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Title: Feasibility studies on selected strains of microalgae for biofuel production in Hong Kong
Authors: Tse, Pui Kam
Degree: Ph.D.
Issue Date: 2017
Abstract: The possibilities of marine based microalgae as multi-functional feedstock are being evaluated in the United States and Europe due to their robustness in cultivation and their high productivity of valuable lipids for both energy and nutrient supplement purpose. However, such assessments had not been done in Hong Kong as a city having high energy consumption and with totally different environmental conditions as in the US. In the first part of this thesis, a Prorocentrum species (HKD2) and a Dunaliella species (HKG4) were chosen from five screened strains to be potential microalgal feedstock due to their abilities to grow in a robust open cultivation condition. Moreover, it was also found that a gram-negative marine bacterium (PS1) had stimulated the growth of HKG4 for more than three times in terms of cell number, and nearly two times in terms of dried weight. However, none of the potential stimulators tested (mung bean extracts, recombinant insulins and PS1 bacterium) were found to have effects on growth of HKD2, a dinoflagellate. In the second part, the two microalgal cultures were up-scaled from laboratory incubators to a 100L scale cultivation system with different forms of aeration. It was shown that 5% carbon dioxide had improved the cell growth for 47-68% in terms of cell numbers and dried weight. Moreover, co-cultivation of HKG4 with PS1 in 100L scale cultures would also increase 69% of the dried biomass of HKG4. Gas chromatography analysis also showed that lipid extracts of HKG4 contain a lower degree of fatty acid unsaturation, which are preferable for biodiesel production. In contrast, HKD2 produces over 45% of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in combination of their total fatty acid content, which are preferable for poly-unsaturated fatty acid refinery. Further assessment of cultivation sustainability of the two cultures in open, semi-continuous cultivation in Hong Kong had recorded an estimated productivity of 2,774kg ha⁻¹ year⁻¹ of biodiesel from HKG4. It was also estimated that 1,198kg ha⁻¹ year⁻¹ of EPA and DHA can be achieved from HKD2, although the HKD2 cultures were not sustainable in peak summertime with temperature over 32°C. By the assessments of different harvesting methods, it was also find that continuous centrifugation system is the best method for large scale microalgae harvesting. In the last part, to find ways to increase algal biomass productivity further, the blooming mechanism of a dinoflagellate was studied. As an algal bloom describes the massive grow of microalgae in certain sea area, finding bloom mechanism may help promoting microalgal growth. The biomass of a local Scrippsiella trochoidea bloom in August 2012 were harvested. Laboratory cultures of the same species were established by picking living clones from the bloom biomass. The transcriptome library of the species was constructed using illumina sequencing platform. Then, the proteomes of the cells in the laboratory in early growth phase (EG), as well as the bloom cells in early bloom (EB) and maximum population stage (MP) were compared using the late growth phase of the laboratory cells (LG) as the denominator with the combined method of ¹⁵N metabolic protein labeling and shotgun proteomic approaches. The mass spectra data acquired by the liquid-chromatography-linked mass spectrometry analysis were searched against the transcriptome library established for protein identification. Using this approach, it was revealed that proteins involved in light harvesting and oxidative phosphorylation process of the bloom cells were more abundant in the EB stage. When the bloom progressed to the MP stage, these two processes were down-regulated. More importantly, the interconnective pathways of these two process did not show co-expression. These patterns of expressional changes were now shown in the laboratory comparisons (EG vs LG). it is then hypothesized that the bloom initiating events or chemicals stimulated the pre-EB cells by increasing its synthesis of ATP, and decreased the connecting pathways between light harvesting and oxidative phosphorylation. It is believed that these biological processes prepare the cells for blooming. To conclude, we found two microalgal species which are potential biofuel feedstock and producer of valuable fatty acids and are suitable for large scale cultivation in Hong Kong. Co-cultivation of the algae HKD4 with a bacterium PS1 could promote growth of the green algae species tremendously. The energy demand and cost of different harvesting strategies were also studied. Finally, some potential preparative biomolecular events were found in S. trochoidea in its early bloom stage.
Subjects: Hong Kong Polytechnic University -- Dissertations
Microalgae -- Biotechnology
Biomass energy
Biomass chemicals
Biomass energy -- China -- Hong Kong
Pages: xxv, 469 pages : color illustrations
Appears in Collections:Thesis

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