| Abstract: | The degradation of morpholine, often reported as a recalcitrant compound, by a mixed culture consisting of nine bacteria and two yeasts in a bioreactor is described. The fermentation process was first carried out in discontinuous culture using different initial morpholine concentrations. The time variation of biomass and morpholine concentrations were used to determine the parameters characterizing the specific growth rate which is based on Monod's model modified to take into account the inhibition due to the substrate. In discontinuous cultures, the biomass concentration reached a maximum of 4·5 g dm-3 with an initial morpholine concentration of 7 g dm-3. When switching to continuous culture, the biomass reached 8·8 g dm-3 with a dilution rate varying from 0·024 h-1 to 0·052 h-1 while reducing morpholine concentration to zero within 300 h. A numerical simulation was set up by integrating with time the mass balance equations for morpholine and biomass in the presence of a constant cell death rate. The results of the simulation were in close agreement with the observed data. The model was then extended to a membrane bioreactor. Experiments were first run with partial recycling (bleeding rate of 0·011 h-1). The biomass concentration reached 27 g dm-3 after 200 h while the morpholine concentration stabilized itself at 0·2 g dm-3. With total recycling, the biomass reached 32 g dm-3, when it became limited by the oxygen transfer of the apparatus. Here again the model was in good agreement with the observations except when the dilution rate was changed suddenly. This study indicates that data obtained in discontinuous batch mode can serve to predict the biomass and morpholine concentration variation in continuous mode in a membrane reactor and to determine the correct parameters for steady state operation. |
