This type of photobioreactor can be illuminated by artificial or natural light. The
artificial illumination is technically possible, but expensive compared with outdoor
cultivations, which is just viable for commercial production of high added value
products.
2.2.1 Major Factors Affecting the Tubular Photobioreactor
Performance
Light Supply
In autotrophic microalgae production, the light availability is the most important
factor that influences the cell productivity and is one of the most difficult to control
in outdoor cultures, due to the variation in solar radiation during the day and during
the change of season (Fernandez et al. 1997).
In terms of design, the light capture is influenced by the transparency of the
materials and the surface/volume ratio. The most common materials used for PBR
construction are glass, plexiglass, polyvinyl chloride (PVC), acrylic-PVC, and
polyethylene. All these materials have transparency suitable for the microalgae
cultivations. However, they all have their pros and cons and need to be evaluated
according to the type of process and desired product. Glass is strong and transparent
and very good material for the construction of laboratory-scale PBRs. However, it
requires many connection parts for the construction of large-scale PBRs, which
could be costly. For this reason, the plastic type is most suitable for large-scale
tubular photobioreactor, mainly of polyethylene (Wang et al. 2012).
Temperature
As already mentioned, the optimal temperature for microalgae cultures is generally
around 25 °C, and most microalgae species can tolerate temperatures between
16 °C and 35 °C. In closed PBR, generally, the volume is small because a thin
optical thick mixing ness is applied for the sake of light transfer. Therefore, variations in temperature during the day/night cycle and the seasons’ changes have
significant effects on microalgal cultivation. In this sense, it is necessary to set up a
cost-effective cooling system (Huang et al. 2017).
Several methods have been tested to prevent overheating of the microalgae
cultivation. Among them are as follows: (i) shading of the tubes with dark-colored
sheets (Torzillo 1997), (ii) cooling of the culture by spraying water on the surface of
the photobioreactor (Becker 1994), (iii) submerging part of the photobioreactor or
the entire culture on a large body of water (Becker 1994), and (iv) installing a heat
exchanger for the photobioreactor (Watanabe et al. 2011). However, shading the
PBR is inefficient because it greatly reduces the illumination and consequently in
the yield of biomass. Water spraying is efficient for cooling, but entails an increase
in the cultivation costs. On the other hand, the method of submersion besides
12
M. M. Maroneze and M. I. Queiroz
artificial illumination is technically possible, but expensive compared with outdoor
cultivations, which is just viable for commercial production of high added value
products.
2.2.1 Major Factors Affecting the Tubular Photobioreactor
Performance
Light Supply
In autotrophic microalgae production, the light availability is the most important
factor that influences the cell productivity and is one of the most difficult to control
in outdoor cultures, due to the variation in solar radiation during the day and during
the change of season (Fernandez et al. 1997).
In terms of design, the light capture is influenced by the transparency of the
materials and the surface/volume ratio. The most common materials used for PBR
construction are glass, plexiglass, polyvinyl chloride (PVC), acrylic-PVC, and
polyethylene. All these materials have transparency suitable for the microalgae
cultivations. However, they all have their pros and cons and need to be evaluated
according to the type of process and desired product. Glass is strong and transparent
and very good material for the construction of laboratory-scale PBRs. However, it
requires many connection parts for the construction of large-scale PBRs, which
could be costly. For this reason, the plastic type is most suitable for large-scale
tubular photobioreactor, mainly of polyethylene (Wang et al. 2012).
Temperature
As already mentioned, the optimal temperature for microalgae cultures is generally
around 25 °C, and most microalgae species can tolerate temperatures between
16 °C and 35 °C. In closed PBR, generally, the volume is small because a thin
optical thick mixing ness is applied for the sake of light transfer. Therefore, variations in temperature during the day/night cycle and the seasons’ changes have
significant effects on microalgal cultivation. In this sense, it is necessary to set up a
cost-effective cooling system (Huang et al. 2017).
Several methods have been tested to prevent overheating of the microalgae
cultivation. Among them are as follows: (i) shading of the tubes with dark-colored
sheets (Torzillo 1997), (ii) cooling of the culture by spraying water on the surface of
the photobioreactor (Becker 1994), (iii) submerging part of the photobioreactor or
the entire culture on a large body of water (Becker 1994), and (iv) installing a heat
exchanger for the photobioreactor (Watanabe et al. 2011). However, shading the
PBR is inefficient because it greatly reduces the illumination and consequently in
the yield of biomass. Water spraying is efficient for cooling, but entails an increase
in the cultivation costs. On the other hand, the method of submersion besides
12
M. M. Maroneze and M. I. Queiroz