LONG-TERM CONTINUOUS CULTIVATION OF CLOSTRIDIUM-BEIJERINCKII IN A 2-STAGE CHEMOSTAT WITH ONLINE SOLVENT REMOVAL

A two-stage continuous cultivation experiment with Clostridium beijeri nckii NRRL B592 is described, This strain maintained its ability to pr oduce neutral solvents (acetone, n-butanol, and ethanol) at an overall dilution rate of 0.13 h(-1) and achieved an average overall solvent c oncentration of 9.27 g/liter and an overall solvent productivity of 1. 24 g/liter/h for more than 100 overall retention times, The experiment was performed without pH control on a semisynthetic medium containing yeast extract, and product inhibition was the limiting factor, Solid carrier material was present in both stages, and the solvent productiv ity in both stages was similar, A membrane evaporation module integrat ed into the recirculation loop of a second-stage bioreactor after 2,16 6 h increased solvent productivity and improved the yield of solvents by about 40%, The membrane reduced the concentration of solvents, whic h would otherwise inhibit the fermentation, Additionally, the integrat ed membrane evaporation dampened metabolic oscillations, which are cha racteristic of continuous cultivation of clostridia. It was also demon strated that a moderate concentration buildup (approximately 30% of bi oreactor inflow) caused by water flux through the membrane caused no d etrimental effects to the bacterial cells, However, much higher water fluxes through the membrane, associated with a much more dramatic incr ease in the concentration of salts in the medium, did appear to favor cell degeneration.