Research On Optimization Of Lipid Production Process Of Scenedesmus Obliquus

The widespread use of fossil fuels has led to environmental pollution and global climate change.Research and development of alternative energy sources have become an important way to deal with environmental pollution.Microalgae is currently known as the plant with the highest lipid production capacity per unit area,and is considered to be the optimal source of raw materials for biodiesel production.And Scenedesmus obliquus is one of the most widely used lipid-producing microalgae.However,high cost is still the biggest bottleneck of microalgae biodiesel at present.The growth rate and the lipid productivity of S.obliquus are important factors that determine the production cost of microalgae biodiesel.Therefore,it is imperative to develop a culture method that can both promote the growth rate and increase the lipid productivity of S.obliquus.Most researchers believe that nitrogen starvation is an effective method to increase the microalgae lipid content,and nitrogen starvation will directly limit the biomass of S.obliquus.In addition,aeration and phytohormones are the main factors affecting S.obliquus biomass productivity.Therefore,this study first constructed a process of cultivating S.obliquus with multiple small-dose method of nitrogen supply,and then explored the effect of turbulent energy dissipation rate caused by aeration on the biomass and lipid content of S.obliquus.On the other hand,the addition of phytohormones can increase biomass and lipid production.The main conclusions of this study are as follows:?1?A new process of supplying nitrogen in multiple small-dose method was established,and at the same time promoted the growth and lipid production of Scenedesmus obliquus.Under the cultivation conditions of multiple small-dose of nitrogen supply processes,the addition of Na NO₃ and CO?NH₂?₂ can promote the growth of S.obliquus,while the addition of NH₄Cl inhibits the growth of S.obliquus.Compared with Na NO₃ and NH₄Cl,the addition of CO?NH₂?₂ was more conducive to the accumulation of S.obliquus.Through comparison,it was found that adding 2 mg N L^-1 CO?NH₂?₂daily had the highest biomass and lipid?2?Under sufficient carbon dioxide conditions,the aeration intensity can affect the growth and lipid accumulation of S.obliquus.The computational fluid dynamics?CFD?model was used to calculate the turbulent energy dissipation rate at different aeration rates.the biomass,lipid productivity and chlorophyll content of S.obliquus increased to 1.11×10⁷cells m L^-1,16.0 mg L^-1 d^-1 and 6.90 mg L^-1,respectively.As the turbulent energy dissipation obliquus gradually decreased.For the growth and lipid production of S.obliquus,the optimal?3?The addition of three phytohormones:indoleacetic acid?IAA?,amine fresh ester?DA6?and brassinolide?BR?showed"low concentration shows promotion role,and high concentration shows inhibition role"on the growth and lipid production of S.obliquus.The biomass,lipid content and lipid production of S.obliquus tended to increase first and then decrease with the increase of the concentration of three phytohormones.The optimal dosages of IAA,DA6 and BR were 10^-6 M,10^-9 M and 10^-8 M,respectively.Compared with the three phytohormones,the addition of 10^-9 M DA6 to the biomass,lipid content and lipid productivity of S.obliquus were the most significant,which were 1.77×10⁷ cells m L^-1,30.0%and 16.2 mg L^-1 d^-1,respectively.At the same time,the addition of 10^-9 M DA6 increased the ratio of C18:1 and unsaturated fatty acids.