Influence of Nitrogen to Phosphorus Ratio and CO₂ Concentration on Lipids Accumulation of Scenedesmus dimorphus for Bioenergy Production and CO₂ Biofixation

The potential of Scenedesmus dimorphus microalgae for CO₂ biofixation and lipid biosynthesis for bioenergy applications was evaluated in this study. Batch experiments were conducted using synthetic tertiary municipal wastewater samples at several nitrogen to phosphorus (NP) ratios (1 : 1 to 8 : 1) and CO₂ concentrations (∼0%, 2%, 4%, and 6% CO₂ in supplied air). Scenedesmus dimorphus was cultivated for 25 days and the growth is highly dependent on the CO₂ concentration and the NP ratio. An NP ratio of 2 : 1 produces a biomass yield of 733 mg/L when the microalga culture was supplied with air enriched with 2% CO₂. The maximum CO₂ biofixation rate of 49.6 mg L⁻¹ d⁻¹ is at an NP ratio of 8 : 1 with 4% CO₂. A colorimetric technique depending on sulpho-phospho-vanillin (SPV) was utilized for the determination of the intracellular lipid content. The highest lipid content of 31.6% as the dry weight of the biomass is at an NP ratio of 1 : 1 and 6% CO₂. These results indicate that supplementation of suitable CO₂ with favorable NP ratio has a considerable effect on lipid accumulation in the microalgae Scenedesmus dimorphus biomass.