Integrated in situ transesterification for improved biodiesel production from oleaginous yeast: a value proposition for possible industrial implication

The conventional biodiesel production process using oleaginous yeast biomass often involves multiple energy intensive unit operations and processing steps that increase the overall cost and reduce the economic viability of the biodiesel product. Thus, this study attempts to design and optimize an in situ process for the direct conversion of lipids in disrupted wet biomass of oleaginous Pichia guilliermondii with an average total lipid content of 50 +/- 2% [w/w, on dry cell weight (DCW) basis] to biodiesel, while bypassing important steps of biomass processing such as drying and lipid extraction. The in situ process involved applying sonication as an energy efficient cell disruption strategy that helped extract 44.5 +/- 2.3% (w/w) neutral lipid on a dry cell weight (DCW) basis, using methanol-hexane as the most appropriate binary solvent system. Subsequently, the critical transesterification parameters such as biomass : methanol (w/v), catalyst concentration (v/v, %), reaction time and temperature that influence in situ biodiesel production were standardized. A maximum FAME (fatty acid methyl esters) yield of 92% (w/w of lipid), was achieved. This yield is comparable to that obtained by the ex-situ multistep transesterification process that requires approximately 7 h more than the in situ process, thereby resulting in greater productivity. The properties of the biodiesel product, as calculated from the FAME profile using empirical equations, conformed to the ASTM and CEN standards for it to qualify as an alternative to petro-diesel. Reports on direct transesterification of yeast biomass are scant. Thus, to the best of our knowledge, the developed in situ process integrating cell disruption, lipid extraction and transesterification is more energy efficient and productive as compared to those reported on yeast or algal feedstocks.