At the University of Bath, the yeast Metschnikowia pulcherrima, has been evaluated for its potential to produce lipids from waste streams. M. pulcherrima is most commonly isolated from fruits and flowers, especially grape skins. M. pulcherrima can accumulate 40% dry weight in lipid under favourable conditions and significantly, is both mesophilic and acidophilic, with optimum growth rates at 17-25 �C and pH 3.5-5. The yeast also secretes antimicrobial compounds into the culture medium. These attributes make M. pulcherrima a very promising source of inexpensive lipids for biofuel manufacture, since the combination of antimicrobials, low pH and low temperature dramatically reduce the likelihood of invasion from non-productive species. M. pulcherrima was grown in non-sterile ammonium and nitrate rich wastewater, on a range of sugars and oligosaccharides derived from waste resources and is tolerant to a number of toxic compounds produced by the breakdown of lignocellulose. Significantly, the yeast was grown on a pilot scale (500L) in open raceway ponds with no protection from invasion. The oils produced by M. pulcherrima, while similar to vegetable oils, also contain high levels of sterol. Although the triglyceride portion of the oils can be esterified into biodiesel, the sterols are solids at room temperature. There are some indications that the sterol content could also inhibit catalyst performance during hydrotreating. In this investigation the sterol-rich microbial lipid was converted to a diesel-like fuel in a single step via catalytic cracking. The cracking of the sterol groups appears to liberate hydrogen, resulting in a reduction in the olefin content as well as an increase in the aromatic content of the fuel. The cracking of the oil over Pd/C resulted in a fuel with a comparable product distribution to ultra-low sulphur diesel (ULSD), with high levels of linear alkanes and approximately 10 wt% aromatics.

Hydrocarbons produced from a sterol rich microbial lipid isolated from an oleaginous yeast cultured in non-sterile conditions

248th National Meeting (2014)

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