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Design and operation of a laboratory scale photobioreactor for the cultivation of microalgae

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dc.contributor.advisor Bux, Faizal
dc.contributor.author Bhola, Virthie
dc.date.accessioned 2012-05-21T08:16:48Z
dc.date.available 2013-09-01T22:20:13Z
dc.date.issued 2011
dc.identifier.other 418172
dc.identifier.uri http://hdl.handle.net/10321/716
dc.description Submitted in fulfilment of the requirements of the Degree of Master of Technology: Biotechnology, Durban University of Technology, 2011. en_US
dc.description.abstract Due to greenhouse gas emissions from fossil fuel usage, the impending threat of global climate change has increased. The need for an alternative energy feedstock that is not in direct competition to food production has drawn the focus to microalgae. Research suggests that future advances in microalgal mass culture will require closed systems as most microalgal species of interest thrive in highly selective environments. A high lipid producing microalga, identified as Chlorella vulgaris was isolated from a freshwater pond. To appraise the biofuel potential of the isolated strain, the growth kinetics, pyroletic characteristics and photosynthetic efficiency of the Chlorella sp was evaluated in vitro. The optimised preliminary conditions for higher biomass yield of the selected strain were at 4% CO2, 0.5 g l-1 NaNO3 and 0.04 g l-1 PO4, respectively. Pulse amplitude modulation results indicated that C. vulgaris could withstand a light intensity ranging from 150-350 μmol photons m-2s-1. The pyrolitic studies under inert atmosphere at different heating rates of 15, 30, 40 and 50 ºC min-1 from ambient temperature to 800 oC showed that the overall final weight loss recorded for the four different heating rates was in the range of 78.9 to 81%. A tubular photobioreactor was then designed and utilised for biomass and lipid optimisation. The suspension of microalgae was circulated by a pump and propelled to give a sufficiently turbulent flow periodically through the illuminated part and the dark part of the photobioreactor. Microalgal density was determined daily using a Spectrophotometer. Spectrophotometric determinations of biomass were periodically verified by dry cell weight measurements. Results suggest that the optimal NaNO3 concentration for cell growth in the reactor was around 7.5 g l-1, yielding maximum biomass of 2.09 g l-1 on day 16. This was a significant 2.2 fold increase in biomass (p < 0.005) when compared to results achieved at the lowest NaNO3 cycle (of 3.8 g l-1), which yielded a biomass value of 0.95 g l-1 at an OD of 1.178. Lipid accumulation experiments revealed that the microalga did not accumulate significant amounts of lipids when NaNO3 concentrations in the reactor were beyond 1.5 g l-1 (p > 0.005). The largest lipid fraction occurred when the NaNO3 concentration in the medium was 0.5 g l-1. Results suggest that the optimal trade-off between maximising biomass and lipid content occurs at 0.9 g l-1 NaNO3 among the tested conditions within the photobioreactor. Gas chromatograms showed that even though a greater number of known lipids were produced in Run 8, the total lipid percentage was much lower when compared to Runs 9-13. For maximal biomass and lipid from C. vulgaris, it is therefore crucial to optimise nutritional parameters such as NaNO3. However, suitable growth conditions for C. vulgaris in a tubular photobioreactor calls for innovative technological breakthroughs and therefore work is ongoing globally to address this. en_US
dc.format.extent 113 p en_US
dc.language.iso en en_US
dc.subject.lcsh Biotechnology en_US
dc.subject.lcsh Microalgae--Biotechnology en_US
dc.subject.lcsh Bioreactors--Design and construction en_US
dc.subject.lcsh Biomass energy en_US
dc.subject.lcsh Renewable energy sources en_US
dc.title Design and operation of a laboratory scale photobioreactor for the cultivation of microalgae en_US
dc.type Thesis en_US
dc.dut-rims.pubnum DUT-000717


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