Bicarbonate-Based Cultivation of Chlorella vulgaris: Growth Enhancement, Carbon Losses and Metabolic Trade-Offs

Microalgae are photosynthetic microorganisms with high biotechnological potential, though optimising inorganic carbon supply remains a critical challenge to enhance growth, biomass quality, and carbon use efficiency. To address this, this study evaluated the impact of sodium bicarbonate supplementation (0, 0.5, 1.5, and 3.0 g L−1) on Chlorella vulgaris growth, carbon dynamics, biochemical composition, and metabolism over 11 days. Higher carbon availability (3.0 g L−1 NaHCO3) increased the specific growth rate to 0.472 ± 0.004 d−1, accelerated nitrogen removal (85% by day 4), enhanced phosphorus removal (up to 90% by the end of cultivation), and increased dissolved inorganic carbon uptake (93 ± 6 mg L−1). Carbohydrate and lipid contents were not significantly affected by bicarbonate concentration, whereas protein and pigment levels were higher in non-supplemented conditions due to prolonged exponential growth. Bicarbonate supplementation enhanced MUFA content, improving biodiesel quality. Amino acid profiles were similar across conditions, with glutamic acid as the predominant amino acid (up to 17 mg g−1 DW) and higher values under moderate bicarbonate supplementation (1.5 g L−1). Overall, bicarbonate supplementation enhanced microalgal growth, nutrient removal efficiency, and fatty acid composition, highlighting its potential to improve carbon availability for C. vulgaris cultivation.