A comparison of three pH control methods for revealing effects of undissociated butyric acid on specific butanol production rate in batch fermentation of Clostridium acetobutylicum

AMB Express

Table 1 Effect of different pH regulation methods on cell growth and butanol production by C. acetobutylicum

pH control	NaOH neutralization			CaCO ₃ supplementation			NaOAc buffering (pH)
	12 h	24 h	36 h	2 g/L	5 g/L	8 g/L	4.6	5.0	5.6
pH at 24 h^a	4.7 ± 0.0	3.6 ± 0.0	3.6 ± 0.0	4.4 ± 0.0	4.7 ± 0.0	5.3 ± 0.0	4.1 ± 0.0	4.4 ± 0.0	5.0 ± 0.0
C_butanol ^b	11.9 ± 0.7	3.8 ± 0.0	4.9 ± 0.1	8.8 ± 0.4	10.8 ± 0.1	7.9 ± 0.4	6.5 ± 0.3	12.3 ± 0.9	8.3 ± 0.4
C_{butyric acid} ^c	4.3 ± 0.3	1.8 ± 0.2	1.7 ± 0.1	4.0 ± 0.3	5.4 ± 0.5	6.2 ± 0.2	2 ± 0.3	2.7 ± 0.5	4.0 ± 0.2
Biomass	0.69 ± 0.03	0.45 ± 0.06	0.39 ± 0.02	0.45 ± 0.05	0.41 ± 0.02	0.53 ± 0.01	0.51 ± 0.03	0.63 ± 0.02	0.70 ± 0.04
C_UBA ^d	2.18 ± 0.14	1.0 ± 0.08	1.6 ± 0.09	2.68 ± 0.18	3.01 ± 0.26	1.50 ± 0.05	1.70 ± 0.28	1.92 ± 0.32	1.32 ± 0.07
q_p	0.41 ± 0.02	0.22 ± 0.09	0.42 ± 0.02	0.49 ± 0.06	0.52 ± 0.01	0.25 ± 0.02	0.44 ± 0.01	0.58 ± 0.01	0.36 ± 0.02

^a pH at 24 h: pH values at 24 h of fermentation. ^b C_butanol (g/L): Final butanol concentration at 72 h. Biomass (g/L): Cell biomass at 24 h. ^c C_{butyric acid}: Butyric acid concentration at 24 h (peak concentration). C_UBA (g/L): Concentration of undissociated butyric acid at 24 h.
q_p: Specific butanol production rates (between 24 and 36 h, h⁻¹) were calculated based on the following equation: q_p = (C_butanol,36h − C_butanol,24h)/(12 × X_{cell biomass,24h}).