Effects Of Nitrogen Sources On Growth And Lipid Accumulation Of Scenedesmus Obliquus

Microalgae is a new type of raw material for the production of biodiesel.The biomass and lipid content of microalgae are closely related to the production of biodiesel.Nitrogen is an essential nutrient element for the growth of microalgae,and nitrogen source is an important factor affecting the growth and lipid accumulation of microalgae.In this topic,firstly,aiming at the deficiency of the Sulfo-phospho-vanillin method,the conditions for the determination of lipids by the Sulfo-phospho-vanillin method were optimized,and a method that can quickly determine the lipids of microalgae was obtained.The optimized Sulfo-phospho-vanillin method was verified by determining the lipid of Scenedesmus obliquus.Then the effects of nitrogen sources on the growth of microalgae were studied,including the effects on biomass,chlorophyll a,cell density and other indicators of Scenedesmus obliquus.Finally,the effect of nitrogen sources on metabolites of Scenedesmus obliquus were studied,especially the influence of lipid accumulation.The optimal nitrogen source culture conditions was determined to increase lipid content.Meanwhile,the certain technical support was provided for the production of biodiesel by microalgae.The main research results were as follows:（1）The optimized Sulfo-phospho-vanillin method had better sensitivity when determining the lipid of Scenedesmus obliquus;at the same time,the amount of vanillin phosphate solution was reduced by 2 m L,the detection time was shortened by 15 minutes,and the detection efficiency was increased by 150%.The best conditions for the determination of microalgae lipids by Sulfo-phospho-vanillin method:Lipid standard solution was prepared with soybean oil and a 2:1ratio of chloroform methanol.2 m L of concentrated sulfuric acid was added to heat the reaction for 5 min.After cooling,3 m L of phosphate vanilla solution in which vanillin content was 1.2 g·L^-1 and phosphoric acid concentration was 51%were added and react for 5 min,and the absorbance value was measured at 530nm to obtain the quality of microalgal lipids.（2）When the nitrogen source were CO（NH₂）₂ and NaNO₃,it was conducive to the growth of Scenedesmus obliquus;when the nitrogen source was NH₄Cl,it was not conducive to the growth and accumulation of biomass of Scenedesmus obliquus.When the CO（NH₂）₂ concentration was 8.82 m M,the biomass of Scenedesmus obliquus was higher,the OD₆₈₀ of the algae solution was 1.463,the dry cell weight reached 1.155 g·L^-1,and the cell density reached 3.7×107cell·m L^-1;When the concentration of NaNO₃ was 17.64 m M,the biomass of Scenedesmus obliquus was higher,the OD₆₈₀ of the algae solution was 1.535,the dry cell weight reached 1.048 g·L^-1,and the cell density reached 2.98×107 cell·m L^-1.（3）When the nitrogen source was CO（NH₂）₂,it was conducive to the accumulation of lipids of Scenedesmus obliquus,and the content of monounsaturated fatty acids in fatty acids was higher.The lower the nitrogen concentration,the more favorable the accumulation of lipids of Scenedesmus obliquus,and the higher the content of monounsaturated fatty acids in fatty acids.When the nitrogen source was 2.94 m M CO（NH₂）₂,the lipid content of Scenedesmus obliquus could reach 34.48%,the lipid production rate was 21.257mg·L^-1·d^-1,and the monounsaturated fatty acid content in fatty acids could reach57.07%.In addition,the analysis of Fourier Infrared spectroscopy（FTIR）shows that the nitrogen source had an influence on functional groups such as-C-H,-OH,and C=O,which further showed that the nitrogen source had an influence on the lipid synthesis of Scenedesmus obliquus.