In most of the reviewed literatures, the parameters mainly
reported and focused on are product titers, yield and solvent volumetric
productivity. The specific product rate (bioreactor specific
rate) is another variable in the authors’ opinion that should be considered
in order get information on the effectiveness of the process,
as shown by others (Kanchanatawee and Maddoxx, 1991; Meyer
and Papoutsakis, 1989a). In this work the idea to improve the specific
product rate is presented in a form of two-stage fermentation,
where the continuous fermentation in the first reactor is coupled
with a second-stage reactor operated as repeated fed-batch. This
mode of fermentation is also compared with a two-stage reactor
continuous fermentation where pH in the first-stage reactor is varied.
This idea is considered novel as no reference to this mode of
fermentation has been found to date.