Integrating the opposites of biofuel production: absorption of short-chain alcohols into oleaginous yeast cells for butanol recovery and wet-extraction of microbial oil

Abstract

Recovery of two biotechnologically produced fuel components, butanol and microbial oil, is assessed by absorption of the six shortest 1-alcohols into oleaginous yeast cells. We show an unexpectedly high extent of absorption of >C3 alcohols from water into Rhodosporidium fluviale cells with a lipid content of 69% of cell dry weight (CDW). Increasing the carbon chain length of the alcohol boosts both the rate and the quantity of absorption of the alcohol from water containing an initial ratio of 9.5 of CDW to alcohol. Under these conditions, 40% of butanol is removed from water, while the methanol concentration remains unchanged in 48 h incubation with the oleaginous yeast cells. Lower absorption of alcohols into non-oleaginous baker's yeast cells as a reference suggests that a majority of the alcohols combines with the lipid droplets inside oleaginous cells. The partition coefficient of the intracellular microbial oil to butanol exceeds those of oleyl alcohol and rapeseed oil by factors of 4 and 16. The capacity of oleaginous yeast cells to absorb butanol reaches 13% of CDW from 48 g per L butanol solution. Leakage of intracellular microbial oil occurs when the initial butanol concentration exceeds approximately 20 g L⁻¹. Butanol can be recovered after absorption from oleaginous yeast biomass, while microbial oil can be separated by subsequent wet-extraction with the alcohols as solvents. These results suggest that synergistic outcomes can be achieved by process integration both for industry and the environment.