Microalgal Biotechnology: Today’s (Green) Gold Rush - Biotechnological Applications of Microalgae - page 204

Cryopreservation of algae also contributes to death of cultures (Day and Harding,
2008). Such effects become obvious over long periods but are not evident in short
periods—for example, the loss of B 12 requirement in axenic cultures with long-term
maintenance (Andersen, 2005). Continuous vegetative reproduction may lead to
degeneration of cells, and such lost vigor can be restored by periodic sexual repro-
duction or the addition of organic base (Andersen, 2005). Growing multiple species
may provide insight into their competition for nutrients and into the reproductive
capacity of their vegetative stages (Riegman et al., 1996).
Cultivation of microalgae under laboratory conditions in defined sterile media,
controlled temperature, and light influences their cost. For autotrophic microalgae,
more than thirty kinds of media are used (Andersen, 2005; Subba Rao, 2009) and
some of the commercially available nutrient stocks such as f/2 medium cost $25 per
liter. However, for outdoor mass cultivation systems and commercial developments,
less-expensive media based on the enrichment of wastewater should be preferred.
It would be necessary to carry out pilot experiments to critically evaluate the
suitability of these media because of variations in their chemical composition. The
use of wastewater, eutrophified water (Woertz et al., 2009; Kong et al., 2010, Park
et al., 2011), secondary sewage (Orpez et al., 2009), dairy manure (Wang et al.,
2010), swine manure effluent (Kebede-Westhead et al., 2006), farm effluents (Craggs
et al., 2004), and commercial fertilizers such as Clewat-32™ (Ronquillo et al., 1997),
Nualgi, SB07321(LM)M, Dyna-Gro™, and Miracle-Gro ® may substantially reduce
these costs while promoting vigorous algal growth.
Several designs for large-scale, flat-bed plane photobioreactors (PBRs) are
available. Algae are also grown in a closed-loop, vertical or horizontal system of
polyethylene sleeves, known as high density vertical growth (HDVG) systems,
in greenhouses (Ugwu et al., 2008). Where land is at a premium, as at Schiphol
Airport, Holland, it is proposed to construct an “ecobarrier”—a long tent parallel
to the runway (Natural Resources Defense Council, 2009). Although a futuristic
speculation, it is hoped that the ecobarrier supports algal cultivation and biofermen-
tation technologies, and integrates transportation and landscape (Natural Resources
Defense Council, 2009). However, an evaluation of the impact of temperature and
light on their performance to sustain biomass levels is difficult because of the natural
conditions. Because flat-plate photobioreactors suffer from a lack of uniform avail-
ability of light energy, it is suggested that circular-geometry bioreactors are better
suited. Grobbelaar (2009) recommended closed PBRs because of their higher light
utilization efficiencies, nutrient uptake, and biomass yield, and lower compensa-
tion light:dark ratios or respiratory losses, less contamination, and less water loss.
A mean maximum of 98 g m −2 d −1 with a maximum productivity of 170 g m −2 d −1 is
claimed by the Green Fuel reactor (Pulz, 2007), which can be attributed to a high
surface volume ratio (SVR). For industrial purposes, algae are mass cultivated by the
Israel-based Seambiotic in open-pond raceways ranging from 200 L to 1.2 × 10 6 L
covering a 3,400-m 2 area.
Cultivation of algae under natural light and temperature is more cost-effective
than under controlled laboratory conditions. Chlamydomonas sp ., Chlorella
sorokiniana, Dunaliella tertiolecta, D. salina, Haematococcus pluvialis,
Nannochloropsis sp. , Phaeodactylum tricornutum , Porphyridium purpureum,