Butyric acid production from oilseed rape straw by Clostridium tyrobutyricum immobilized in a fibrous bed bioreactor

Butyric acid is an important specialty chemical with wide industrial applications, while economical production via feasible large-scale fermentation requires low-cost substrate and an efficient process. In this study, hydrolyzed oilseed rape (OSR) straw was used as an alternative carbon source for immobilized-cell fermentation of Clostridium tyrobutyricum to produce butyric acid. Compared to the free-cell fermentation, higher butyrate yield (0.43 gig vs. 0.37 g/g), productivity (2.46 g/L/h vs. 0.93 g/L/h) and concentration (13.6 g/L vs. 11.6 g/L) were obtained with immobilized cells of C tyrobutyricum in repeated-batch fermentation. Furthermore, fed-batch fermentation using pretreated OSR straw tiydrolysate resulted in a high butyric acid concentration of 50.2 g/L, with yield of 0.38 g/g. Finally, the repeated batch fermentation was carried out, which achieved high butyrate yield and volumetric productivity during long-term operation. With desirable characteristics such as economic viability and competitiveness, as well as being environmentally friendly, the fermentation developed in this work should provide an efficient process for industrial production of butyric acid. (C) 2016 Elsevier Ltd. All rights reserved.