11 Microalgae-Based Processes for Pigments Production
257
outgrow contaminants such as unwanted microalgae species, bacteria, viruses, and
protozoa (Kotzen et al. 2019). Besides, biomass productivity hardly exceeds 1 g/m
2 /d,
and, given the very low concentration of cells, a very efficient system should be used
to harvest the biomass (Trediti 2004).
The cultivation process in these systems consists of pumping seawater from the
adjacent ocean to the pond, where nutrients are added to this saline water. When the
system has reached the appropriate β-carotene content, the culture is pumped to a
harvesting plant. The rate of harvesting and the growth period varies with changing
climatic conditions throughout the year. After harvesting, the remaining medium
is returned to the unmixed pond, where salinity and nutrient content is adjusted as
needed (Borowitzka 1990).
11.6.2 Closed Systems
Due to the high operational control and high productivity provided by photobioreactors, researchers and companies have invested heavily in the development of a wide
variety of configurations over the last decades. However, for large-scale commercial
use, tubular photobioreactors are almost exclusively used, mainly because they are
easy to scale up, have a large illumination surface area, are suitable for outdoor
cultures, present good biomass productivities, and are economically reasonable.
Although used by only a portion of microalgae-based companies, bioreactors for
heterotrophic and mixotrophic cultures have also gained prominence (Borowitzka
2018). Other systems such as flat-plate and vertical photobioreactors have exploration potential but are still in their early stages where some significant limitations
need to be overcome, which are mainly associated with scale-up difficulty and high
cost (Ugwu et al. 2008).
11.6.2.1 Tubular Photobioreactors
Tubular photobioreactors were first described in 1953 (Tamiya et al. 1953), but
were not consolidated until the 1990s, after being gradually optimized (Gudin and
Chaumont 1983; Pirt et al. 1983; Chaumont et al. 1988; Chaumont 1993; Richmond
et al. 1993). Only from this point is it possible to commercially produce astaxanthin
from microalgae, as far as we know Haematococcus single-phase cultivation in largescale raceway systems has proved unsatisfactory (Bubrick 1991; Margalith 1999;
Olaizola 2000).
Unlike open systems, tubular photobioreactors allow greater control of cultivation
conditions, the possibility of contamination is lower, and the high availability of solar
radiation, which results in higher yields. It this allows using these reactors to produce
sensible strains such as H. pluvialis. Due to the lower water depth (tube diameter),
which ranges from 0.03 to 0.12 m, the biomass concentration can reach 3.0 g/L.
257
outgrow contaminants such as unwanted microalgae species, bacteria, viruses, and
protozoa (Kotzen et al. 2019). Besides, biomass productivity hardly exceeds 1 g/m
2 /d,
and, given the very low concentration of cells, a very efficient system should be used
to harvest the biomass (Trediti 2004).
The cultivation process in these systems consists of pumping seawater from the
adjacent ocean to the pond, where nutrients are added to this saline water. When the
system has reached the appropriate β-carotene content, the culture is pumped to a
harvesting plant. The rate of harvesting and the growth period varies with changing
climatic conditions throughout the year. After harvesting, the remaining medium
is returned to the unmixed pond, where salinity and nutrient content is adjusted as
needed (Borowitzka 1990).
11.6.2 Closed Systems
Due to the high operational control and high productivity provided by photobioreactors, researchers and companies have invested heavily in the development of a wide
variety of configurations over the last decades. However, for large-scale commercial
use, tubular photobioreactors are almost exclusively used, mainly because they are
easy to scale up, have a large illumination surface area, are suitable for outdoor
cultures, present good biomass productivities, and are economically reasonable.
Although used by only a portion of microalgae-based companies, bioreactors for
heterotrophic and mixotrophic cultures have also gained prominence (Borowitzka
2018). Other systems such as flat-plate and vertical photobioreactors have exploration potential but are still in their early stages where some significant limitations
need to be overcome, which are mainly associated with scale-up difficulty and high
cost (Ugwu et al. 2008).
11.6.2.1 Tubular Photobioreactors
Tubular photobioreactors were first described in 1953 (Tamiya et al. 1953), but
were not consolidated until the 1990s, after being gradually optimized (Gudin and
Chaumont 1983; Pirt et al. 1983; Chaumont et al. 1988; Chaumont 1993; Richmond
et al. 1993). Only from this point is it possible to commercially produce astaxanthin
from microalgae, as far as we know Haematococcus single-phase cultivation in largescale raceway systems has proved unsatisfactory (Bubrick 1991; Margalith 1999;
Olaizola 2000).
Unlike open systems, tubular photobioreactors allow greater control of cultivation
conditions, the possibility of contamination is lower, and the high availability of solar
radiation, which results in higher yields. It this allows using these reactors to produce
sensible strains such as H. pluvialis. Due to the lower water depth (tube diameter),
which ranges from 0.03 to 0.12 m, the biomass concentration can reach 3.0 g/L.