Biodiesel-derived crude glycerol as alternative feedstock for single cell oil production by the oleaginous yeast Candida viswanathii Y-E4

In recent years, much attention has been paid to microbial lipids as promising raw materials for biodiesel production. The use of industrial by-products as carbon sources seems to be a feasible strategy for cost-effective lipid fermentation with oleaginous microorganisms on a large scale. In this work, biodiesel-derived crude glycerol was used as a renewable feedstock for microbial lipid production. Chemical characterization has shown that used crude glycerol sample is mainly composed of 64.5 % glycerol, 5.9 % methanol, 11 % water and 5.8 % ash in addition to other impurities. This industrial waste was used as only carbon source in the culture media of 13 oleaginous yeast strains. Candida viswanathii Y-E4 stood out above the other strains, achieving a higher amount of biomass and lipid content (17.2 g/L and 41 %, respectively). Culture conditions were optimized using response surface methodology to enhance the Y-E4 lipid yield. Box-Behnken model was performed to determine the optimum levels of three independent variables and the eventual effect of their interactions on the response. Under optimal conditions, the total biomass of 26.6 g/L with lipid content of 51.9 % (corresponding to a lipid yield of 13.6 g/L) could be achieved after 166 h of culture. The characterization of obtained lipid showed that fatty acids composition and lipid profile were very different between pure and crude glycerol based cultures, with a predominance of long-chain fatty acids, particularly polyunsaturated fatty acids such as linoleic acid (45 %). The predictive determination of biodiesel properties suggests that this oil may effectively be used for biodiesel manufacture. The current study, therefore, opens new perspectives in relation to the valorization of biodiesel-derived crude glycerol, through completely eco-friendly processes.