Microalgae: A Renewable Source of Bioproducts - Food and Industrial Bioproducts and Bioprocessing - page 219

macronutrients, such as nitrogen and phosphorus, as well as micronutrients, such as iron,
zinc, cobalt, cadmium and molybdenum, and vitamins, such as vitamins B 1 and B 12 as well
as biotin (vitamin H). Some media, such as f medium (Guillard and Ryther, 1962), have
been used for over 40 years for diverse microalgae. Several media have been developed that
contain low levels of selenium as selenite, as this has been found to be essential for some
oceanic species (K medium; Keller et al ., 1987) or assists with long term maintenance of
fastidious microalgae such as dinoflagellates (GSe medium; Blackburn et al ., 2001 ). Details
of methods for growing microalgae, including information on the different media available,
can be found in Andersen (2005) as well as on the web sites of some algal culture collections
(Table 9.1 ).
There is an increasing move to cryopreserve strains in liquid nitrogen, either as an
alternative to culturing in 'fresh' media or as the sole form of preservation for some classes
of microalgae that have proven robust enough for long term preservation by this method
(Andersen and Sexton, 2009). Cryopreservation is a reliable form of maintenance for
chlorophytes and cyanobacteria (Mori et al ., 2002), but further testing of genetic stability is
needed for other classes.

9.5 MICROALGAL PRODUCTION SYSTEMS

To grow microalgae for bioproducts and other industrial applications it is necessary to scale
up production of microalgae using large scale production systems. There are many different
types of algal growth technologies ranging from very simple to complicated engineering
works. The main types of growth systems are described in the following sections.

9.5.1 Plastic bags and tanks
With the development of the aquaculture industry and the need by hatcheries to rear larval
and juvenile aquaculture animals came the need for production of microalgae as live feeds.
While some hatcheries grow microalgae in multiples of relatively small scale culture con-
tainers, for example 20 litre carboys, it is more common for microalgal cultures to be grown
in disposable plastic bags (200-1000 litres is typical) that are either supported vertically
(Plate 9.1b) in metal frames or lie horizontally.

9.5.2 Open ponds
Open ponds include naturally occurring ponds as well as low technology constructions that
are low cost and relatively easy to build and operate. Different types of ponds varying in
size, shape, construction material, method of mixing, and inclination have been designed.
Overall, other than natural ponds or lakes, there are three major types constructed: (1)
inclined systems where mixing is achieved through pumping and gravity flow, (2) circular
ponds with agitation provided by a rotating arm, and (3) raceway ponds constructed as an
endless loop, in which the culture is circulated by paddle wheels (Tredici, 2004). For
commercial algal production, natural ponds and lakes, circular ponds with agitation, and
raceways are successfully used. Examples of commercial production from natural ponds or
lakes include the harvesting of natural blooms of the cyanobacterium (blue-green alga)
Aphanizomenon flos-aquae var. flos aquae (Carmichael et al ., 2000 ). In Australia, artificial
hypersaline 'lakes' are used by Cognis Australia to grow Dunaliella salina for

β -carotene