An integrated strategy of reusing acid hydrolysate combining adapted Bacillus coagulans fermentation for comprehensive utilize carbohydrates of Chinese fir sawdust

In this study, an efficient and economical method for fractionation and sequential utilization of whole components of Chinese fir sawdust (CFS) was explored. By reusing hemicellulose hydrolysate, 54 % sulfuric acid was saved during the pretreatment process. Additionally, a robust strain of Bacillus coagulans CC17B was obtained through adaptive evolution, which not only could utilize the 100 % (v/v) reused hydrolysate without detoxification but was also unaffected by carbon catabolism repression. Combined with fed-batch simultaneous saccharification and fermentation, 54.8 % of the carbohydrate of Chinese fir sawdust was finally converted to lactic acid through B. coagulans CC17B. Furthermore, 44.6 % of the lignin was recovered from the liquid fraction, showing potential for efficient conversion to bio-oil. Overall, the hydrolysate reusing process and high robust strain of B. coagulans CC17B was applied to improve the economics of CFS biorefinery, which provides a promising strategy for the complete utilization of softwood biomass.