Influence of nitrogen-limitation regime on the production by Chlorella vulgaris of lipids for biodiesel feedstocks

Microalgae have the potential to provide large amounts of lipid-containing biomass that could be used as a renewable oil feedstock for biofuel use. Many fast-growing algae, such as Chlorella vulgaris, when grown under nutrient-sufficient conditions, have a lipid profile that is unsuitable for biodiesel use, since the triacylglyceride content is too low. However, growth under nitrogen limitation has been shown to increase triacylglycerides. Here we investigate the most effective nitrogen-limitation regime and find that rather than transferring cells to a medium without nitrogen, the maximal triacylglyceride productivity (46 mg/l/day) is achieved by allowing the cells to deplete the nitrogen naturally. Detailed ana-lysis of the fatty acid composition of the lipids indicated that there was a high proportion of a-linolenic acid (C18: 3) under all conditions, so that it would have to be blended with other feedstocks in order to adhere to international standards for biodiesel.