Carbon dioxide biofixation and lipid accumulation potential of an indigenous microalga Scenedesmus obliquus (Turpin) Kützing GA 45 for biodiesel production

Abstract

The environmental precedence of the reduction of greenhouse gases catches the attention of researchers for CO₂ biomitigation vis-a-vis biodiesel production using microalgae. In this study, a locally isolated microalga, Scenedesmus obliquus (Turpin) Kützing GA 45 presented a biomass yield of 3.74 g L⁻¹ with a concurrent lipid yield of 850 mg L⁻¹ for a 16-day incubation period under 15% CO₂ sparging at 0.6 vvm air flow in a photobioreactor system. These values were raised up to 7.01 and 1.69 g L⁻¹, respectively, for biomass and lipid yield for 10 days incubation with 1% glucose under the above conditions. The maximum CO₂ bio-fixation rate was found to be as high as 0.77 g L⁻¹ d⁻¹. Moreover, under one week’s biphasic nitrogen starvation, lipid content was boosted up to 43.9% of dry cell weight (dcw) with a yield of 2.0 g L⁻¹. This yield can be projected to an areal lipid productivity of 180 tons per ha per year, and a CO₂ biofixation rate of 1170 tons per ha per year with 200 algal ponds (size: 15 × 3 × 0.5 m), assuming 18 cultivation cycles per year. The GC-MS study revealed that the test microalgal biodiesel was rich in saturated and monounsaturated fatty acid methyl esters (>80%). The fuel properties, viz. density, viscosity, acid value, iodine value, calorific value, cetane index, ash and water contents were analyzed, and found to be comparable with national and international biodiesel standards. This study thus demonstrated that the mixotrophic culture conditions followed by nitrogen starvation are superlative among all other conditions for obtaining high biomass and lipid yields with qualitative biodiesel production, and ensured the prospects of the test microalga S. obliquus (Turpin) Kützing GA 45 for large-scale exploitation.