Because concentrations of carbon dioxide in the air are low, maximum photosynthesis activity cannot be obtained, and the rate of dissolution into the culture
medium is low. Under typical agitation conditions, a rate of carbon dioxide dissolution greater than 2.4–9.6 g/m
2 day cannot be expected in the air. Production of
24 g of leaf body dry weight per square meter-day typically requires a supply of
carbon dioxide. For this reason, the culture ground must be maintained in an
enclosed system to increase the usage rate when carbon dioxide is artificially
ventilated (Liu and Hu 2013).
The mixotrophic culture approach attempts growth simultaneously through
organic carbon such as acetic acid and through photosynthesis. It is general performed with outdoor media. Mixotrophic multiplication of Chlorella includes both
multiplication through organic carbon and multiplication through photosynthesis.
Because productivity per unit area and unit medium is higher than with photoautotrophic culture, some degree of culturing temperature control is possible. The
absence of light as a limiting factor results in higher leaf body concentrations and
easier harvesting. Another great advantage is that large quantities of CO 2 are
emitted into the culture medium as the Chlorella cells consume one mole of acetic
acid, which can then be used for photosynthesis.
Heterotrophic culture uses organic carbon such as glucose or acetic acid to
multiply Chlorella in a tank with no light present. Conditions within the tank can be
fully controlled for culturing. High-concentration culturing of 50 g/L or more in
cell dry weight can be achieved, and productivity per unit area is very high
(Fig. 7.3) (Liu and Hu 2013; Maruyama and Ando, 1992).
While Chlorella cells can synthesize the pigments and proteins needed for
photosynthesis even when cultured under light-free conditions, the amounts are
slightly lower than in photosynthesizing Chlorella cells.
Chlorella production is performed through selection of one of these culturing
methods. In many cases, two approaches are used simultaneously, such as
pure-breed culturing through heterotrophic or photoautotrophic culture and productive culturing through mixotrophic culture.
(2) Strains
Because proliferation properties differ between strains (Table 7.3), the productivity
of mass culturing depends on the strain used. Natural lines are typically separated
into many strains, and those with outstanding proliferation are used with the culture
method suited to the purpose. Varieties typically used include Chlorella vulgaris,
C. ellipsoidea, C. pyrenoidosa, and C. regularis.
For photoautotrophic culture using sunlight, it is beneficial to use strains with
how solar light usage efficiency (energy transformation efficiency). At around
150 klx, sunlight is more intense than the photosynthesis saturation value (2.7–
28 klx) for the Chlorella genus. Light that is more intense than the saturation value
cannot be used for photosynthesis. Accordingly, it is beneficially to select and use
strains with high photosynthesis saturation values to increase energy transformation
efficiency.
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7 Microalgae, a Biological Resource for the Future
medium is low. Under typical agitation conditions, a rate of carbon dioxide dissolution greater than 2.4–9.6 g/m
2 day cannot be expected in the air. Production of
24 g of leaf body dry weight per square meter-day typically requires a supply of
carbon dioxide. For this reason, the culture ground must be maintained in an
enclosed system to increase the usage rate when carbon dioxide is artificially
ventilated (Liu and Hu 2013).
The mixotrophic culture approach attempts growth simultaneously through
organic carbon such as acetic acid and through photosynthesis. It is general performed with outdoor media. Mixotrophic multiplication of Chlorella includes both
multiplication through organic carbon and multiplication through photosynthesis.
Because productivity per unit area and unit medium is higher than with photoautotrophic culture, some degree of culturing temperature control is possible. The
absence of light as a limiting factor results in higher leaf body concentrations and
easier harvesting. Another great advantage is that large quantities of CO 2 are
emitted into the culture medium as the Chlorella cells consume one mole of acetic
acid, which can then be used for photosynthesis.
Heterotrophic culture uses organic carbon such as glucose or acetic acid to
multiply Chlorella in a tank with no light present. Conditions within the tank can be
fully controlled for culturing. High-concentration culturing of 50 g/L or more in
cell dry weight can be achieved, and productivity per unit area is very high
(Fig. 7.3) (Liu and Hu 2013; Maruyama and Ando, 1992).
While Chlorella cells can synthesize the pigments and proteins needed for
photosynthesis even when cultured under light-free conditions, the amounts are
slightly lower than in photosynthesizing Chlorella cells.
Chlorella production is performed through selection of one of these culturing
methods. In many cases, two approaches are used simultaneously, such as
pure-breed culturing through heterotrophic or photoautotrophic culture and productive culturing through mixotrophic culture.
(2) Strains
Because proliferation properties differ between strains (Table 7.3), the productivity
of mass culturing depends on the strain used. Natural lines are typically separated
into many strains, and those with outstanding proliferation are used with the culture
method suited to the purpose. Varieties typically used include Chlorella vulgaris,
C. ellipsoidea, C. pyrenoidosa, and C. regularis.
For photoautotrophic culture using sunlight, it is beneficial to use strains with
how solar light usage efficiency (energy transformation efficiency). At around
150 klx, sunlight is more intense than the photosynthesis saturation value (2.7–
28 klx) for the Chlorella genus. Light that is more intense than the saturation value
cannot be used for photosynthesis. Accordingly, it is beneficially to select and use
strains with high photosynthesis saturation values to increase energy transformation
efficiency.
206
7 Microalgae, a Biological Resource for the Future