Production of poly(3-hydroxybutyrate) in an airlift bioreactor by Ralstonia eutropha

Abstract

The influence of different aeration rates ( Q air), 12, 20, 30, 35, 40, and 50 l min −1, on the production of poly(3-hydroxybutyric acid) (PHB) by Ralstonia eutropha DSM 545 during the accumulation phase, was investigated in an airlift bioreactor and the results were compared to the ones obtained in a stirred tank bioreactor. The time constants for mixing, oxygen transfer, oxygen consumption, power consumption, and kinetic parameters were the tools used to compare the systems. The results showed that, for a superficial gas velocity ( V s) greater than or equal to 10 m s −1, the PHB productivity reached 0.6 g l −1 h −1 at 50% of PHB cell content, although, for the velocity of 0.10 m s −1 the observed value of dissolved oxygen concentration in fermentation medium was zero. The analysis of time constants calculated in the accumulation phase showed that, for V s under 0.11 m s −1, the rate of oxygen consumption was larger than the rate of oxygen transfer indicating that this was the rate-limiting step. In the conventional stirred tank bioreactor, the PHB productivity achieved 0.82 g l −1 h −1 at 50% of PHB. However, the latter demand higher power consumption than the airlift bioreactor, indicating that, for these bacteria, the low supply of oxygen in airlift leads to better performances on PHB production with the advantage of lower demand of energy.