(641b) Biodiesel Production Through Microwave Assisted Transesterification of Microbial Cells

One strain of oleaginous yeasts, Cryptococcus curvatus (ATCC 20509) has been studied to grow on several substrates including  biodiesel production byproduct crude glycerol and sweet sorghum juice. After cultivation, yeast cells were heated under microwave radiation to extract lipid and produce biodiesel through in-situ transesterification.

Firstly, the yeast growth with crude glycerol was studied.On the second step, an optimization of yeast fermentation with crude glycerol was conducted. The resulting parameters of the response surface method optimization were used in a fed-batch fermentation where crude glycerol was automatically pumped in responding to exhausted oxygen levels in the fermentor.At the end of 12 days, the biomass density and lipid content were 44.53 g/L and 49%. Compared with our previous fed-batch experiment which was conducted under un-optimized condition, the yield of biomass and lipid increased 35.26% and 25.29%.

Considering its capability to utilize a broad range of substrates, C. curvatus was tested on its lipid productivity on sweet sorghum juice. When cultured in a fed batch process for 3 days, the final biomass density was 23.6 g/L with a lipid content of 51%. To extract lipids from cells in an effective and fast fashion, a domestic microwave oven was used with different solvents. With only methanol, a lipid yield of 33.2% of yeast cells was obtained in 4 min.

In the end, to convert yeast lipids to biodiesel directly without the step of lipid extraction,the in-situ transesterification method used microwave irradiation on the simultaneous extractionand transesterification of wet yeast biomass to biodiesel. Based on the experimental results and RSM analysis, the optimal conditions for this process were determined as: methanol to yeast biomass (v:w) ratio of around 50:1, catalyst concentration about 5 wt.%, and reaction time of 2 min. The biodiesel samples were analyzed with GC and the FAME content in biodiesel is about 50%. Compare the with other researches, this process proved to be a fast and easy method to produce biodiesel from wet yeast biomass.