Potential utilization of agro-industrial wastewaters for lipid production by the oleaginous yeast Debaryomyces etchellsii

The present study was carried out in order to investigate the ability of the oleaginous yeast Debaryomyces etchellsii strain BM1 to convert a variety of low-cost carbon sources, i.e. deproteinized cheese whey, olive mill wastewater, wastewaters from confectionary industries and expired soft drinks, into single cell oil with simultaneous pollution load removal. Interestingly, this strain was able to grow and to accumulate significant quantities of reserve lipids (14.7-25.9% wt/wt in dry biomass) of similar fatty acid composition to that of vegetable oils currently used in the biodiesel manufacture such as palm and high oleic sunflower oils. Biodiesel produced from different substrates satisfied the limits imposed by the European Standard EN 14214 for critical parameters like cetane number, iodine value and cold filter plugging point. Medium optimization was performed using simplex-centroid mixture design method based on three media components, i.e. expired soft drinks, olive mill wastewaters (25%, v/v in water) and deproteinized cheese whey. The model estimated that a maximum lipid content of 28.1% wt/wt in dry biomass, a lipid yield of 1.2 g/L and a cell mass yield of 4 g/L could be obtained when a mixture of expired soft drinks and olive mill wastewater (25% in water, v/v) is used as substrate at percentages 62.4% and 37.6%, respectively. On the other hand, a medium containing cheese whey and expired soft drinks at 50:50 (v/v) yielded 7.9 g/L dry biomass containing 15.1% lipids, leading to the same lipid yield (1.2 g/L). In this medium, a significant reduction (around 58%) of the chemical oxygen demand was observed. This research provides an efficient approach for simultaneous biodiesel recovery and wastewater treatment.