Production of Single-Cell Oil from Olive Mill Wastewater: Effects of Process Variables on Lipid Content and Fatty Acid Profile

Olive mill wastewater (OMW), due to its high organic load and phenolic content, represents both a major environmental challenge and a promising low-cost substrate for microbial bioprocesses. In this study, lipid production by Yarrowia lipolytica using OMW was optimized through a mixed-level Taguchi experimental design. The effects of OMW dilution (%), nitrogen supplementation, NaCl concentration, sterilization, and carbon source (glucose or glycerol) were evaluated in terms of biomass production, lipid accumulation, and fatty acid composition. The results demonstrated a clear inverse relationship between biomass formation and lipid accumulation. The highest lipid content (33.49%) was achieved under nitrogen-limited conditions combined with a high OMW dilution. After 168 h of fermentation, the calculated lipid yield was 0.51 g/L. Biomass and lipid productivities were calculated as 0.22 g/L/day and 0.073 g/L/day, respectively. ANOVA analysis revealed that nitrogen concentration was the dominant factor affecting lipid production (67.71%), followed by NaCl concentration (18.83%). In contrast, OMW dilution, sterilization, and carbon source type were not statistically significant (p > 0.05), indicating that lipid production can be effectively performed under non-sterile conditions with flexible substrate utilization. Fatty acid analysis revealed that the produced lipids were rich in oleic acid (C18:1n9c), reaching up to 57.97%, with unsaturated fatty acids generally accounting for the majority of the total fatty acid composition. Although the carbon source had a limited effect on lipid yield, it contributed to variations in fatty acid composition, suggesting the possibility of tailoring lipid quality through substrate selection.