Bioconversion of volatile fatty acids from macroalgae fermentation into microbial lipids by oleaginous yeast

•Repeated fed-batch process was used for microbial oil production.•Carbon sources were derived from Laminaria japonica anaerobic fermentation with CSTR.•No additional nutrients or synthetic medium was used.•The total volatile fatty acid yield was 0.47 g/g COD.•The highest lipid content was 61.00%.

Marine biomass is a potential carbon resource for the production of bio-based energy and chemicals. Microbial lipids are competitive in producing biodiesel. In this study, Laminaria japonica (Saccharina japonica) was chosen as a model marine biomass producer due to its fast rate and well-established cultivation technology. A mixed culture system was established by inoculating it with sludge from an anaerobic digester, and then operated in a continuous mode for over 1000 days by feeding it a non-sterile suspension of dried L. japonica in tap water without additional nutrients. The average yield and productivity of total organic acids during the stationary phase were as high as 0.47 g/g COD and 2.45 g/L/day at pH 7 with 84.08% of acetate in total organic acids. The volatile fatty acids (VFAs) from the continuously-stirred tank reactor (CSTR) were used by oleaginous yeast (Cryptococcus curvatus) to produce lipids in a repeated batch system. The highest lipid content was 61%. The composition of the fatty acids was quite similar to that of vegetable oils. This system has potential application to biodiesel production.

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