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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