Effect of Mn2+, Co2+ and H2O2 on biomass and lipids of the green microalga Chlorella vulgaris as a potential candidate for biodiesel production

The present study examined the effect of heavy metals (Mn2+ and Co2+) and hydrogen peroxide (H2O2) on biomass, lipid content and lipid productivity of Chlorella vulgaris. Manganese chloride at 2 μM, 10 μM and 12 μM increased the lipid content significantly by 14 %, 16 % and 15 %, respectively, above the corresponding controls after 8 days of incubation, resulting in a significant (18 %) increase in lipid productivity with respect to the control at 12 μM manganese chloride. All applied concentrations of cobalt nitrate increased the lipid content up to 25 % more than the corresponding controls. The optimum concentration of cobalt nitrate for high lipid productivity was 2.5 μM, which resulted in a 22 % increase in lipid productivity over the control. Furthermore, lipid productivity was increased significantly by 29 % over the control when 4 mM hydrogen peroxide was included in the culture medium. Additionally, the proportion of total saturated fatty acids extracted from Chlorella vulgaris treated with 12 μM manganese chloride, 2.5 μM cobalt nitrate and 4 mM hydrogen peroxide ranged between 40 % and 45 % of total fatty acids. The present study concluded that heavy metals and oxidative stress efficiently increased the lipid productivity of the promising biodiesel feedstock chlorophyte Chlorella vulgaris. In addition, the type and proportion of individual fatty acids meet the biodiesel standards.