Method for continuously producing citric acid by dual hollow fiber membrane bioreactor
Patent 4910139 Issued on March 20, 1990. Estimated Expiration Date: August 1, 2008. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
Aspergillus niger B60 was immobilized in a dual hollow fiber bioreactor to produce citric acid continuously. The fungi proliferated well in the interstitial region formed by a parallel arrangement of three microporous polypropylene hollow fibers contained within a silicone tube. Excessive fungal cell growth could be controlled by supplying a nitrogen-deficient medium at the production stage, and also uniform cell distribution in the reactor could be obtained by changing the direction of medium flow. With pure oxygen aeration and nitrogen-deficient medium, volumetric productivity reached 1.62 g/l.h at a residence time of 4.02 h, which corresponded to a 27-fold increase over that of shake-flask fermentation. When the residence time was increased to 20.1 h, citric acid at a concentration of 26 g/l was continuously produced, with a yield of 80-90% and a volumetric productivity of 1.3 g/l.h. This represents a significant improvement in final concentration, yield and the volumetric productivity over the equivalent values of the corresponding batch formentation, which were 18 g/l, 40% and 0.06 g/l.h, respectively.