Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/29528
Title: ENHANCED LIPID PRODUCTION OF MARINE MICROALGAE FOR BIODIESEL FEEDSTOCK
Authors: DOAN THI THAI YEN
Keywords: marine microalgae, biodiesel feedstock, flow cytometry, Nile red, Nannochloropsis sp., microalgal lipid
Issue Date: 19-Jan-2011
Source: DOAN THI THAI YEN (2011-01-19). ENHANCED LIPID PRODUCTION OF MARINE MICROALGAE FOR BIODIESEL FEEDSTOCK. ScholarBank@NUS Repository.
Abstract: Biodiesel production from microalgae lipids is increasingly regarded as a more sustainable and feasible alternative to conventional biodiesel feedstocks derived from terrestrial bioenergy crops. To render microalgae-based fuels feasible, development of an effective and rapid technique for oleaginous microalgae isolation/screening, and enhancing intrinsic lipid content of selected strain(s) is required. Therefore, this thesis aims to achieve following objectives: 1) To develop a high throughput screening and isolation technique to select indigenous strains of marine microalgae for intrinsic high biomass and lipid production capacity; 2) To enhance lipid production of a selected microalgae strain using flow cytometry techniques; 3) To cultivate the improved strain in a culture system (i.e. a pilot-scale raceway pond). To achieve Objective 1, a technique for microalgae isolation was developed based on flow cytometric cell-sorting (FACS), whereby cell-sorting was based on the two dimensional distribution of algal cells for red fluorescence (representing chlorophyll auto-fluorescence) against forward light scatter (representing cell size). From a total of ninety six strains of marine microalgae isolated from the coastal waters of Singapore, Nannochloropsis strains were selected as promising candidates for biodiesel feedstock, where lipid content ranged from 39.4% to 44.9% of dry weight biomass. For Objective 2, methods to determine total and neutral lipids in Nannochloropsis via gravimetric extraction or Nile red (NR) fluorescence measurements were optimized. For the gravimetric method, factors affecting intracellular lipid extraction from marine microalgae were investigated. Freeze-, oven- and solar drying did not affect lipid yield using accelerated solvent extraction (ASE). A chloroform-methanol (2:1) solvent mixture yielded maximum total lipid extraction with a range of 16 to 35% and amount of neutral lipids and polar lipids at 17.9 and 10.6% respectively, where hexane extracted the least at 10.6 and 3.3%, respectively. For the NR fluorescence method was modified and improved as a rapid and sensitive screening tool to estimate levels of intracellular neutral lipid in Nannochloropsis sp. Addition of either glycerol or DMSO into microalgae cultures greatly increased fluorescence intensity of stained cells. The optimized procedure requires a mix of glycerol or DMSO at a concentration of 0.1 and 0.165g.mL-1 respectively for peak fluorescence in a live culture of Nannochloropsis sp. Lipid production in Nannochloropsis sp. was enhanced using two procedures were utilized i) a FASC system to select oil-rich cells; and ii) random mutagenesis to induce cellular lipid production, followed by FACS to select oil-rich mutants. With the first procedure, the intracellular lipid content was doubled to 55 % (biomass dry weight) in the daughter cells after three consecutive rounds of cell sorting, and maintained for approximately one hundred subsequent cell generations. For the second procedure, Nannochloropsis sp. were treated with the mutagen EMS, and then followed by FACS to isolate mutants. The study shows that FACS and random mutagenesis are powerful tools for the enhancement of intracellular lipid content and improvement of fatty acid composition in microalgae exploited for biodiesel feedstock. Objective 3 focused on the cultivation of the improved strain at a larger scale, where the balance of biomass production and lipid accumulation was investigated. The mutant strain of Nannochloropsis was cultivated in 250L raceway ponds under single phase and bi-phasic mode. Under bi-phasic mode, with a supplement of sodium acetate (NaAc), total lipid content net FAME content was 2.6 times and 2.3-fold greater than that of single phase cultivation. Generally, the mutant strain of Nannochloropsis was cultivated in bi-phasic mode inducing lipid content and improved fatty acid profile.
URI: http://scholarbank.nus.edu.sg/handle/10635/29528
Appears in Collections:Ph.D Theses (Open)

Show full item record
Files in This Item:
File Description SizeFormatAccess SettingsVersion 
DoanTTY.pdf2.45 MBAdobe PDF

OPEN

NoneView/Download

Page view(s)

806
checked on Dec 11, 2017

Download(s)

150
checked on Dec 11, 2017

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.