Utilization of Industrial-wastes for the production of biodiesel and docosahexaenoic acid by microalgae = 산업 폐기물을 이용한 미세조류 유래 바이오 디젤 및 디에이치에이 생산 연구

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The large amount of fossil fuels has been consumed since industrialization began in the 18th century. In addition, the expenditure of fossil fuels is being increasingly accelerated by an exploding population, nowadays. Although fossil fuels drove economic growth and supported the conveniences of life, they also gave rise to serious environmental problems since carbon dioxide $(CO^2)$. Therefore, in order to meet the present level of energy demands and alleviate climate change, it is inevitable that fossil fuels must be replaced by renewable, sustainable, and eco-friendly next-generation fuel. Moreover, it should be used as transportation fuel in liquid form. Microalgae can capture light energy from the sun and convert carbon dioxide to organic matter by photosynthesis. Due to its high oil productivity and rapid growth potential, microalgae are used as feedstock for third generation biofuel, which has potential to replace petroleum fuels in the foreseeable future. Some microalgae species can uptake organic carbon sources as energy and nutrients for their growth and lipid induction. This type of cultivation mode is called heterotrophic or mixotrophic cultivation. Although microalgae grow much faster with high lipid accumulation than phototrophic cells, organic carbon sources are required. Therefore, heterotrophic and mixotrophic cultivations can be costly and less economically feasible. In order to decrease the costs associated with microalgal cultivation including the carbon source and nutrients, we must find inexpensive carbon and nutrient sources for microalgae cultivation. In chapter 3, we measured the growth of and lipid production by the model microalga Chlamydomonas reinhardtii under different phototrophic, heterotrophic, and mixotrophic conditions to determine the optimal conditions for growth and biodiesel production. In particular, we examined cell growth and yield of fatty acid methyl esters (FAMEs) when C. reinhardtii was cultured in the presence of different organic carbon sources (acetate, glucose, glycerol, and sucrose). C. reinhardtii grew under various conditions, but mixotrophic cultivation was best. The greatest biomass production ($2.15 gL^{-1}$ in 5 days) and FAME yield (16.41% of biomass) were observed under mixotrophic cultivation with acetate $(10 gL^{-1})$. As an alternative to acetate, we additionally tested the use of volatile fatty acids (VFAs; acetic, propionic, and butyric acids), which can be inexpensively produced through fermentation of food waste. The highest FAME yield (19.02% of biomass) and biomass production ($2.05 gL^{-1}$ in 5 days) were obtained with $5 gL^{1}$ of VFAs. This result indicates that VFAs can serve as an inexpensive alternative carbon source for maximizing lipid production in mixotrophic cultivation of C. reinhardtii. In chapter 4, the present study assessed the use of hydrolysate of lipid extracted algae (LEA) combined with the sugar factory wastewater (SFW) as a low cost nutrient and a carbon source, respectively for microalgal cultivation. Microalgal strain Ettlia sp. YC001 was both mixotrophically and heterotrophically cultivated using various amounts of hydrolysate and SFW. The culture which was grown in medium containing 50% LEA hydrolysate showed highest growth, achieving $5.26 ± 0.14 gL^{-1}$ after 12 days of cultivation. The addition of SFW increased the lipid productivity substantially from 5.8 to 95.5 $mgL^{-1}d^{-1}$ when the culture medium was fortified with 20% SFW. Gas chromatography analysis indicated a noticeable increase of 20% in C16 and C18 fraction in FAME distribution under above condition. Therefore, it can be concluded that the combination of LEA hydrolysate and sugar factory waste water can be a powerful growth medium for economical algal cultivation. In chapter 5, we considered the usage of sugar factory wastewater (SFW) as an inexpensive carbon source for cultivation of heterotroph marine strain Aurantiochytrium sp. KRS101 for the production of docosahexaenoic acid (DHA). The highest biomass yield (20.03 $gL^{-1}$ in 5 days) was obtained using 30% of SFW in medium, which was higher than that of pure glucose control (concentration of glucose: 30 $gL^{-1}$). In addition, the biomass was maximized to 22.44 ± 0.41 $gL^{-1}$ in 5 days by optimizing the concentration of N and P sources to 20 $gL^{-1}$ of yeast extract and 9 $gL^{-1}$ of monopotassium phosphate, respectively. Lipid accumulation and composition are affected by chemical and physical environmental stimuli such as salinity, temperature, and medium pH. In order to increase the DHA yield with a large amount of biomass, sea salt was added to medium on different cell growth phase. The highest DHA yield (2.03 $gL^{-1}$ in 5 days) was obtained when we increase initial sea salt concentration from 15 $gL^{-1}$ to 35 $gL^{-1}$ at stationary phase. In this study, we confirmed Aurantiochytrium sp. KRS101 can be successfully cultivated heterotrophically using an alternative carbon source from wastewaters. Moreover, DHA yield can be increased by environmental stimuli such as salinity. We believe that these findings may have a significant impact on the future technology development for DHA production using Aurantiochytrium sp. KRS101
Chang, Yong Keunresearcher장용근researcherYang, Ji-Wonresearcher양지원researcher
한국과학기술원 :생명화학공학과,
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학위논문(박사) - 한국과학기술원 : 생명화학공학과, 2016.2 ,[x, 105 p. :]


Microalgae; Industrial-wastes; Biodiesel; Docosahexaenoic acid (DHA); Alternative nutrient sources; 미세조류; 산업 폐기물; 바이오 디젤; 디에이치에이; 저가 영양분

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