A scale-up study of the continuous ABE fermentation in a packed bed coupled with the extraction/gas-stripping in situ butanol recovery process

Abstract

A 5-L pilot-scale packed-bed bioreactor with integrated in situ extraction/gas-stripping was designed and manufactured for automated acetone-butanol-ethanol (ABE) fermentation using immobilized Clostridium acetobutylicum. A continuous run of 770-h demonstrated the robustness of the bioreactor. Optimal inoculation protocols were developed to prevent mass transfer hindrance and improve butanol productivity and bacterial growth. At a dilution rate of 0.1 h−1, an improvement of 0.44 g L−1 h−1 in butanol productivity was observed with the continuous process coupled with extraction/gas-stripping. However, it was found that the bacterial formation within the packed bed was inhomogeneous, with dense bacterial growth observed only at the bottom. Therefore, inhomogeneous bacterial growth cannot be simply overcome with the in situ extraction/gas-stripping process. This highlights the need to address the issue of inhomogeneous bacterial growth in pilot-scale packed-bed reactors to improve their efficiency.