
The investment cost of tubular PBRs is a limiting factor in the use of these systems,
as it can exceed twice the amount reported for raceways. According to Nosker et al.
(2011), this value varies around 0.51 Me/ha at 100 ha scale. On the other hand, high
productivity is achieved in these systems. It has been reported biomass productivities
of 10–40 g/m
2 /d for Spirulina (Delrue et al. 2017), 13 g/m
2 /d for Haematococcus
pluvialis (Olaizola 2000). Regarding the cost of biomass production, the values are
quite variable, as they depend on the species used, productivity, and the stages of
the production process. Delrue et al. (2017) reported costs ranging from 18 to 74
e/kg, Molina Grima (2009) found a cost of 25 e/kg, and Nosker et al. (2011) 4.15
e/kg. Despite the innumerable advantages of closed cultivation systems, the high
cost of both investment and production is still the most significant limitation in the
establishment of processes and products based on microalgae.
M. M. Maroneze et al.
The company Algatechnologies Ltd. (Ketura, Israel) established tubular photobioreactors in two stages for astaxanthin production from Haematococcus pluvialis
(Ayalon 2014), and similar systems are widely employed in other companies around
the world, as was showed in Table 11.1 (Maeda et al. 2018).
Tubular photobioreactors consist of an array of straight transparent tubes that
are usually made of plastic or glass and have a diameter of 0.1 m or less, in
which the culture is circulated by pumps or air streams (airlift) (Acién et al. 2017;
Maroneze and Queiroz 2018). These transparent tubes can be arranged in different
patterns, including horizontal/serpentine (Chaumont et al. 1988; Molina Grima et al.
2001), vertical (Chen et al. 2016), near-horizontal (Tredici and Zittelli 1998), conical
(Watanabe and Hall 1996), and inclined (Ugwu et al. 2002, 2008).
This distribution of the tubes in the solar collector, together with the tube diameter,
will determine the amount of solar radiation that the culture will be able to capture,
which will directly reflect on the productivity in biomass and photosynthetic bioproducts. Besides, the choice of the diameter of the tube will affect the temperature of
the culture, the oxygen concentration in the culture, and the length of the tubes. It is
already well established that smaller diameters favor the performance of the system
since it will reflect in a higher surface-volume ratio (S/V) (Torzillo and Zitelli 2015).
Generally, tubes lower than 0.1 m required, but it must be considered that although it
can increase the kinetic performance of the process, the use of very small diameters
leads to a significant increase in energy consumption; therefore, minimum values of
0.03 m are recommended (Molina Grima et al. 2001).
As for the length, it must be dimensioned so that there is no accumulation of
excess oxygen in the PBR loop. Photosynthesis is a well-established biochemical
reaction, where to produce one ton of microalgal biomass, it generates 1.9 tons of
oxygen. Which needs to be efficiently removed as its excess presence has a toxic
effect on cells. In this sense, it is recommended that the maximum length is in the
range of 100 to 400 m, depending on the configuration (Torzillo and Zitelli 2015).
The investment cost of tubular PBRs is a limiting factor in the use of these systems,
as it can exceed twice the amount reported for raceways. According to Nosker et al.
(2011), this value varies around 0.51 Me/ha at 100 ha scale. On the other hand, high
productivity is achieved in these systems. It has been reported biomass productivities
of 10–40 g/m
2 /d for Spirulina (Delrue et al. 2017), 13 g/m
2 /d for Haematococcus
pluvialis (Olaizola 2000). Regarding the cost of biomass production, the values are
quite variable, as they depend on the species used, productivity, and the stages of
the production process. Delrue et al. (2017) reported costs ranging from 18 to 74
e/kg, Molina Grima (2009) found a cost of 25 e/kg, and Nosker et al. (2011) 4.15
e/kg. Despite the innumerable advantages of closed cultivation systems, the high
cost of both investment and production is still the most significant limitation in the
establishment of processes and products based on microalgae.