Yeasts such as Cutaneotrichosporon oleaginosum can convert low-value side streams into single-cell oils with fatty acid profiles comparable to vegetable oils. Crude glycerol (CG), a byproduct of biodiesel production, offers a cost-effective substrate, but its variable impurity load often causes strong growth inhibition. In this study, two untreated industrial CG batches were characterized and evaluated in 2.5 L and 19 L stirred-tank fermentations. Direct batch cultivation on CG resulted in no measurable growth, whereas an adapted step- wise feeding strategy effectively mitigated early inhibition and restored biomass formation, metabolic activity, and lipid accumulation. In 2.5 L cultivations, apparent growth rates up to 0.51 h−1 and volumetric productivities up to 0.22 g L−1 h−1 were achieved, with lipid contents of ~30% and oleate-dominated fatty acid profiles. Fatty acid profiles remained oleate-dominated (~53–55% C18:1). Transition-scale (19 L) repeated-batch fermentations confirmed process robustness across > 640 h of operation, during which lipid content (~30– 36%) and fatty acid composition (oleate ~51–53%) remained stable despite pronounced substrate-batch variability and increasing nitrogen limitation. These results demonstrate that untreated CG can be reliably valorized for lipid production using scalable feeding strategies without prior detoxification. This closes a gap between laboratory-scale feasi- bility studies and process-oriented, multi-cycle operation on industrial-grade feedstocks, confirming that feeding-driven inhibition control can ensure robust performance without substrate purification.
Schulz et al. (Thu,) studied this question.