Intermediate culture
Intermediate culture volumes, typically 4-L flasks to
20-L carboys, are used to inoculate larger vessels, typically
100- to 200-L translucent fiberglass cylinders or polyethylene
bags, or even larger fiberglass tanks and raceways.
The complexity of the culture operation depends on the
requirement for algae and cost constraints. The simplest
culture system may be just a scaled-up version of the
starter cultures using 4-L flasks or 20-L carboys. Sterile,
nutrient-enriched seawater with an inoculum should be
aerated with a mixture of 2 percent CO2 carried in compressed
air. Illumination for culture growth is provided
by fluorescent lamps, usually mounted externally to the
culture flasks. The number of lamps used is determined
by the height and diameter of the culture vessels, with the
object of providing 15,000 to 25,000 lux measured at the
center of the empty culture container. Two 65- or 80-W
lamps are sufficient to illuminate 3-L glass flasks, which
are about 18 cm in diameter, whereas five lamps of the
same light output are necessary for 20-L carboys (Fig. 9).
Cultures 4 to 8 days old from carboys (20-L) are used
to inoculate 200-L translucent fiberglass cylinders or
polyethylene culture bags. In most cases, these larger volume
cultures are housed in greenhouses and receive natural light (adequate illumination from fluorescent bulbs
is usually cost prohibitive). The vessels are filled with
filtered, UV-irradiated, and usually chlorinated/dechlorinated
seawater, enriched and inoculated. Each cylinder
is carefully labeled to document the date of the sterilization
process, the enrichment, and the species inoculated.
Under optimal environmental conditions, the culture will
be harvested in 4 days or used to inoculate large-scale cultures
in tanks or outdoor ponds. (Fig. 10).