Optimization of Euglena gracilis Growth on By-Products from a food industry

The use of wastewater from the food industry for microalgae cultivation represents a sustainable approach to valorizing nutrient-rich by-products. This study investigated the growth of Euglena gracilis on anaerobic digestate and vinasse, both derived from wheat starch processing, to optimize cultivation conditions for its potential use in fish feed formulations. In addition to assessing growth performance, the study evaluated nutrient removal efficiency and the synthesis of key biomolecules essential for aquafeed applications. Euglena was cultivated in 4 L photobioreactors (1.5 L working volume) using the liquid fraction of anaerobic digestate combined with vinasse under different pH conditions and vinasse concentrations. Both batch (up to 216 hours) and semicontinuous (HRT = 10 days) cultivation modes were tested and compared to a synthetic Cramer-Myers medium. The best results were achieved in batch at pH 5 with 2.5% vinasse, where a TSS growth rate of 160 mg/L/d was recorded at 48 h—exceeding that of the synthetic medium. The final algal count reached 9.1×10⁵ cells/mL, with total nitrogen and phosphate removals of 48% and 31%, respectively, and COD removal of 42%, indicating efficient mixotrophic growth. Biomass analysis revealed a paramylon content of 35%, highlighting its potential as a functional feed ingredient. Additionally, pigment concentrations were higher than in the synthetic medium, with chlorophyll a at 2.64%, chlorophyll b at 1.12%, and carotenoids at 0.37%, suggesting enhanced metabolic activity under these conditions. These results demonstrate the feasibility of using industrial by-products to support Euglena gracilis cultivation, offering a sustainable alternative for aquafeed production.