Effects of substrates and light on the growth and lipid production of Chlorella protothecoides

John P O'Grady, Purdue University

Abstract

Algae have been used by human civilizations for thousands of years. In light of increasing energy costs and the search for a renewable source of fuel for the transportation sector, studies of algae have received renewed support. Algae are capable of producing multiple forms of alternative fuels, including biodiesel. Some algae have been found to have potential for biodiesel because of their high lipid content. However, algal production of lipids is dependent on the growth conditions in which the algae are produced. It is essential that oleaginous strains of algae be characterized in order to discern the optimal production parameters for the manufacture of biodiesel. In this work, initial screening of growth conditions for Chlorella protothecoides was done by varying the carbon source on which it was grown. This study examined carbon dioxide, glucose, glycerol, and acetate as carbon sources. The effect of the presence or absence of light was also examined. The growth conditions showing the highest rates of biomass production were then analyzed to determine their rate of lipid production. It was found that the UTEX 255 strain of C. protothecoides does not exhibit an increase in specific growth rate or yield under mixotrophic growth conditions as compared to heterotrophic conditions, and growth on an organic carbon substrate is significantly faster than autotrophic growth. This strain also grows on glycerol at the same specific growth rate as it grows on glucose, although the overall rate of lipid production is higher on glucose. It was discovered that the two substrates, glucose and glycerol, may be uptaken by C. protothecoides simultaneously. Substitution of glycerol in place of glucose has no effect on the rate of lipid production up to 10% of the overall substrate. An examination of industrial applicability, including a glycerol `recycle' rate of 3% and the effects of using crude glycerol from the production of biodiesel in place of high purity (99.9%) glycerol, was studied. In the recycle study, glycerol was entirely consumed during exponential growth and showed no detrimental effect to lipid production. The crude glycerol produced the same growth rate and yields that had been observed.

Degree

M.S.Ch.E.

Advisors

Morgan, Purdue University.

Subject Area

Microbiology

COinS