Biomedical Engineering Reference
In-Depth Information
and covered with a plastic lining. The largest raceway pond in operation is 5,000 m 2 ,
located at Earthrise Nutritionals, a commercial Spirulina producer in Southern
California (Spolaore et al., 2006).
By convention, in continuous production, nutrients are introduced in front of the
paddlewheel and harvesting takes place behind the wheel (Brennan and Owende,
2010). CO 2   is provided by gas exchange via natural contact with the surrounding
air (Singh et  al., 2011). Occasionally, submerged aerators are installed to enhance
CO 2  absorption. Light provision is by natural sunlight. Ponds can be placed inside
covered tunnels to aid in temperature regulation.
Raceway ponds incur relatively low capital investment as well as operational costs.
Weekly monitoring is usually sufficient, and the main costs are in the media compo-
nents and the energy consumed for mixing (Singh et al., 2011). Biomass concentra-
tions are normally in the region of 0.5 g L −1 , with a biomass productivity of 10 to
25 g m −2 d −1 (Sheehan et al., 1998; Lee, 2001). Raceway ponds have been in use since
the first commercial microalgal ventures were established, and extensive experience
in their design and operation exists. Examples of the productivities obtained with
various microalgal species in raceway ponds are given in Table 5.2.
The only open system to achieve very high cell densities sustainably is the cascade
system developed in the Czech Republic and used for cultivation of Chlorella
(Setlik et al., 1970). With a culture depth of less than 1 cm, cell densities of up to
TABLE 5.2
Examples of Productivities Achieved in Open Ponds with
Various Microalgal Species
Highest Productivity
Species
g m −2 d −1
g l −1 d −1
Ref.
Amphora
39
Sheehan et al., 1998
Ankistrodesmus falcatus
0.18
Sheehan et al., 1998
Chaetoceros muelleri
26
0.18
Sheehan et al., 1998
Chlorella sp.
14
Sheehan et al., 1998
Chlorella sp.
2
Setlik et al., 1970
Chlorella vulgaris
40
Piorreck et al., 1984
Cyclotella cryptica
27
Sheehan et al., 1998
Isochrysis galbana
28
Sheehan et al., 1998
Nannochloropsis
15
Sheehan et al., 1998
Nannochloropsis salina
25
Sheehan et al., 1998
Porphyridium purpureum
0.18
Sheehan et al., 1998
Scenedesmus obliquus
48
Grobbelaar, 2000
Spirulina platensis
12
Piorreck et al., 1984
Spirulina platensis
27
0.18
Richmond et al., 1990
Spirulina sp.
69
De Morais et al., 2009
Spirulina sp.
19
0.15, 0.32
Pushparaj et al., 1997
Tetraselmis suecica
19
Sheehan et al., 1998
 
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