CHARACTERISTICS OF IMMOBILIZED LACTOBACILLUS-DELBRUECKII IN A LIQUID-SOLID FLUIDIZED-BED BIOREACTOR FOR LACTIC-ACID PRODUCTION

Continuous lactic acid production using immobilized L. delbrueckii was investigated. To evaluate the performance of the liquid-solid fluidiz ed bed reactor using immobilized cells, the release rate of free cells from support surfaces and contribution of the free cells, which co-ex ist with immobilized cells in the broth, to lactic acid production wer e studied quantitatively. The results showed that the free cells playe d an important role at low dilution rate. If the dilution rate was inc reased, the effect of free cells on lactic acid production decreased q uickly. Increasing the holdup of immobilized particles in the reactor lowered the contribution of free cells to the lactic acid production. Finally, the performance of the reactor was studied under the conditio ns of low growth nutrients. The results suggested that there was more active cell growth within the gel beads in the fluidized bed reactor t han in the cell recycle reactor using membrane.