Efficient production of butyric acid by Clostridium tyrobutyricum immobilized in an internal fibrous bed bioreactor (IFBB)

An internal fibrous bed bioreactor (IFBB) was constructed in an anaerobic stirred fermenter for butyric acid production by immobilized Clostridium tyrobutyricum ATCC 25755. In the IFBB system, porous cotton terry cloth was used as a fibrous matrix and the matrix was fixed on agitation shaft and inside baffles. Firstly, free-cell fermentations with batch and fed-batch modes were carried out under pH 6.0. The yield and butyric acid/acetic acid (B/A) ratio reached 0.387 g/g and 4.70 g/g in batch mode, and 0.426 g/g and 8.09 g/g in fed-batch mode, respectively. When implementing fed-batch fermentation with immobilized cells in IFBB, the concentration and productivity of butyric acid reached 45.38 g/L and 0.630 g/L/h, respectively, which were enhanced by 10 % in comparison with the free-cell fed-batch fermentation. Furthermore, a high yield of 0.440 g/g and B/A ratio of 12.75 g/g were also achieved in IFBB with fed-batch mode. Finally, the productivity of butyric acid could be further elevated to similar to 0.90 g/L/h with repeated-batch in IFBB, while it was only 0.444 g/L/h in free-cell batch fermentation. These results obtained might show the potential for efficient butyric acid production in the IFBB system from renewable resources.