Automatic Fed-Batch Cultivation Enhances Microbial Lipid Production from Volatile Fatty Acids

Organic waste is generated worldwide, and its disposal and recycling are becoming a challenge. Due to its high carbon content, however, it may be converted into valuable products. Carbon neutrality is essential, and unstable international oil prices stress the increasing importance of biofuels significantly. Volatile fatty acids (VFA) derived from organic waste can be converted to microbial lipids by oleaginous yeast using it as a carbon source. When VFA is consumed by oleaginous yeast, the pH of the medium rises; hence, acidic agents have to be added to the medium to maintain the broth's pH. In this study, we enhanced microbial lipid productivity by automatic fed-batch cultivation using VFA as an acidic agent, and the modified cultivation showed 48.9% and 69.0% higher biomass and lipid productivity than manual multi-fed culture. At a VFA concentration of 5 g/L and pH 7.0, a lipid yield of 0.25 g/g alongside lipid productivity of 0.11 g/L/h was obtained from an automatic fed-batch system. Oleic acid accounted for the largest proportion of microbial lipids, and the fatty acid composition was suitable for biodiesel production.