Microalgae have been considered as a potential feedstock for sustainable production of biofuel, animal and aquaculture feed, antioxidants and bioactive compounds. These organisms are the primary producers of organic matter in aquatic environments due to their photosynthetic activities; they possess several advantages when compared to terrestrial plants. However, commercial scale microalgae application is rarely economical due to slow-growing high-lipid producing microalgal strains and high

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... sting costs. The first problem is essentially that microalgae cannot grow rapidly and produce large amounts of lipids simultaneously. The second problem is that microalgae are microscopic organisms that are currently mostly harvested by centrifugation, a very expensive and energy-intensive step that is not easily scalable. Here we present a new approach that addresses both problems. UV-C radiation was used as an easily-applied external stimulant to rapidly induce lipids and also as a new method to induce overnight settling of microalgae for harvesting (a step that would normally require expensive flocculants or centrifuges). In the first study conducted on Chlorella sp. BR2 with different dosages of UV-C radiation, maximum lipid fluorescence was measured after cultures were radiated with 500 mJ/cm 2 . Moreover, the lipid induction was also reflected by an increase in total fatty acids after exposing to 100 and 250 mJ/cm 2 of UV-C radiation. One of the major findings in this study was that there was a significant increase in total unsaturated fatty acid when compared to total saturated fatty acids in the microalgae. In the second phase of this study, to test whether nutrient starvation and UV-C treatment can lead to further lipid biosynthesis and facilitate settling in flagellate microalgae, combined sequential stress treatments were carried out on Tetraselmis sp. (M8). Maximum lipid induction was displayed by cultures radiated with 100 mJ/cm 2 and 250 mJ/cm 2 under laboratory conditions, and a dose of 48 J/cm 2 was found suitable for 12 cm-deep Tetraselmis 1000-L outdoor raceway pond cultures containing1.5x106 cells/mL.