Valorisation of whey by mixotrophic and heterotrophic cultivation of microalgae for biomass and lipid production

The dairy industry generates large volumes of whey, a nutrient rich by-product that is a threat to the environment because of a high lactose concentration. In this research, a potential of four microalgae strains – Tetradesmus obliquus MSCL 1710, Graesiella emersonii MSCL 1711, Chlorella vulgaris CCAP 211/111 and Scenedesmus quadricauda CCAP 276/16 was investigated to evaluate their growth under heterotrophic and mixotrophic conditions of lactose and its monosaccharides. This work specifically compares sweet whey (SW) and acid whey (AW) as a promising substrates for microalgal growth and lipid synthesis. Peculiar focus was given to local isolates—G. emersonii MSCL 1711 and T. obliquus MSCL 1710 cultivated in sweet (SW) and acidic whey (AW) at different concentrations and temperatures (15 °C and 25 °C). Mixotrophic cultivation in SW enhanced biomass productivity, with G. emersonii MSCL 1711 achieving 0.30 g/L/d and T. obliquus MSCL 1710 0.29 g/L/d at 25 °C. The highest lipid accumulation was observed in SW for G. emersonii MSCL 1711 at 15 °C, representing a 158.31% increase compared with the autotrophic control (mg/g dry weight). Additionally, β – galactosidase activity correlated with lactose assimilation in the medium for both cultures, suggesting that it is suitable for cultivation on whey substrates. The results confirm the ability of local microalgal strains to grow on SW, and on AW, demonstrating their potential for dairy by-product bioconversion into microalgal biomass for broad applications.