Aerobic fungal cell immobilization in a dual hollow‐fiber bioreactor: Continuous production of a citric acid

Abstract

Aspergillus niger B60 was immobilized in a dual hollow-fiber bioreactor (DHFBR) 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. Long-term operation with nitrogen-enriched medium was not possible due to expansion of the silicone tubes by continual cell growth. The fungal growth could be controlled by supplying a nitrogen-deficient medium at the production stage. 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 fermentation, which were 18 g/L, 40%, and 0.06 g/L h, respectively.

Physiological aspects of free and immobilized Aspergillus niger cultures producing citric acid under various glucose concentrations

“…Several attempts have also been reported on the production of citric acid by A. niger grown immobilized in surface cultures, as well as biomass recycle processes, where A. niger biomass was repeatedly used, by means of medium replacement. Anderson et al [26] have used a disc fermenter for extended and continuous production of citric acid, while in other work devices such as magnetic drum contactors [27], reciprocated jet bioreactors [28], hollow fibre reactors [29], have been used. There are many studies therefore which investigated the effects of cell immobilization of a wide range of micro-organisms and supporting materials.…”

Liquid Fermentation Systems and Product Recovery of Aspergillus

“…One bioreactor that appeared promising was the dual hollow fiber bioreactor. It was used to produce citric acid using entrapped A. niger cells (Chung and Chang, 1988), allowing the separation of microorganism and liquid and gas phases. In addition to achieving very high productivities, this arrangement wou]d ease subsequent processing, since the product stream would be effectively cell-free.…”

Biomass production, carbon and oxygen consumption by Rhizopus arrhizus grown in submerged cultures on thin liquid films or immobilized on fibrous and particulate materials

“…Chung and Chang (1988) and Toda et al (1989) cultures. This latter process seems to be worthwhile because oxygenation is not a problem any more as no medium agitation is required.…”