efficient in the control of the temperature has been demonstrated to promote the
average light intensity in the culture (Huang et al. 2017).
CO 2 /O 2 Balance and Mixing
As explained in Sects. 2.1.1.3 and 2.1.1.4, the carbon dioxide and oxygen must be
maintained in equilibrium and in moderate concentrations, since the excess of both
causes damage to the cells. In this sense, the photobioreactor must contain a space
for exhaust gases and an efficient mixing system, where promote turbulence and
therefore mass transfer between the gas and liquid phases inside a photobioreactor
(Wang et al. 2012).
In addition to its key role in the balance of gases and pH of the system, the
mixing also is necessary to prevent sedimentation of algal cells, ensure that all cells
of the population have uniform average exposure to light and nutrient and facilitate
heat transfer and avoid thermal stratification. In tubular photobioreactor, the mixing
is usually provided by aeration with CO 2 -enriched gas bubbles or pumping,
mechanical agitation, or a combination of these means. The choice depends on the
scale of the system and the microalga species used, because some do not tolerate
vigorous agitations (Suh and Lee 2003; Wang et al. 2012; Huang et al. 2017).
2.2.2 Biomass Productivity in Tubular Photobioreactor
The high biomass productivity is the greatest advantage of tubular photobioreactors,
especially if compared to raceway ponds. Table 2 shows the biomass productivities
in different tubular photobioreactors. The values range from 0.05 to 1.9 g/L/d. This
variation is due to the type of geometric configuration used, microalgae species and
operating and environmental conditions used in each study. If we compare these
productivities values with those found in raceway ponds (Table 1), it is possible to
see that except to the values found by Olaizola (2000), all the other productivities in
tubular PRBs are greater than found in raceways.
2.2.3 Costs of Construction and Operation of Tubular
Photobioreactors
The cost of PBRs has a major influence on production cost for large-scale biomass.
The company AlgaeLink NV (Yerseke, The Netherlands) commercializes a horizontal serpentine PBR made of large-diameter transparent plastic tubes. For a
system of 97 m
3 , 1200 m
2 of occupied area, made of 2000 m long, 25 cm diameter
PMMA tubes, according to Zitelli et al. (2013), the price was about € 194,000 in
2012. Through inflation calculation described in Chisti (2013), this price in 2017 is
about € 202,798.
2 Microalgal Production Systems with Highlights …
13
average light intensity in the culture (Huang et al. 2017).
CO 2 /O 2 Balance and Mixing
As explained in Sects. 2.1.1.3 and 2.1.1.4, the carbon dioxide and oxygen must be
maintained in equilibrium and in moderate concentrations, since the excess of both
causes damage to the cells. In this sense, the photobioreactor must contain a space
for exhaust gases and an efficient mixing system, where promote turbulence and
therefore mass transfer between the gas and liquid phases inside a photobioreactor
(Wang et al. 2012).
In addition to its key role in the balance of gases and pH of the system, the
mixing also is necessary to prevent sedimentation of algal cells, ensure that all cells
of the population have uniform average exposure to light and nutrient and facilitate
heat transfer and avoid thermal stratification. In tubular photobioreactor, the mixing
is usually provided by aeration with CO 2 -enriched gas bubbles or pumping,
mechanical agitation, or a combination of these means. The choice depends on the
scale of the system and the microalga species used, because some do not tolerate
vigorous agitations (Suh and Lee 2003; Wang et al. 2012; Huang et al. 2017).
2.2.2 Biomass Productivity in Tubular Photobioreactor
The high biomass productivity is the greatest advantage of tubular photobioreactors,
especially if compared to raceway ponds. Table 2 shows the biomass productivities
in different tubular photobioreactors. The values range from 0.05 to 1.9 g/L/d. This
variation is due to the type of geometric configuration used, microalgae species and
operating and environmental conditions used in each study. If we compare these
productivities values with those found in raceway ponds (Table 1), it is possible to
see that except to the values found by Olaizola (2000), all the other productivities in
tubular PRBs are greater than found in raceways.
2.2.3 Costs of Construction and Operation of Tubular
Photobioreactors
The cost of PBRs has a major influence on production cost for large-scale biomass.
The company AlgaeLink NV (Yerseke, The Netherlands) commercializes a horizontal serpentine PBR made of large-diameter transparent plastic tubes. For a
system of 97 m
3 , 1200 m
2 of occupied area, made of 2000 m long, 25 cm diameter
PMMA tubes, according to Zitelli et al. (2013), the price was about € 194,000 in
2012. Through inflation calculation described in Chisti (2013), this price in 2017 is
about € 202,798.
2 Microalgal Production Systems with Highlights …
13