HYBRID EXTRACTION-FERMENTATION SYSTEM
The need to achieve high product concentration in the fermentation broth is
essential for both the fermentation (product yield) and recovery (extraction
efficiency). One engineering approach is to couple the extraction with the fermentation
step so that the inhibitory metabolic products can be continuously removed from the
aqueous broth so that the inhibitory effects and/or degradation phenomena can be
avoided or minimized throughout the fermentation. In this manner, the product
formed may also be concentrated, which will facilitate the eventual purification steps
as well as avoiding the metabolic inhibition and degradation phenomena. Various
attempts have been made to improve fermentation yield and alleviate product
inhibition using ion-exchange resins, solvents, and membrane processes (TABLE 1).
Certain criteria of the specific extractant must be met in order to carry out this type of extraction-fermentation process (TABL2E) . After reviewing various separating agents,
such as nonaqueous solvents, ion-exchange resins, and activated carbon, we found that
the nonionic polymeric resins such as XAD-2 and XAD-4 (Rohm and Haas,
Philadelphia, PA) that do not contain any specific function groups are most suitable
for this purpose.