Abstract
Study of increasing lipid production from fresh water microalgae Chlorella vulgaris was conducted by investigating several important factors such as the effect of CO 2 concentration, nitrogen depletion and harvesting time as well as the method of extraction. The drying temperature during lipid extraction from algal biomass was found to affect not only the lipid composition but also lipid content. Drying at very low temperature under vacuum gave the best result but drying at 60 °C still retained the composition of lipid while total lipid content decreased only slightly. Drying at higher temperature decreased the content of triacylglyceride (TG). As long as enough pulverization was applied to dried algal sample, ultrasonication gave no effect whether on lipid content or on extraction time. In addition to the increase of total lipid content in microalgal cells as a result of cultivating in nitrogen depletion media, it was found that changing from normal nutrient to nitrogen depletion media will gradually change the lipid composition from free fatty acid-rich lipid to lipid mostly contained TG. Since higher lipid content was obtained when the growth was very slow due to nitrogen starvation, compromising between lipid content and harvesting time should be taken in order to obtain higher values of both the lipid content and lipid productivity. As the growth was much enhanced by increasing CO 2 concentration, CO 2 concentration played an important role in the increase of lipid productivity. At low until moderate CO 2 concentration, the highest lipid productivity could be obtained during N depletion which could surpassed the productivity during normal nutrition. At high-CO 2 concentration, harvesting at the end of linear phase during normal nutrition gave the highest lipid productivity. However, by reducing the incubation time of N depletion, higher lipid content as well as higher lipid productivity may still be achieved under this condition.
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