The dispersion of Trichosporon fermentans was controlled by optimizing the shear environment in the reactor to improve the cell sedimentation and separation performance

The morphology of pseudomycelium in Trichosporon fermentans is not conducive to the accumulation of lipids and the recovery of yeast cells by sedimentation. In this study, the computational fluid dynamics method was used to study the effects of shear force on the flow field distribution and on the dimorphism transition and dispersion of yeast cells in a 5 L stirred bioreactor, and to explore the sedimentation performance of yeast cells in different forms. It was shown that under the condition of moderate shear force, such as 3.45 Pa corresponding to a stirring speed of 300 rpm as selected in this experiment, most of the yeast cells in the fermentation broth were spherical or short rod-shaped, and there were almost no pseudohyphal yeasts, which contributed to the good sedimentation performance of the yeast cells. The results showed that the appropriate shear force could effec-tively inhibit the transformation of yeast cells into pseudohyphae, retain a large number of cells in a single cell shape, enhance cell dispersion and facilitate cell contact, absorption and utilization of organic substrates, as well as increase the lipid accumulation in yeast cells. By controlling the shear force, after 40 h of treatment of RSOW using Trichosporon fermentans, the chemical oxygen demand and oil content removal were approximately 95.81% and 88.09%, respectively, which indicate a significant improvement compared with those before optimizing the shear environment. Therefore, based on shear control of the cell morphology to improve yeast cell dispersion and sedimentation performance, the oily wastewater treatment method established in this study can be used to guide the process design of fermented Trichosporon fermentans for the treatment of RSOW and the resource recycling of yeasts.