Biodiesel From Microalgae: Strain Selection Evaluation Of Lipid Production And Optimization Of The Culture Conditions

Biodiesel from microalgae are considered as a promising substitute for fossil fuels in the future. The choice of microalgae species can affect every steps of the microalgae to biofuels supply chain. Most of microalgae have the ability to produce 20-50% total lipid of dry cell weight (dw), and the lipid yield may vary greatly between species, photo-bioreactor design and culture strategies, especially the choice of species. Robust, higher biomass productivity and with a relatively high lipid content are the key desirable characteristics of a species for biodiesel production. In order to use microalgae as an economically viable biofuel feedstock, the costs of producing biodiesel from microalgae need to be reduced. The microalgae should contained valuable co-products or by-products which would be complementary to biofuel production, such as biopolymers, proteins, carbohydrate and residual biomass, which may be used as feed, fertilizer or pharmaceutical. So the aims of this work were select strains, evaluate lipid Production and optimize the culture conditions to improve the lipid yield.In this study, 77 microalgae strains were selected to evaluate for biomass and lipid production. The total lipid content of these microalgae ranges from 13% to 57% of dry cell weight, with an average of 34%. Among them, 21 microalgae strains showed lipid production rates greater than 0.10 g/L/day. The best lipid content in these microalgal species was Desmodesmus sp. (with the average lipid content of 36% dw), the lipid content of Desmodesmus armatus var. was the lowest with the average lipid content of 26% dw. The species Desmodesmus armatus var. had high average algae biomass of 3.52 g·L^-1; By testing the fatty acid composition of the microalgae which the lipid content over 30% of the total lipid, the major components of the fatty acids composition was C18:1 and C16:0; to screen for the robust microalgae to grow in the outdoor environment for biodiesel production in the future, the specific growth rate and doubling time of 16 strains microalgae which the lipid content over 40% dw were surveyed, These microalgae are all belong to Chlorophyta. The doubling time of those green algae is 6 h to 31 h with an average of 16 h. Scenedesmus obliquus 0947 had the low doubling time of 6.3 h. Desmodesmus sp.0952 has the high doubling time of 31.4 h. 77 microalgae strains were tested for biomass and lipid content and analyzed the fatty acid composition of them. Strain 0961 had the potential to produce biodiesel.The microalgae strain 0961 was identi?ed by physiological and molecular approaches. The production of biodiesel and effect of nutrition on growth and lipid accumulation of M. afer 0961 was investigated. The biomass yield and total lipid productivity increased as the nitrogen concentrations increased. The highest biomass yield and lipid productivity was 3.29 g·L^-1 and 1.62 g·L^-1, respectively, when were both culture at nitrogen concentrations of 3.0 g·L^-1. The major components of the fatty acids composition was also C18:1 and C16:0, but the ratio of fatty acid composition in total lipid was changed. With the increased of nitrogen in medium, C16:0,C16:2,C18:2 and C18:4 was increase, but C14:0,C16:1,C18:1,C24:0 and C24:1 was decreased. The biomass yield increased as the nitrogen concentrations increased, but there was no influence on lipid content.The phosphorus concentrations could influence the biomass yield and total lipid content. The highest lipid content and lipid yield was 50.5% dw and 1.60 g·L^-1, respectively, when were both culture at phosphorus concentrations of 40 mg L^-1. Different initial K₂HPO₄·3H₂O concentration could influenced the fatty acid composition in total lipid. With the increased of phosphorus in medium, C16:0,C18:0,C18:2 and C18:4 was increase, but C18:0 and C24:1 was decreased. By adjusting K₂HPO₄·3H₂O concentration in the medium could influence the lipid productivity and fatty acid composition of M. afer 0961, but there were many differences with the regulation way of nitrogen iron.The maximum biomass of M. afer 0961 was 3.30 g·L^-1 under 6 g·L^-1 of initial Ions. The biomass of M. afer 0961 was only 2.62 g·L^-1 under lack of initial Ions. The content trend of C16:0,C16:1 and C16:2 were correlated to the lipid content, so when M. afer 0961 cultured under different Ions concentration could adjust the fatty acid composition.