Influence of continuous membrane bioreactor operation on ferrichrome production using Ustilago maydis

Fermentations, utilizing a membrane bioreactor (MBR) can be advantageous as cells are retained in the vessel while soluble products are continuously withdrawn. It can be operated at high cell density, which allows increased productivity. Since hydraulic and solids residence times are independent of each other, MBRs offer an additional degree of freedom for process control. MBRs can be biologically distinguished from batch fermentors for various reasons: Like chemostats, by being operated in a distinct growth phase production of unwanted metabolites can be reduced. In addition, high cell densities may cause changes in metabolism. Although MBR fermentations have been studied frequently this influence of the operational mode, i.e. the membrane''s presence, has rarely been the main research focus. In this study, influences of the operational mode on kinetic parameters and productivity of Ustilago maydis are investigated by comparison with batch and chemostat cultures. In MBR fermentations, biomass concentrations rise up to 40 g·L−1. Possibly due to the effect of these high cell densities a low growth rate state is reached even at non-limiting substrate concentrations. MBR productivity reaches a maximum just after the onset of continuous fermentation and later decreases. Although the general possibility of MBR fermentation is shown, this highlights the need for optimization. [Copyright &y& Elsevier]