Continuous propionic acid fermentation by immobilized Propionibacterium acidipropionici in a novel packed-bed bioreactor.

Continuous propionic acid fermentations of lactate by Propionibacterium acidipropionici were studied in spiral wound fibrous bed bioreactors. Cells were imobilized by natural attachment to fiber surfaces and entrapment in the void volume within the fibrous matrix. A high cell density of approximately 37 g/L was attained in the reactor and the reactor productivity was approximately 4 times higher than that from a conventional batch fermentation. The bioreactor was able to operate continuously for 4 months without encountering any clogging, degeneration, or contamination problems. Also, the reactor could accept low-nutrient and low-pH feed without sacrificing much in reactor productivity. This new type of immobilized cell bioreactor is scalable and thus is suitable for industrial production of propionate.