| As an alternative renewable fuel, biodiesel is produced by transforming biological resources to long-chain fatty acid methyl esters through decomposition and esterification. Rapidly rising oil prices and increasing environmental concerns are catalasts for the development of biodiesel. Currently, it is the high price of the feedstock which accounts for more than70%of the cost of biodiesel that impede the application of biodiesel. Therefore, how to develop cheap feedstock is essential for production cost reduction and large-scale application of biodiesel.Microalgae are autotrophic organisms with strong photosynthetic capacity. Lipid content of some microalgae in nature can reach more than20%of dry weight, which can be used as the ideal feedstock for biodiesel generation. Another strength of employing microalgae is their short production cycle. Furthermore, the microalgal biodiesel production does not occupy the cultivated land covered by crops and is not restricted by climatic conditions. Consequently, more and more researches are concentrated on this hotspot topic recently. However, there still are many problems needed to be resolved during the application of microalgal biodiesel, which includes the selection and high efficient cultivation of oil-rich algae species, high efficient extraction of lipid and lipid transesterification.In view of this, radioisotope tracer technique and other advanced biotechnologies coupled with modern analytical instruments (HPLC, GC-MS) were adopted in this study to investigate the effect of a new growth promoter on the lipid synthesis and illustrate the effect of addition of ethanol on the composition of long-chain fatty acids in Scenedesmus sp. and Chlorella FACHB-40. The main results are revealed as follows:(1) The influence of culture conditions on algae growth and lipid accumulationThe optimization of incubation time, initial pH and M solvent concentration for the culture of Scenedesmus sp. as well as the accumulation of algal long-chain lipid were tested. An alkaline environment (pH8-10) is suitable for algae. Further tests showed that the addition of M solvent in the BG11medium was effective in promoting the growth and lipid accumulation.(2) The optimization of algal fatty acid extractionThirty extraction methods were tested in this study. Fatty acid methyl ester produced by the long-chain fatty acid via esterification was analyzed by GC. The results showed that the shaking-assisted dichloromethane/methanol (V:V,2:1) extraction coupled with vacuum freeze-drying was the optimum long-chain fatty acid extraction method among the methods tested, in which more define acid esters were extracted.(3) The effect of addition of ethanol on its fatty acid compositionScenedesmus sp. was cultured for20d by the BG11medium and the modified medium in which ethanol was added (2.4‰). GC-MS analysis showed that addition of ethanol has a significant impact on the composition of long-chain fatty acid of Scenedesmus sp.. The stearic acid content decreased significantly (47.7%) because of the addition of ethanol, while the content of other fatty acids increased.(4) The transformation of ethanol in Scenedesmus sp.In this experiment, the14C labeled ethanol was used as a tracer to identify the distribution of radioactive ethanol in the long-chain fatty acid methyl esters. Radioactivity data and GC data showed that the radioactivity was mainly concentrated in the methyl palmitate (49.19%), methyl linoleate (35.48%), methyl linolenate (7.12%) and methyl stearate (8.21%). |
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