Enhancing lipid productivity of Chlorella vulgaris using oxidative stress by TiO2 nanoparticles

Ability to increase the lipid production in microalgae is one of the heavily sought-after ideas to improve the economic feasibility of microalgae-derived transportation fuels for commercial applications. We used the oxidative stress by TiO2 nanoparticles, a well-known photocatalyst, to induce lipid production in microalgae. Chlorella vulgaris UTEX 265 was cultivated under various concentrations of TiO2 ranging from 0.1 to 5 g/L under UV-A illumination. Maximum specific growth rate was affected in responding to TiO2 concentrations. In the presence of UV-A, chlorophyll concentration was decreased at the highest concentration of TiO2 (5 g/L TiO2) by oxidative stress. The fatty acid ethyl ester (FAME) composition analysis suggested that oxidative stress causes the accumulation and decomposition of lipids. The highest FAME productivity was 18.2 g/L/d under low concentrations of TiO2 (0.1 g/L) and a short induction time (two days). The controlled condition of TiO2/UV-A inducing oxidative stress (0.1 g/L TiO2 and two days induction) could be used to increase the lipid productivity of C. vulgaris UTEX 265. Our results show the possibility of modulating the lipid induction process through oxidative stress with TiO2/UV-A.