Biology Reference
In-Depth Information
and utilization of CO
2
reach maximum values of 6 and 38%, after 4 and
7 d, respectively. Instead of mineral medium, the possibility of growing
the alga on biogas slurry, swine waste water, cattle waste or water from
aquaculture ponds with proper supplementation of nutrients including
CO
2
and minerals suggests the possibility of recycling waste water for
economic benefi ts.
Spirulina
grows relatively slowly, with an output of
about 5 g dry mass/m
2
/day, in a medium of solid cattle waste extract in
water containing sodium chloride at 10 g/l. The growth rate and output
rate were substantially increased when the waste-based medium was
fortifi ed with carbon, nitrogen and phosphorus. Aeration of the algal
cultures considerably improved the output rate of algal biomass (Mitchell
and Richmond, 1998).
After cultivation,
Spirulina
and other microalgae
can be harvested by simple fi ltration process through cloth. They are
dewatered by centrifugation and dried to a powder. The biomass is usually
dehydrated by sun-, drum-, or spray-drying.
Spirulina
are available in
powder, fl ake, capsule, and tablet form (Becker and Venkataraman, 1984;
Mitchell and Richmond, 1998).
The development of effi cient photo bioreactors signifi cantly extends the
number of species that can be cultivated under controlled conditions and
the range of extractible products, for example:
-carotene, phycocyanin,
phycoerythrin and glycerol (Borowitzka, 1999). Nutrient composition
of the biomass of microalgae cultivated in a photo-reactor is highly
infl uenced by residence time in the reactor. The biomass harvested for
short residence times is generally richer in protein and unsaturated fatty
acids than biomass harvested for high residence time (Rebolloso-Fuentes et
al., 2001; Madigan and Martinko, 2005). A helical tubular photo bioreactor
system has also been developed which allows these algae to be grown
reliably outdoors at high cell densities in semi-continuous culture. Other
closed photo bioreactors such as fl at panels are also being developed.
The high cost of microalgae culture systems relates to the need for light
and the relatively slow growth rate of the algae. Developments in photo
bioreactors allow successful cultivation of different species of microalgae
under controlled conditions for a range of extractible products including
β-carotene, phycocyanin, phycoerythrin, glycerol, etc. These organisms
range in size from microscopic single cells to giant kelp averaging several
meters. The problems of propagation of mixed culture populations and
frequent contaminations by bacteria, fungi, protozoa etc. hamper the
production affecting the quality of the microalgae. For safety reasons, the
microalgae used for human and animal consumption should be grown
in good quality water
(Borowitzka, 1999; Lorenz and Cysewski, 2000;
Matsunaga et al., 2005; Venugopal, 2008).
β
