Continuous xylose fermentation by Clostridium acetobutylicum – Kinetics and energetics issues under acidogenesis conditions

The paper reports the assessment of the growth kinetics of Clostridium acetobutylicum DSM 792 adopting xylose as carbon source. Xylose is the fundamental component of hemicellulose hydrolysis, a relevant fraction of lignocellulosic feedstocks for biofuel production. Tests were carried out in a CSTR operated under controlled pH. The effects of acids (acetic and butyric) and solvents (acetone, ethanol and butanol) on the fermentation were investigated. The conversion process was characterized under steady-state conditions in terms of concentration of xylose, cells, acids, and pH. The growth kinetics was expressed by means of a multiple product inhibition and it was able to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production. The mass fractional yield of biomass and products were expressed as a function of the specific growth rate taking into account the Pirt model.