A study on the citric acid production using $\underline{S}. \underline{lipolytica}$ was carried out in shake-flask, bubble column, dual hollow fiber bioreactor (DHFBR) and membrane cell recycle reactor.
In the immobilized cell culture system the optimum concentration of yeast extract as a nitrogen source was about 5 g/L. Substrate inhibition occurred above 8% (W/V) glucose concentration. Use of 1% $CaCO_3$ as a neutralizing agent greatly enhanced the production of citric acid (40-50 g/L). Repeated batch fermentation for re-use of the cells and long-term operation was carried out and showed higher yield (54%) than any other flask culture.
The batch operation in a bubble column showed 63% yield using nitrogen-deficient medium (NDM).
In a dual hollow fiber bioreactor operation the volumetric productivity of citric acid (4.55 g/L·h) was superior to those of other reactors (4-20 fold). Use of pure oxygen in stead of air increased the citric acid concentration, the yield and the volumetric productivity.
In a membrane cell recycle reactor operation maximum dry cell mass concentration was 39g/L at dilution rate of 0.02 $h^{-1}$ and the yield (69%) with NDM was higher than that (23-38%) with nitrogen-including medium (NIM).
