The growth of oleaginous Rhodotorula glutinis in an airlift bioreactor on crude glycerol through a non-sterile fermentation process

While the use of oleaginous Rhodotorula glutinis as a feedstock for biodiesel production is an attractive idea, as it can avoid the pollutions associated with over-consumption of fossil fuels. Nevertheless, the related costs, including the energy required for sterilization, remain a barrier to commercialization. This study thus used a low-pH non-sterile medium, instead of a completely sterilized one, to grow R. glutinis in a 5-L airlift bioreactor. The results show that R. glutinis can grow well at a low pH level of 4.0 and without sterilization of the medium, producing a final biomass of 11.7 g/L. Nevertheless, such a low pH will lead to fewer total lipids accumulation, and so a two-stage process of pH control in a non-sterile batch was proposed. Even this two-stage pH operation was also able to produce a similar final biomass of 11.7 g/L. However, the batch with two-stage pH control had a far higher lipid content of 55 +/- A 4 % as compared to that of 21 +/- A 3 % in the batch grown at pH 4.0. This study shows the potential of the proposed non-sterile process with two-stage pH control applied to the growth of R. glutinis to enhance the total lipid accumulation.