The culture of coccolithophorid algae is an attractive option for sequestration or
recycling of CO2 as they can fix carbon by photosynthesis as well as in calcium
carbonate scales known as coccoliths. They also produce high amounts of lipids which
have a potential application as a renewable fuel.
Five species of coccolithophorids (Pleurochrysis carterae, CCMP647, Pleurochrysis sp.
CCMP1211, Gephyrocapsa oceanica CS-335/2, Emiliania huxleyi CCMP371, and
Emiliania huxleyi CS-369) were screened for their ability to grow at high temperature.
All species grew up to 28oC except E. huxleyi CS-369. However, Pleurochrysis sp.
CCMP 1211 which was found to clump and can therefore not be recommended for
large-scale cultivation. The salinity tolerance of these species was also examined.
Growth of P. carterae, G. oceanica, and E. huxleyi in laboratory scale closed
photobioreactors (plate, carboy, airlift, and tubular photobioreactors) showed the plate
photobioreactor to be the best closed cultivation system. The highest productivities
were achieved by P. carterae in the plate photobioreactor and were 0.54 g.L-1.d-1, 0.12
g.L-1.d-1, 0.06 g.L-1.d-1 for total dry weight, lipid and CaCO3 respectively.
The growth of P. carterae and E. huxleyi was also examined in an outdoor raceway
pond. The E. huxleyi culture was easily contaminated resulting in the loss of the culture
in less than three weeks, but P. carterae grew well over a period of 13 months. The
overall total dry weight productivity of P. carterae was 0.19 g.L-1.d-1 with lipid and
CaCO3 contents of up to 33% and 10% of dry weight respectively. There was little
protozoan and bacterial contamination. Medium pH increased to pH 11 during the day
and was found to be a reliable variable for maintaining the health of the culture. A
maximum pH achieved during the day of less than pH 8.5 indicated the imminent collapse of the culture. Heavy rain and low temperature were the main reasons for
culture loss in mid winter, whereas high temperature during summer favoured P.
carterae growth. A comparison of the growth of P. carterae and Dunaliella salina
MUR8 in the raceway ponds showed no significant differences between these two
species with regard to areal total dry weight productivity and lipid content.
The effects of several limiting factors were also examined. A reduction in medium pH
resulting from CO2 addition inhibited the growth of E. huxleyi in the plate
photobioreactor, whereas P. carterae growth and productivities increased in the pH
range of pH 7.7 to 8.0 in the plate photobioreactor and pH 9.1 to 9.6 in the outdoor
raceway pond. The best operational pond depth for outdoor raceway culture of P.
carterae was between 16 cm and 21 cm. Early morning temperatures, especially during
the winter, highly affected the growth of P. carterae in the raceway pond, whereas
artificially increasing the medium temperature improved the health of the culture but
resulted in little increase in productivity. Photosynthesis of P. carterae was found to be
highly inhibited by high oxygen concentration in the medium irrespective of
temperature or irradiance.
An economic model of P. carterae in a 63 ha raceway plant resulted in a cost for the
biomass of between 7.35 Aus$.Kg-1 and 14.17 Aus$.Kg-1 depending on the harvesting
method used.
| Identifer | oai:union.ndltd.org:ADTP/221666 |
| Date | January 2005 |
| Creators | n_moheimani@hotmail.com, Navid Reza Moheimani |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Navid Reza Moheimani |
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