256
M. M. Maroneze et al.
species, but most raceway-grown species are mesophilic, which have ideal growth
temperatures in the range of 24–40 °C. Since cultivations in these systems are usually
operated continuously, temperature control can be done by cooling or heating the feed
water or by circulating the culture in external heat exchangers. However, these are
unlikely to be affordable options, so control is rarely done. Because of this, the process
performance of open systems is dependent on the prevailing weather conditions in
a particular locality. Therefore, to achieve a viable process, the selection of suitable
locations as a function of its climatic conditions is critically important (Brusca et al.
2017).
In terms of cost, one of the great appeals of this type of system is the relatively
low investment value that varies from 0.13 to 0.37 Me/ha at 100 ha scale (Norsker
et al. 2011; Chisti 2012). The data from raceway ponds are evidently highly variable
depending on the species, culture medium, climate, geographical position, in addition to other variables. Although high biomass productivities, like 37 g/m
2 /d for D.
salina has been reported (Moheimani and Borowitzka 2006), in average much lower
productivities are usually described, such as 9–13 g/m
2 /d for Spirulina sp. (Olguin
et al. 2003), 1.6–3.5 g/m
2 /d when producing D. salina (Garcia-González et al. 2003),
and 4–10 for Spirulina sp. (Delrue et al. 2017). This variation will also reflect on
the cost of biomass production, which, according to Acién et al. (2019), is 4.5 e/kg.
Delrue et al. (2017) estimated that the cost to produce Spirulina in raceway ponds
ranges from 3.8 to 9.5 e/kg depending on the system’s productivity.
11.6.1.2 Extensive Unmixed Ponds
The two largest producers of β-carotene from D. salina in the world are
Western Biotechnology Ltd. (Perth, Western Australia) and Betatene Ltd. (BASF)
(Melbourne, Victoria) in Australia. These and other Australian companies grow
microalgae in extensive and shallow ponds built on the bed of a hypersaline coastal
lagoon or formed by the artificial expansion of a lagoon (Borowitzka 2013). The
extensive unmixed ponds or shallow ponds, Unmixed extensive lagoons or shallow
lagoons are so-called because they are generally less than 0.5 m deep, up to 250 ha
in area, and do not have a mixing system, except for wind and convection (Kumar
2015).
Unmixed ponds can represent the most economical and least technical of all
commercial culture methods when suitable climatic conditions allow almost yearround cultivation, as is the case in some regions of Australia. In Western Australia and
South Australia, where are located the two largest commercial microalgae production
plants in the world, there is very high annual irradiance, warm weather, and low
rainfall, ideal conditions for growth in natural ponds (Trediti 2004).
The main advantages of this type of approach are linked to the economic appeal as
they operate without CO 2 addition with minimal control, plus in Australia, the cost
of land is low, and water is free except for pumping costs (del Campo 2007). On the
other hand, such ponds are mainly limited to growing microalgae which are capable
of surviving in poor conditions or have a competitive advantage that allows them to
M. M. Maroneze et al.
species, but most raceway-grown species are mesophilic, which have ideal growth
temperatures in the range of 24–40 °C. Since cultivations in these systems are usually
operated continuously, temperature control can be done by cooling or heating the feed
water or by circulating the culture in external heat exchangers. However, these are
unlikely to be affordable options, so control is rarely done. Because of this, the process
performance of open systems is dependent on the prevailing weather conditions in
a particular locality. Therefore, to achieve a viable process, the selection of suitable
locations as a function of its climatic conditions is critically important (Brusca et al.
2017).
In terms of cost, one of the great appeals of this type of system is the relatively
low investment value that varies from 0.13 to 0.37 Me/ha at 100 ha scale (Norsker
et al. 2011; Chisti 2012). The data from raceway ponds are evidently highly variable
depending on the species, culture medium, climate, geographical position, in addition to other variables. Although high biomass productivities, like 37 g/m
2 /d for D.
salina has been reported (Moheimani and Borowitzka 2006), in average much lower
productivities are usually described, such as 9–13 g/m
2 /d for Spirulina sp. (Olguin
et al. 2003), 1.6–3.5 g/m
2 /d when producing D. salina (Garcia-González et al. 2003),
and 4–10 for Spirulina sp. (Delrue et al. 2017). This variation will also reflect on
the cost of biomass production, which, according to Acién et al. (2019), is 4.5 e/kg.
Delrue et al. (2017) estimated that the cost to produce Spirulina in raceway ponds
ranges from 3.8 to 9.5 e/kg depending on the system’s productivity.
11.6.1.2 Extensive Unmixed Ponds
The two largest producers of β-carotene from D. salina in the world are
Western Biotechnology Ltd. (Perth, Western Australia) and Betatene Ltd. (BASF)
(Melbourne, Victoria) in Australia. These and other Australian companies grow
microalgae in extensive and shallow ponds built on the bed of a hypersaline coastal
lagoon or formed by the artificial expansion of a lagoon (Borowitzka 2013). The
extensive unmixed ponds or shallow ponds, Unmixed extensive lagoons or shallow
lagoons are so-called because they are generally less than 0.5 m deep, up to 250 ha
in area, and do not have a mixing system, except for wind and convection (Kumar
2015).
Unmixed ponds can represent the most economical and least technical of all
commercial culture methods when suitable climatic conditions allow almost yearround cultivation, as is the case in some regions of Australia. In Western Australia and
South Australia, where are located the two largest commercial microalgae production
plants in the world, there is very high annual irradiance, warm weather, and low
rainfall, ideal conditions for growth in natural ponds (Trediti 2004).
The main advantages of this type of approach are linked to the economic appeal as
they operate without CO 2 addition with minimal control, plus in Australia, the cost
of land is low, and water is free except for pumping costs (del Campo 2007). On the
other hand, such ponds are mainly limited to growing microalgae which are capable
of surviving in poor conditions or have a competitive advantage that allows them to