Producing Omega-3 Polyunsaturated Fatty Acids from Biodiesel Waste Glycerol by Microalgae Fermentation

Crude glycerol is a major byproduct if the biodiesel industry. Biodiesel manufacturers are currently facing the challenges of appropriate disposal of this waste material. Crude glycerol is expensive to purify for use in food, cosmetic, and pharmaceutical industries and therefore, alternative methods for use of this crude glycerol are needed. A promising alternative is to use this crude glycerol as a carbon source for microalgae fermentation. In this project, we investigated the use of crude glycerol as a less expensive substrate for the fermentation of the microalgae Schizochytrium limacinum and Pythium irregulare which are prolific producers of omega-3 polyunsaturated fatty acids. Omega-3 fatty acids have many beneficially effects on treating human diseases such as cardiovascular diseases, cancers, and neurological disorders. In addition, the omega-3 fatty acids docosahexaenoic acid (DHA) has been shown to be an important factor in infant brain and eye development. The first part of this study focused on the continuous fermentation of S. limacinum, a prolific producer of DHA. The objective of this study was to examine the algal cellular physiology and maximize its DHA productivity. Two important parameters used in continuous fermentation were studied: dilution rate (D) and feed glycerol concentration (S0). The highest biomass productivity of 3.88 g/L-day was obtained at D = 0.3 day -1 and S0 = 60 g/L, while the highest DHA productivity (0.52 g/L-day) was obtained at D = 0.3 day -1 and S0 = 90 g/L. The cells had a true growth yield of 0.283 g/g, a maximum specific growth rate of 0.692 day -1 , and a maintenance coefficient of 0.2216 day -1 . The second part of this study focused on morphology issues with P. irregulare, a prolific producer of eicosapentaenoic acid (EPA). P. irregulare has a filamentous morphology, which can make fermentation difficult. The mycelium can stick to the agitation blades resulting in mechanical problems. In addition, this filamentous morphology prevents adequate amounts of oxygen from reaching some cells resulting in decreased productivities. The focus of this research was to control the fermentation conditions to make the algae grow in small pellets, a