An Assessment of the kinetics of butanol production by Clostridium acetobutylicum

Results of a research activity aiming at investigating the feasibility of the acetone-butanol-ethanol (ABE) production by Clostridium acetobutylicum ATCC824 are reported. The kinetics of the ABE production process by free C. acetobutylicum in batch reactors has been assessed. A CSTR equipped with a microfiltration unit has been set-up and operated to assess the kinetics in the solventogenic phase. Solutions of lactose-concentration ranging between 10 and 100 g/L-were adopted as medium with the aim of emulating cheese whey. The conversion process was characterized in terms of cells, acids, solvents, pH and total organic compounds as a function of time. Tests carried out under batch conditions show that: i) cells growth is constant for lactose concentration (CL) smaller than 100 g/L; ii) the butanol specific production rate - estimated at the onset of the solventogenic phase - as a function of CL may be represented by a Monod-like kinetics; iii) the lactose conversion - measured at the end of the solventogenesis phase - decreases with CL; iv) the selectivity of butanol with respect to total solvents increases with CL and stabilizes at about 72%W for CL larger than 30 g/L. Preliminary tests carried out under continuous conditions show that the process takes advantage from the steady state operation under solventogenic conditions. In particular, the butanol conversion rate is larger in the CSTR than in the STR, despite the lower final lactose concentration experienced in the CSTR.