(626f) Production of Total Lipid and Fatty Acids From Cassava Bagasse Hydrolysate by Heterotrophic Chlorella Protothecoides Under N-Stavation

With the rising price of crude oil, biodiesel from microalgae has become attractive and popular as an alternative biofuels in recent years. Heterotrophic fermentation of green microalgae Chlorella has been successfully validated for biomass and total lipid production from various biomass hydrolysate. Cassava bagasse is the most abundant byproduct from starch industry in south China and Southeastern Asian countries, consisting of 35-45% residual starch and 16-18% cellulose plus hemicellulose. The goal of this work was to evaluate the feasibility of using cassava bagasse as a cheap feedstock for the production of total lipid and fatty acids by heterotrophic Chlorella protothecoides under nitrogen starvation.

In this study, 10% (w/v) superfine powder of cassava bagasse was hydrolyzed by cellulase ACCELLERASE 1500 with dosage of 0.05mL/g biomass at pH 4.8, 50ºC for 36 h, and the hydrolysate contained 27.4g/L glucose. The Basal medium containing 20g/L reducing sugar and 1mM urea was prepared from the hydrolysate and used for the culture of Chlorella at 28±0.5ºC, pH 6.5 and DO>50% in 5L bioreactor, while the control medium contained 20g/L glucose as carbon source. To compare the effect of two media in the batch culture for 8 days, the biomass, total lipid content and the ratio of total fatty acids in lipid reached 6.9g/L, 53.6%DW and 67.4% in the hydrolysate medium, while 7.7g/L, 64.7%DW and 62.3% were obtained in control medium, respectively, resulting a similar productivities of total fatty acids (0.31 and 0.39 g/L/d). For the production of total lipid and fatty acids, repeated fed-batch culture was performed for 15 days with renewable rate at 20% in 5L bioreactor. The fed medium containing 200g/L reducing sugar and 10mM urea was prepared from the hydrolysate and fed repeatedly to keep reducing sugar concentration between 8-20g/L. The final biomass and total lipid content reached 9.95g/L and 58.3%DW, while the ratio of total fatty acids in lipid reached 66.7%, resulting in a lower productivity of total fatty acid reached 0.26 g/L/d. C16 and C18 fatty acids were over 85% of total fatty acid in cells, and the content of C18 fatty acids was increasing during the culture. Several inhibitors including acetic acid, furfural and benzoic acid were found in the hydrolysate by GC-MS, they probably affected the growth of Chlorella and lipid accumulation in long-term operation. Our study demonstrated the possibility of using cassava bagasse hydrolysate as carbon source instead of glucose for lipid and fatty acids production by heterotrophic Chlorella, and it is worthy of further study for the large-scale production.