Enhanced lipid productivity coupled with carbon and nitrogen removal of the diatom Skeletonema costatum cultured in the high CO2 level

Abstract

Rising CO2 is causing noticeable environmental and social problems and thus to reduce CO2 emission is becoming extremely urgent. Biodiesel from microalgae is considered to have immense potential in replacing fossil fuels and reducing CO2 emission, apart from remediating eutrophic waters. How to increase biodiesel yield with low cost is the key for successful application of biofuel. In this study, we used high CO2 concentration (5%) to culture the marine diatom Skeletonema costatum and aimed to enhance lipid productivity through the combination of low temperature shock. High CO2 first inhibited the specific growth rate but then increased it after a 24 h pause of gas supply. High CO2 increased lipid content by 26.8% and lipid productivity by 29.0%; the combination with low temperature shock resulted in a further stimulation (50.0% for lipid content and 42.5% for lipid productivity). High CO2 also stimulated carbon and nitrogen assimilation, leading to the increase of carbon and nitrogen removal rates by 28.9% and 22.7%, respectively; while low temperature shock did not show a significant effect. High CO2 increased maximum photochemical efficiency but reduced non-photochemical quenching, with insignificant effects of low temperature shock on either. Therefore, the stimulating effects of high CO2 on lipid accumulation could be attributed to increased photosynthetic performance because photosynthesis can supply ATP and carbon skeleton for lipid synthesis. These findings indicate the success of the combination of high CO2 and low temperature shock in enhancing algal lipid yield and bioremediation capacity.