Sustainable Valorization of Olive Mill Wastewater via Oleaginous Yeasts: Single-Cell Oil Production and Effluent Detoxification

Produced as a residual output of olive oil extraction, olive mill wastewater (OMW) is characterized by a high organic load and significant levels of phenolic compounds, posing notable environmental challenges. While it resists biodegradation, OMW serves as a nutrient-rich resource for microbial growth. In this study, OMW was used as renewable feedstock for microbial lipid production by oleaginous yeasts. Chemical characterization revealed that the OMW sample primarily contained 18 g/L total sugars, 3.4 g/L phenolic compounds, and high organic and mineral content of 85 and 15 g/L, respectively. Among the tested yeasts, Rhodotorula babjevae Y-SL7 stood out with a lipid accumulation yield of approximately 38% and a significant phenolic compound detoxification rate of 53.7%. To enhance lipid yield, the most effective nitrogen source was selected following preliminary evaluation, and culture conditions were then optimized using response surface methodology (RSM) based on the Box-Behnken model, incorporating three independent factors. The lipids produced from OMW showed a fatty acid composition dominated by oleic acid (69%) and palmitic acid (23%). Predictive analyses of biodiesel properties suggest this oil could be advantageous for biodiesel production. Additionally, lipid production was accompanied by carotenoid synthesis, mainly torulene (68.2%) and torularhodin (31.7%), both demonstrating significant antibacterial and antioxidant activities. The capacity of Y-SL7 to detoxify OMW and generate valuable by-products positions this approach as a promising alternative to conventional OMW treatment methods.