Date of Award

8-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biosystems Engineering

Committee Member

Terry H. Walker, Committee Chair

Committee Member

Caye M. Drapcho, Committee Co-chair

Committee Member

David A. Ladner

Committee Member

William C. Bridges

Abstract

Algae-based technologies are fast growing and the growing demand for sustainable technologies is evident from the growing energy demand and global warming. Microalgae culturing for higher lipid contents have been a hot topic of intense discussion in the past years. Crude glycerol, a byproduct from biodiesel production seems to be an attractive feedstock for microbial cultivation and crude glycerol has been proven as a good alternative feedstock for cultivation of Chlorella protothecoides. The effect of impurities present in the crude glycerol is important to develop a method for high-density cultivation of microalgae to increase the commercialization potential of algae systems. Through this study, a method to partially refine crude glycerol was developed to increase the suitability of biodiesel-derived glycerol for high-density cultivations. C. protothecoides grew best at an initial glycerol concentration of 90 g/L and a maximum biomass and lipid productivity of 4.45 and 2.28 g/L-day was achieved at an initial glycerol concentration of 120 g/L. Fed-batch studies increased the biomass and lipid concentrations and productivities. A maximum biomass and lipid concentration of 95.3 and 49.5 g/L-day was achieved while using PRG as a carbon source with a maximum productivity of 10.6 g/L-day. Yield biomass per substrate in the fed batch mode was observed to be 0.53. Comparing the data to published literature, these are the best results. Fatty acid profiles were observed to be very comparable to data published by other researches on C.protothecoides. Further studies on the effect of salinity on the growth of C.protothecoides, yielded no statistical significance in the biomass concentration and lipid content at a KCl concentration of 10 and 20 g/L, and a NaCl concentration of 10 g/L. Further increase in NaCl concentration to 20 g/L decreased the maximum biomass concentration. No growth was observed at salt concentrations of 40 g/L. Increasing salt concentrations had no impact on the relative fatty acid percentage of oleic acid (most abundant fatty acid produced by Chlorella protothecoides). Biomass productivities were significantly lower in the presence of salts, indicating that the present of salts decreases the biomass productivity. Increasing methanol concentrations were evaluated, and the results proved that methanol was not significantly consumed but evaporated by this species of algae. A methanol concentration 1 % (v/v) yielded similar biomass and lipid concentrations, Yx/sand Yp/s. The biomass productivity, however, was significantly lower with increase in methanol concentrations. Xylose proved to be detrimental to the growth of C. protothecoides as increasing xylose concentrations decreased biomass concentration. No growth was observed at a xylose concentration of 30 g/L. In summary, the effect of some impurities present in crude glycerol was evaluated and a method to refine crude glycerol proved successful. A method for high-density cultivation of C. protothecoides for increased productivities while using a waste stream is presented.

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