REACTOR COMPARISON AND SCALE-UP FOR THE MICROAEROBIC PRODUCTION OF 2,3-BUTANEDIOL BY ENTEROBACTER-AEROGENES AT CONSTANT OXYGEN-TRANSFER RATE

Stirred tank (STR), bubble column (BCR) and airlift (ALR) bioreactors of 0.05 and 1.5 m3 total volume were compared for the production of 2, 3-butanediol using Enterobacter aerogenes under microaerobic condition s. Batch fermentations were carried out at constant oxygen transfer ra te (OTR = 35 mmol/1h). At 0.05 m3 scale, the STR reactor achieved much higher biomass and product concentrations than the BCR and ALR reacto rs. At 1.5 m3 scale, however, exactly the same biomass and product con centrations could be obtained in both STR and ALR reactors. The 1.5 m3 ALR reactor performed also much better than its counterpart at small scale, achieving a productivity 2.4-fold as high as that of the 0.05 m 3 BCL and ALR reactors. No differences in performances were observed b etween BCR and ALR. As compared to STR the tower reactors have a 12 ti me higher energetic efficiency (referred to product formation) and thu s should be the choice for large scale production of 2,3-butanediol. T he criterion of constant OTR or constant k(L) is not applicable for th e scale-up of this oxygen-sensitive culture due to strong influence of reactor hydrodynamics under microaerobic conditions. The effects of m ixing and circulation time on growth and metabolism of E. aerogenes we re quantitatively studied in scaled-down experiments with continuous c ulture. For a successful scale-up of this microaerobic culture it is n ecessary to have an homogeneous oxygen supply over the entire reactor volume. Under conditions of inhomogeneous oxygen supply an optimum liq uid circulation time exists which gives a maximum production of 2,3-bu tanediol.