Activity of immobilized Clostridium acetobutylicum P262 during the fermentation of lactose for the production of acetone-butanol.

摘要

In the literature there is no information about immobilization of biofilms of C. acetobutylicum P262 on glass fibers. Furthermore, most researchers have reported that continuous cultures of C. acetobutylicum is unstable. The goal of this study was to investigate development of a biofilm of C. acetobutylicum P262 on glass fiber in a packed bed reactor and its effect on stability of Clostridium acetobutylicum in continuous perfusion culture.; Lactose was used as a substrate. The concentration of fermentation products such as acids/solvents, exopolysaccharides/cell mass, and ATP were analyzed with an HPLC, visible spectrophotometer and luminometer respectively. All photographs of stained cells were taken using a Zeiss microscope and camera attachment.; To understand the physiological and morphological types of biomass present on support particles, we compared the performance of free and immobilized cells in a packed bed batch cell system where the effect of carrier mass and types, hydrodynamics and pH on formation of biofilm and products were investigated. Typical solvent productivities of batch fermentation processes without support material were in the range of 0.1--0.15 g/l.h. Solvent yields approximated 0.20--0.25% based on lactose utilized. Solvent productivity and yield increased to 0.17--0.21 and 0.3--0.35 respectively when the reactor was packed with glass fiber in batch fermentation. In order to increase lactose utilization and relieve product inhibition in batch culture, a side stream from the reactor was stripped of solvents using nitrogen gas, and recycled to the reactor. A large improvement in substrate utilization (45.32 g/l) was observed. To study the effect of pH on the solvent productivities and yield, the fermentation was carried out in a pH-controlled fermenter without N2 stripping. Cells were most active at pH 5.5. High lactose utilization (58.2 g/l), solvent productivity (0.21 g/1.h) and yield (0.21) were observed at this pH.; In an effort to improve productivity and to obtain a stable process, continuous packed bed fermentation integrated with stripper was used at pH 5.5. 10 times higher solvent productivity (2.6 g/1.h) was achieved compared to batch fermentation, and the system remained stable for 120 hours, though solvent yield and lactose utilization were not improved compared to batch fermentation. Both product removal and exopolysaccharides appear to be involved in the yield improvement and stabilization of the immobilized culture.