Study on the lipid production from microalgal cultures and producing biodiesel from the microalgal lipid

• Main Author: 蔡明達
• Other Authors: 林志生
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/58544722020504351959

碩士 === 國立交通大學 === 生物科技系所 === 97 === In recent years, people over the world face some acute problem with regard to global warming and energy crisis. Humans exploited the fossil energy and developed the industry and civilization well in past hundred years to result in the environmental problems, green-house gas emission rising, and petrochemical fuel exhausting. Photosynthetic organism, microalgae, can use solar energy efficiently to combine water with CO2 to produce biomass. Microalgae can not only produce biomass but accumulate lipid in microalgal cells. Lipids from microalgae can be extracted and converted to biodiesel fuel by transesterification. In the study, the biomass and lipid productivity of Chlorella sp. and Nannochloropsis oculata were evaluated in the different conditions of culture in the closed photobioreactors. Results showed that the lipid accumulation of Chlorella sp. and N. oculata from logarithmic phase to stationary phase were significantly increased from 12% to 24% and 21% to 50%, respectively. In the semiconscious culture of Chlorella sp. and N. oculata, the total lipid productivity was 0.143 and 0.142 (g/L/d), respectively although the cultures were daily replaced half of broth. The results showed that Chlorella sp. and N. oculata were potential candidates for biomass and lipid production by semicontinuous cultures. The comparison of lipid productivities in the semicontinuous systems in which the culture broth were replaced at an interval of 24 h (one-day replacement) or 72 h (three-day replacement) was performed. The result indicated the total lipid yield in the semicontinuous culture operated by one-day replacement was more efficient. Moreover, different carbon sources supplied in the culture could make distinct growing ability and lipid accumulation. The results showed the cultivation of N. oculata using sucrose as carbon source in mixotrophic growth gave the highest maximum biomass (0.80 g/L) and the lipid productivity was up to 0.284 (g/L). Although the lipid contents from the heterotrophic cultivations with sucrose could increase to 54%, the biomass productivity decreased in the heterotrophic cultures. Therefore, the recovery of microalgal cells from semicontinuous cultures can transfer to mixotrophic cultivation for higher lipid production. The fast analysis of lipid contents of live microalgal cells by Nile red staining under fluorescence was established. The linear regression of fluoresce intensity of lipid content was established to measure the lipid contents of microalgae. The typical transesterification method used in this study was chemical and enzymatic processes. The results indicated the efficiency of transesterification by acid catalyst could approach 88% and the efficiency by lipase-catalyzed transesterification could reach 82% by the optimal oil/methanol molar ratio. The high cost and long reaction time of enzymatic processes may be not convenient for usage. In industrial and commercial application, the chemical catalyst is common for transesterification to reach the purposes of low-cost and fast reaction rate. Therefore, the fast and suitable transesterification method in this study is acid-catalytic process.