| Microalgae can use photosynthesis of carbon dioxide and environmental nutrients to synthesize bioactive substances such as proteins,polysaccharides,lipids and pigments.It has many applications and development prospects in bioenergy,medicine,feed,aviation and aerospace.Therefore,in view of the high production cost and low yield in microalgae culture,this paper mainly starts from two aspects of nutrient conditions and culture methods,to study different nutrient conditions and culture methods on microalgae by batch culture.The effects of growth and lipid accumulation of microalgae,and the intrinsic relationship between pH change,nitrogen source and phosphorus consumption,and microalgae growth were analyzed.In this study the autotrophic culture of C.vulgaris and S.obliquus were investigated systematically with carbon dioxide as carbon source to study the growth and lipid production of two strains of microalgae under different nitrogen source medium.The study found that urea can significantly promote the growth and increase the biomass of the two microalgae,and C.vulgaris is less tolerant to ammonium chloride.Moreover that micro-algae can regulate water quality,absorb nitrogen and phosphorus in water,reduce nitrogen and phosphorus content in water environment,and the highest FAME?Fatty acid methyl ester?content of algae was obtained in nitrogen deficient media.C.pyrenoidosa was cultivated autotrophiclly with CO2 as the carbon source.The effects of different nitrogen and phosphorus supply levels on C.pyrenoidosa were investigated.It was found that the highest biomass productivity(151.20 mg·L-1·d-1)of algae was obtained under N&P condition,and the presence of phosphorus had a great influence on the absorption of NO3--N under nitrogen sufficient conditions.The absorption rate of phosphorus under N-&P conditions is twice that of N&P,and a large amount of absorbed phosphorus is stored in cells,but the specific form remains to be further studied.In addition,the study also found that the effects of nitrogen and phosphorus conditions on FAME content and yield are not consistent.The growth and fatty acid productivity of Scenedesmus obliquus under different nitrogen conditions in autotrophic,heterotrophic and mixotrophic cultures were also investigated and compared in this study.It was demonstrated that the biomass and biodiesel productivities of mixotrophic algae cells exceeded the combination of autotrophic and heterotrophic cells under both nitrogen-replete and nitrogen-deplete conditions when using acetate as the organic carbon source.Moreover,the highest FAME productivity was obtained in mixotrophic N-culture,and it was 2 times higher than under nitrogen sufficient condition.Furthermore,the fatty acid yield from mixotrophic culture was 1.25 times greater than that from heterotrophic culture under nitrogen starvation,indicating that S.obliquus converted the assimilated carbon to lipid more effectively under mixotrophic cultivation.This study shows that nitrogen and phosphorus conditions are one of the important factors affecting both the biomass and fatty acid productivities of mixotrophic algae.Although urea can promote the growth of microalgae,it is not conducive to oil accumulation.Nitrogen-deficient culture not only stimulates the accumulation of microalgae oil,but also reduces the biomass of microalgae,which leads to its yield is not very satisfactory;In addition,the biomass yield and lipid accumulation of different algae species under the three culture modes are also different.Therefore,in the production,the optimal nitrogen source and nitrogen and phosphorus concentration of microalgae growth are selected according to the demand,and the optimal culture mode is combined to increase the microalgae biomass and oil yield.The results of this study provide a strong theoretical basis for the control of nitrogen and phosphorus conditions,the determination of culture mode and the denitrification and dephosphorization of wastewater in microalgae culture. |
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