Pyrolytic lignin depolymerization by ozone treatment followed by microbial conversion towards lipids and fusel alcohols

Obtaining high-value compounds from pyrolytic lignin (PyL), one of the main fractions in lignocellulose-derived pyrolysis liquids, is challenging. Herein, we demonstrate a proof-of-concept, three-step strategy to produce valuable compounds from a commercial pinewood PyL via a novel integration of pyrolysis, ozonolysis, and microbial conversion. Straightforward ozonolysis of PyL in acetic acid led to a depolymerized product stream of lower chemical complexity containing vanillin (1.9 mM) as the main monomeric unit. The ozonolyzed PyL stream was distilled in vacuo to yield an upgraded fraction enriched in vanillin (15.3 mM) and other methoxyphenols (8.6 mM on average), containing 85 % less furfural (82.0 mM) —a common fermentation inhibitor. Finally, the fermentation of the upgraded stream containing PyL-derived monomers was tested by means of the oleaginous yeast Yarrowia lipolytica MUCL 28849. Depending on the C/N ratio in the broth, we demonstrated the formation of (un)saturated lipids (0.01–1.1 wt% cell dry weight (CDW) basis) and fusel alcohols, like 2-phenylethanol (0.02 g/L, equivalent to 0.30 wt% CDW), at the expense of vanillin, acetoxypropanone, and unidentified components. This work shows that it is possible to coproduce specialty compounds like microbial fatty acids and higher alcohols from the chemical and biological processing of an inexpensive C source like PyL, providing a solid basis for improvement via further (bio)chemical engineering. • 3-Step strategy producing microbial lipids and fusel alcohols from pyrolytic lignin. • Ozonolysis in acetic acid depolymerized the pyrolytic lignin. • Vacuum distillation enriched the stream in vanillin and other methoxyphenols. • Y. lipolytica MUCL 28849 produced lipids or fusel alcohols from the upgraded stream.