The Research Of Kinetic On Growth, Metabolism Of Oleaginous Monoraphidium Sp. FXY-10

The depletion of fossil fuel reserves has caused an increase in demand and price of diesel. In recent years, research has been directed to explore alternate fuels from various biological renewable sources. Biodiesel is an alternative to diesel fuel. It is nontoxic, biodegradable and has the potential to replace the conventional diesel fuel. The use of biodiesel will ultimately leads to reduction of harmful emissions of carbon monoxide, hydrocarbons and particulate matter and to the elimination of SOx emissions. Presently, biodiesel is produced from different crops, such as, soybean, rapeseed, sunflower, palm, coconut, jatropha, karanja, used fried oil and animal fats. There will be certain limitations in the use of these oilsas altemate fuels because of its food demand, life span, lower yield/ha, higher land usage and higher price inter alia It is necessary to search for non-food based altemate feedstocks for biodiesel production. Selection of biodiesel feedstock is based on higher yields, short duration, lower production cost and less land usage. Among the various biodiesel feedstocks, the microalgae oil has the potential to replace the conventional diesel fuel.Monoraphidium sp. FXY-10is a unicellular microalga with fast growth and high lipid content. Additionally, it can be cultured in heterotrophic conditions. In phototrophic, heterotrophic and mixotrophic cultivations, the crude lipid content of Monoraphidium sp. FXY-10were44.92%,34.29%and35.67%with basal BG-11medium, respectively. Monoraphidium sp. FXY-10was a kind of oleaginous microalgae because its intracellular accumulating lipid exceeded30%according to literature reported. In order to establish the kinetic model between growth、metabolic of Monoraphidium sp. FXY-10and the environmental factors, the main research contents were as follows in this study:(1) Several cultivation parameters, including pH, speed and initial concentration of NaNO3, K.2HPO4-3H2O and glucose in the medium, which influenced cell growth, lipid synthesis and fatty acid composition of Monoraphidium sp. FXY-10under phototrophic, heterotrophic and mixotrophic conditions, were investigated by means of shaking flask. It was found that NaNO3and K2HPO4·3H2O were necessary for both cell growth and lipid synthesis. They can not only promote the growth of microalga within a certain concentration range of but also inhibit the growth with high concentrations. However, NaNO3and K2HPO4·3H2O with low concentrations were be beneficial to increase lipid content of microalga.The effect of NaNO3and K2HPO4·3H2O with different concentrations on the fatty acid compositions of Monoraphidium sp. FXY-10was significant pH and glucose concentration were found to be two predominant factors influencing the cell growth and lipid synthesis of Monoraphidium sp. FXY-10. At pH7, the microalgae grew most rapidly. The biomass productivity, lipid productivity and lipid content of algal cells were high when pH was6or7. Moreover, the biomass productivity, lipid productivity and lipid content of algal cells were the highest with10g/L glucose. The effect of pH and glucose had little influence on the fatty acid compositions of Monoraphidium sp. FXY-10. Furthermore, the rotation speed was another significant factor affecting cells growth but it had little influence on the lipid contents and fatty acid compositions of Monoraphidium sp. FXY-10. At the same time, the contents of C16:0and C18:1in microalgae cells under heterotrophic and mixotrophic conditions were high which suggested that intracellular accumulating lipid may be ideal feedstock for biodiesel.(2) Relationship between variations of NaNO3, K2HPO4·3H2O and glucose concentration in the cultivation medium and accumulation of chlorophyll-a, lipid of microalgae under different cultivation conditions was investigated by shaking flask. The substrates (NaNO3, K2HPO4-3H2O and glucose) consumption kinetic models, the production kinetic including chlorophyll a and lipid were obtained under phototrophic, heterotrophic and mixotrophic conditions. Finally, yield rates of product of Monoraphidium sp. FXY-10under different cultivation conditions were calculated. The biomass productivity, lipid productivity and lipid content, saturated fatty acid, and monounsaturated fatty acid contents of Monoraphidium sp. FXY-10were higher, and the Degree of unsaturation (DU) value was lower than the European Standard (EN14214) which is required DU value less than137. So Monoraphidium sp. FXY-10may be an ideal feedstock with potential application in the production of biodiesel.