Removal of zinc by Selenastrum sp. and simultaneous biodiesel production from metal-resistant biomass for energy and environmental sustainability

In this study, the phycoremediation of zinc by the unicellular green alga, Selenastrum sp. and simultaneous biodiesel production from heavy metal resistant biomass was investigated. The microalga Selenastrum sp. was used to remove the zinc amended at 1, 3, 5, 7 ppm in the BG II medium. In all the tested zinc concentrations (1–7 ppm), there was no noticeable heavy metal stress on the microalga and the algal culture showed a steady and better growth pattern in zinc amended medium than that control (no zinc added). Furthermore, on the 24th day, the biomass concentration was 1.63 g/L for the 5 ppm and 7 ppm zinc dosed experiments, which was higher than the control. Atomic adsorption spectroscopic analysis showed that zinc concentration in the medium (5 and 7 ppm) was reduced to ~0.44 ppm, which is equivalent to 90 % heavy metal removal efficiency. The total lipid content and biodiesel yield from zinc-resistant Selenastrum biomass was 17.6 and 65.1 %, respectively. Finally, test microalga grown in zinc-added media produced beneficial fatty acids such as palmitic, palmitoleic, oleic, stearic, linoleic, and linolenic acid for high-quality biodiesel production.