Studies On The Characteristics Of Growth And Lipid Productivity Of Two Oleaginous Microalga

Microalgae can be used as highly promising feedstock material for biofuel production, but the higher cost of microalgal biofuel hinders its commercial application. In order to reduce the cost of algae based biofuel, this study focused on screening oleaginous microalgal strains can grow fast under low temperatures and/or can utilize biogas slurry as culture medium. And then the characteristic of the growth and lipid accumulation of these algal strains will be studied. The results are shown as follows:1. Scenedesmus2008-88, which was collected in Arctic, grew fastly in a wide range of temperatures, from10℃to30℃in the laboratory. Its highest totoal lipid content is52%and the maximal biomass concentration is5.92gL-1. Both lower and higher photon flux densities inhibited its growth. Lower nigtrogen concentration in the medium inhibited its growth and lipid accumulation too. But CO2supply stimulated its growth, nitrogen utilization and lipid accumulation. When Scenedesmus2008-88was grown at20℃in BG11medium(0.75gL-1NaNO3) and bubbled with CO2enriched air (0.5%.,V/V) under continuous illumination of80μmolm-2s-1, the relative growth rate was0.41d-1and biomass concentration on10th day was5.0gL-1and total lipid content was47.6%of its dry weight. This alga can be cultured in the lower temperature envirment to maintain higher oil productivity, and this will prolong the time suitable for growth of algae to produce biofuel in late autum and winter in some areas.2. A strain of Chlorella sp. was screened out by using the full swine biogas slurry. It grew fast in full swine biogas slurry and the relative growth rate reached0.92d"1. Its biomass concentration was5.0gL-1and lipid content was58.9%. Biomass growth and lipid accumulation of this Chlorella sp. were synchronized. CO2supply stimulated the growth of Chlorella sp. and the utilization of nitrogen in the medium. CO2supply also stimualated its lipid accumulation and shortened the time to reach high lipid content. Chlorella sp. is an excellent algal strain to utilize biogass slurry and municipal sewage to produce algae based bifuel.3. When there were eough CO2and less nitrogen in the environment, these two algae prefred to synthesize more saccharide and lipid in the cells. Saccharides were decomposed and the released carbons were used to synthesize more lipids when the protein content decreased in the cell due to the growth of alge. When there were enough nitrogen sources and less carbon sources in the environment, they preferred to synthesize more protein in the cells. These proteins were decomposed to release the carbon to synthesize more lipids with the depletion of nitrogen in the medium.4. Lipid accumulation was started closed to the cell membrane of Chlorella sp. Small lipid bodies were formed first near to the cell membrane with the increase of the lipid. Then small lipid bodies fused each other to form medium lipid body and medium lipid bodies fused to form big lipid bodies.