Cunninghamella echinulata produced from soybean wastewater cleanly harvests oleaginous yeasts in soybean oil refinery effluent by efficient adhesion and improves microbial lipid quality

The oleaginous yeast Trichosporon fermentans can degrade oils and fats in soybean oil refinery effluent (SORE) and accumulate intracellular lipids. Effective harvesting techniques for oleaginous yeasts can improve their utilization efficiency. Considering its excellent adhesion properties, Cunninghamella echinulata, a lipid-producing fungus, was introduced to harvest the yeast in SORE via a two-step process. Compared with C. echinulata cultured in traditional medium, namely, potato starch wastewater (PSW), C. echinulata produced from soybean wastewater (SW) achieved a better adhesion for the yeast, reaching 95.24%. Based on kinetic and thermodynamic analysis, it was found that yeasts are gathered by mycelium pellets of C. echinulata by physical adsorption, and the process is controlled by liquid film diffusion and intraparticle diffusion. The porosity of these mycelium pellets was as high as 79.3 ± 0.5%, which contributed significantly to C. echinulata's ability to adhere to the yeasts. However, when the pH was between 6 and 7, an electric neutralization effect was responsible for the higher adhesion of C. echinulata from SW to T. fermentans compared with that of C. echinulata from PSW. Because the microbial lipids produced by C. echinulata are rich in unsaturated fatty acids (UFAS), the highest proportion of UFAS reached 79.8% of the total fatty acids in microbial lipids extracted from the adhesion products. Compared with the traditional techniques used for harvesting oleaginous yeasts, the efficient adhesion of C. echinulata from SW to the yeasts in SORE represented a cleaner harvest process and improved the quality of the microbial lipids.