Screening Of Oil-rich Microalgae And Its Oil For Biodiesel Production

With the increasing depletion of oil resources and the deterioration of ecological environment, every country in the world has been actively exploring environmentally-friendly alternatives to fossil fuels. Biodiesel, namely fatty acid methyl ester, is a clean environmentally-friendly renewable energy resource. At present, biodiesel production by microalgae is technically feasible, and it will be one of optimal solutions to achieving a perfect substitute for fossil fuels.In this work, a great amount of work of screening dominant microalgae species was conducted according to the climate and environmental characteristics of natural lakes of central and western regions in Inner Mongolia and one oil-rich strain of Navicula sp. was obtained. Then the conditions of its growth and lipid accumulation were optimized. Next algal cells were collected through the large-scale cultivation and dried to produce algal powder. Finally solvent extraction method was utilized to extract algal oil for biodiesel production. Major research results are shown as follows:1. One oil-rich strain of Navicula sp. was successfully screened and algae species preservation methods were analyzed by comparison, one of which is able to make the algae live to be 9 months and its growth improve faster when it is cultured again. The improved B&D oil extraction method has the ability to produce the maximum oil yield from algal powder.2. Based on aquatic diatom medium, the optimal culture conditions for the growth of Navicula sp. were optimized as follows: temperature 20℃, light intensity 3000lx, pH 8; the optimization of optimal concentrations of five kinds of nutrients was carried out by L₁₆(45) orthogonal experiments and the results were obtained: urea 50 mg/L, K₂HPO₄·3H₂O 40 mg/L, Na₂SiO₃·9H₂O 200 mg/L, NaHCO₃ 10 mg/L, MgSO₄·7H₂O 70 mg/L. Vitamin B₁ played significant role in promoting the multiplication of the algae, so its optimal concentration was 200μg/L; Vitamin B₁₂ and vitamin H do not have evident propagation functions and the three vitamins don't interact each other in the growth of algae. Navicula sp. went into the stationary phase on the 11^th day grown on the optimized culture medium and biomass accumulation reached 1.269 at spectrophotometrically at 680nm wavelength. 3. The results of stress of nutrients on lipid accumulation of Navicula sp. indicate that nitrogen deficiency has significant role in lipid accumulation and the optimal urea concentration for oil accumulation was 30 mg/L, resulting in increase of comprehensive lipid content from 30.60% to 39.29%.4. Base catalysis transesterification method was utilized to convert algal oil into biodiesel. Gas chromatography analysis demonstrated that main component of biodiesel was aliphatic acid containing C₁₆ and C₁₈. Key performance indexes such as density, kinematic viscosity, flash point, acid value and iodine number were determined according to U.S. standard ASTM 6751-03 and the Chinese standard GB/T 20828-2007 and it can be an ideal substitute for diesel.The utilization of algal oil of Navicula sp. for biodiesel production has unique advantages that can alleviate the greenhouse effect, will not compete with grains and cereals consumed by mankind and takes up farmland on which crops are grown. This will definitely lay the foundation for large-scale biodiesel production from non-food feedstock and it has broad prospects in the future.