Screening And Identification Of Oleaginous Microalgae And Study On The Cultivation Conditions

Due to the shortage of useable fossil energy and deterioration of ecological environment,the development of renewable and environment-firendly energy has become one of theimportant directions in energy field. As biodiesel has a very high similarity with fossil dieselin energy density, combustion performance, and is environmentally friendly and renewable. Itis considered to be one of the best alternative energy to solve the energy crisis. Microalgaehave been considered the most promising raw materials of biodiesel due to the characteristicsof high biomass，high oil content, easily culturing and fast growth.In this paper, a lot of work has been done about screening microalgae from the watersamples collected from Wuxi. A strain of microalgae with high oil-producing potential wasisolated. With the aim of provide technical reserves and theoretical basis for solving problemsduring the industrialization process of energy microalgae, the oil extraction craft, rapidquantification of lipid, optimization of cultivation conditions, two-step cultivation andculturing microalgae with wastewater and molasses to reduce the production cost were alsostudied. The main contents and results are as follows:1) Fourteen strains of microalgae were isolated from the natural water and preliminarilyidentified by their morphological characteristics. The growth characteristics and lipidproduction property of twelve strains of microalgae were compared under autotrophic andheterotrophic conditions. The following results were obtained: strain Y06, identified asScenedesmus abundans by18S rDNA analysis, had the highest oil production andproductivity in the twelve strains of microalgae. The lipid productivity of Y06were9.40mg/(L d) and201.29mg/(L d) under autotrophic and heterotrophic conditions, respectively.2) According to the research results of the oil extraction process, this article choosechloroform-methanol as the extraction solvent and acid hydrolysis as the extraction method.The standard curve of strain Y06was established for rapid determination of lipid content byphosphoric acid-vanillin reaction, and the total lipid content of strain Y06was quicklyestimated according to this standard curve.3) The culture conditions of strain Y06was optimized through singer factor andorthogonal experiment. The optimal culture conditions are as follows:35g/L glucose,3.5g/Lpeptone,120mg/L K2HPO4·3H2O,1mL/L seaweed liquid fertilizer,150mg/L MgSO4·7H2O;and other medium components remained unchanged according to BG11. Cultured with theoptimized medium, the biomass and lipid content of strain Y06after7days reached18.88g/Land24.76%, respectively.4) In order to improve the lipid yield of strain Y06and evaluate effect of cultureconditions on the nutrient contents, strain Y06was cultivated by a two-step method, changesin fatty acid and amino acid contents before and after the two-step cultivation were compared.The following results were obtained: biomass, lipid content and yield of strain Y06were up to23.57g/L,33.49%and7.58g/L after a10-day two-step cultivation, respectively. Comparedwith primitive method, monounsaturated fatty acids (MUFAs) relative content, especiallyC18:1(n-9), in strain Y06increased, while saturated fatty acids (SFAs) and polyunsaturated fatty acids (PUFAs) were opposite; the total amino acids content, especially necessary aminoacids, in strain Y06decreased, yet the Ser and Met content slightly increased.5) In order to reduce cultivation cost, municipal wastewater (secondary effluents) andmolasses were used to culture strain Y06. The effect of wastewater on strain Y06was asfollows: after some ingredients including MgSO4, citric acid, CaCl2and Na2EDTA wereremoved, biomass of strain Y06reached7.56g/L after a7-day Culture, which would weighagainst the biomass under heterotrophy; Strain Y06could absorb80～90mg/L of totalphosphorus and210～220mg/L total nitrogen. The results strain Y06cultured by molassesshowed that the strain Y06grown in the hydrolysis of molasses is better than molasseswithout pretreatment; The sugar in both of different molasses cannot be fully utilized by strainY06, and a high concentration of molasses will inhibit the growth of strain Y06. When thestrain Y06was cultivated in the combined wastewater and molasses as mixed medium, theoptimal growth in devoid of nitrogen source was obtained and the biomass could reach11.53g/L after a7-day cultivation.