Study On Production Of Fumaric Acid From Biodisesl-Derived Crude Glycerol By Rhizopus Arrhizus

Fumaric acid, as a four-carbon unsaturated dicarboxylic acid, has many potential industrial applications in the fields of food, chemical, materials and pharmaceutical industries. In this paper, biodiesel-derived crude glycerol was targeted for production of fumaric acid through fermentation. The capability of R. arrhizus to assimilate biodiesel-derived crude glycerol and convert it into fumaric acid was investigated. It was found that R. arrhizus could assimilate crude glycerol without purification for growth. After optimizing the initial pH, glycerol concentration, spore inoculum and yeast extract concentration, the optimal condition for R. arrhizus forming pellet: initial pH3.5, glycerol concentration25g/L, spore inoculum concentration4.8×107/mL and the yeast extract concentration1.5g/L was obtained when growing on crude glycerol. Under the optimal condition, small (0.7mm) and hairy pellets were formed. Compared to the pellets formed on glucose or pure glycerol medium, there were more pellets on glycerol medium, and the pellet diameter was much smaller. When used as inoculums for fumaric acid fermentation, the pellet formed on crude glycerol medium was more conducive to the accumulation of fumaric acid. The fumaric acid production was enhanced by46.59%compared to the pellet formed on glucose medium, and the ethanol production was very low.When using crude glycerol as sole carbon source, the fumaric acid production was very low (4.37g/L), and there was much residual glycerol in the fermentation medium at the end of the fermentation. Therefore, a novel two-stage fermentation strategy utilizing crude glycerol and glucose for fumaric acid production was developed. Crude glycerol was first used as the carbon source for R. arrhizus growth, then glucose was used as the carbon source for fumaric acid production. After optimizing the inoculum age, inoculum size and liquid volume in the two-stage fermentation, the highest fumaric acid production was34.51g/L, which was enhanced by11%compared to glucose-direct fermentation.The co-fermentation of glycerol and glucose was studied for fumaric acid production. The concentrations of crude glycerol and glucose in co-fermentation were investigated for their effect on fumaric acid production. After the optimization, the optimal concentration of crude glycerol and glucose were30g/L and80g/L, respectively. The fumaric acid production of40.59g/L was achieved, which was enhanced by41.8%compared to glucose (80g/L) fermentation, and the fumaric acid yield was0.369.By the two-stage fermentation and the co-fermentation strategies, R. arrhizus could use crude glycerol to grow and produce fumaric acid, which helps to solve the problem of waste glycerol disposal. Moreover, a cost-effective way for fumaric acid production was developed, which is beneficial to promote the industrial production process of fumaric acid.