Role of microbubbles coupling fibrous-bed bioreactor in butyric acid production by Clostridium tyrobutyricum using Brewer’s spent grain as feedstock

Background: Microbubbles coupling fermentation is an efficient technology for improving oxygen transfer to aerobic microorganisms in a bioreactor containing an air sparger. However, the effect of this technology on anaerobic Clostridium tyrobutyricum, whose morphology develops viscous broth rheology and lumps impeding the nutrient mass transfer, has not been reported yet. Therefore, in this study, we evaluated the role of microbubbles coupling fibrous-bed bioreactor (MBFBB) on butyrate production by immobilized Clostridium tyrobutyricum cells obtained from renewable feedstock brewer’s spent grain (BSG). Results: Compared with the conventional FBB fermentation, two-fold shorter fermentation time and two-fold higher butyrate productivity were achieved by MBFBB-immobilized C. tyrobutyricum cells. Furthermore, long-term stability and reliability for butyrate production were obtained in ten cycle process using BSG hydrolysate. Finally, fed-batch fermentation using BSG hydrolysate produced a high butyrate titer of 43.68 g/L, with a significantly higher selectivity of 11.67, reducing the production cost of downstream processing. The results indicated that butyrate productivity of 4.21 and 4.36 g/L·h were successfully obtained in BSG and glucose medium, thereby representing the highest productivity reported to date in C. tyrobutyricum. To our knowledge, this is also the first report related to microbial production of butyrate from brewer’s spent grain.Conclusion: The MBFBB-based fermentation process with BSG is a robust and ecofriendly technique, which would provide insights into future development of commercial biobutyrate production for the animal feed supplement market.