| Summary: | 碩士 === 國立雲林科技大學 === 環境與安全衛生工程系 === 102 === Microbial lipid has many advantages, such as short life cycle, no demand of large farm land, no influence by weather, easily large-scale production and similar fatty acids compositions with vegetable oils. Oleaginous yeast with high growth rate, no need of illumination and fast lipid accumulation has attracted much interest in recent decades. Crude glycerol is a major byproduct in the biodiesel manufacturing process. Along with increasing demand for biofuels,it consequentially produces the massive quantity of crude glycerol needed to be treated. To deal with crude glycerol and transform it into useful oil feed for biodiesel,in this study, oleaginous yeasts were isolated from activated sludge tank of a biodiesel plant, and the bioconversion of crude glycerol into cellular oil using isolated yeasts was investigated.
The factors affecting yeast growth and lipid accumulation include carbon source, nitrogen source, temperature, pH, and carbon/nitrogen ratio. This study used different incubation parameters to realize the cell growth and lipid accumulation. In addition, to avoid excess use of organic solvent to extract lipid, this study also established optimum lipid extraction conditions to receive efficient lipid yield.
The results showed that 4 yeast strains were isolated from the biodiesel plant. Strain LP-1 and LP-2 were identified as Candida rugosa and Rhodotorula mucilaginosa,respectively. Different biomass weight significantly influenced lipid extraction efficiency. Higher biomass amount caused lower extraction efficiency. The optimal biomass weight for lipid extraction was 30 mg. The lipid contents of strain Candida rugosa LP-1 and strain Rhodotorula mucilaginosa LP-2 could be improved more than 1 time and 65%, respectively, by ultrasonication when extracting lipid. However, long ultrasonication duration obtained decline of extraction efficiency. The optimal ultrasonication duration for lipid extraction was 30 min. The numbers of freeze-thaw cycles had no significant impact on lipid extraction.
The optimum temperatures of strain Candida rugosa LP-1 and strain Rhodotorula mucilaginosa LP-2 for maximum lipid productivity were 27oC and 33oC, respectively. The most suitable carbon sources for strain Candida rugosa LP-1 and strain Rhodotorula mucilaginosa LP-2 to accumulate lipid were crude glycerol and pure glycerol, respectively. Yeast extract was the most suitable nitrogen source for both strains. Although, (NH4)2SO4 was a cheap nitrogen source, it caused pH decrease so that cell growth and lipid accumulation were both influenced. Low carbon/nitrogen ratio was beneficial to biomass growth. In contrast, the cellular lipid content increased with the increase of the carbon/nitrogen ratio. Higher carbon/nitrogen ratio not only inhibited cell growth, but also oil accumulation. The most suitable carbon/nitrogen ratios for strain Candida rugosa LP-1 and strain Rhodotorula mucilaginosa LP-2 were 45 and 65, respectively. Carbon/nitrogen ratio caused a significant impact on the fatty acid desaturation, especially to strain Rhodotorula mucilaginosa LP-2.
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