Mixotrophic cultivation of microalgae using agro-industrial waste: Tolerance level, scale up, perspectives and future use of biomass

Abstract

Alternative culture media make large-scale microalgae biomass production more viable and cost-effective. The aim of this work was to study the addition of whey as an alternative source of organic nutrients in fed-batch mode for the cultivation of microalgae (Spirulina platensis, Chlorella homosphaera and Scenedesmus obliquus). The microalgae demonstrated acceptance of whey at low concentrations, causing the increasing in the maximum specific growth rates (μmax) and biomass concentrations ([X]max) compared with the cultivation without whey in standard medium (μmax of 0.168 d−1 versus 0.075 d−1, and [X]max of 2.274 g L−1 versus 0.970 g L−1, respectively, for S. platensis). Therefore, a cost savings in cultivation media of up to 32 %, 57 %, and 73 % were possible in the cultivation of S. obliquus, S. platensis, and C. homosphaera, respectively, considering the production of 1 kg of biomass. The addition of whey presented different effects in the levels of intracellular protein considering the species of microalgae: an increasing was observed in C. homosphaera (24.18 to 43.96 g/100 g of biomass) and a decreasing in S. platensis (73.75 to 44.06 g/100 g of biomass), comparing with the controls. Scale-up with a natural light source can affect microalgal productivity and biomass composition in a medium supplemented with whey, because of the influence of irradiation. Optimizing the large-scale production of microalgae using agro-industrial residues can lead to significant advancements in biomass production at reduced costs. These biomasses can be integrated into bioenergy production, biofertilizer manufacturing, and animal feed production. By utilizing waste as a nutritional source and optimizing cultivation processes and biomass generation, a closed-loop cycle is established, aligning with the principles of circular bioeconomy and enhancing the sustainability of the process.