Continuous and biomass recycle fermentations of Clostridium acetobutylicum

Abstract

Using experimental data from continuous cultures of Clostridium acetobutylicum with and without biomass recycle, relationships between product formation, growth and energetic parameters were explored, developed and tested. For glucose-limited cultures the maintenance models for, the Y _ATP and biomass yield on glucose, $(Y_{X/G} ),1/Y_{{\text{ATP}}} = 1/Y_{{\text{ATP}}}^{\max } + m_e /\mu$ and $1/Y_{X/G} = 1/Y_{X/G}^{\max } + m_G /\mu$ were found valid, as well as the following relationships between the butanol (Y _B/G) or butyrate (Y _BE/G) yields and the ATP ratio (R _ATP, an energetic parameter), Y _B/G =0.82-1.35 R _ATP, Y _BE/G =0.54 + 1.90 R _ATP. For non-glucose-limited cultures the following correlations were developed, Y _B/G =0.57-1.07 μ, Y _B/G =0.82-1.35 R _ATPATP and similar equations for the ethanol yield. All these expressions are valid with and without biomass recycle, and independently of glucose feed or residual concentrations, biomass and product concentrations. The practical significance of these expressions is also discussed.