Evaluation of algal strains for carbohydrate production: Potentials of Chlorella lewinii FwC1 under different trophic modes and in open-pond conditions

Microalgae-based carbohydrates have been identified as a potential feedstock for third-generation biofuel production, but with several limitations from strain selection to mass production. Thus, identifying an appropriate microalgal cellular factory for mass-scale production of carbohydrates is essential. The present study screened eight algal strains with a multi-criteria approach, identifying Chlorella lewinii FwC1 as the most effective, with carbohydrate productivity of 19.76 mg L⁻¹ day⁻¹ and biomass yield of 0.15 g mol⁻¹ photon under photoautotrophic conditions. This strain thrived across various temperatures (24–36 °C) and pH (5.5–10.5). Under mixotrophic conditions with glucose, it achieved maximum biomass and carbohydrate productivity of 414 and 208 mg L⁻¹ day⁻¹, respectively, significantly surpassing heterotrophic and photoautotrophic growth. Sodium bicarbonate supplementation enhanced biomass productivity by ∼2-fold under photoautotrophic and 1.67-fold under mixotrophic conditions. Further, optimization of photoautotrophic condition improved biomass and carbohydrate productivity to 190 and 64.6 mg L⁻¹ day⁻¹, respectively, with a biomass yield of 0.38 g mol⁻¹ photon. Under open-pond conditions at a 300 L scale with optimal media composition, productivity reached 100.2 mg L⁻¹ day⁻¹ for biomass and 34.5 mg L⁻¹ day⁻¹ for carbohydrates. Thus, Chlorella lewinii FwC1 is a promising candidate for carbohydrate production.