In situ product separation in butanol fermentation by membrane-assisted extraction

Abstract

Application of membrane-assisted extraction to butanol fermentation was investigated as a means of product separation and also as a way of alleviating the problems concerning the end-product inhibition. The coupled reactor-separator system was found to be stable enough to sustain continuous operation lasting several weeks. The data on continuous run reaffirmed most of the advantages found in our previous study on fed-batch system in that the reactor separator system rendered high productivity and yields due primarily to reduced product inhibition. The improvement in productivity was particularly notable, as a fourfold increase over straight batch operation was obtained. In normal continuous operation, spontaneous cell deactivation occurred after 200–400 h of operation despite the removal of inhibitory products. In further investigation, the presence of autolysin was found to be one of the probable causes of cell deactivation. The cell viability, however, was prolonged significantly when the bioreactor was operated under glucose-limited conditions.