Due to the numerous disadvantages associated with the use of fossil fuels, focus has been
drawn on the environmentally friendly, renewable and carbon-neutral alternative, algalbased
biofuels. Many microalgal species have been studied due to their ability to
produce significant lipid yields which may be converted to biodiesel. In the present study
three microalgal species were screened and a model organism that produced maximal
lipid yields, had the greatest lipid productivity and showed potential to be used on a large
scale basis, was selected. The selected species was identified, using both morphological
and molecular methods, as Isochrysis galbana U4. Nitrogen (N) limitation and depletion
studies showed that an internal N reservoir determines cell growth and eventual lipid
accumulation in I. galbana when the external N reserves are deplete. Intracellular N
depletion was associated with a decrease in the pyrenoid size and chlorophyll content, a
breakdown of the chloroplast and the production of large lipid bodies which is
advantageous in terms of lipid sequestration for biodiesel production. Cost reduction
approaches for the mass culture of I. galbana were investigated. Factors that were proven
to reduce costs, without altering the final lipid yield, included the use of urea as a N
source and the supply of lower phosphorus (P) levels since this species is capable of
growing optimally with as little as 0.25 ppm P. Furthermore, I. galbana cells demonstrated spontaneous flocculating abilities when cultured for prolonged periods.
This is advantageous in the cost reductions of downstream harvesting processes. Both, 7
L and 16 L photobioreactors (PBR) were tested. Culture upscale resulted in the
concomitant decrease in algal growth rate which was attributed to the limitations on the
carbon dioxide and light supply in scaled up systems. Hence, it is suggested that multiple
smaller units be used in an industrial setup. Overall, I. galbana is a promising candidate
for biodiesel production, due to its ability to produce large amounts of lipid, its elevated
growth rates and low P demand. The use of a two-phase PBR (The first phase being
nutrient replete, promoting cell growth and division, and the second phase nutrient
deplete, promoting lipid production) for the mass culture of this species in industry is
recommended.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/14945 |
| Date | 21 July 2014 |
| Creators | Roopnarain, Ashira |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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