Valorization of Biodiesel-Derived Crude Glycerol for Producing Yeast Oil as an Alternative Biodiesel Production Feedstock: Productivity Improvement in Batch and Repeated Batch Fermentation

Biodiesel-derived crude glycerol (BCG) was investigated as a cost-effective carbon source for microbial oil (MO) production using Pseudozyma parantarctica CHC28. Optimal conditions were determined for repeated batch fermentation (RBF) strategies to enhance MO production as glycerol concentration 56.20 g/L, KH₂PO₄ 3.98 g/L, and fermentation temperature 27.2 °C. Under these conditions, maximum biomass and MO yields of 5.80 g/L and 2.46 g/L were achieved, respectively with an oil content of 42.41% (w/w). The RBF strategy, employing a 90% (v/v) repeated batch ratio, significantly increased MO production by 9.4% compared to batch fermentation (BF), resulting in an oil content of 44.64% (w/w). RBF eliminated the need for repeated starter preparation, a requirement in BF. Fatty acid (FA) analysis revealed that the MO primarily comprised long-chain C16 and C18 FAs. The estimated biodiesel properties derived from these FA compositions met the ASTM and EU biodiesel standards. Results demonstrated the potential of BCG as a valuable carbon source for MO synthesis and highlighted the efficacy of the RBF strategy in boosting MO production rates as an alternative feedstock.