Figure Captions
Figure 1 . Experimental setup for the continuous fermentation with clostridial cells immobilized in a fibrous bed bioreactor (FBB). Inset diagram shows the construction of the spirally wound fibrous matrices with stainless steel wire mesh as the mechanical support with gaps between adjacent layers as flow channels for liquid, gas, and solids (cells) to move freely. The highly porous fibrous matrix has a large surface area and void volume (>90% reactor volume) to allow high densities of viable cells (up to 100 g/L cell dry weight) to be immobilized by attachment to fiber surfaces and entrapment within the matrix.
Figure 2 . Effect of butyric acid on cell growth. Cells ofC. acetobutylicum ATCC 55025 were cultured in P2 medium containing 20 g/L glucose and various amounts of butyric acid (0, 2, 5, or 10 g/L) in serum bottles at 37 oC.
Figure 3 . Kinetics of batch fermentation with free cells cultured in medium containing ~50 g/L glucose and 4 g/L butyric acid as carbon sources in a stirred-tank bioreactor at 35oC and pH controlled at ~5.0.
Figure 4 . Kinetics of continuous fermentation with 50 g/L glucose and 4 g/L butyric acid at the dilution rate of 0.06 h-1. (a) Time course data of cell density (OD), glucose, solvents (acetone, butanol, and ethanol), and acids (acetic acid and butyric acid) in the reactor outlet stream; (b) Butanol and ABE yields and butanol productivity.
Figure 5 . Kinetics of continuous fermentation with 60 g/L glucose and 6.8 g/L butyric acid at the dilution rate of 0.12 h-1. (a) Time course data of cell density (OD), glucose, solvents (acetone, butanol, and ethanol), and acids (acetic acid and butyric acid) in the reactor outlet stream; (b) Butanol and ABE yields and butanol productivity.
Figure 6 . Kinetics of continuous fermentation with 60 g/L glucose and 5.0 g/L butyric acid at the dilution rate of 1.88 h-1. (a) Time course data of cell density (OD), glucose, solvents (acetone, butanol, and ethanol), and acids (acetic acid and butyric acid) in the reactor outlet stream; (b) Butanol and ABE yields and butanol productivity.
Figure 7. Scanning electron micrographs of cells immobilized in the fibrous matrix in the fibrous bed bioreactor. Cells adsorbed on the fiber surface formed a thick layer of biofilm. Most of cells had an elongated rod shape between 3 to 5 µm.
Table 1. Comparison of fermentation kinetics of C. acetobutylicum ATCC55025 in batch and continuous fermentations at different dilution rates.