Extracellular biosurfactants from yeast and soil–biodiesel interactions during bioremediation

The aim of this study was to select cultivation conditions for the production of extracellular biosurfactants from Saccharomyces cerevisiae. This yeast has been recognized due to the production of intracellular biosurfactants, and this work presented a technique to produce extracellular biosurfactants, allowing the reduction in costs with downstream processes. We studied the scale up of production in bioreactors and their effects on bioremediation in soils contaminated with biodiesel. Furthermore, we also evaluated the effects of biosurfactant addition on the adsorption of contaminants in these soils. The concentration and types of inducer (glycerol, soybean oil and diesel oil), pH levels and temperatures were studied to maximize the production through factorial designs. The results that obtained the maximum emulsifying production (6.95 UE d−1) were found in the concentration of 5 g L−1 of glycerol, a pH 5.5 and a temperature of 30 °C. In the scale up of the 5 L bioreactor, the maximum productivity of 3.85 UE d−1 was achieved in 2 days. The addition of 0.05%, 0.1% and 0.5% of biosurfactant in soil contaminated with 20% of biodiesel for 90 days allowed a biodegradation of 56.71% with a 0.5% of biosurfactant. For all evaluated conditions, 25% of the biodegradation value should actually be attributed to the adsorption process. The addition of biosurfactants does not affect the retention of the contaminant in the soil, demonstrating that the biosurfactants improved biodegradation without interfering in the adsorption process of the contaminant in the selected soil, which is important in order to avoid influencing the movement processes of contamination plumes.