Date of Award
Master of Science
The present study investigated the capability of Schizochytrium limacinum SR21 to utilize various industrial or agricultural by-products for the production of lipids. The substrates analyzed were used restaurant oil (yellow grease) and animal fat (white grease) derived crude glycerol from biodiesel production, and sweet sorghum juice. Crude glycerol is the primary by-product from biodiesel production - 0.66 lb is generated for each gallon of biodiesel produced. The crude glycerol can be purified and used in food, chemical, drug, and other industries. Purification however, is an expensive and complicated process therefore other economical uses of crude glycerol must be identified such as the one described in this study - fermentation of crude glycerol via S. limacinum SR21 to produce lipids which then serve as biodiesel feedstocks. Sweet sorghum juice is harvested from the sweet sorghum plant, a C4 plant possessing high photosynthetic efficiency and high sugar yield including glucose, sucrose, and fructose. The juice is typically used for white sugar production, but may be a good substitution for common substrates used in lipid production via S. limacinum SR21. S. limacinum SR21 is a fast growing microalga capable of accumulating large quantities of lipids, which have applications in human health products, biodiesel, and animal feed. In separate batch studies, S. limacinum SR21 was grown on each substrate and monitored. On crude glycerol derived from yellow grease, 25 and 35 g/l were the optimal doses for untreated and treated crude glycerol, respectively. Biomass dry weights of 8.3 and 11.3 g/l were attained for these doses, respectively. The highest crude lipid content of all doses, 73.3%, was with 35 g/l treated crude glycerol. Crude glycerol derived from animal fats also provided similar results to these. S. limacinum SR21 grown on sweet sorghum juice furnished similar biomass density and lipid content. The optimum does of 50% juice produced a biomass dry weight of 9.4 g/l and 73.4% lipid content. While biomass dry weight was lower than that grown on glucose (10.9 g/l), lipid content was higher than typical values (50%). Of the three sugars, only glucose was utilized for growth. The remaining medium may still be used for white sugar production since fructose and sucrose were not consumed. Both crude glycerol and sweet sorghum juice caused substrate inhibition at high doses, and presence of methanol in crude glycerol presented an additional prohibitory effect on cell growth. Major fatty acids were nearly identical among the lipids produced from different substrates. This research shows that at certain concentrations of both crude glycerol and sweet sorghum juice can be utilized by S. limacinum SR21 to yield substantial quantities of lipids. Based upon the results revealed from the batch stage studies, large scale lipid production from industrial or agricultural by-products could be a reality in the near future. This production process will: 1) eliminate excessive crude glycerol from the market, 2) produce high-value lipids in an environmentally friendly, economical, and sustainable way, and 3) provide lipid feedstocks for various industrial applications.
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