For n-butanol production by Clostridium pasteurianum DSM 525, a modified reinforced Clostridium medium was used, where glucose was alternated with glycerol and two kinds of continuous fermentation were tested using suspended and surface immobilized cells on corn stover pieces. A steady state, with butanol productivity of 4.2g/Lh, was reached during the packed-bed continuous fermentation at a dilution rate of 0.44h(-1). The average n-butanol concentration, yield and the ratio of n-butanol/liquid by-products were 10.4g/L, 33 % and 2.5, respectively. Unexpectedly, during continuous fermentation with suspended cells, at a dilution rate of 0.01h(-1), steady-state was not achieved and regular oscillations occurred in all measured variables, i.e. concentrations of glycerol, products and the number of cells stained with the fluorescent dyes carboxy fluorescein diacetate and propidium iodide. A possible explanation for oscillatory/steady-state behavior of suspended/surface-attached cells, respectively, may be specific butanol toxicity (toxicity per cell), which was higher/lower in respective cases, and which might be caused by lower/higher cell numbers respectively in both systems.

Department of Biotechnology and Life Sciences University of Insubria Varese Italy; The Protein Factory Research Center Politecnico of Milano ICRM CNR Milano and University of Insubria Varese Italy

Department of Biotechnology University of Chemistry and Technology Prague Czech Republic

Department of Biotechnology University of Chemistry and Technology Prague Czech Republic; Department of Biotechnology and Life Sciences University of Insubria Varese Italy; The Protein Factory Research Center Politecnico of Milano ICRM CNR Milano and University of Insubria Varese Italy

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